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ABSTRACT
The search for a new, safe and stable renewable energy source led to the idea of building a power station in space which transmits electricity to Earth. The concept of Solar Power Satellites (SPS) was invented by Glaser in 1968.Research is still going on in this field and NASA is planning to implement one by 2040. SPS converts solar energy into microwaves and transmit it to a receiving antenna on Earth for conversion to electric power. The key technology needed to enable the future feasibility of SPS is Microwave Power Transmission.
SPS would be a massive structure with an area of about 56 sq.m and would, weigh about 30,000 to 50,000 metric ton. Estimated cost is about $74 billion and would take about 30 years for its construction. In order to reduce the projected cost of a SPS suggestions are made to employ extraterrestrial resources for its construction. This reduces the transportation requirements of such a massive structure. However the realization of SPS concept holds great promises for solving energy crisis.

INTRODUCTION
The new millennium has introduced increased pressure for finding new renewable energy sources. The exponential increase in population has led to the global crisis such as global warming, environmental pollution and change and rapid decrease of fossil reservoirs. Also the demand of electric power increases at a much higher pace than other energy demands as the world is industrialized and computerized. Under these circumstances, research has been carried out to look into the possibility of building a power station in space to transmit electricity to Earth by way of radio waves-the Solar Power Satellites. Solar Power Satellites(SPS) converts solar energy in to micro waves and sends that microwaves in to a beam to a receiving antenna on the Earth for conversion to ordinary electricity.SPS is a clean, large-scale, stable electric power source. Solar Power Satellites is known by a variety of other names such as Satellite Power System, Space Power Station, Space Power System, Solar Power Station, Space Solar Power Station etc.[1].One of the key technologies needed to enable the future feasibility of SPS is that of Microwave Wireless Power Transmission.WPT is based on the energy transfer capacity of microwave beam i.e,energy can be transmitted by a well focused microwave beam. Advances in Phased array antennas and rectennas have provided the building blocks for a realizable WPT system [2].
WHY SPS
Increasing global energy demand is likely to continue for many decades. Renewable energy is a compelling approach “ both philosophically and in engineering terms. However, many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements. The burning of fossil fuels resulted in an abrupt decrease in their .it also led to the green house effect and many other environmental problems. Nuclear power seems to be an answer for global warming, but concerns about terrorist attacks on Earth bound nuclear power plants have intensified environmentalist opposition to nuclear power. Moreover, switching on to the natural fission reactor, the sun, yields energy with no waste products. Earth based solar panels receives only a part of the solar energy. It will be affected by the day & night effect and other factors such as clouds. So it is desirable to place the solar panel in the space itself, where, the solar energy is collected and converted in to electricity which is then converted to a highly directed microwave beam for transmission. This microwave beam, which can be directed to any desired location on Earth surface, can be collected and then converted back to electricity. This concept is more advantageous than conventional methods. Also the microwave energy, chosen for transmission, can pass unimpeded through clouds and precipitations.
SPS “THE BACKGROUND
The concept of a large SPS that would be placed in geostationary orbit was invented by Peter Glaser in 1968 [1].The SPS concept was examined extensively during the late 1970s by the U.S Department of Energy (DOE) and the National Aeronautics and Space Administration (NASA). The DOE-NASA put forward the SPS Reference System Concept in 1979 [2]. The central feature of this concept was the creation of a large scale power infrastructure in space, consisting of about 60 SPS, delivering a total of about 300GW.But, as a result of the huge price tag, lack of evolutionary concept and the subsiding energy crisis in 1980-1981, all U.S SPS efforts were terminated with a view to re-asses the concept after about ten years. During this time international interest in SPS emerged which led to WPT experiments in Japan.
RECENT NASA EFFORTS
Fresh look Study
During 1995-96, NASA conducted a re-examination of the technologies, system concepts of SPS systems [2],[3].The principal objective of this ËœFresh Look Studyâ„¢ was to determine whether a SPS and associated systems could be defined. The Fresh Look Study concluded that the prospects for power from space were more technically viable than they had been earlier.
SSP Concept Definition Study
During 1998, NASA conducted the SSP Concept Definition Study which was a focused one year effort that tested the results of the previous Fresh Look Study. A principal product of the efforts was the definition of a family of strategic R&T road maps for the possible development of SSP technologies.
SSP Exploratory and Research Technology Program
In 2000, NASA conducted the SERT Program which further defined new system concepts. The SERT Program comprised of three complementary elements:
¢ System studies and analysis
Analysis of SSP systems and architecture concepts to address the economic viability as well as environmental issue assessments.
¢ SSP Research and technology
Focused on the exploratory research to identify system concepts and establish technical viability
¢ SPS technology demonstration
Initial small scale demonstration of key SSP concepts and / or components using related system / technologies.
SPS-A GENERAL IDEA
Solar Power Satellites would be located in the geosynchronous orbit. The difference between existing satellites and SPS is that an SPS would generate more power-much more power than it requires for its own operation.
The solar energy collected by an SPS would be converted into electricity, then into microwaves. The microwaves would be beamed to the Earthâ„¢s surface, where they would be received and converted back into electricity by a large array of devices known as rectifying antenna or rectenna.(Rectification is the process by which alternating electrical current ,such as that induced by a microwave beam , is converted to direct current). This direct current can then be converted to 50 or 60 Hz alternating current [4].
Each SPS would have been massive; measuring 10.5 km long and 5.3 km wide or with an average area of 56 sq.km.The surface of each satellite would have been covered with 400 million solar cells. The transmitting antenna on the satellite would have been about 1 km in diameter and the receiving antenna on the Earthâ„¢s surface would have been about 10 km in diameter [5].The SPS would weigh more than 50,000 tons.
The reason that the SPS must be so large has to do with the physics of power beaming. The smaller the transmitter array, the larger the angle of divergence of the transmitted beam. A highly divergent beam will spread out over a large area, and may be too weak to activate the rectenna.In order to obtain a sufficiently concentrated beam; a great deal of power must be collected and fed into a large transmitter array.

Figure 1 Configuration of SPS is space.
The day-night cycle ,cloud coverage , atmospheric attenuation etc.reduces the amount of solar energy received on Earthâ„¢s surface.SPS being placed in the space overcomes this .Another important feature of the SPS is its continuous operation i.e,24 hours a day,365 days a year basis. Only for ma total of 22 in a year would the SPS would be eclipsed for a period of time to a maximum of 72 min.If the SPS and the ground antenna are located at the same longitude, the eclipse period will center around midnight [7].
The power would be beamed to the Earth in the form of microwaves at a frequency of 2.45 GHz. Microwaves can pass unimpeded through clouds and rain .Microwaves have other features such as larger band width , smaller antenna size, sharp radiated beams and they propagate along straight lines. Because of competing factors such as increasing atmospheric attenuation but reducing size for the transmitting antenna and the other components at higher frequency , microwave frequency in the range of 2-3 GHz are considered optimal for the transmission of power from SPS to the ground rectenna site[7].A microwave frequency of 2.45 GHz is considered particularly desirable because of its present uses for ISM band and consequently probable lack of interference with current radar and communication systems. The rectenna arrays would be designed to let light through, so that crops or even solar panels could be placed underneath it. Here microwaves are practically nil [4].
The amount of power available to the consumers from one SPS is 5 GW.the peak intensity of microwave beam would be 23 mW/cm².So far, no non thermal health effects of low level microwave exposure have been proved, although the issue remains controversial [4]. SPS has all the advantage of ground solar, plus an additional advantage; it generates power during cloudy weather and at night. In other words SPS receiver operates just like a solar array. Like a solar array, it receives power from space and converts it into electricity. If the satellite position is selected such that the Earth and the Sun are in the same location in the sky, when viewed from the satellite, same dish could be used both as solar power collector and the microwave antenna. This reduces the size and complexity of satellite [8].

However, the main barrier to the development of SPS is social, not technological. The initial development cost for SPS is enormous and the construction time required is very long. Possible risks for such a large project are very large, pay-off is uncertain. Lower cost technology may be developed during the time required to construct the system. So such a large program requires a step by step path with immediate pay-off at each step and the experience gained at each step refine and improve the risk in evolutionary steps [9].

Figure 2
WIRELESS POWER TRANSMISSION
Transmission or distribution of 50 or 60 Hz electrical energy from the generation point to the consumer end without any physical wire has yet to mature as a familiar and viable technology.However, the reported works on terrestrial WPT have not revealed the design method and technical information and also have not addressed the full-scale potential of WPT as compared with the alternatives, such as a physical power distribution line [10]. However the main thrust of WPT has been on the concept of space-to-ground (extraterrestrial) transmission of energy using microwave beam.
Fig.3 shows the block diagram of a conceptual WPT system annexed to a grid [10].

Figure 3. conceptual model for a WPT system annexed to a grid.
The 50 Hz ac power tapped from the grid lines is stepped down to a suitable voltage level for rectification into dc. This is supplied to an oscillator fed magnetron. Inside the magnetron electrons are emitted from a central terminal called cathode. A positively charged anode surrounding the cathode attracts the electrons. Instead of traveling in a straight line, the electrons are forced to take a circular path by a high power permanent magnet. As they pass by the resonating cavities of the magnetron, a continuous pulsating magnetic field i.e., electromagnetic radiation in microwave frequency range is generated. After the first round of cavity-to-cavity trip by the electrons is completed the next one starts, and this process continues as long as the magnetron remains energized. Fig.4 shows the formation of a re-entrant electron beam in a typical six cavity magnetron. The output of the rectifier decides the magnetron anode dc voltage. This in turn controls the radiation power output. The frequency of the radiation is adjusted by varying the inductance or capacitance of the resonating cavities.

Figure 4. Re-entrant electron beam in a six-cavity magnetron
The microwave power output of the magnetron is channeled into an array of parabolic reflector antennas for transmission to the receiving end antennas. To compensate for the large loss in free space propagation and boost at the receiving end the signal strength as well as the conversion efficiency, the antennas are connected in arrays. Moreover, arrayed installation of antennas will necessitate a compact size.
A series parallel assembly of schottky diodes, having a low standing power rating but good RF characteristics is used at the receiving end to rectify the received microwave power back into dc. Inverter is used to invert the dc power into ac.
A simple radio control feedback system operating in FM band provides an appropriate control signal to the magnetron for adjusting its output level with fluctuation in the consumers demand at the receiving side. The feedback system would switch of the supply to the oscillator and magnetron at the sending end if there is a total loss of load.
The overall efficiency of the WPT system can be improved by
¢ Increasing directivity of the antenna array
¢ Using dc to ac inverters with higher conversion efficiency
¢ Using schottky diode with higher ratings.


MICROWAVE POWER TRANSMISSION IN SPS
The microwave transmission system as envisioned by NASA and DOE would have had three aspects [5]:
1. The conversion of direct power from the photovoltaic cells, to microwave power on the satellites on geosynchronous orbit above the Earth.
2. The formation and control of microwave beam aimed precisely at fixed locations on the Earths surface.
3. The collection of the microwave energy and its conversion into electrical energy at the earthâ„¢s surface.
The ability to accomplish the task of efficiently delivering electrical power wirelessly is dependent upon the component efficiencies used in transmitting and receiving apertures and the ability to focus the electromagnetic beam onto the receiving rectenna.
Microwave WPT is achieved by an unmodulated, continuous wave signal with a band width of 1Hz. Frequency of choice for microwave WPT has been 2.45GHz due to factors such as low cost power components, location in the ISM band, extremely low attenuation through the atmosphere [2]. The next suggested band centered at 5.8GHz system reduces the transmitting and receiving apertures. But this is not preferred due to increased attenuation on higher frequency.

The key microwave components in a WPT system are the transmitter, beam control and the receiving antenna called rectenna .At the transmitting antenna, microwave power tubes such as magnetrons and klystrons are used as RF power sources. However, at frequencies below 10 GHz, high power solid state devices can also be used. For beam safety and control retro directive arrays are used. Rectenna is a component unique to WPT systems. The following section describes each of these components in detail.
TRANSMITTER
The key requirement of a transmitter is its ability to convert dc power to RF power efficiently and radiate the power to a controlled manner with low loss. The transmitterâ„¢s efficiency drives the end-to-end efficiency as well as thermal management system i.e., any heat generated from inefficiencies in the dc-RF conversion, should be removed from the transmitter as it reduces the life time of RF devices and control electronics [2]. Passive inter modulation is another field which requires critical attention. Filtering of noise and suppression of harmonics will be required to meet he regulatory requirement.
The main components of a transmitter include dc-to-RF converter and transmitting antenna. . The complexity of the transmitter depends on the WPT application. For the large scale WPT application such as SPS, phased array antennas are required to distribute the RF power sources across the aperture and electronically control the power beam. Power distribution at the transmitting antenna=v (1-r²), where r is the radius of antenna [7].
There are mainly three dc-to-RF power converters: magnetrons, klystrons and solid state amplifiers.

Klystron
Fig.5 shows the schematic diagram of a klystron amplifier [15].

Figure 5 Klystron amplifier schematic diagram.
Here a high velocity electron beam is formed, focused and send down a glass tube to a collector electrode which is at high positive potential with respect to the cathode. As the electron beam having constant velocity approaches gap A, they are velocity modulated by the RF voltage existing across this gap. Thus as the beam progress further down the drift tube, bunching of electrons takes place. Eventually the current pass the catcher gap in quite pronounce bunches and therefore varies cyclically with time. This variation in current enables the klystron to have significant gain. Thus the catcher cavity is excited into oscillations at its resonant frequency and a large output is obtained.
Fig.6 shows a klystron transmitter [2]. The tube body and solenoid operate at 300°C and the collector operates at 500°C. The overall efficiency is 83%. The microwave power density at the transmitting array will be 1 kW/m² for a typical 1 GW SPS with a transmitting antenna aperture of 1 km diameter. If we use 2.45 GHz for MPT, the number of antenna elements per square meter is on the order of 100. Therefore the power allotted to the individual antenna element is of the order of 10 W/element. So we must distribute the high power to individual antenna through a power divider [1].

Figure 6 Klystron transmitter
BEAM CONTROL
A key system and safety aspect of WPT in its ability to control the power beam. Retro directive beam control systems have been the preferred method of achieving accurate beam pointing.

As shown in fig.7 a coded pilot signal is emitted from the rectenna towards the SPS transmitter to provide a phase reference for forming and pointing the power beams [2]. To form the power beam and point it back forwards the rectenna, the phase of the pilot signal is captured by the receiver located at each sub array is compared to an onboard reference frequency distributed equally throughout the array. If a phase difference exists between the two signals, the received signal is phase conjugated and fed back to earth dc-RF converted. In the absence of the pilot signal, the transmitter will automatically dephase its power beam, and the peak power density decreases by the ratio of the number of transmitter elements.

Figure 7 Retro directive beam control concept with an SPS.
RECTENNA
Brown was the pioneer in developing the first 2.45GHz rectenna [2].
Rectenna is the microwave to dc converting device and is mainly composed of a receiving antenna and a rectifying circuit. Fig .8 shows the schematic of rectenna circuit [2]. It consists of a receiving antenna, an input low pass filter, a rectifying circuit and an output smoothing filter. The input filter is needed to suppress re radiation of high harmonics that are generated by the non linear characteristics of rectifying circuit. Because it is a highly non linear circuit, harmonic power levels must be suppressed. One method of suppressing harmonics is by placing a frequency selective surface in front of the rectenna circuit that passes the operating frequency and attenuates the harmonics.

Figure 8 Schematic of rectenna circuit.
For rectifying Schottky barrier diodes utilizing silicon and gallium arsenide are employed. In rectenna arrays, the diode is the most critical component to achieve higher efficiencies because it is the main source of loss. Diode selection is dependent on the input power levels. The breakdown voltage limits the power handling capacity and is directly related to series resistance and junction capacitance through the intrinsic properties of diode junction and material .For efficient rectification the diode cut off frequency should be approximately ten times the operating frequency.
Diode cut off frequency is given by Æ’=1/ [2pRsCj], where Æ’ is the cut off frequency, Rs is the diode series resistance, Cj is the zero-bias junction capacitance.

RECENTLY DEVELOPED MPT SYSTEMS
The Kyoto University developed a system called Space Power Radio Transmission System (SPORTS) [1]. The SPORTS is composed of solar panels, a microwave transmitter subsystem, a near field scanner, a microwave receiver. The solar panels provide 8.4 kW dc power to the microwave transmitter subsystem composed of an active phased array. It is developed to simulate the whole power conversion process for the SPS, including solar cells, transmitting antennas and rectenna system.
Another MPT system recently developed by a team of Kyoto University ,NASDA and industrial companies of Japan , is an integrated unit called the Solar Power Radio Integrated Transmitter (SPRITZ),developed in 2000 [1]. This unit is composed of a solar cell panel, microwave generators, transmitting array antennas and a receiving array in one package. This integrated unit as shown in fig.9 could be a prototype of a large scale experimental module in the orbit

Figure 9 SPRITZ (Solar Power Radio Integrated Transmitter 2000)
CONSTRUCTION OF SPS FROM NON TERRESTRIAL MATERIALS: FEASIBILITY AND ECONOMICS
SPS, as mentioned before is massive and because of their size they should have been constructed in space [5]. Recent work also indicate that this unconventional but scientifically well “based approach should permit the production of power satellite without the need for any rocket vehicle more advanced than the existing ones. The plan envisioned sending small segments of the satellites into space using the space shuttle. The projected cost of a SPS could be considerably reduced if extraterrestrial resources are employed in the construction [9].One often discussed road to lunar resource utilization is to start with mining and refining of lunar oxygen, the most abundant element in the Moon™s crust, for use as a component of rocket fuel to support lunar base as well as exploration mission. The aluminum and silicon can be refined to produce solar arrays [12].
A number of factors combine to make the concept of using non conventional materials appear to be feasible. Among them are the shallow gravity wells of the Moon and asteroids; the presence of an abundance of glass, metals and oxygen in the Apollo lunar samples; the low cost transport of those materials to a higher earth orbit by means of a solar-powered electric motor; the availability of continuous solar energy for transport, processing and living [12].
Transportation requirement for SPS will be much more needed for known for known commercial applications. One major new development for transportation is required: the mass driver [12].The mass driver is a long and narrow machine which converts electrical energy into kinetic energy by accelerating 0.001 to 10 kg slugs to higher velocities. Each payload-carrying bucket contains superconducting coils and is supported without physical contact by means of dynamic magnetic levitation. As in the case of a linear synchronous motor-generator, buckets are accelerated by a magnetic field, release their payload, decelerate with return energy and pick up another pay load for acceleration. The power source can be either solar or nuclear. The mass driver conversion efficiency from electrical to kinetic energy is close to 100 percent. The mass driver can be used as a launcher of lunar material into free space or as a reaction engine in space, where payloads are transferred from orbit to orbit in a spiral trajectory. The performance of the mass driver could match that of the space shuttle main engines. But the mass driver has the advantage that any material can be used as fuel and continuous solar power in space is the common power source.
An alternative to the use of lunar resources for space manufacturing is the use of earth-approaching asteroidal materials.
MICROWAVES-ENVIRONMENTAL ISSUES
The price of implementing a SPS includes the acceptance of microwave beams as the page link of that energy between space and earth. Because of their large size, SPS would appear as a very bright star in the relatively dark night sky. SPS in GEO would show more light than Venus at its brightest. Thus, the SPS would be quite visible and might be objectionable.
SPS posses many environmental questions such as microwave exposure, optical pollution that could hinder astronomers , the health and safety of space workers in a heavy-radiation (ionizing) environment , the potential disturbance of the ionosphere etc.The atmospheric studies indicate that these problems are not significant , at least for the chosen microwave frequency [13].
On the earth, each rectenna for a full-power SPS would be about 10 km in diameter. This significant area possesses classical environmental issues. These could be overcome by siting rectenna in environmentally insensitive locations, such as in the desert, over water etc. The classic rectenna design would be transparent in sunlight, permitting growth and maintenance of vegetation under the rectenna.
However, the issues related to microwaves continue to be the most pressing environmental issues. On comparing with the use of radar, microwave ovens , police radars, cellular phones and wireless base stations, laser pointers etc. public exposures from SPS would be similar or even less. Based on well developed antenna theory, the environmental levels of microwave power beam drop down to 0.1µW/cm² [12]. Even though human exposures to the 25 mW/cm²will, in general, be avoided, studies shows that people can tolerate such exposures for a period of at least 45 min. So concern about human exposure can be dismissed forthrightly [4]. Specific research over the years has been directed towards effects on birds, in particular. Modern reviews of this research show that only some birds may experience some thermal stress at high ambient temperatures. Of course, at low ambient temperatures the warming might be welcomed by birds and may present a nuisance attraction [13].
Serious discussions and education are required before most of mankind accepts this technology with global dimensions. Microwaves, however is not a Ëœpollutantâ„¢ but , more aptly , a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustence

ADVANTAGES AND DISADVANTAGES
The idea collecting solar energy in space and returning it to earth using microwave beam has many attractions.
1. The full solar irradiation would be available at all times expect when the sun is eclipsed by the earth [14]. Thus about five times energy could be collected, compared with the best terrestrial sites
2. The power could be directed to any point on the earthâ„¢s surface.
3. The zero gravity and high vacuum condition in space would allow much lighter, low maintenance structures and collectors [14].
4. The power density would be uninterrupted by darkness, clouds, or precipitation, which are the problems encountered with earth based solar arrays.
5. The realization of the SPS concept holds great promises for solving energy crisis
6. No moving parts.
7. No fuel required.
8. No waste product.
The concept of generating electricity from solar energy in the space itself has its inherent disadvantages also. Some of the major disadvantages are:
1. The main draw back of solar energy transfer from orbit is the storage of electricity during off peak demand hours [15].
2. The frequency of beamed radiation is planned to be at 2.45 GHz and this frequency is used by communication satellites also.
3. The entire structure is massive.
4. High cost and require much time for construction.
5. Radiation hazards associated with the system.
6. Risks involved with malfunction.
7. High power microwave source and high gain antenna can be used to deliver an intense burst of energy to a target and thus used as a weapon[15].
CONCLUSION
The SPS will be a central attraction of space and energy technology in coming decades. However, large scale retro directive power transmission has not yet been proven and needs further development. Another important area of technological development will be the reduction of the size and weight of individual elements in the space section of SPS. Large-scale transportation and robotics for the construction of large-scale structures in space include the other major fields of technologies requiring further developments. Technical hurdles will be removed in the coming one or two decades. Finally, we look forward to universal acceptance of the premise the electromagnetic energy is a tool to improve the quality of life for mankind. It is not a pollutant but more aptly, a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustenance. From this view point, the SPS is merely a down frequency converter from the visible spectrum to microwaves.
REFERENCES
[1] Hiroshi Matsumoto, Research on solar power satellites and microwave power transmission in Japan, IEEE microwave magazine, pp.36-45, Dec 2002.
[2] James O. Mcspadden & John C. Mankins,Space solar power programs and microwave wireless power transmission technology, IEEE microwave magazine, pp.46-57, Dec 2002.
[3] J.C. Mankins,A fresh look at space solar power: new architectures, concepts and technologies in 38th Astronautical Federation.
[4] Seth Potter, Solar power satellites: an idea whose time has come [online] Available on freemarshistory/sps.html, last updated on Dec.1998
[5] Consumer Energy Information: EREC Reference Briefs [online] Available on eere.gov/consumerinfo/rebriefs/123.html,last updated on Apr.03.
[6] Mc GrawHill Encyclopedia of Science and Technology, vol.16, pp.41.
[7] Om P.Gandhi,Microwave engineering and application, PHI.
[8] Geoffrey A.Landis,A super synchronous solar power , Presented at SPS-97: Space &electric power for humanity, 24-25 Aug 1997, Montreal, Canada.
[9] Geoffrey A.Landis,An evolutionary path to SPS, Space power, vol.9, no.4, pp.365-371, 1990.
[10] S.S.Ahmed, T.W.Yeong and H.B.Ahmad,Wireless power transmission and its annexure to the grid system, IEE Proc.-Gener.Transm.Distrib., Vol.150, No.2, March 2003.
[11]Kennedy Electronics Communication Systems, Tata McGraw Hill.
[12] B.Oâ„¢Leary,The construction of satellite solar power stations from non terrestrial materials: feasibity and economics, Alternative energy sources, Vol.3, pp.1155-1164.
[13] John M.Osepchuk,How safe are microwaves and solar power from space, IEEE microwave magazine, pp.58-64, Dec.2002.
[14] International Encyclopedia of Energy, Vol.4, pp.771.
[15] David M.Pozar,Microwave Engineering, Wiley




CONTENTS
INTRODUCTION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦............. 01
WHY SPS¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.............. 02
SPS-THE BACKGROUND¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 03
SPS-A GENERAL IDEA¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.......... 05
WIRELESS POWER TRANSMISSION ¦¦¦¦¦¦¦¦¦¦¦¦.. 09
MICROWAVE POWER TRANSMISSION IN SPS¦¦¦¦¦¦¦¦ 12
TRANSMITTER¦¦¦¦¦¦¦¦¦¦.. 13
BEAM CONTROL¦¦¦¦¦¦¦¦¦.. 15
RECTENNA ¦¦¦¦¦¦¦¦¦¦¦.. 16
RECENTLY DEVELOPED MPT SYSTEMS ........................................ 18
CONSTRUCTION OF SPS FROM NON TERRESTRIAL MATERIALS: FEASIBILITY AND ECONOMICS¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 19
MICROWAVES-ENVIRONMENTAL ISSUES ¦¦¦¦¦¦¦¦. 21
ADVANTAGES AND DISADVANTAGES¦¦¦¦¦¦¦¦¦¦¦ 23
CONCLUTION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 24
REFERENCES¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 25


ACKNOWLEDGEMENT
I extend my sincere gratitude towards Prof . P.Sukumaran Head of Department for giving us his invaluable knowledge and wonderful technical guidance
I express my thanks to Mr. Muhammed kutty our group tutor and also to our staff advisor Ms. Biji Paul for their kind co-operation and guidance for preparing and presenting this seminars.
I also thank all the other faculty members of AEI department and my friends for their help and support.

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SOLAR POWER SATELLITE

solar power satellite

INTRODUCTION
The new millennium has introduced increased pressure for finding new renewable energy sources
Building a power station in space to transmit electricity to Earth by way of radio waves-the Solar Power Satellites.
Microwave Wireless Power Transmission
SPS is a clean, large-scale, stable electric power source


WHY SPS
Increasing global energy demand
Limitation of renewable energy sources
Environmental problems due to fossil fuels.

Overcome day & night effect and other factors such as clouds.
Overcome energy crisis.

SPS“ THE BACKGROUND
Peter Glaser invented the concept of a large SPS.
The U.S Department of Energy (DOE) and the
National Aeronautics and Space Administration
(NASA) examined the SPS concept extensively
during the late 1970s.
Fresh look Study, SSP Concept Definition Study.
SSP Exploratory and Research Technology
SPS- A GENERAL IDEA
It is located in the geosynchronous orbit.
Comparison between ordinary satellite.
Its operation.
About structure.
Comparison between terrestrial station

WIRELESS POWER TRANSMISSION
The 50Hz ac power tapped from grid line is stepped down to suitable voltage level for rectification in to dc.
The it is supplied to oscillator fed magnetron.
Magnetron consist of electrons supplied by cathode which are collected by positively charged anode.
The electrons are forced to move in a circular path by a high power permanent magnet.
Electromagnetic radiation in microwave range is generated

MICROWAVE TRANSMISSION IN SPS
The conversion of direct power to microwave power
The formation and control of microwave beam
The collection of the microwave energy and its conversion into electrical energy at the earthâ„¢s surface.
The key microwave components in a WPT system are the transmitter, beam control and the receiving antenna called RECTENNA

TRANSMITTER
The key requirement of a transmitter is its ability to convert dc power to RF power efficiently and radiate the power to a controlled manner with low loss.
The transmitterâ„¢s efficiency drives the end-to-end efficiency as well as thermal management system.
The main components of a transmitter include dc-to-RF converter and transmitting antenna.
The main dc-RF converter s are klystrons

KLYSRON TRASMITTER
The tube body and solenoid operate at 300°C and the collector operates at 500°C.
The overall efficiency is 83%.
The microwave power density at the transmitting array will be 1 kW/m² for a typical 1 GW SPS with a transmitting antenna aperture of 1 km diameter.
If we use 2.45 GHz for MPT, the number of antenna elements per square meter is on the order of 100.

BEAM CONTROL
A key system and safety aspect of WPT in its ability to control the power beam.
Retro directive beam control systems have been the preferred method of achieving accurate beam pointing.
A coded pilot signal is emitted from the rectenna towards the SPS transmitter to provide a phase reference for forming and pointing the power beams

RECTENNA
RECTENNA is the microwave to dc converting device .
It is mainly composed of a receiving antenna and a rectifying circuit.
Fig. shows schematic of RECTENNA. It consists of a receiving antenna, an input low pass filter, a rectifying circuit and an output smoothing filter.
In RECTENNA arrays, the diode is the most critical component to achieve higher efficiencies because it is the main source of loss.
Diode cut off frequency is given by Æ’=1/ [2pRsCj], where Æ’ is the cut off frequency, Rs is the diode series resistance, Cj is the zero-bias junction capacitance.
ADVANTAGES
The power could be directed to any point on the earthâ„¢s surface.
The power density would be uninterrupted by darkness, clouds, or precipitation, which are the problems encountered with earth based solar arrays.
The realization of the SPS concept holds great promises for solving energy crisis
No moving parts.
No fuel required.
No waste product.

DISADVANTAGES
The main draw back of solar energy transfer from orbit is the storage of electricity during off peak demand hours.
The frequency of beamed radiation is planned to be at 2.45 GHz and this frequency is used by communication satellites also.
The entire structure is massive.
High cost and require much time for construction.
Radiation hazards associated with the system.
Risks involved with malfunction.
High power microwave source and high gain antenna can be used to deliver an intense burst of energy to a target and thus used as a weapon

CONCLUSION
The SPS will be a central attraction of space and energy technology in coming decades. However, large scale retro directive power transmission has not yet been proven and needs further development. Another important area of technological development will be the reduction of the size and weight of individual elements in the space section of SPS. Large-scale transportation and robotics for the construction of large-scale structures in space include the other major fields of technologies requiring further developments. Technical hurdles will be removed in the coming one or two decades. Finally, we look forward to universal acceptance of the premise the electromagnetic energy is a tool to improve the quality of life for mankind. It is not a pollutant but more aptly, a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustenance. From this view point, the SPS is merely a down frequency converter from the visible spectrum to microwaves.

great work thanks man.keep it up

thanks a lot for help!!

Abstract
The selling price of electrical power varies with time. The economic viability of space solar power is maximum if the power can be sold at peak power rates, instead of baseline rate. Price and demand of electricity was examined from spot-market data from four example markets: New England, New York City, suburban New York, and California. The data was averaged to show the average price and demand for power as a function of time of day and time of year. Demand varies roughly by a factor of two between the early-morning minimum demand, and the afternoon maximum; both the amount of peak power, and the location of the peak, depends significantly on the location and the weather . The demand curves were compared to the availability curves for solar energy and for tracking and non-tracking
satellite solar power systems, in order to compare the market value of terrestrial and solar electrical power.
In part 2, new designs for a space solar power (SSP) system were analyzed to provide electrical power to Earth for economically competitive rates. The approach was to look at innovative power architectures to more practical approaches to space solar power. A significant barrier is the initial investment required before the first power is returned. Three new concepts for solar power satellites were invented and analyzed: a solar power satellite in the Earth-Sun L2 point, a geosynchronous no-moving parts solar power satellite, and a nontracking geosynchronous solar power satellite with integral phased array. The integral-array satellite had several advantages, including an initial investment cost approximately eight times lower than the conventional design.
1. Introduction
The Solar Power Satellite (or "Space Solar Power," SPS) is a concept to collect solar power in space, and then transport it to the surface of the Earth by microwave beam, where it is converted into electrical power for terrestrial use. In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases. Average solar energy per unit area outside Earth's atmosphere is on the order of ten times that available on Earth's surface.
The collection of solar energy in space for use on Earth introduces the new problem of transmitting energy from the collection point, in space, to the place where the energy would be used, on Earth's surface. Since wires extending from Earth's surface to an orbiting satellite would be impractical, many SPS designs have proposed the use of microwave beams to transmit power wirelessly. The collecting satellite would convert solar energy into electrical energy, which would then be used to power a microwave emitter directed at a collector on the Earth's surface. Dynamic solar thermal power systems are also being investigated.
Many problems normally associated with solar power collection would be eliminated by such a design, such as the high sensitivity of conventional surface solar panels to corrosion and weather, and the resulting maintenance costs. Other problems may take their place though, such as cumulative radiation damage or micrometeoroid impacts.
Producing electricity from sunlight in space is not a new or untried technology. Many space faring craft are covered in solar cells, such as rovers and shuttles, and hundreds of operating satellites use solar energy as their main source of power. What has never been tried before is transmitting that power back to Earth for our use.
Being a clean and safe energy design, space-based solar power has the potential to play a significant role in solving global energy and environmental problems. It utilizes space outside of Earth's ecological system, and may essentially produce no by-products.
2. History
The SPS concept, originally known as Satellite Solar Power System ("SSPS") was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e g from an SPS to the Earth's surface) using microwaves from a very large (up to one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
Glaser then worked at Arthur D. Little, Inc., as a vice-president. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems -- chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research.
Between 1978 and 1981 the US Congress authorized DOE and NASA to jointly investigate. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date. Several reports were published investigating possible problems with such an engineering project. They include:
¢ Resource Requirements (Critical Materials, Energy, and Land)
¢ Financial/Management Scenarios
¢ Public Acceptance
¢ State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities
¢ Centralization/Decentralization
¢ Mapping of Exclusion Areas For Rectenna Sites
¢ Economic and Demographic Issues Related to Deployment
¢ Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers
¢ Power Transmission and Reception Technical Summary and Assessment
¢ Space Transportation
The Office of Technology Assessment concluded
Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture.
More recently, the SPS concept has again become interesting, due to increased energy demand, increased energy costs, and emission implications.
3. Sert
In 1999 NASA's Space Solar Power Exploratory Research and Technology program (SERT) was initiated for the following purpose:
¢ Evaluate studies of the general feasibility, design, and requirements.
¢ Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
¢ Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
¢ Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements.
It was to develop a solar power satellite (SPS) concept for a future gigawatt space power systems to provide electrical power by converting the Sunâ„¢s energy and beaming it to the Earth's surface. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux into electricity.
Some of SERT's conclusions include the following:
¢ The environmental impact of conventional power plants and their impact on world energy supplies and geopolitical relationships can be problematic.
¢ Renewable energy is a compelling approach, both philosophically and in engineering terms.
¢ Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
4. Design
Space-based solar power essentially consists of three parts :
1. a means of collecting solar power in space, for example via solar cells or a heat engine
2. a means of transmitting power to earth, for example via microwave or laser
3. a means of receiving power on earth, for example via a microwave antennas (rectenna)
The space-based portion will be in a freefall, vacuum environment and will not need to support itself against gravity other than relatively weak tidal stresses. It needs no protection from terrestrial wind or weather, but will have to cope with space-based hazards such as micrometeorites and solar storms. The reason that the SPS must be so large has to do with the physics of power beaming. The smaller the transmitter array, the larger the angle of divergence of the transmitted beam.
4.1. Supersynchronous Solar Power Satellite :
It is proposed here to analyze a solar power satellite put into a completely different orbit, the Earth-sun L-2 halo orbit. The location of the Earth-sun L2, and a typical halo orbit around it. This is referred to as a super synchronous" location for a solar power satellite, since it is located beyond synchronous orbit. While the halo orbits around the lagrangian points are slightly unstable, the instability is so weak that several space probes have used the L1 halo orbit for operational use, with only minimal amounts of propellant needed to keep them in position. At first consideration, it would seem that the Earth-sun L2 point is a poor choice for a space solar power system transmitter. At a distance of point 1.5 million kilometers from the Earth, it will be forty times further away from the Earth than a satellite placed in geosynchronous orbit. However, it turns out that this orbit allows design simplifications to the satellite solar power design that more than compensate
for this disadvantage. Thus, it is perfectly suited to fill in night power to solar arrays which receive solar power during the daytime. This allows a ground-based solar array field to be "upgraded" to a 24-hour power source, and hence, by upgrading the status of the power from "intermittent" to "baseload," increases the selling price of the power from low intermittent power levels, to higher baseload power levels.
Design Details: Since the sun and Earth are nearly the same direction, it can feature:
Integrated solar concentrator dish/microwave transmission dish
Integrated solar cell/solid state transmitters
No rotating parts or slip-rings
Frequency: 30 GHz
transmitter diameter: 3 km
receiver diameter: 6 km
3 ground sites, receive 8 hours per day
Total Mass 1,300 tonnes
At assumed transmitter efficiency 33% (todayâ„¢s technology): 1 GW power output
At assumed transmitter efficiency 67% (future technology): 2 GW power output.
4.2. Fixed Geosynchronous Solar Power Satellite :

While the size and the electrical generation profile with the Earth-sun L2 solar power satellite make it a poor choice for a financially successful design, one aspect of the design remains extremely attractive: the absence of a rotary joint makes the L2 solar power satellite a design with no moving parts. The baseline figure of merit for this design was to examine how the power production profile fits with the demand (and price) profile for terrestrial electrical power ,assuming that the power is to "fill in" for a ground solar power system.
The satellite designed with the same design criteria: maximum simplicity; no moving parts; mission is to power when ground solar power is not available. A fixed microwave transmitter is permanently mounted on a bifacial solar array, which can be illuminated from either side. Figures shows that this concept produces maximum power at dawn and at dusk, with zero power production at noon and at midnight.
By employing a fixed transmitter attached to the solar array, the power management and distribution system size can be greatly simplified and reduced in mass. The difficulties associated with power transfer from the array to the transmitter are minimized, and the mass and cost of the SPS are reduced. The new SPS needs only gravity-gradient stabilization to ensure that the transmitter remains pointed to the rectenna site on the Earth.
4.3. Fixed Design with integrated microwave transmitter:
If the design constraint of a single array is relaxed, two arrays can be base lined, and the arrays can be tilted outward to accommodate the actual demand peak (after subtraction of solar) at 8 AM and 4 PM .With the addition of tilt, it is no longer true that the microwave beam is perpendicular to the solar arrays. The backside of each solar array is in the view of the Earth. A significant difficulty of the earlier design is the fact that the initial size of the system requires an extremely high initial investment. The redesign of the solar power satellite opens the possibility of integrating the solar array directly to the microwave transmission. By placing solid-state microwave transmitters directly on the back of the solar array, power management and distribution, as well as all voltage conversion, is eliminated.
Figure shows the conceptual design for a satellite to deliver maximum power at 8 AM and 4 PM, where the back side of each array is an integrated microwave transmitter. The advantages of integration of the solar arrays and the transmitter are discussed in reference and by integrating solar array with the microwave transmitter, the transmitter aperture becomes as large as the solar array area. This results in a narrower beam. A narrow beam allows smaller rectenna areas, thereby permitting much smaller solar power satellites. The smaller scale reduces the initial capital investment.
V-shaped fixed orientation solar power satellite to provide fill-in power for a ground solar installation
4.4. Solar energy conversion (solar photons to DC current):
Two basic methods of converting sunlight to electricity have been studied: photovoltaic (PV) conversion, and solar dynamic (SD) conversion.Most analyses of solar power satellites have focused on photovoltaic conversion (commonly known as solar cells). Photovoltaic conversion uses semiconductor cells (e.g., silicon or gallium arsenide) to directly convert photons into electrical power via a quantum mechanical mechanism. Photovoltaic cells are not perfect in practice, as material purity and processing issues during production affect performance; each has been progressively improved for some decades. Some new, thin-film approaches are less efficient (about 20% vs. 35% for best in class in each case), but are much less expensive and generally lighter. In an SPS implementation, photovoltaic cells will likely be rather different from the glass-pane protected solar cell panels familiar to many from current terrestrial use, since they will be optimized for weight, and will be designed to be tolerant to the space radiation environment, but will not need to be encapsulated against corrosion by the elements. They may not require the structural support required for terrestrial
use, where the considerable gravity loading imposes structural requirements on terrestrial implementations.
5. WIRELESS POWER TRANSMISSION (WPT)
BACKGROUND
5.1. Introduction:
A major problem facing Planet Earth is provision of an adequate supply of clean energy. It has been that we face ...three simultaneous challenges -- population growth, resource consumption, and environmental degradation -- all converging particularly in the matter of sustainable energy supply. It is widely agreed that our current energy practices will not provide for all the world's peoples in an adequate way and still leave our Earth with a livable environment. Hence, a major task for the new century will be to develop sustainable and environmentally friendly sources of energy.
Projections of future energy needs over this new century show an increase by a factor of at least two and one Half, perhaps by as much as a factor of five. All of the scenarios from reference 3 indicate continuing use of fossil sources, nuclear, and large hydro. However, the greatest increases come from "new renewables" and all scenarios show extensive use of these sources by 2050. Indeed, the projections indicate that the amount of energy derived from new renewables by 2050 will exceed that presently provided by oil and gas combined. This would imply a major change in the worldâ„¢s energy infrastructure. It will be a Herculean task to acquire this projected amount of energy. This author asserts that there are really only a few good options for meeting the additional energy needs of the new century in an environmentally acceptable way.
One of the so-called new renewables on which major reliance is almost certain to be placed is solar power. Solar power captured on the Earth is familiar to all. However, an alternative approach to exploiting solar power is to capture it in space and convey it to the Earth by wireless means. As with terrestrial capture, Space Solar Power (SSP) provides a source that is virtually carbon-free and sustainable. As will be described later, the power-collecting platforms would most likely operate in geosynchronous orbit where they would be illuminated 24 hours a day (except for short eclipse periods around the equinoxes). Thus, unlike systems for the terrestrial capture of solar, a space-based system would not be limited by the vagaries of the day-night cycle. Furthermore, if the transmission frequency is properly chosen, delivery of power can be carried out essentially independent of weather conditions. Thus Space Solar Power could provide base load electricity.
The vision of achieving WPT on a global scale was proposed over 100 years ago when Nikola Tesla first started experiments with WPT, culminating with the construction of a tower for WPT on Long Island, New York, in the early 1900s. Tesla's objective was to develop the technology for transmitting electricity to anywhere in the world without wires. He filed several patents describing wireless power transmitters and receivers. However, his knowledge of electrical phenomena was largely empirical and he did not achieve his objective of WPT, although he was awarded the patent for wireless radio in 1940.
The development of WPT was not effectively pursued until the 1960s when the U.S. Air Force funded the development of a microwave-powered helicopter platform. A successful demonstration of a microwave beam-riding helicopter was performed in 1965. This demonstration proved that a WPT system could be constructed and that effective microwave generators and receivers could be developed for efficient conversion of microwaves into DC electricity.
The growing interest in solar energy conversion methods and solar energy applications in the 1960s and the limitations for producing cost-effective base load power caused by adverse weather conditions and diurnal changes led to the solar power satellite concept in 1968 as a means to convert solar energy with solar cell arrays into electricity and feed it to a microwave generator forming part of a planar, phased-array antenna. In geosynchronous orbit, the antenna would direct a microwave beam of very low power density precisely to one or more receiving antennas at desired locations on Earth. At a receiving antenna, the microwave energy would be safely and very efficiently reconvened into electricity and then transmitted to users.
The first technical session on solar power satellites (SPS) was held in 1970 at the International Microwave Power Institute Symposium at which representatives of Japan,
European countries, and the former Soviet Union were present. Based on preliminary studies, a plan for an SPS program was prepared by an NSF/NASA panel in 1972 and the first feasibility study of SPS was completed for NASA/Lewis Research Center in 1974.
Shortly after the "oil shock" of October 1973, Japan staned to implement the Sunshine Plan to develop renewable energy sources. Japan's Plan included, as a long-term objective, the development of SPS. Back in the U.S. in 1975, a successful demonstration of microwave wireless power transmissions was performed at the NASA Deep Space Antenna facility at Goldstone, California. In this demonstration of point-to-point WPT, 30 kW of microwaves were beamed over a distance of one mile to a receiving antenna. Microwaves were converted directly into DC at an average efficiency of 82%, confounding critics who claimed that such high conversion efficiencies could not be achieved. By 1976 engineering, environmental and economic analyses of several SPS concepts had been performed by NASA the office of Management and Budget, in its deliberations on the Fry 1977 budget, directed that further study of this concept be the responsibility of the Energy Research and Development Administration (ERDA), which subsequently became the Department of Energy (DoE). The SPS Concept Development and Evaluation Program (CDEP), performed by DoE/NASA and its contractors, used a NASA-developed SPS Reference System configuration as a basis for conducting environmental, societal, and comparative economic assessments, The DOE/NASA assessment team, as well as a majority of scientists, engineers, and analysts who participated in the CDEP recommended that the program be continued at a modest funding level, and SPS assessments directed at resolving or reducing significant uncertainties associated with microwave radiation effects and SPS design considerations, and to continue some promising experiments. By 1980 the CDEP was brought to its scheduled conclusion and not continued in a follow-on program, partly because the economic pressures of the oil crisis had passed, partly because of changed priorities for renewable energy development, and partly because of expectations that nuclear and eventually fusion power would meet future growth in energy demands.
A substantial body of work, both analytical and experimental, has established the technical feasibility of wireless transmission of useful amounts of power. Wireless transmission of power is similar in concept to information transmission by communications satellites, but at a higher intensity. However, because the radio frequency power beam is engineered for conversion back to electricity at very high efficiency, useful amounts of power could be transmitted at intensities less than that of sunlight. Experimental transmissions of power in amounts up to 30 kW have been accomplished over short distances (1.6 km) with conversion efficiencies in excess of 85% from incoming radio frequency power into electrical power.
Recent studies indicate that collection and transmission of power from space could become an economically viable means of exploiting solar power within the next couple of decades. A substantial maturation of certain technologies is needed and, most importantly, the cost of launching material to space must be significantly reduced. Very active efforts are being pursued in the aerospace community to achieve both of these goals.
Two types of WPT:
1) Ground based power transmission
2) Space based power transmission
But Space-based power transmission is preferred over Ground-based power transmission.
Ground is (obviously) cheaper per noontime watt, but:
¢ Space gets full power 24 hours a day
“ 3X or more Watt-hours per day per peak watt
“ No storage required for nighttime power
¢ Space gets full power 7 days a week “ no cloudy days
¢ Space gets full power 52 weeks a year
“ No long winter nights, no storms, no cloudy seasons
¢ Space delivers power where it™s needed
“ Best ground solar sites (deserts) are rarely near users
¢ Space takes up less, well, space
“ Rectennas are 1/3 to 1/10 the area of ground arrays
“ Rectennas can share land with farming or other uses
5.2. Wireless power transmission to the Earth:
Wireless power transmission was early proposed to transfer energy from collection to the Earth's surface. The power could be transmitted as either microwave or laser radiation at a variety of frequencies depending on system design. Whatever choice is made, the transmitting radiation would have to be non-ionizing to avoid potential disturbances either ecologically or biologically if it is to reach the Earth's surface. This established an upper bound for the frequency used, as energy per photon, and so the ability to cause ionization, increases with frequency. Ionization of biological materials doesn't begin until ultraviolet or higher frequencies so most radio frequencies will be acceptable for this.
To minimize the sizes of the antennas used, the wavelength should be small since antenna efficiency increases as antenna size increases relative to the wavelength used. More precisely, both for the transmitting and receiving antennas, the angular beam width is inversely proportional to the aperture of the antenna, measured in units of the transmission wavelength. The highest frequencies that can be used are limited by atmospheric absorption (chiefly water vapor and CO2) at higher microwave frequencies.
Conceptual model for a WPT system annexed to a grid.
The 50 Hz ac power tapped from the grid lines is stepped down to a suitable voltage level for rectification into dc. This is supplied to an oscillator fed magnetron. The microwave power output of the magnetron is channeled into an array of parabolic reflector antennas for transmission to the receiving end antennas. To compensate for the large loss in free space propagation and boost at the receiving end the signal strength as well as the conversion
efficiency, the antennas are connected in arrays. A series parallel assembly of schottky diodes, having a low standing power rating but good RF characteristics is used at the receiving end to rectify the received microwave power back into dc. Inverter is used to invert the dc power into ac.A simple radio control feedback system operating in FM band provides an appropriate control signal to the magnetron for adjusting its output level with fluctuation in the consumers demand at the receiving side.
5.3. Evolving WPT Markets:
Markets that will be made accessible with WPT will have a profound influence on global business activities and industry competitiveness. The following are examples of the future commercial opportunities of WPT:
1. Roadway powered electric vehicles for charging electric batteries with WPT from microwave generators embedded in the roadway while a vehicle is traveling at highway speed, thus eliminating stops to exchange or recharge batteries greatly extending travel range.
2. High-altitude, long-endurance aircraft maintained at a desired location for weeks or months at 20 km for communications and surveillance instead of satellites, at greatly reduced costs.
3. Power relay satellites to access remote energy sources by uncoupling primary electricity generation from terrestrial transmission lines (15). Power is transmitted from distant sites to geosynchronous orbit and then reflected to a receiver on Earth in a desired location.
4. Solar power satellites in low-Earth or geosynchronous orbit or on the Moon to supply terrestrial power demands on a global scale.
6. Spacecraft sizing
The size of an SPS will be dominated by two factors. The size of the collecting apparatus (eg, panels, mirrors, etc) and the size of the transmitting antenna which in part depends on the distance to the receiving antenna. The distance from Earth to geostationary orbit (22,300 miles, 35,700 km), the chosen wavelength of the microwaves, and the laws of physics, specifically the Rayleigh Criterion or Diffraction limit, used in standard RF (Radio Frequency) antenna design will all be factors.
It has been suggested that, for best efficiency, the satellite antenna should be circular and the microwave wavelength should be about 1 kilometers in diameter or larger; the ground antenna (rectenna) should be elliptical, 10 km wide, and a length that makes the rectenna appear circular. Smaller antennas would result in increased losses to diffraction/sidelobes. For the desired (23mW/cm²) microwave intensity these antennas could transfer between 5 and 10 gigawatts of power.
To be most cost effective, the system should operate at maximum capacity. And, to collect and convert that much power, the satellite would require between 50 and 100 square kilometers of collector area (if readily available ~14% efficient monocrystalline silicon solar cells were deployed). State of the art (currently, quite expensive, triple junction gallium arsenide) solar cells with a maximum efficiency of 40.7% could reduce the necessary collector area by two thirds, but would not necessarily give overall lower costs for various reasons.
6.1. LEO instead of GEO
A collection of LEO (Low Earth Orbit) space power stations has been proposed as a precursor to GEO (Geostationary Orbit) space power beaming systems. There would be both advantages (much shorter energy transmission path lengths allowing smaller antenna sizes, lower cost to orbit, energy delivery to much of the Earth's surface, assuming appropriate antennas are available, etc.) and disadvantages (constantly changing antenna geometries, increased debris collision difficulties, requirement of many more power stations to provide continuous power delivery at any particular point on the Earth's surface, etc.). It might be possible to deploy LEO systems sooner than GEO because the antenna development would take less time, but it would certainly take longer to prepare and launch the number of required satellites. Ultimately, because full engineering feasibility studies have not been conducted, it is not known whether this approach would be an improvement over a GEO installation.
6.2. Earth-based infrastructure(Rectenna)
The Earth-based receiver antenna (or rectenna) is a critical part of the original SPS concept. It would probably consist of many short dipole antennas, connected via diodes. Microwaves broadcast from the SPS will be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is still better, but the cost and complexity is also considerably greater, almost certainly prohibitively so. Rectennas would be multiple kilometers across. Crops and farm animals may be raised underneath a rectenna, as the thin wires used for support and for the dipoles will only slightly reduce sunlight, so such a rectenna would not be as expensive in terms of land use as might be supposed.
7. Comparison of Power Sources
Power
Generation Costs Cost/Watt Pros Cons
Nuclear Power State of the art facilities can generate up to 366 Gigawatts 3-5 billion for the facility $61.32 Extensive scientific data available
Technology has been established and used for decades
No greenhouse effects Nuclear proliferation
Larger capital costs
Security and risks of containment breaches
Fossil Fuels Dependent upon usage Currently oil is at $100 a barrel and expected to rise $53.42 Inexpensive and established
Currently Abundant and highly Versatile Pollution , acid rain and global warming
Extensive transportation
Limited Supply Increasing costs
Solar Power 19-56 watts per square meter. Max power generation limited only by size at a rate of <$1.00, dependent upon the size of the station <$1.00 (employing new technologies) Free as long as sunlight is available Requirement of special materials
Current technology requires large amounts of land for small amounts of energy generation
Solar Powered Satellites 230 watts per square meter up to 8.75 terawatts 70-80 billion including launch costs <$1.00 (employing new technologies) Can produce electricity 24 hours a day, 7 days a week.
Satellite can transmit power to different areas globally Extremely expensive
8. Advantages & Disadvantages
8.1. Advantages:
The SPS concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power. There is no air in space, so the collecting surfaces would receive much more intense sunlight, unaffected by weather. In geostationary orbit, an SPS would be illuminated over 99% of the time. The SPS would be in Earth's shadow on only a few days at the spring and fall equinoxes; and even then for a maximum of 75 minutes late at night when power demands are at their lowest. This characteristic of SPS based power generation systems to avoid the expensive storage facilities (eg, lakes behind dams, oil storage tanks, coal dumps, etc) necessary in many Earth-based power generation systems. Additionally, an SPS will have none of the polluting consequences of fossil fuel systems, nor the ecological problems resulting from many renewable or low impact power generation systems (eg, dam retention lakes).
Economically, an SPS deployment project would create many new jobs and contract opportunities for industry, which may have political implications in the country or region which undertakes the project. Certainly the energy from an SPS would reduce political tension resulting from unequal distribution of energy supplies (eg, oil, gas, etc). For nations on the equator, SPS provides an incentive to stabilise and a sustained opportunity to lease land for launch sites.
Developing the industrial capacity needed to construct and maintain one or more SPS systems would significantly reduce the cost of other space endeavours. For example, a manned Mars mission might only cost hundreds of millions, instead of tens of billions, if it can rely on an already existing capability.
Space solar power would be the only means of acquiring direct solar energy to supplement the burning of fossil fuels or nuclear energy sources under the most extreme conditions of a global catastrophic volcanic winter (or similarly, nuclear winter).
1. Unlimited energy resource.
2. Energy delivered anywhere in the world.
3. Zero fuel cost.
4. Zero CO2 emission.
5. Minimum long-range environmental impact.
6. Solar radiation can be more efficiently collected in space.
8.2. Disadvantage:
1. Storage of electricity during off peak demand hours .
2. The frequency of beamed radiation is planned to be at 2.45 GHz and
this frequency is used by communication satellites also.
3. The entire structure is massive.
4. High initial cost and require much time for construction.
5. Radiation hazards associated with the system.
6. Launch costs.
7. Capital cost even given cheap launchers.
8. Would require a network of hundreds of satellites.
9. Possible health hazards.
10. The size of the antennas and rectennas.
11. Geosynchronous satellites would take up large sections of space.
12. Interference with communication satellites.


9. Conclusion
The economic case for a solar power satellite is most compelling if the solar power satellite can generate power that sells at peak, rather than average, price.. Several new designs for solar power satellites were considered, in an attempt to maximize the amount of power produced at peak rates. This study has given researchers a remarkable insight into uncertain future of development of power from space.
There is little doubt that the supply of energy must be increased dramatically in coming decades. Furthermore, it appears almost certain that there will be a shift toward renewable sources and that solar will be a major contributor. It is asserted that if the energy system of the world is to work for all its people and be adequately robust, there should be several options to develop in the pursuit of and expanded supply. While the option of Space Solar Power may seem futuristic at present, it is technologically feasible and, given appropriate conditions, can become economically viable. It is asserted that it should be among those options actively pursued over coming decades. The challenges to the implementation of Space Solar Power are significant, but then no major expansion of energy supply will be easy. These challenges need to be tackled vigorously by the space, energy and other communities.
Finally, it should be emphasized that if we fail to develop sustainable and clean energy sources and try to limp along by extrapolating present practices, the result is very likely to be thwarted development of economic opportunities for many of the Earth's people and, almost certainly, adverse changes to the planetary environment.
The resolve of the synthesis problem of the WPT shows that WPT efficiency may be improved by using special current discontinuous distribution on the antenna. Here we have three possibilities:
1. To use a discontinuous equidistant array with the quasi Gauss distribution.
2. To use a discontinuous non-equidistant array with the uniform distribution.
3. To use uniform continuous phase synthesis antenna array.
All of these methods are original and they have been modeled only in the frame of International Science and Technology Center Project.
The possibility of decrease of the wave beam expansion permits to make the WPT systems less expensive. Such approach to the problem of the continuous radiators and of the real antennas, which can be created, is new.
Due to high launch costs, SPS is still more expensive than Earth-based solar power and other energy sources. Yet, even now, a small SPS system could be economically justified to provide otherwise unavailable emergency power for natural disaster situations, urban blackouts and satellite power failures.
10. Reference
1. P.E. Glaser «Method and Apparatus for Converting Solar radiation toElectrical Power», U.S. Patent 3 781 647, 1973.
2. R. Bryan Erb, "Space-Based Solar Power - How Soon and How Much", 49th Congress of the International Astronautical Federation, Paper IAF-98-R.2.02, Melbourne, Australia, September 28 - October 2, 1998.
3. WEC/IIASA, Global Energy Perspectives, Nakicenovic, Nebojsa, et al, Cambridge University Press, 1998.
4. P. E. Glaser, "An overview of the solar power satellite option," IEEE Transactions on Microwave Theory and Techniques, vol. 40, no. 6, pp. 1230-1238, June 1992.
5. W. C. Brown and E. E. Eves, "Beamed microwave power transmission and its application to space," IEEE Transactions on Microwave Theory and Techniques, vol. 40, no. 6, June 1992.
6. World Energy Council, "Energy for Tomorrowâ„¢s World - Acting Now", WEC Statement 2000, worldenergy.org.
7. nspri.com

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Solar Power Satellites and Microwave Power Transmission

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Presented By:
Andrew K. Soubel
Chicago-Kent College of Law

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Outline
Background
Solar Power Satellite
Microwave Power Transmission
Current Designs
Legal Issues
Conclusion
Background
1899-1990
Nikola Tesla
1856-1943
Innovations:
Alternating current
Wireless power transmission experiments at Wardenclyffe
Wardenclyffe
1899
Able to light lamps over 25 miles away without using wires
High frequency current, of a Tesla coil, could light lamps filled with gas (like neon)
1940â„¢s to Present
World War II developed ability to convert energy to microwaves using a magnetron, no method for converting microwaves back to electricity
1964 William C. Brown demonstrated a rectenna which could convert microwave power to electricity
Brief History of Solar Power
1940-50â„¢s Development of the Photovoltaic cell
1958 First US Satellite that used Solar Power
1970â„¢s Oil embargo brought increased interest and study
Solar Power from Satellites
1968â„¢s idea for Solar Power Satellites proposed by Peter Glaser
Would use microwaves to transmit power to Earth from Solar Powered Satellites
Idea gained momentum during the Oil Crises of 1970â„¢s, but after prices stabilized idea was dropped
US Department of Energy research program 1978-1981
Details of the DOE Study
Construct the satellites in space
Each SPS would have 400 million solar cells
Use the Space Shuttle to get pieces to a low orbit station
Tow pieces to the assembly point using a purpose built space tug (similar to space shuttle)
Advantages over Earth based solar power
More intense sunlight
In geosynchronous orbit, 36,000 km (22,369 miles) an SPS would be illuminated over 99% of the time
No need for costly storage devices for when the sun is not in view
Only a few days at spring and fall equinox would the satellite be in shadow
Continued
Waste heat is radiated back into space
Power can be beamed to the location where it is needed, donâ„¢t have to invest in as large a grid
No air or water pollution is created during generation
Problems
Issues identified during the DOE study
Complexity”30 years to complete
Size”6.5 miles long by 3.3 miles wide
Transmitting antenna ½ mile in diameter(1 km)
Continued
Cost”prototype would have cost $74 billion
Microwave transmission
Interference with other electronic devices
Health and environmental effects
1980â„¢s to Present
Japanese continued to study the idea of SPS throughout the 1980â„¢s
In 1995 NASA began a Fresh Look Study
Set up a research, technology, and investment schedule
NASA Fresh Look Report
SPS could be competitive with other energy sources and deserves further study
Research aimed at an SPS system of 250 MW
Would cost around $10 billion and take 20 years
National Research Council found the research worthwhile but under funded to achieve its goals
Specifications
Collector area must be between 50 (19 sq miles) and 150 square kilometers (57 sq miles)
50 Tons of material
Current rates on the Space Shuttle run between $3500 and $5000 per pound
50 tons (112,000lbs)=$392,000,000
Continued
There are advantages
Possible power generation of 5 to 10 gigawatts
If the largest conceivable space power station were built and operated 24 hours a day all year round, it could produce the equivalent output of ten 1 million kilowatt-class nuclear power stations.
Possible Designs


Deployment Issues
Cost of transporting materials into space
Construction of satellite
Space Walks
Maintenance
Routine
Meteor impacts
Possible Solutions
International Space Station
Presidentâ„¢s plan for a return to the moon
Either could be used as a base for construction activities
Microwave Power Transmission
How the power gets to Earth
From the Satellite
Solar power from the satellite is sent to Earth using a microwave transmitter
Received at a rectenna located on Earth
Recent developments suggest that power could be sent to Earth using a laser
Microwaves
Frequency 2.45 GHz microwave beam
Retro directive beam control capability
Power level is well below international safety standard
Microwave vs. Laser Transmission
Microwave
More developed
High efficiency up to 85%
Beams is far below the lethal levels of concentration even for a prolonged exposure
Cause interference with satellite communication industry
Laser
Recently developed solid state lasers allow efficient transfer of power
Range of 10% to 20% efficiency within a few years
Conform to limits on eye and skin damage
Rectenna
An antenna comprising a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.
Microwaves are received with about 85% efficiency
Around 5km across (3.1 miles)
95% of the beam will fall on the rectenna
Rectenna Design
Currently there are two different design types being looked at
Wire mesh reflector
Built on a rigid frame above the ground
Visually transparent so that it would not interfere with plant life
Magic carpet
Material pegged to the ground
5,000 MW Receiving Station (Rectenna). This station is about a mile and a half long.
Rectenna Issues
Size
Miles across
Location
Aesthetic
Near population center
Health and environmental side effects
Although claim that microwaves or lasers would be safe, how do you convince people
Current Developments
SPS 2000
Details
Project in Development in Japan
Goal is to build a low cost demonstration model by 2025
8 Countries along the equator have agreed to be the site of a rectenna
Continued
10 MW satellite delivering microwave power
Will not be in geosynchronous orbit, instead low orbit 1100 km (683 miles)
Much cheaper to put a satellite in low orbit
200 seconds of power on each pass over rectenna
Power to Mobile Devices
If microwave beams carrying power could be beamed uniformly over the earth they could power cell phones
Biggest problem is that the antenna would have to be 25-30 cm square

Low Orbit
Communications industry proposing to have hundreds of satellites in low earth orbit
These satellites will use microwaves to beam communications to the ground
Could also be used to beam power
Continued
Since a low orbit microwave beam would spread less, the ground based rectenna could be smaller
Would allow collectors on the ground of a few hundred meters across instead of 10 kilometers
In low orbit they circle the Earth in about every 90 minutes
Issues
Would require a network of hundreds of satellites
Air Force currently track 8500 man made objects in space, 7% satellites
Would make telecommunications companies into power companies
Reliability
Ground based solar only works during clear days, and must have storage for night
Power can be beamed to the location where it is needed, donâ„¢t have to invest in as large a grid
A network of low orbit satellites could provide power to almost any point on Earth continuously because one satellite would always be in range
Legal Issues
Who will oversee?
Environmental Concerns
International
NASA
Funding the research
In charge of space flight for the United States
Would be launching the satellites and doing maintenance
FCC
Federal Communications Commission
The FCC was established by the Communications Act of 1934 and is charged with regulating interstate and international communications by radio, television, wire, satellite and cable.
Environmental
Possible health hazards
Effects of long term exposure
Exposure is equal to the amount that people receive from cell phones and microwaves
Location
The size of construction for the rectennas is massive
International
Geosynchronous satellites would take up large sections of space
Interference with communication satellites
Low orbit satellites would require agreements about rectenna locations and flight paths
Conclusions
More reliable than ground based solar power
In order for SPS to become a reality it several things have to happen:
Government support
Cheaper launch prices
Involvement of the private sector

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1.Abstract:
A solar power satellite as originally proposed would be a satellite built in high Earth orbit that uses microwave power transmission to beam solar power to a very large antenna on Earth. Space-based solar power (SBSP) is a theoretical design for the collection of solar power in space, for use on Earth. SBSP differs from the usual method of solar power collection in that the solar panels used to collect the energy would reside on a satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface
Introduction:
An artist's depiction of a solar satellite, which could send energy wirelessly to a space vessel or planetary surface.
A solar power satellite, or SPS or Powersat, as originally proposed would be a satellite built in high Earth orbit that uses microwave power transmission to beam solar power to a very large antenna on Earth. Advantages of placing the solar collectors in space include the unobstructed view of the Sun, unaffected by the day/night cycle, weather, or seasons. It is a renewable energy source, zero emission, and generates no waste. However, the costs of construction are very high, and SPS will not be able to compete with conventional sources (at current energy prices) unless at least one of the following conditions is met.
Low launch costs can be achieved
A space-based manufacturing industry develops that is capable of building solar power satellites in orbit, using off-Earth materials.
In common with other types of renewable energy such a system could have advantages to the world in terms of energy security via reduction in levels of conflict, military spending, loss of life, and avoiding future conflict over dwindling energy sources.
An artist's concept of a solar power satellite, 1976. (NASA)
The SPS concept was first described in November 1968. At first it was regarded as impractical due to the lack of a workable method of sending power collected down to the Earth's surface. This changed in 1973 when Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (eg, from an SPS to the Earth's surface) using microwaves from a, perhaps square kilometer, antenna on the satellite to a much larger one on the ground, which came to be known as a rectenna.
Glaser then worked at Arthur D. Little, Inc., as a vice-president. NASA became interested and signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems -- chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research.
Description:
The SPS essentially consists of three parts:
¢ a solar collector, typically made up of solar cells
¢ a microwave antenna on the satellite, aimed at Earth
¢ one or more paired, and much larger, antennas (rectennas) on the Earth's surface
Spacecraft design:
In many ways, the SPS is a simpler conceptual design than most power generation systems previously proposed. The simple aspects include the physical structure required to hold the SPS together and to align it orthogonally to the Sun. This will be considerably lighter than any similar structure on Earth since it will be in a zero-g, vacuum environment and will not need to support itself against a gravity field and needs no protection from terrestrial wind or weather.
Solar photons will be converted to electricity aboard the SPS spacecraft, and that electricity will be fed to an array of Klystron tubes which will generate the microwave beam.
Solar energy conversion (solar photons to DC current):
Two basic methods of converting photons to electricity have been studied,
¢ Solar dynamic (SD) and
¢ Photovoltaic (PV).
SD uses a heat engine to drive a piston or a turbine which connects to a generator or dynamo. Two heat cycles for solar dynamic are thought to be reasonable for this: the Brayton cycle or the Stirling cycle. Terrestrial solar dynamic systems typically use a large reflector to focus sunlight to a high concentration to achieve a high temperature so the heat engine can operate at high thermodynamic efficiencies; an SPS implementation is expected to be similar.
PV uses semiconductor cells (e.g., silicon or gallium arsenide) to directly convert sunlight photons into voltage via a quantum mechanical mechanism. These are commonly known as solar cells, and will likely be rather different from the glass panel protected solar cell panels familiar to many and in current terrestrial use. They will, for reasons of weight, probably be built in membrane form, not suitable to terrestrial use which is subject to considerable gravitational loading.
Comparison of PV versus SD:
The main problems with PV are that PV cells continue to be relatively expensive, and require a relatively large area to be acceptable. In addition, being semiconductors, the PV panels will require a reasonably large amount of energy to produce.
SD is a more mature technology, having been in widespread use in many contexts for centuries. But, SD has a much more severe pointing requirement than PV because most proposed designs require accurate and stable optical focus. If a PV array drifts off a few degrees, the power being produced will drop a few percent. But, if an SD array drifts off a few degrees, the power produced will drop off very quickly to zero, or near to it.
Currently, PV cells weigh between 0.5kg/kW and 10kg/kW depending on design. SD designs also vary but most seem to be heavier per kW produced than PV cells and thus this pushes up launch costs.
Lifetime:
The lifetime of a PV based SPS is limited mainly by the ionizing radiation from the radiation belts and the Sun. Without some method of protection, this is likely to cause the cells to continuously degrade by about a percent or two per year. Deterioration is likely to be more rapid during periods of high exposure to energetic protons from solar particle events[. If some practical protection can be designed, this also might be reducible.
Lifetimes for SD based SPS designs will be limited by structural and mechanical considerations, such as micrometeorite impact, metal fatigue of turbine blades, wear of sliding surfaces (although this might be avoidable by hydrostatic bearings or magnetic bearings), degradation or loss of lubricants and working fluids in vacuum, from loss of structural integrity leading to impaired optical focus amongst components, and from temperature extreme effects. As well, most mirror surfaces will degrade from both radiation and particle impact, but such mirrors can be designed simply (and so light and cheap), so replacement may be practical.
In either case, another advantage of the SPS design is that waste heat developed at collection points is re-radiated back into space, instead of warming the adjacent local biosphere as with conventional sources; thus thermal efficiency will not be in itself an important design parameter except insofar as it affects the power/weight ratio via operational efficiency and hence pushes up launch costs. (For example SD may require larger radiators when operating at a lower efficiency). Earth based power handling systems must always be carefully designed, for both economic and purely engineering reasons, with operational thermal efficiency in mind.
Energy payback:
Clearly for a system (including manufacture, launch and deployment) to provide net power it must repay the energy needed to construct it. For current silicon PV panels the energy needs are relatively high and typically several years of deployment in a terrestrial environment are needed to recover this energy. With SPS net energy received on the ground is higher (more or less necessarily so, for the system to be worth deploying), so this energy payback period would be somewhat reduced; however SD, being made of conventional materials, are more similar to conventional powerstations and are likely to be less energy intensive and would be expected to give quicker energy break even, depending on construction technology.
Wireless power transmission to the Earth:
Wireless power transmission was early proposed to transfer energy from collection to the Earth's surface. The power could be transmitted as either microwave or laser radiation at a variety of frequencies depending on system design. Whatever choice is made, the transmitting radiation would have to be non-ionizing to avoid potential disturbances either ecologically or biologically if it is to reach the Earth's surface. This established an upper bound for the frequency used, as energy per photon, and so the ability to cause ionization, increases with frequency. Ionization of biological materials doesn't begin until ultraviolet or higher frequencies so most radio frequencies will be acceptable for this.
William C. Brown demonstrated in 1964 on CBS news with Walter Cronkite, a microwave-powered model helicopter that received all the power needed for flight from a microwave beam. Between 1969 and 1975 Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW over a distance of 1 mile at 84% efficiency.
As well, to minimize the sizes of the antennas used, the wavelength should be small (and frequency correspondingly high) since antenna efficiency increases as antenna size increases. But, higher radio frequencies are typically more absorbed in the atmosphere than lower radio frequencies.
For these reasons, 2.45 GHz has been proposed as being a reasonable compromise. However, that frequency results in large antenna sizes at the GEO distance. A loitering stratospheric airship has been proposed to receive higher frequencies (or even laser beams), converting them to something like 2.45 GHz for retransmission to the ground. The proposal has not been as carefully evaluated for engineering plausibility as other aspects of SPS design.
Spacecraft sizing:
The sizing will be dominated by the distance from Earth to geostationary orbit (22,300 miles, 35,700 km), the chosen wavelength of the microwaves, and the laws of physics, specifically the Rayleigh Criterion or Diffraction limit, used in standard RF (Radio Frequency) antenna design.
For best efficiency, the satellite antenna should be circular and about 1 kilometers in diameter or larger; the ground antenna (rectenna) should be elliptical and around 14 kilometers by 10 kilometers. Smaller antennas would result in increased losses to diffraction/sidelobes. For the desired (23mW/cm²) microwave intensity these antennas could transfer between 5 and 10 gigawatts of power. To be most cost effective, the system needs to operate at maximum capacity. And, to collect and convert that much power, the satellite would need between 50 and 100 square kilometers of collector area (if readily available ~14% efficient monocrystalline silicon solar cells were deployed). State of the art (currently, quite expensive, triple junction gallium arsenide) solar cells with a maximum efficiency of 40.7% could reduce the necessary collector area by two thirds, but would not necessarily give overall lower costs. In either case, the SPS's structure would be kilometers wide, making it larger than most man-made structures here on Earth. While almost certainly not beyond current engineering capabilities, building structures of this size in orbit has not yet been attempted.
Earth based infrastructure:
The Earth-based receiver antenna (or rectenna) is a critical part of the original SPS concept. It would probably consist of many short dipole antennas, connected via diodes. Microwaves broadcast from the SPS will be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is still better, but the cost and complexity is also considerably greater, almost certainly prohibitively so. Rectennas would be multiple kilometers across. Crops and farm animals may be raised underneath a rectenna, as the thin wires used for support and for the dipoles will only slightly reduce sunlight, so such a rectenna would not be as expensive in terms of land use as might be supposed.
Advantages of an SPS:
The SPS concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power. There is no air in space, so the collecting surfaces would receive much more intense sunlight, unaffected by weather. In geostationary orbit, an SPS would be illuminated over 99% of the time. The SPS would be in Earth's shadow on only a few days at the spring and fall equinoxes; and even then for a maximum of 75 minutes late at night when power demands are at their lowest. This allows the power generation system to avoid the expensive storage facilities (eg, lakes behind dams, oil storage tanks, etc) necessary in many Earth-based power generation systems. Additionally, an SPS will avoid entirely the polluting consequences of fossil fuel systems, the ecological problems resulting from many renewable or low impact power generation systems (eg, dams).
More long-term, the potential amount of power production is enormous. If power stations can be placed outside Earth orbit, the upper limit is vastly higher still. In the extreme, such arrangements are called Dyson spheres.
Problems:
Problems are:-
¢ Launch costs
¢ Safety
¢ Defending solar power satellites
Launch costs:
Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility, that high efficiency (but slower) engines could move SPS material from LEO to GEO at acceptable cost. Examples include ion thrusters or nuclear propulsion. They might even be designed to be reusable.
Safety
The use of microwave transmission of power has been the most controversial issue in considering any SPS design, but any thought that anything which strays into the beam's path will be incinerated is an extreme misconception. Consider that quite similar microwave relay beams have long been in use by telecommunications companies world wide without such problems.
The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe "death ray" levels, even in principle.
In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations.
Defending solar power satellites
Solar power satellites would normally be at a high orbit that is difficult to reach, and hence attack.
However, it has been suggested that a large enough quantity of granular material placed in a retrograde orbit at the geostationary altitude could theoretically completely destroy these kinds of system and render that orbit useless for generations.
Whether this is a realistic attack scenario is arguable, and in any case at the present time there is only a small list of countries with the necessary launch capability to do this, such an attack would probably be considered an act of war, and conventional power generators are more easily attacked.
SPS's economic feasibility
SPSâ„¢s economic feasibility are
¢ Current energy price landscape
¢ Comparison with fossil fuels
¢ Comparison with nuclear power (fission)
¢ Comparison with nuclear fusion
¢ Comparison with terrestrial solar power
¢ Comparison with Other Renewables (wind, tidal, hydro, geothermal)
Current energy price landscape
In order to be competitive on a purely economic level, an SPS must cost no more than existing supplies (Such costs must include the costs of cleaning waste from construction, operation and dismantling of the generating systems--including lifestyle and health costs.. Currently(2007) most Earth-based power generation does not include these costs. The cost figures below are undated, but are obsolete as of 2007. This greatly reduces the prices paid for power currently reducing the apparent benefits of SPS'.) This may be difficult, especially if it is deployed for North America, where energy costs have been relatively low. It must cost less to deploy, or operate for a very long period of time, or offer other advantages. Many proponents have suggested that the lifetime is effectively infinite, but normal maintenance and replacement of less durable components makes this unlikely. Satellites do not, in our now-extensive experience, last forever. (But with regular maintenance there is no reason that a high orbit satellite has to 'die.' Currently (2007) the majority of such satellites--weather and communications, fail due to correctable maintenance issues which we do not correct because we have no repair people on site. Common failures are: running out of station keeping fuel or dead batteries-no longer holding a charge. Neither of these failure modes is much of a problem if service is available. With available refueling and battery replacement, the life of a satellite can be greatly increased. Structural components, which make up the largest percentage of mass, seldom fail. Nearly all of the other components can be modularized for easy replacement/upgrade.)
Comparison with fossil fuels:
The relatively low price of energy today is entirely dominated by the low cost of carbon based fossil fuels (eg, petroleum, coal and natural gas).
There are several problems with existing energy delivery systems. They are subject to political instability for various reasons in various locations -- so that there are large hidden costs in maintaining military or other presence so as to continue supplies depletion (some well regarded estimates suggest that oil and gas reserves have been in net decline for some time and that price increases and supply decreases are inevitable), greenhouse pollution -- all fossil fuel combustion emits enormous quantities of carbon dioxide (CO2), a greenhouse gas, contributing to global warming and climate change.
Comparison with nuclear power (fission);
Detailed analyses of the problems with nuclear power specifically (nuclear fission) are published elsewhere. Some are given below, with some comparative comments: nuclear proliferation -- not a problem with SPS disposal and storage of radioactive waste -- not a problem with SPS preventing fissile material from being obtained by terrorists or their sponsors -- not a problem with SPS public perception of danger -- problem with both SPS and nuclear power consequences of major accident, e.g., Chernobyl -- effectively zero with SPS, save on launch (during construction or for maintenance)military and police cost of protecting the public and loss of democratic freedoms -- control of SPS would be a power/influence center, perhaps sufficient to translate into political power. However, this has not yet happened in the developed world with nuclear power.
On balance, SPS avoids nearly all of the problems with current nuclear power schemes, and does not have larger problems in any respect, although public perception of microwave power transfer (ie, in the beams produced by an SPS and received on Earth) dangers could become an issue.
Comparison with nuclear fusion
Nuclear fusion is a process used in thermonuclear bombs (e.g., the H-bomb). Projected nuclear fusion power plants would not be explosive, and will likely be inherently failsafe. However, sustained nuclear fusion generators have only just been demonstrated experimentally, despite well funded research over a period of several decades (since approximately 1952). There is still no credible estimate of how long it will be before a nuclear fusion reactor could become commercially possible; fusion research continues to receive substantial funding by many nations. For example, the ITER facility currently under construction will cost ‚¬10 billion. There has been much criticism of the value of continued funding of fusion research. Proponents have successfully argued in favor of ITER funding.
By contrast, SPS does not require any fundamental engineering breakthroughs, has already been extensively reviewed from an engineering feasibility perspective over some decades, and needs only incremental improvements of existing technology to be deployed. Despite these advantages, SPS has received minimal research funding to date.
Comparison with terrestrial solar power
Let us consider a ground-based solar power system versus an SPS generating an equivalent amount of power.
Such a system would require a very large solar array built in a well-sunlit area, the Sahara Desert for instance. An SPS requires much less ground area per kilowatt (approx 1/5th). There is no such area in the UK.
The rectenna on the ground is much larger than the area of the orbiting solar panels. A ground-only solar array would have the advantage, compared to a GEO (Geosynchronous orbit) solar array, of costing considerably less to construct and requiring no significant technological advances. A small version of such a ground based array has recently been completed by General Electric in Portugal.
Weather conditions would also interfere with power collection, and will cause wear and tear on solar collectors which will be avoided in Earth orbit; for instance, sandstorms cause devastating damage to human structures via, for example, abrasion of surfaces as well as mechanically large wind forces causing direct physical damage. Terrestrial systems are also more vulnerable to terrorism than an SPS's rectenna since they are more expensive, complex, intolerant of partial damage, and harder to repair/replace. Wear and tear on orbital installations will be of very different character, for quite different reasons, and can be reduced by care in design and fabrication. Long experience with terrestrial installations shows that there is substantial, inescapable maintenance for any economically feasible electrical installation.
Remote tropical location of an extensive photovoltaic generator is a somewhat artificial scenario, as photovoltaic costs continue to decline. Deployment of ground-based photovoltaics can be distributed (say to rooftops), but nevertheless, the required acreage (at any credible solar cell efficiency) will remain very large, and maintenance cost and effort will increase substantially compared to a large centralized design. In any case, dispersed installation is not possible for some terrestrial solar collectors.
Both SPS and ground-based solar power could be used to produce chemical fuels for transportation and storage, as in the proposed hydrogen economy. Or they could both be used to run an energy storage scheme (such as pumping water uphill at a hydropower generation station).
Many advances in solar cell efficiency (eg, improved construction techniques) that make an SPS more economically feasible might make a ground-based system more economic as well. Also, many SPS designs assume the framework will be built with automated machinery supplied with raw materials, typically aluminium. Such a system could be (more or less easily) adapted for operation on Earth, no launching required. However, Earth-based construction already has access to inexpensive human labor that would not be available in space, so such construction techniques would have to be extremely competitive to be significant on Earth.
Comparison with Other Renewables (wind, tidal, hydro geothermal)
Other renewable energy sources (e.g., wind energy, tidal energy, hydro-electric, geothermal, ethanol), have the capacity to supply only a tiny fraction of the global energy requirement, now or in the foreseeable future. For most, the limitation is geography as there simply are very few sites in the world where generating systems can be built, and for hydro-electric projects in particular, there are few sites still open. For 2005, in the US, hydro-electric power accounted for 6.5% of electricity generation, and other renewables 2.3%. The U.S. Govt. Energy Information Administration projects that in 2030 hydro-power will decline to 3.4% and other renewables will increase to 2.9%.
Ocean-based wind power is one possibility (there being large areas for potential installations), but it is strongly affected by two factors; the difficulty of long distance power transmission as many regions of high demand are not near the sea, and be the very large difficulty of coping with corrosion, contamination, and survivability problems faced by all seaborne installations.
Ethanol power production depends on farming in the case of corn or sugar cane origin ethanol, currently the two leading sources. There is insufficient farming capacity for both significant energy production and food production. Corn prices have risen substantially in 2006 and 2007, partly as a result of nascent ethanol production demand. Ethanol from cellulose (eg, agricultural waste or purpose collected non-cultivated plants, eg, switchgrass) is not practicable as of 2007, though pilot plants are indevelopment. Processing improvements (eg, a breakthrough in enzyme processing) may change this relative disadvantage.
Current work:
For the past several years there has been no line item for SPS in neither the NASA nor DOE budgets, a minimal level of research has been sustained through small NASA discretionary budget accounts. NASA's "Fresh Look" study in 2000--NASA (Japan's national space agency) has been researching in this area steadily for the last few years. In 2001 plans were announced to perform additional research and prototyping by launching an experimental satellite of capacity between 10 kilowatts and 1 megawatt of power.
The National Space Society (a non-profit NGO) maintains a web page where the latest SPS related references are posted and kept current.
In May 2007 a workshop was held at MIT in the U.S.A. to review the current state of the market and technology.
In 2007 the U.S. Department of Defense expressed interest in studying the concept. On 10/10/2007 The National Security Space Office of the US Department of Defense, published an assessment report [71]. The report was released at a press conference which simultaneously announced the formation of the Space Solar Alliance for Future Energy which intends to pursue the recommendations of the NSSO-Led Study.
Conclusion:
In order to sustain todayâ„¢s competition and to implement a disturbance less communication all over the world, solar power satellite play a vital role. Even though it requires a lot of money to implement but the final product is durable, more efficient and of course since it is based on solar power which is non-exhaustive and hence does not require any external power source.
Reference:
http://google.com
http://wikipedia.com

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satellite

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Satellite Imagery

An Unusual Approach to Introducing Physics
A Princeton University “Freshman Seminar” created by Dan Marlow and
Eric Prebys

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Why focus on weather satellites?

Although it sounds like an obscure hobbyist’s niche, this topic will allow us to highlight a wide variety of basic physics topics, including…
Newton’s laws and Kepplerian orbits (rocket and satellite motion).
Basic optics (image formation)
Electromagnetic waves (signal transmission)
Signal encoding (amplitude modulation, frequency modulation)
Fundamental electronics (construction of the FM receiver)
Computerized data acquisition and analysis (decoding the signal and displaying the picture)
Dynamics of weather (convection, Coriolis force, etc).

[attachment=8999]
SOLAR POWER SATELLITE
SPS
 COLLECTOR
 TRANSMMITER
 BEAM CONTROLLER
COLLECTOR
Solar Energy Conversion
SPS
 TRANSMMITER
 BEAM CONTROLLER
 RECEIVER
What Happens When The Sun Is Hidden ?
APPLICATION
• Power to the Earth
• Power delivery to Moon Element
• Power delivery to Mars
ADVANTAGES
• WEATHER
• EFFECT ON HEALTH
CONCLUSION
The SPS system appears as a promising solution for power delivery to elements on planet surfaces. In both Mars and Moon cases, it could be a solution for users, which face the problem of either low solar energy density and environment attenuation or long eclipse duration. It appears as today’s only alternative to nuclear power sources.

Submitted By
Pranay G. Umate

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[attachment=9835]
ABSTRACT
The Solar Power Satellite (SPS) system is a candidate solution to deliver power to space vehicles or to elements on planetary surfaces. It relies on RF or laser power transmitting systems, depending on the type of application and relevant constraints. The SPS system is characterized by the frequency of the power beam, its overall efficiency and mass. It is driven by user needs and SPS location relative to the user. Several wavelengths can be considered for laser transmission systems. The visible and near infrared spectrum, allowing the use of photovoltaic cells as receiver surface, has been retained. Different frequencies can be used for the RF transmission system. The 35 GHz frequency has been considered as a good compromise between transmission efficiency and available component performances.
The utilization of the SPS to deliver power to small rovers or human outpost on Mars, and to an infrastructure on the Moon allows to assess different drivers in terms of user needs, receiver surface, distance between SPS and target, and to perform a preliminary sizing, based on current or reasonably achievable technologies, with respect to different sets of constraints. The SPS system appears as an attractive solution for these applications. The use of advanced or new technologies would drastically lower mass and increase the performances of the SPS system.
INTRODUCTION
Power generation is one of the crucial elements of space vehicles and of future infrastructures on planets and moons. The increased demand for power faces many constraints, in particular the sizing of the power generation system, driven by eclipse periods and the solar intensity at the operational spot. In the medium term, Earth orbiting platforms will require higher power levels. Interplanetary exploration vehicles face the problem of distance to the Sun, especially when high power levels may be needed. Large infrastructures on the Moon and planets, like Mars, are constrained by environment attenuation, long eclipse or distance to the Sun.
New systems and technologies have to be found, which go beyond simple improvements of the current technologies. Solar Power Satellite (SPS) systems, based on wireless power transmission, are attractive candidate solutions to provide power to space vehicles or to elements on planetary surfaces Studies have been carried out for many years on the problem of providing renewable electrical energy from space to Earth with SPS. The initializing for the solar power satellite (SPS) was optimized to a 1-km transmitting antenna producing 5 GW of DC power from a receiving antenna approximately 10 km in diameter. There are advantages to a lower power output and a smaller rectenna. Commercial utility companies prefer to integrate lower power levels into the irgrids .Rectennas smaller than the 10-km diameter in the reference configuration would make more rectenna sites available. Satellites are a revolution in telecommunication (in 20th century) has changed the way the people live.
Solar Power Satellite
A solar power satellite is a way to produce commercial electric power. A solar power satellite at GEO or other orbit sends the electric power gathered by its large solar panels to Earth using few GHz microwaves. The ground based receiver is an antenna field of about ten square kilometer area. The overall efficiency of microwave transfer from solar panel DC power to earthly grid AC power is about 50% and the power produced by a single satellite is of order one gigawatt. The power density of the microwave beam has been selected to be safely low so that for example a bird can conveniently fly through it without feeling a need to land and cool off. On the other hand, the microwave beam spreads during the long transfer distance, which is why the receiving antenna field has to be fairly large. From the constraints follows a characteristic unit power of GW order. This power level suits well for electricity production, although it complicates the building of small demonstration plants.
Taking the solar panels to space has two important benefits compared to installing them on ground. First, there is no night, clouds or winter in space, thus the plant can produce continuous electric power and consequently there is no energy storage problem. Second, in space one can use concentrator type solar collectors. The majority of the surface area of these collectors consists of lightweight parabolic reflector or Fresnel lens so that one needs much less of the expensive semiconductor. In ground-based panels, it is usually not economical to use concentrator type collectors because they produce no electricity in cloudy weather, require a sun-follower mechanism and support structures to withstand the wind load. If the production costs of solar panels come down markedly from their present level (at least by an order of magnitude), the latter benefit gets eliminated, but the first benefit, i.e. the absence of the energy storage problem, remains in any case.
Transmitter
The MPT use to the semiconductor amplifier is linearity of amplifier because power level of the MPT is much higher than that for wireless communication system and we have to suppress unexpected spurious radiation to reduce interference. The maximum efficiency usually is realized at saturated bias voltage. It does not guarantee the linearity between input and output microwaves and non-linearity causes high spurious which must be suppressed in the MPT. Therefore, dissolution of tortuous relationship between efficiency and linearity is expected by the MPT. There are unique development items for the SPS from the microwave point of view distinguished from the ordinary use of the microwave technology such as telecommunications
Receivers (Rectenna)
SPS, we need a huge rectenna site and a power network connected to the existing power networks on the ground. On contrary, there are some MPT applications with one small rectenna element such as RF-ID. The word “rectenna” is composed of “rectifying circuit” and “antenna”. The single shunt full-wave rectifier is always used for the rectenna.

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presented by:
PRANEETH DHANRAJ

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INTRODUCTION
 The concept of SATELLITE POWER SYSTEM was proposed by P.E.GLASER in 1968 to meet both space based and earth based power needs.
 This power station a satellite for transmission of its generated power called SOLAR POWER SATELLITE(SPS).
SOLAR POWER SATELLITE
 The concept of the Solar Power Satellite (SPS) is very simple.
 It is a gigantic satellite designed as an electric power plant orbiting in the Geostationary Earth Orbit (GEO).
RECTEENA
(RECTifying anTENNA rectifies received microwaves into DC current)
 A rectenna comprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.
 Its elements are usually arranged in a mesh pattern, giving it a distinct appearance from most antennae.
 A simple rectenna can be constructed from a schottky diode placed between antenna dipoles
SPACE SETTELEMENT
 Space settlement is a unique concept for colonization beyond the Earth
 It can be utilized as a reaction engine, which can use literally anything for fuel
 The mass-driver has been assembled from components lifted by several shuttle flights, and soon will be ready to begin hauling cargo for a small moon base to lunar orbit
 There, a lunar shuttle soft-lands cargo for the moon base onto the surface.
 The cargo includes small habitats, solar arrays, mining equipment, and components for the assembly of another mass-driver on the surface.
 This mass-driver will be used as a catapult to launch lunar ores to a point in space where they can be collected.
A Solar Power Satellite (SPS) with a thoroughly energized Earth in the background
 One of the first things we will begin doing once we are using space resources is constructing a SPS, a vast solar array which gathers the constant solar power in orbit and beams energy to Earth in the form of a safe, low-density microwave beam.
 On Earth, the beam is intercepted by a rectenna several miles across, where it is converted back into electricity.
 The electricity is then rectified to AC, and fed into the power grid.
 The goal is to undersell power generated by fossil fuels or nuclear energy.
 The rectennas will be huge, but the land underneath need not go to waste.
 Since the array absorbs the microwaves, but allows sunlight and rainfall through, the land could be used for farming or ranching.
 Or, as in this case, the rectenna could be built as a vast set of greenhouses, feeding millions.

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Solar Powered Satellites
ABSTRACT :
Space-based solar power (SBSP) (or historically space solar power (SSP)) is a theoretical design for the collection of solar power in space, for use on Earth. SBSP differs from the usual method of solar power collection in that the solar panels used to collect the energy would reside on a satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface. In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases. Average solar energy per unit area outside Earth's atmosphere is on the order of ten times that available on Earth's surface.
KEY WORDS :
Solar power satellite, Solar Energy, Thermal Power.
Solar Power Satellite :
The collection of solar energy in space for use on Earth introduces the new problem of transmitting energy from the collection point, in space, to the place where the energy would be used, on Earth's surface. Since wires extending from Earth's surface to an orbiting satellite would be impractical, many SBSP designs have proposed the use of microwave beams to transmit power wirelessly. The collecting satellite would convert solar energy into electrical energy, which would then be used to power a microwave emitter directed at a collector on the Earth's surface. Dynamic solar thermal power systems are also being investigated.
Many problems normally associated with solar power collection would be eliminated by such a design, such as the high sensitivity of conventional surface solar panels to corrosion and weather, and the resulting maintenance costs. Other problems may take their place though, such as cumulative radiation damage or micrometeoroid impacts.
Producing electricity from sunlight in space is not a new or untried technology. Many space faring craft are covered in solar cells, such as rovers and shuttles, and hundreds of operating satellites use solar energy as their main source of power. What has never been tried before is transmitting that power back to Earth for our use.
Being a clean and safe energy design, space-based solar power has the potential to play a significant role in solving global energy and environmental problems. It utilizes space outside of Earth's ecological system, and may essentially produce no by-products.
History of Solar Power Satellites:
The SPS concept, originally known as Satellite Solar Power System ("SSPS") was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g., from an SPS to the Earth's surface) using microwaves from a very large (up to one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna. Generation of Solar power on Earth:
Glaser then worked at Arthur D. Little, Inc., as a vice-president. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems -- chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research .
Between 1978 and 1981 the US Congress authorized DOE and NASA to jointly investigate. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date. Several reports were published investigating possible problems with such an engineering project. They include:
• Resource Requirements (Critical Materials, Energy, and Land)
• Financial/Management Scenarios
• Public Acceptance
• State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities
• Student Participation
• Potential of Laser for SPS Power Transmission
• International Agreements
• Centralization/Decentralization
• Mapping of Exclusion Areas For Rectenna Sites
• Economic and Demographic Issues Related to Deployment
• Some Questions and Answers
• Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers
• Public Outreach Experiment
• Power Transmission and Reception Technical Summary and Assessment
• Space Transportation
The Office of Technology Assessment concluded
Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture.
More recently, the SPS concept has again become interesting, due to increased energy demand, increased energy costs, and emission implications, starting in 1997 with the NASA "Fresh Look". In assessing "What has changed" since the DOE study, this study asserts that
Another important change has occurred at the US national policy level. US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO [Earth to Orbit] transportation down dramatically. This is, of course, an absolute requirement of space solar power.
SERT
In 1999 NASA's Space Solar Power Exploratory Research and Technology program (SERT) was initiated for the following purpose:
• Perform design studies of selected flight demonstration concepts;
• Evaluate studies of the general feasibility, design, and requirements.
• Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
• Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
• Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements.
It was to develop a solar power satellite (SPS) concept for a future giga watt space power systems to provide electrical power by converting the Sun’s energy and beaming it to the Earth's surface. It was also to provide a developmental path to solutions for current space power architectures. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux into electricity. Collection systems were assumed to be in sun-synchronous orbit.
Some of SERT's conclusions include the following:
• The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
• The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic.
• Renewable energy is a compelling approach, both philosophically and in engineering terms.
• Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements.
• Based on their Concept Definition Study, space solar power concepts may be ready to reenter the discussion.
• Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin.
• Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
• The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of exceptionally low cost access to space) however, the same can be said of many other advanced power technologies options.
• Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.

SUBMITTED BY:-
ANCHAL SRIVASTAVA

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SOLAR POWER SATELLITES
Space-based solar power (SBSP) (or historically space solar power (SSP)) is a system for the collection of solar power in space, for use on Earth. SBSP differs from the usual method of solar power collection in that the solar panels used to collect the energy would reside on a satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface. In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases.
The world Radiation Centre's 1985 standard extraterrestrial spectrum for solar irradiance is 1367 W/m2. The integrated total terrestrial solar irradiance is 950 W/m2. A major interest in SBSP stems from the length of time the solar collection panels can be exposed to a consistently high amount of solar radiation.
The collection of solar energy in space for use on Earth introduces the new problem of transmitting energy from the collection point, in space, to the place where the energy would be used, on Earth's surface. Since wires extending from Earth's surface to an orbiting satellite would be impractical, many SBSP designs have proposed the use of microwave beams for wireless power transmission. The collecting satellite would convert solar energy into electrical energy, which would then be used to power a microwave emitter directed at a collector on the Earth's surface.
INTRODUCTION
The SBSP concept, originally known as Satellite Solar Power System ("SSPS") was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g., from an SPS to the Earth's surface) using microwaves from a very large (up to one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
Dr. Peter Glaser introduces the concept of a large solar power satellite system of square miles of solar collectors in high geosynchronous orbit (GEO is an orbit 36,000 km above the equator), for collection and conversion of sun's energy into an electromagnetic microwave beam to transmit usable energy to large receiving antennas (rectennas) on earth for distribution on the national electric power grid.
Dr. Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g., from an SPS to the Earth's surface) using microwaves from a very large (up to one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
John Mankins of NASA testifies in the U.S. House "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities. A technology roadmap has been developed that lays out potential paths for achieving all needed advances — albeit over several decades.
CONSTRUCTIONAL FEATURES (SPS)
Space-based solar power essentially consists of three parts:
1. a means of collecting solar power in space, for example via solar cells or a heat engine.
2. a means of transmitting power to earth, for example via microwave or laser.
3. a means of receiving power on earth, for example via a microwave antenna (rectenna).
The space-based portion will be in a freefall, vacuum environment and will not need to support itself against gravity other than relatively weak tidal stresses. It needs no protection from terrestrial wind or weather, but will have to cope with space-based hazards such as micrometeors and solar storms.
SOLAR ENERGY CONVERSION
Two basic methods of converting sunlight to electricity have been studied: photovoltaic (PV) conversion, and solar dynamic (SD) conversion.
Most analyses of solar power satellites have focused on photovoltaic conversion (commonly known as “solar cells”).
Photovoltaic conversion uses semiconductor cells (e.g., silicon or gallium arsenide) to directly convert photons into electrical power via a quantum mechanical mechanism. Photovoltaic cells are not perfect in practice, as material purity and processing issues during production affect performance; each has been progressively improved for some decades. Some new, thin-film approaches are less efficient (about 20% vs 35% for best in class in each case), but are much less expensive and generally lighter.
In an SPS implementation, photovoltaic cells will likely be rather different from the glass-pane protected solar cell panels familiar to many from current terrestrial use, since they will be optimized for weight, and will be designed to be tolerant to the space radiation environment (it turns out fortuitously, that thin film silicon solar panels are highly insensitive to ionising radiation), but will not need to be encapsulated against corrosion by the elements. They do not require the structural support required for terrestrial use, where the considerable gravity and wind loading imposes structural requirements on terrestrial implementations.
Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth's surface. The power could be transmitted as either microwave or laser radiation at a variety of frequencies depending on system design.
LASER POWER BEAMING EXPERIMENTS
A large-scale demonstration of power beaming is a necessary step to the development of solar power satellites.
Laser power beaming was envisioned by some at NASA as a stepping stone to further industrialization of space.
In the 1980’s researchers at NASA worked on the potential use of lasers for space-to-space power beaming, focusing primarily on the development of a solar-powered laser.
In 1989, it was suggested that power could also be usefully beamed by laser from Earth to space. In 1991 the SELENE project (Space Laser Energy) was begun, which included the study of laser power beaming for supplying power to a lunar base.
In 1988, the use of an Earth-based laser to power an electric thruster for space propulsion was proposed by Grant Logan, with technical details worked out in 1989. He proposed using diamond solar cells operating at six hundred degrees to convert ultraviolet laser light, a technology that has yet to be demonstrated even in the laboratory. His ideas were adapted to be more practical.
The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project was ended in 1993, before reaching a space-based demonstration.

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ABSTRACT
The search for a new, safe and stable renewable energy source led to the idea of building a power station in space which transmits electricity to Earth. The concept of Solar Power Satellites (SPS) was invented by Glaser in 1968.Research is still going on in this field and NASA is planning to implement one by 2040. SPS converts solar energy into microwaves and transmit it to a receiving antenna on Earth for conversion to electric power. The key technology needed to enable the future feasibility of SPS is Microwave Power Transmission.
SPS would be a massive structure with an area of about 56 sq.m and would, weigh about 30,000 to 50,000 metric ton. Estimated cost is about $74 billion and would take about 30 years for its construction. In order to reduce the projected cost of a SPS suggestions are made to employ extraterrestrial resources for its construction. This reduces the transportation requirements of such a massive structure. However the realization of SPS concept holds great promises for solving energy crisis.
INTRODUCTION
The new millennium has introduced increased pressure for finding new renewable energy sources. The exponential increase in population has led to the global crisis such as global warming, environmental pollution and change and rapid decrease of fossil reservoirs. Also the demand of electric power increases at a much higher pace than other energy demands as the world is industrialized and computerized. Under these circumstances, research has been carried out to look into the possibility of building a power station in space to transmit electricity to Earth by way of radio waves-the Solar Power Satellites. Solar Power Satellites(SPS) converts solar energy in to micro waves and sends that microwaves in to a beam to a receiving antenna on the Earth for conversion to ordinary electricity.SPS is a clean, large-scale, stable electric power source. Solar Power Satellites is known by a variety of other names such as Satellite Power System, Space Power Station, Space Power System, Solar Power Station, Space Solar Power Station etc.[1].One of the key technologies needed to enable the future feasibility of SPS is that of Microwave Wireless Power Transmission.WPT is based on the energy transfer capacity of microwave beam i.e,energy can be transmitted by a well focused microwave beam. Advances in Phased array antennas and rectennas have provided the building blocks for a realizable WPT system [2].
WHY SPS
Increasing global energy demand is likely to continue for many decades. Renewable energy is a compelling approach “ both philosophically and in engineering terms. However, many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements. The burning of fossil fuels resulted in an abrupt decrease in their .it also led to the green house effect and many other environmental problems. Nuclear power seems to be an answer for global warming, but concerns about terrorist attacks on Earth bound nuclear power plants have intensified environmentalist opposition to nuclear power. Moreover, switching on to the natural fission reactor, the sun, yields energy with no waste products. Earth based solar panels receives only a part of the solar energy. It will be affected by the day & night effect and other factors such as clouds. So it is desirable to place the solar panel in the space itself, where, the solar energy is collected and converted in to electricity which is then converted to a highly directed microwave beam for transmission. This microwave beam, which can be directed to any desired location on Earth surface, can be collected and then converted back to electricity. This concept is more advantageous than conventional methods. Also the microwave energy, chosen for transmission, can pass unimpeded through clouds and precipitations.
SPS “THE BACKGROUND
The concept of a large SPS that would be placed in geostationary orbit was invented by Peter Glaser in 1968 [1].The SPS concept was examined extensively during the late 1970s by the U.S Department of Energy (DOE) and the National Aeronautics and Space Administration (NASA). The DOE-NASA put forward the SPS Reference System Concept in 1979 [2]. The central feature of this concept was the creation of a large scale power infrastructure in space, consisting of about 60 SPS, delivering a total of about 300GW.But, as a result of the huge price tag, lack of evolutionary concept and the subsiding energy crisis in 1980-1981, all U.S SPS efforts were terminated with a view to re-asses the concept after about ten years. During this time international interest in SPS emerged which led to WPT experiments in Japan.
RECENT NASA EFFORTS
Fresh look Study
During 1995-96, NASA conducted a re-examination of the technologies, system concepts of SPS systems [2],[3].The principal objective of this ËœFresh Look Studyâ„¢ was to determine whether a SPS and associated systems could be defined. The Fresh Look Study concluded that the prospects for power from space were more technically viable than they had been earlier.
SSP Concept Definition Study
During 1998, NASA conducted the SSP Concept Definition Study which was a focused one year effort that tested the results of the previous Fresh Look Study. A principal product of the efforts was the definition of a family of strategic R&T road maps for the possible development of SSP technologies.
SSP Exploratory and Research Technology Program
In 2000, NASA conducted the SERT Program which further defined new system concepts. The SERT Program comprised of three complementary elements:
¢ System studies and analysis
Analysis of SSP systems and architecture concepts to address the economic viability as well as environmental issue assessments.
¢ SSP Research and technology
Focused on the exploratory research to identify system concepts and establish technical viability
¢ SPS technology demonstration
Initial small scale demonstration of key SSP concepts and / or components using related system / technologies.
SPS-A GENERAL IDEA
Solar Power Satellites would be located in the geosynchronous orbit. The difference between existing satellites and SPS is that an SPS would generate more power-much more power than it requires for its own operation.
The solar energy collected by an SPS would be converted into electricity, then into microwaves. The microwaves would be beamed to the Earthâ„¢s surface, where they would be received and converted back into electricity by a large array of devices known as rectifying antenna or rectenna.(Rectification is the process by which alternating electrical current ,such as that induced by a microwave beam , is converted to direct current). This direct current can then be converted to 50 or 60 Hz alternating current
Each SPS would have been massive; measuring 10.5 km long and 5.3 km wide or with an average area of 56 sq.km.The surface of each satellite would have been covered with 400 million solar cells. The transmitting antenna on the satellite would have been about 1 km in diameter and the receiving antenna on the Earthâ„¢s surface would have been about 10 km in diameter [5].The SPS would weigh more than 50,000 tons.
The reason that the SPS must be so large has to do with the physics of power beaming. The smaller the transmitter array, the larger the angle of divergence of the transmitted beam. A highly divergent beam will spread out over a large area, and may be too weak to activate the rectenna.In order to obtain a sufficiently concentrated beam; a great deal of power must be collected and fed into a large transmitter array.

Presented by:
RAVINDRA CHANDRA

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SOLAR POWER SATELLITES ( SPS )
Innovations:
Alternating current
Wireless power transmission experiments at Wardenclyffe
Wardenclyffe
1899
Able to light lamps over 25 miles away without using wires
High frequency current, of a Tesla coil, could light lamps filled with gas (like neon)
1940’s to Present
World War II - ability to convert energy to microwaves using a magnetron, no method for converting microwaves back to electricity
1964 - William C. Brown demonstrated a rectenna which could convert microwave power to electricity
1968’s - idea for Solar Power Satellites proposed by Peter Glaser
Would use microwaves to transmit power to Earth from Solar Powered Satellites
Solar Power satellite
Space Solar Power System
consists of three parts:
a means of collecting solar power in space, for example via solar cells or a heat engine
a means of transmitting power to earth, for example via microwave or laser
a means of receiving power on earth, for example via a microwave antenna (rectenna)
EFFECIENCY
BLOCK DIAGRAM OF SPS SYSTEM
Solar energy conversion (solar photons to DC current)
Solar panels of the SPS would be placed in geostationary orbit (GEO) at a distance of 36000 km from the Earth’s surface which converts solar energy into DC current .
In an SPS implementation, photovoltaic cells used are different from the pv cells in current terrestrial use
optimized for weight, tolerant of the space radiation environment, anti corrosion
Solar arrays
Weight – 0.5 kg/kw to 10 kg/kw
Life cycle – 20 yrs
Degrades about 1- 2% per yr
Solar radiation is 5- 10 times greater in space
SPS location
GEO
antenna geometry stays constant, and so keeping the antennas lined up is simpler.
continuous power transmission.
LEO/MEO instead of GEO
shorter energy transmission path, lower cost
frequent changes in antenna geometries, i, more power stations needed to receive power continuously
From the Satellite
Solar power from the satellite is sent to Earth using a microwave transmitter
Received at a “rectenna” located on Earth
Recent developments suggest that power could be sent to Earth using a laser
Microwaves
Frequency 2.45 GHz microwave beam
Retro directive beam control capability
Power level is well below international safety standard
On the left: Part of the solar energy is lost on its way through the atmosphere by the effects of reflection and absorption.
On the right: Space-based solar power systems convert sunlight to microwaves outside the atmosphere, avoiding these losses, and the downtime due to Earth's rotation, experienced by surface installations
Microwave vs. Laser Transmission
Microwave
More developed
High efficiency up to 85%
Beams is far below the lethal levels of concentration even for a prolonged exposure
Cause interference with satellite communication industry
Laser
Recently developed solid state lasers allow efficient transfer of power
Range of 10% to 20% efficiency within a few years
Conform to limits on eye and skin damage
Rectenna
“An antenna comprising a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.”
Microwaves are received with about 85% efficiency
Around 5km across (3.1 miles)
95% of the beam will fall on the rectenna
5,000 MW Receiving Station (Rectenna). This station is about a mile and a half long.
Theory of Operation
Block diagram
Electromagnetic Radiation
Antenna basics
Phased-array antenna
Diffraction analogy
Energy distribution
Rectenna
Physical limitations & relationships
Block Diagram
Physics of Wireless Power Transmission
Forms of Electromagnetic radiation
Travel at same speed
F = frequency
C = velocity of light
L =wavelength
Dipole Antenna
Transmission of power is simpler than TV & Radio
Transmitter: wire half a wavelength
Pushes electrons back and forth
Receiver: wire half a wavelength
Phased-array antenna
The λs for microwaves are small  dipoles small
Beam focusing: phased-array antenna
Electronically steered by varying the timing or phase
Waves will merge together
Phased-Array Antenna
Diffraction analogy
Light same properties
Laser beam shinning trough a narrow opening & spreads out or diffracts
Bright spot in the center w/fainter spots on the side
Diffraction & Microwaves
Waves reinforce at some points and they cancel out at other points (bright and fainter points)
In microwaves: is a scaled up version of diffraction
Intensity
Main lobe energy
Circular central max
 Main lobe
84% of energy
Sidelobes surround
No energy  minima
Intensity 84% in main lobe
Rectenna
Array of dipole antennas known as rectifying antenna or Rectenna
Diameter = Dr
Rectenna
Physical Limitations
The receiving diameter Dr increases with transmitter receiver separation distance S.
Dr increases if transmitter diameter Dt decreases
Physical Limitations
Calculations/Analysis
Frequency, f (Hz)
Intensity, I (watts per square meter)
Wave-Length, L (meters)
Received Main Beam Lope (“spot”) Diameter, Dr (meters or kilometers)
Transmitting Phased Array Diameter, Dt (meters or kilometers)
Example: how to estimate Intensity, I ?
Frequency Formula Dt * Dr
Frequency, f (Hz) = -------------- (2)
(L * S)
Dt: transmitting phased array diameter
Dr: received main beam lobe (“spot”)
diameter
L: wavelength
S: separation
Frequency Analysis
Dt * Dr
If (Frequency, f (Hz) = ----------- )  2.44 GHz (2)
(L * S)
Then at least, 84% of the energy of the beam will be captured
Note:
This energy is not linear; 42% of the energy is not equivalent to 1.22 GHz.
Equation (2) represent a best case scenario.
Practical antenna sizes may have to be larger if most of the beam is to be captured.
The rectenna will have to be at least as large as Dt, even if (2) says Dr is smaller.
Frequency Analysis
Such a wide beam can be focused, but only to a minimum size Dr.
For low Earth-orbit power-beaming demonstrations, it is easier to put the smaller antenna in space and the larger antenna on Earth.
Early demonstrations may capture only a small percentage of the total power, in order to keep antenna sizes small.
to light up a 60 watt bulb, thousands of watts may have to be transmitted.
Since costly to launch such a power generating apparatus, the most feasible demonstration project may be Earth-to-space transmission from a large transmitting antenna (such as the Arecibo dish) to a smaller rectenna in space.
Intensity, I Formula
Intensity, I (watts per square meter)
P Dt
= ½ ( Pi * -----) * ( --------- ) (3)
4 L * S

Pi: 3.14…
P: total power transmitted
Dt: transmitted phased array diameter
L: wave length
S: transmitter to receiver distance (separation)
Wave-Length, L Calculations
Wave-Length, L (meters)
c 300,000,000 meter/sec
= ----- = ( -------------------------------- ) = 0.1224 (1)
f 2,450,000,000/sec meter

c: speed of light
f: frequency

Received Main Beam Lope Diameter, Dr Calculations
Received Main Beam Lope (“spot”) Diameter, Dr (meters or kilometers)
f * L * S 2.44 * 0.12224m * 35,800,000m
= -------------- = --------------------------------------------
Dt 1000m

= 10,700 meter = 10.7 kilometers

L: wave length
S: separation
Dt: transmitting phased array diameter
Transmitting Phased Array Diameter, Dt Calculations

Transmitting Phased Array Diameter, Dt (meters or kilometers)
f * L * S 2.44 * 0.12224m * 35,800,000m
= -------------- = ----------------------------------------------
Dr 10,700 meter

= 1000m = 1 kilometers

L: wave length
S: separation
Dr: received main beam lope (“spot”) diameter
Example
What is the Intensity, I = ?
Given: f, Dr, and a typical solar power satellite transmitting 5 billion watts from geostationary orbit 35800 kilometers high.

Solution: Use the following (1), (2), & (3)
C
f = -----  L (1)
L
Dt * Dr
Frequency, f (Hz) = --------------  Dt (2)
(L * S)
P Dt
Intensity, I (watts/m^²) = ½ ( Pi * -----) * ( --------- ) (3)
4 L * S

Example Calculations

Intensity, I (watts per square meter)

P Dt
= ½ ( Pi * -----) * ( --------- ) (3)
4 L * S

2287485.869w 1000m
= ½ ( Pi * ---------------------------) * ( ----------------------------------- )
4m 0.1224m* 35800,000m

= 205 watts/m^² or 20.5 milliwatts/cm^²

Example Analysis

peak beam intensity, Ip = 20.5 milliwatts/cm^²
 This is about twice US industrial standard for human exposure
 This is converted (by rectenna) to electricity by 90% efficiency

Average intensity, Ia  1/3 * 20.5 milliwatts/cm^²
Rectangular Transmitting antenna array Calculations
Mathematics slightly different, but the same general principles apply.
Central maximum of the beam contain 82% of the transmitted energy.
Rectangular in shape, but will spread out more along TX array’s short direction than its long direction.
Example: Canada’s Radar sat
rectangular transmitting antenna: 1.5m × 15m
“footprint” on the ground: 7,000m × 50,000m
frequency: 5.3 GHz
altitude: 800,000m
output power: 5000 watts
 The power is too spread out at the ground to use in a practical demonstration project.
Two more points
Use certain transmitting methods
to reduce the level of the sidelobes
to put some of the sidelobe energy into the main lobe
 Price to pay: Larger Rectenna (because main lobe spreads out)

Principal of diffraction also limits the resolution of optical systems:
Lenses
Telescopes
1979 SPS Reference System concept (GEO)
Accomplishments of Solar Power Satellites
1980, 30 kW of microwave power was transmitted to a receiving antenna over one mile
1993, Japan successfully transmitted a 800W microwave beam from a rocket to a free-flying satellite in space.
1998, Microwave to DC conversion efficiency of 82% or higher by the rectenna.
SPS 2000
Details of SPS 2000
Japan is to build a low cost demonstration of SPS by 2025.
Eight countries along the equator agreed to be the rectenna sites.

10 MW satellite delivering microwave power in the low orbit 1100 km(683 miles)
Will not be in geosynchronous orbit, instead low orbit 1100 km (683 miles)
Much cheaper to put a satellite in low orbit
Advantages over Earth-based solar power
More intense sunlight
In geosynchronous orbit, 36,000 km (22,369 miles) an SPS would be illuminated over 99% of the time
No need for costly storage devices for when the sun is not in view
Waste heat is radiated back into space
Power can be beamed to the location where it is needed, don’t have to invest in as large a gri
Cont.
No air or water pollution is created during generation
Ground based solar only works during clear days, and must have storage for night. Thus it is More reliable than ground based solar power
Vision on Future Development
Conclusion
More reliable than ground based solar power
In order for SPS to become a reality it several things have to happen:
Government support
Cheaper launch prices
Involvement of the private sector

PRESENTED BY
T.SRINIVASA SATISH
T.Anudeep Kumar

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[attachment=13932]
[attachment=13933]
[attachment=13934]
[attachment=13935]
ABSTRACT:
Can’t we generate solar power during night times? Yes my paper suggests a solution to generate solar power during night times. It is probably well known that we are running out of fossil fuel. Most of the energy sources we are using are non renewable. Oil and gas are not to last longer than about fifty years, whereas coal will probably last another two or three centuries. Uranium and nuclear plants will not last forever either. So, in order to provide the generations to come with energy, we have to find the way to use unlimited sources. And this is where SPS gets in action. It provides solutions to use one of the most renewable and unlimited source on earth: the SUN.
SPS great idea!
Still someone might ask why using SPS and not solar panels on the surface of the earth? With the SPS, problems such as daylight and bad-weather conditions, which one might have to deal with, when using solar panels, do not exist. Neither does the need of storage in order to have continual provision of energy and especially considering our inability for adequate energy storage on earth. With SPS the maximum energy loss due to eclipses is only a hundred and twenty hours a year. Furthermore the energy received by the rectennas on earth is ten times more than that received by solar panels of the same surface.
The solar panels used on the surface of the earth prevent sun beams to go through them and consequently prevent any kind of cultivation of the earth under them. But with SPS the photo voltaic cells are in space, so we have no problem with the area needed. In addition the rectennas on earth are semi-transparent allowing sun light to go through them and making possible the cultivation of the soil. So we have no waste of space. SPS might be one of several renewable energies we will use in the future.
Now that we have seen several reasons why SPS could be a great project, let's keep our feet on the ground. There are still some problems to solve before we can see the first SPS working.
INTRODUCTION TO SPS:
The Solar Power Satellite (SPS) concept would place solar power plants in orbit above Earth, where they would convert sunlight to electricity and beam the power to ground-based receiving stations. The ground-based stations would be connected to today's regular electrical power lines that run to our homes, offices and factories here on Earth.
Why put solar power plants in space? The sun shines 24 hours a day in space, as if it were always noontime at the equator with no clouds and no atmosphere. Unlike solar power on the ground, the economy isn't vulnerable to cloudy days, and extra generating capacity and storage aren't needed for our nighttime needs. There is no variation of power supply during the course of the day and night, or from season to season. The latter problems have plagued ground based solar power concepts, but the SPS suffers none of the traditional limitations of ground-based solar power.
INTRODUCTION TO RECTENNA:
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a mesh pattern, giving it a distinct appearance from most antennae.
A simple rectenna can be constructed from a Schottky diode placed between antenna dipoles. The diode rectifies the current induced in the antenna by the microwaves. Schottky diodes are used because they have the lowest voltage drop and therefore waste the minimum power.
Rectennae are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity. Some experimentation has been done with inverse rectennae, converting electricity into microwave energy, but efficiencies are much lower—only in the area of 1%
Due to their high efficiency and relative cheapness, rectennae feature in most microwave power transmission.
BLOCK DIAGROM OF SPS MODEL:
The satellites would be placed in so-called "geostationary" or "Earth synchronous" orbit, a 24-hour orbit which is thus synchronized with Earth's rotation, so that satellites placed there will stay stationary overhead from each's receiving antenna. (Likewise, today's communications satellites are put into geostationary orbit, and each TV satellite dish on the ground is pointed towards one satellite "stationary" in orbit.) The receiving antenna is called a "rectenna" (pronounced "rektenna").
Geostationary orbit is very high, 36,000 km (22,500 miles) above the surface of the Earth. It is far above the range of the Space Shuttle, which has a maximum range of about 1000 km (600 miles) above Earth's surface
The SPS will consist of a large sheet of solar cells mounted on a frame of steel-reinforced lunarcrete or astercrete. The solar cells produce electricity from sunlight with no moving parts. The only moving part on the satellite is the transmitter antenna(s) which slowly tracks the ground-based rectenna(s) while the solar cell array keeps facing the sun. Each transmitter antenna is connected to the solar cell array by two rotary joints with sliprings.
The transmitter on the SPS is an array of radio tubes (klystrons), waveguides, and heat radiators. They convert the electricity from the SPS solar cell power plant into a radio or microwave beam. The ground-based rectenna consists of an array of antennas and standard electronics to convert the energy into regular AC electricity which can then be supplied into today's power lines.

Solar Power Tower

Abstract:
The solar power tower (also knows as 'Central Tower' power plants or 'Heliostat' power plants or power towers) is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, moveable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a substance that can store the heat for later use. The more recent heat transfer material that has been successfully demonstrated is liquid sodium. Sodium is a metal with a high heat capacity, allowing that energy to be stored and drawn off throughout the evening. That energy can, in turn, be used to boil water for use in steam turbines. Water had originally been used as a heat transfer medium in earlier power tower versions (where the resultant steam was used to power a turbine). This system did not allow for power generation during the evening.
1.1 OVERVIEW
To date, the largest power towers ever built are the 10 MW Solar One and Solar Two plants. Assuming success of the Solar Two project, the next plants could be scaled-up to between 30 and 100 MW in size for utility grid connected applications in the Southwestern United States and/or international power markets. New peaking and intermediate power sources are needed today in many areas of the developing world. India, Egypt, and South Africa are locations that appear to be ideally suited for power tower development. As the technology matures, plants with up to a 400 MW rating appear feasible. As non-polluting energy sources become more favored, molten-salt power towers will have a high value because the thermal energy storage allows the plant to be dispatch able. Consequently, the value of power is worth more because a power tower plant can deliver energy during peak load times when it is more valuable. Energy storage also allows power tower plants to be designed and built with a range of annual capacity factors (20 to 65%). Combining high capacity factors and the fact that energy storage will allow power to be brought onto the grid in a controlled manner (i.e., by reducing electrical transients thus increasing the stability of the overall utility grid); total market penetration should be much higher than an intermittent solar technology without storage. One possible concern with the technology is the relatively high amount of land and water usage. This may become an important issue from a practical and environmental viewpoint since these plants are typically deployed within desert areas that often lack water and have fragile landscapes. Water usage at power towers is comparable to other Rankine cycle power technologies of similar size and annual performance.
____________
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
Solar Panels Australia

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