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.
WIRELESS POWER TRANSMISSION (WPT) BACKGROUND
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 itâ„¢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
INTRODUCTION TO LARGE SPS
Since 1967, Solar Power Satellites (SPS) have proposed to collect solar energy in
space and beam it down to the Earth. With the energy crisis of the early 1970's, SPS
was seriously considered as an alternative to producing electric power from fossil fuels
(during the 1970s, petroleum was used to produce a significant fraction of the U.S.
electric power supply). With worldwide demand for electric power increasing as well as
concern growing over urban smog and the greenhouse effect, SPS is again attracting
mainstream interest.
There are several advantages to SPS. Solar radiation can be more efficiently collected in space, where it is roughly three times stronger than on the surface of the Earth and it can be collected 24 hours per day (since there are no clouds or night in high Earth orbit). SPS does not use up valuable surface area on the Earth and can be beamed to areas with the
highest demand at any particular time. Most of these systems would utilize photovoltaic
(PV) cells similar to those on Earth-based systems (such as those used by home power systems and highway sign panels). Others would utilize reflectors and mechanical
collectors similar to those used in special large-scale solar facilities in France and the
California desert (Barstow). Some PV systems would also use reflective concentrators.
Most of these systems collect solar energy in space and transmit it via a microwave energy beam to an Earth-based rectenna which converts the beam into electricity for use on Earth.
Microwave beams have a fairly low wavelength (lower than visible light) and do not appear to pose any danger to the Earth's atmosphere. In fact, telephone companies have been beaming microwaves through the atmosphere for over thirty years without any known problems. High launch costs, which can run roughly between $1,000 to $10,000 per pound, are the greatest barrier to the development of SPS. Most SPS proposals require launch costs of about $200 per pound to compete with your local utility company. However, growing demand for electric power could outstrip traditional production capability, driving prices up to the point where SPS would be competitive. If limits on producing electricity by burning coal (in order to reduce pollution) are enacted, SPS could become competitive even earlier.
Four basic steps involved in the conversion of solar energy to electricity and delivery are:
Capture solar energy in space and convert it to electricity
Transform the electricity to radio frequency energy and transmit it to Earth
Receive the radio frequency energy on Earth and convert it back to electricity
Provide the electricity to the utility grid
Using photovoltaic cells does the conversion of solar energy to electric energy. There are different types of photovoltaic cells. The single crystal silicon is one type of photovoltaic cell, which is formed by a doped wafer formed from a slice of single crystal. Though it has good efficiency it is less used due to expense factor, which comes in due to necessity of high grade of silicon. Its follower is poly crystalline silicon with moderate efficiency and reduced cost. Gallium arsenide is but most commonly used due to high efficiency in comparison to all other types. Then there are dynamic cells which use Solar concentrators to concentrate upon a mechanical heat engine (not photovoltaic). But these are expensive and involve higher maintenance. Often not suitable for small applications. But they do have high conversion efficiencies of the range 30% and above.
Developing any substantial source of energy requires the dedication of significant amounts of capital, land, technical skills, etc. The exploitation of Space Solar Power will require all of these plus some that are unique. As noted before, SSP systems will likely operate in geosynchronous orbit. This orbit is at an altitude such that the platform appears to be stationary over a specific point on the surface of the Earth. As a result, this particular orbit is highly desirable for Earth-oriented activities, for example communications, hence international control is exercised over the assignment of positions or "slots" in this orbit.
TRANSMISSION
Solar power from the satellite is sent to Earth using a microwave transmitter. This transmission is transmitted to the relevant position via an antenna. The transmission is transmitted through space and atmosphere and received on earth by an antenna called the rectenna. Recent developments suggest using laser by using recently developed solid state lasers allow efficient transfer of power. A range of 10% to 20% efficiency within a few years can be attained, but further experimentation still required taking into consideration the possible hazards that it could cause to the eyes. In comparison to laser transmission microwave transmission is more developed, has high efficiency up to 85%, beams is far below the lethal levels of concentration even for a prolonged exposure. The microwave transmission designed has the power level well below the international safety standard (Frequency 2.45 GHz microwave beam). The electric current generated from the photovoltaic cells is passed through a magnetron which converts the electric current to electromagnetic waves. This electromagnetic wave is passed through a waveguide which shapes the characteristics of the electromagnetic wave.
Effectiveness of Wireless Power Transmission (WPT) depends on many parameters. Only a part of WPT system is discussed below, which includes radiating and receiving antennas and the environment between them. The wave beam is expanded proportionately to the propagation distance and a flow power density is increased inversely proportional to the square of this distance. However the WPT has some peculiarities, which will be mentioned here. WPT systems require transmitting almost whole power that is radiated by the transmitting side. So, the useful result is the power quantity at the receiving antenna, but not the value of field amplitude as it is usually required. Efficiency of WPT systems is the ratio of energy flow, which is intercepted by receiving antenna to the whole radiating energy.
Field distribution on the receiving antenna usually is uniform because its size is small comparatively to the width of the beam. For WPT systems this distribution isnâ„¢t uniform. It has a taper form and it depends on the field distribution on the transmitting antenna.
For increasing of the energy concentration on the receiving antenna the phase distribution on the radiating antenna has usually a spherical form with the center in the point on crossing of the receiving plate and the radiating axis. Radiating antenna of the WPT systems usually has a taper distribution of the field. This distribution allows to increase the efficiency and to decrease the field out of the receiving antenna.
The efficiency of energy transmission is expressed by the functional 2. To increase the field distribution on radiating aperture is made as a tapered distribution. High value of is supposed to be in the majority of known projects of the WPT systems.
However, the effectiveness of the WPT system is defined not only by the value of . It is also determined by the rectangularity of the field distribution on the radiating aperture, the rectangular distribution factor in the theory of antennas is usually called the surface utilization factor . The meaning of these two parameters and is discrepant because to increase 2 it is necessary to have the field falling down to edges, but to increase it is necessary to have a uniform field.
To increase the effectiveness of WPT system it is necessary to increase the product 2, though the requirements for each of both multipliers are opposite. This product is named a generalize criterion! It is possible to find the way out of this contradiction if the antenna is discontinuous (discrete) one. Let us produce the field distribution in the radiating discrete antenna falling to its edges not by means of creation of non-uniform distribution of the field but with the help of irregular situation of identical sub apertures, each of them having the uniform field distribution. It is supposed that the number of these apertures is sufficiently high in order to admit the approximation of the integral optimum monotonous Gauss distribution by means of step function. The places of sub aperture disposition can be found by the differentiation of this step function. Discrete distribution of sub apertures presents non-equadistant antenna
array consisting of the similar elements. Such optimization is optimal in Chebyshevâ„¢s sense since the maximum error tends to zero while the number of sub apertures is tended to infinity. So the field in the place of observerâ„¢s disposition would be similar to step and the monotonous signal source. The falling to the edge field distribution is typical for the WPT problems. For the discrete-step distributions that means the concentration of sub apertures in the center and their gradual discharge on the edges. Thus all sub apertures are similar and have the uniform distribution of the field with the equal amplitude, which may reach the maximum admissible value.
The dismemberment of continuous apertures and slight moving of them apart in the space when all of apertures are equal and uniformly feed increases their effectiveness (the generalized criterion is increased). The generalized criterion determines the quality of the WPT Systems better than usual criterion. The optimal distribution form may be reached for the large radiating apertures where dismemberment at many parts is easily realized by disposition of sub aperture clots in places, which correspond to high field intensity (first of all it concerns the center of the radiator) and relieving sub aperture density at edges of antenna. This construction allows to approach to unit the value both of coefficients 2 and . As a result the effectiveness of the WPT system will be essentially increased.
For receiving these transmitted waves rectennas are set up at the Earth. 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 and 95% of the beam will fall on the rectenna but the rectenna is around 5km across (3.1 miles). Currently there are two different design types being looked at- Wire mesh reflector and Magic carpet. Wire mesh reflector type rectennas are built on a rigid frame above the ground and are visually transparent so that it would not interfere with plant life whereas in the magic carpet type material pegged to the ground.
CHALLENGES
The development and implementation of any new energy source present major challenges. And it is acknowledged that bringing about the use of Space Solar Power on the Earth may be particularly daunting because it is so different. The major challenges are perceived to be:
(1) The mismatch between the time horizon for the implementation of SSP and that for the expansion of conventional energy resources
(2) The fact that space power is intrinsically global, requiring enterprise models that give every player a suitable stake and adequate safeguards
(3) The potential for concerns over reliability, safety and environmental implications
(4) The need to obtain publicly-allocated resources outside the normal purview of the energy community
(5) The prevailing mind set which tends to view the future energy infrastructure as an extrapolation of the present one.
However great the challenges, it is important to enhance global energy systems so they work for all the people of the Earth. It is asserted that a prudent course would be to give serious attention to all plausible options and prepare to implement several if needed.
It is well understood that something as vast as the global energy system can change only slowly. In fact, it takes from 50 to 75 years for one source to lose dominance and be replaced by another. Even if it is recognized and agreed that a shift to different sources is needed, penetration would be slow.
The time horizon for implementing Space Solar Power will be at least a couple of decades. Current work being carried out in the US by the National Aeronautics and Space Administration (NASA) and in Japan by the Ministry of Economy, Trade and Industry (METI) indicate that demonstrations of space-to-ground transmission of power could come in the current decade and initial commercial power delivery in about 20 years. A significant contribution in terms of global energy would clearly take substantially longer. The challenge presented by this mismatch can be addressed in two ways:
First, governments will need to underwrite, to a major extent, the R&D needed to bring the enabling technologies to maturity. Governments have traditionally
supported R&D efforts as a spur to new economic activity. Examples can be found in the development of rail and air transport systems, computers and, most recently, the internet.
Second, a near-term involvement by the users (the electric utilities and their suppliers) should be promoted. It is very important for these prospective users to keep abreast of progress as the technology matures.
The global scope of Space Solar Power will present another significant challenge in terms of appropriate enterprise models that give every player a suitable stake and adequate safeguards. International cooperation in the energy area is commonplace and indeed the infrastructure for energy is highly interdependent around the world. Energy acquisition, distribution, and utilization tend to involve multiple countries and far-flung networks along which various forms of energy flow. Similarly, international collaboration has been important in major space ventures of which Space Solar Power would certainly be an example.
Briefly, there are several reasons for international collaboration. The most compelling are:
The need for increased energy supplies is a global need
The impact on the environment of present energy practices is a matter of worldwide concern
International coordination in energy provisioning is common today and the interdependence will only grow in the future
The needed technology is widely distributed and no one country has all the capability
The large scale of Space Solar Power will require international financing
International regulations control critical resources, specifically slots in geosynchronous orbit and appropriate transmission frequencies
Recognition of Space Solar Power as a viable and safe approach to energy will require an international consensus.
Space Solar Power is perceived as very different from all other power sources because of its wireless delivery. A significant challenge will be to allay concerns about the safety of this transmission mechanism. A substantial body of theoretical and experimental work exists and this work indicates that, for the power density levels being considered for importation of power from space, there are no troublesome effects to life forms. Since radio frequency power is non-ionizing, the only likely effects are thermal and these should be modest in view of the fact that the intensity of the transmitted beam Space Solar Power is perceived as very different from all other power sources because of its wireless delivery. A significant challenge will be to allay concerns about the safety of this transmission mechanism. A substantial body of theoretical and experimental work exists and this work indicates that, for the power density levels being considered for importation of power from space, there are no troublesome effects to life forms. Since radio frequency power is non-ionizing, the only likely effects are thermal and these should be
modest in view of the fact that the intensity of the transmitted beam.
Developing any substantial source of energy requires the dedication of significant amounts of capital, land, technical skills, etc. The exploitation of Space Solar Power will require all of these plus some that are unique. As noted before, SSP systems will likely operate in geosynchronous orbit. This orbit is at an altitude such that the platform appears to be stationary over a specific point on the surface of the Earth. As a result, this particular orbit is highly desirable for Earth-oriented activities, for example communications, hence international control is exercised over the assignment of positions or "slots" in this orbit.
The changes in dominant source over time were noted in an earlier figure and we see a continuing change. Considering the relative role of the various sources over just the last century, we have seen the prominence of wood vanish and that of coal diminish greatly. At the same time, the contributions of oil and gas rose from virtually nothing to dominance, and nuclear became a significant contributor in a matter of only 25 years.
Considering the changes washing over our world in almost all areas of life and the economy, can we expect anything less dramatic in the energy arena over the 21st century
Today we the opportunity and the challenge to create a future that is energy-rich and sustainable, but we must be open to a departure from past and present practices and expect that the energy situation in 2100 will be very different from that of today.
The prudent response is a pro-active assessment of all reasonable options and pursuit of those that appear most viable, however futuristic they may seem at present.
ADVANTAGES
Unlimited energy resource
Energy delivered anywhere in the world
Zero fuel cost
Zero CO2 emission
Minimum long-range environmental impact
Solar radiation can be more efficiently collected in space
DISADVANTAGES
Launch costs
Capital cost even given cheap launchers
Would require a network of hundreds of satellites
Possible health hazards
The size of the antennas and rectennas
Geosynchronous satellites would take up large sections of space
Interference with communication satellites
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.
CONCLUSION
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.
REFERENCE
P.E. Glaser «Method and Apparatus for Converting Solar radiation toElectrical Power», U.S. Patent 3 781 647, 1973.
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.
WEC/IIASA, Global Energy Perspectives, Nakicenovic, Nebojsa, et al, Cambridge University Press, 1998.
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.
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.
World Energy Council, "Energy for Tomorrowâ„¢s World - Acting Now", WEC Statement 2000, worldenergy.org.
nspri.com
wirelees powertransmission via solar satellite included sum pictures and diagrams also.
[attachment=3463]
¢ Wireless Power Transmission Options
for Space Solar Power
¢
Presented By:
¢
¢ Henley, M.W. (1), Potter, S. D. (1), Howell, J. (2), and Mankins, J.C. (3)
¢ (1) The Boeing Company, (2) NASA Marshall Space Flight Center, (3) NASA Headquarters
¢ Wireless Power Transmission Options
for Space Solar Power
¢ Far Term Space Systems to beam power to Earth
“ Radio-Wave WPT System
“ Light-Wave Systems
“ Near term Technology Flight Demonstrations
“ Model System Concept 1A: 100 kWe satellite
“ Model System Concept 1B: 10 kWe lunar system
¢ Global Power Consumption
¢ Initial Photovoltaic / Microwave SPS
GEO Sun Tower Conceptual Design
¢ Photovoltaic / Laser-Photovoltaic SPS
GEO Sun Tower-Like Concept
Solar Panel Segment Dimensions: 260 m x 36 m
¢ Synergy Between Sunlight and Laser-PV WPT
for Terrestrial Photo-Voltaic Power Production
¢ Large photo-voltaic (PV) power plants in Earth™s major deserts (Mojave, Sahara, Gobi, etc.) receive & convert light from 2 sources:
1) Directly from the Sun, and
2) Via WPT from SSP systems
¢ Laser light is transmitted and converted more efficiently than sun-light
“ Wavelength is selected for good atmospheric transmissivity
“ Efficient Light Emitting Diode wavelengths match common PV band-gaps
¢ Gravity gradient-stabilized SPSs are in peak insolation at ~6 AM and ~6 PM, with shadowing or cosine loss at mid-day and midnight
“ Heavy, complex gimbaled arrays add little extra power at these times
“ Both sides of rigid (not gimbaled) solar arrays can be light-sensitive
¢ Back-side produces less power due to occlusion by wires
¢ Translucent substrate (e.g., Kapton) also reduces back-side power levels
“ Even gimbaled arrays suffer a loss of power around noon and midnight
¢ The combination of ambient sunlight plus laser illumination combines, at the terrestrial PV array, to match the daily electricity demand pattern
¢ Sunlight + Laser-PV WPT = ~ Power Requirement
Photo-Voltaic (PV) Power Station Receives Both
¢ WPT Wavelength Trade for SSP
¢ MSC-1A: Near Term Demonstration
100 kWe Power Plug Satellite
¢ Power System derived from existing ISS IEA (Integrated Energy Assembly)
“ IEA is successfully deployed in orbit now
“ IEA includes energy storage (batteries)
“ Current ISS array pair produces 61.5 kWe
“ Advanced PV cells can double IEA power
¢ ~120 kWe with derivative array
¢ MSC-1 demonstrates solar-powered WPT
“ Efficient power generation
¢ Light Emitting Diodes (LEDs) achieve >30% conversion efficiency
¢ ~36 kW transmitted in light beam
“ Effective heat dissipation via IEA radiators
“ Accurate pointing of beam via reflector
¢ MSC-1A: Lunar and Mars Power (LAMP) Application
Laser WPT to Photo-Voltaics on the moon or Mars
¢ MSC 1B: Lunar Polar Science Applications
¢ Technology for Laser-Photo-Voltaic Wireless Power Transmission (Laser-PV WPT) is being developed for lunar polar applications by Boeing and NASA Marshall Space Flight Center
¢ A lunar polar mission could demonstrate and validate Laser-PV WPT and other SSP technologies, while enabling access to cold, permanently shadowed craters that are believed to contain ice
“ Craters may hold frozen water and other volatiles deposited over billions of years, recording prior impact events on the moon (& Earth)
“ A photo-voltaic-powered rover could use sunlight, when available, and laser light, when required, to explore a large area of polar terrain
¢ The National Research Council recently found that a mission to the moon™s South Pole-Aitkin Basin should be a high priority for Space Science
¢ See paper IAC-02-r4.04, Space Solar Power Technology Demonstration for Lunar Polar Applications, for further details
¢ Summary
¢ Farther-term micro-wave WPT options are efficient, and can beam power through clouds / light rain, but require large sizes for long distance WPT and a specialized receiver (rectenna).
¢ Nearer-term Laser-Photovoltaic WPT options are less efficient, but allow synergistic use of the same photo-voltaic receiver for both terrestrial solar power and SSP.
“ The smaller aperture size also allows smaller (lower cost) initial systems.
“ Laser-Photovoltaic WPT systems open new SSP architecture options.
“ Gravity gradient-stabilized Sun Tower SSP satellites may make more sense for laser systems than than for microwave systems, because the receiver also converts sunlight into electricity, to correct for the cosine loss otherwise observed in power production at mid-day.
¢ Technology flight demonstrations can enable advanced space science and exploration in the near term.
“ Power Plug or LAMP spacecraft and Lunar Polar Solar Power outpost advance technology for far-term commercial SSP systems, while providing significant value for near-term applications.
please send me the report
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hiii...please send me more information regarding wireless power transmission via solar sattelite.
i need full report of 25-30 pages.
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plz send me report of wireless power transmission
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[attachment=5195]
Wireless Power Transmission
ABSTRACT:
The technology used for wireless power transmission is known as witricity. Wireless power transmission is not a new idea, Nikola Tesla proposed theories of wireless power transmission in the late 1800s and early 1900s. Tesla's work was impressive, but it did not immediately lead to wide spread practical methods for wireless power transmission. Since then many researchers have developed several techniques for moving electricity over long distances without wires. Some exist only as theories or prototypes, but others are already in use. In 2006 researchers at Massachusetts Institute of Technology led by Marine Soijacic discovered an efficient way to transfer power between coils separated by a few meters. They have dubbed this technology as “witricity”. The physical phenomenon of long-lifetime resonant electromagnetic states with localized slowly-evanescent field patterns used to transfer energy efficiently over non-negligible distances like 8 times the radius of the coil, even in the presence of extraneous environmental objects was experimentally demonstrated.
[attachment=6054]
SOLAR POWER SATELLITES AND MICROWAVE
WIRELESS POWER TRANSMISION TECHNOLOGY
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
[attachment=6281]
Wireless Power Transmission via Solar Power Satellite full report
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.
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This article is presented by:
R .Venkatesh
L .Krishnam Raju SOLAR POWER SATELLITES
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.
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.
Probably in the future there will be other sources of energy such as fusion, in fact we are already using renewable sources like either hydroelectricity or geothermal energy. 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%.
WIRELESS POWER TRANSMISSION VIA SOLAR POWER SATELLITE
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 2020.Many studies are going on now in this field . 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. Another important area of technological development will be the reduction of the size and weight of individual elements in the space section of SPS.
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.
CHAPTER-1
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 price 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. 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.
CHAPTER-2
LITERATURE REVIEW
2.1 SPS –THE BACKGROUND
The concept of a large SPS that would be placed in geostationary orbit was invented by Peter Glaser in 1968.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. 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.
2.1.1 RECENT NASA EFFORTS
Fresh look Study-During 1995-96, NASA conducted a re-examination of the technologies, system concepts of SPS systems. The principal objective of this ‘Fresh Look Study’ 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.
2.2 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.
2.3 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 Earth’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 Earth’s surface would have been about 10 km in diameter. 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.
Fig 2.1 Configuration of SPS is space.
The day-night cycle ,cloud coverage , atmospheric attenuation etc.reduces the amount of solar energy received on Earth’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. 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. 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.
Fig.2.2 Typical SPS configuration
The amount of power available to the consumers from one SPS is 5GW 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. 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. However ,the main barrier to the development of SPS is social, and not technological . This 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.
2.4 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 . However the main thrust of WPT has been on the concept of space-to-ground (extraterrestrial) transmission of energy using microwave beam.
Fig2.3 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.
Fig2.4 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.
2.5 MICROWAVE POWER TRANSMISSION IN SPS
The microwave transmission system as envisioned by NASA and DOE would have had three aspects,
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 earth’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. 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.
2.5.1 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 transmitter’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. 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=√ (1-r²), where r is the radius of antenna. There are mainly three
2.5.2 Klystron
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. 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.
Fig2.5 Klystron transmitter
2.5.3 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 below fig 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. 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.
Fig 2.6 Retro directive beam control concept with an SPS.
2.5.4 RECTENNA
Brown was the pioneer in developing the first 2.45GHz rectenna . Rectenna is the microwave to dc converting device and is mainly composed of a receiving antenna and a rectifying circuit. Fig below shows the schematic of rectenna circuit. 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 2.7 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 ƒ=1/ [2πRsCj], where ƒ is the cut off frequency, Rs is the diode series resistance, Cj is the zero-bias junction capacitance.
2.6 RECENTLY DEVELOPED MPT SYSTEMS
The Kyoto University developed a system called Space Power Radio Transmission System (SPORTS). 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 below could be a prototype of a large scale experimental module in the orbit
Figure 2.8 SPRITZ (Solar Power Radio Integrated Transmitter 2000)
2.7 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. 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. 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 .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. 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. 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.
2.8 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. 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. 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 . 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 .Serious discussions and education are required before most of mankind accepts this technology with global dimensions. Microwaves, however is not a ‘pollutant’ but , more aptly , a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustence
2.9 ADVANTAGES
• The full solar irradiation would be available at all times expect when the sun is eclipsed by the earth.Thus about five times energy could be collected, compared with the best terrestrial sites
• The power could be directed to any point on the earth’s surface.
• The zero gravity and high vacuum condition in space would allow much lighter, low maintenance structures and collectors .
• 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.
2.10 DISADVANTAGES
• The entire structure is massive.
• High cost and require much time for construction.
• Radiation hazards associated with the system.
CHAPTER-3
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.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
• Kennedy“ElectronicsCommunicationSystems”,TataMcGrawHill
• International Encyclopedia of Energy, Vol.4, pp.771.
• David M.Pozar ,”Microwave Engineering”, Wiley
sir send more info about wirless power transmission via solar
sir send more info about wirless power transmission via solar satellite
sir send more info about wirless power transmission via solar satellite
Wireless Power Transmission via Solar Power Satellite
INTROUCTION
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 world'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 cen
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 world'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
thank you sir for your deatile information on sps
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Wireless Power Transmission via Solar Power Satellite full report
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.
WIRELESS POWER TRANSMISSION (WPT) BACKGROUND
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 itâ„¢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
INTRODUCTION TO LARGE SPS
Since 1967, Solar Power Satellites (SPS) have proposed to collect solar energy in
space and beam it down to the Earth. With the energy crisis of the early 1970's, SPS
was seriously considered as an alternative to producing electric power from fossil fuels
(during the 1970s, petroleum was used to produce a significant fraction of the U.S.
electric power supply). With worldwide demand for electric power increasing as well as
concern growing over urban smog and the greenhouse effect, SPS is again attracting
mainstream interest.
There are several advantages to SPS. Solar radiation can be more efficiently collected in space, where it is roughly three times stronger than on the surface of the Earth and it can be collected 24 hours per day (since there are no clouds or night in high Earth orbit). SPS does not use up valuable surface area on the Earth and can be beamed to areas with the
highest demand at any particular time. Most of these systems would utilize photovoltaic
(PV) cells similar to those on Earth-based systems (such as those used by home power systems and highway sign panels). Others would utilize reflectors and mechanical
collectors similar to those used in special large-scale solar facilities in France and the
California desert (Barstow). Some PV systems would also use reflective concentrators.
Most of these systems collect solar energy in space and transmit it via a microwave energy beam to an Earth-based rectenna which converts the beam into electricity for use on Earth.
Microwave beams have a fairly low wavelength (lower than visible light) and do not appear to pose any danger to the Earth's atmosphere. In fact, telephone companies have been beaming microwaves through the atmosphere for over thirty years without any known problems. High launch costs, which can run roughly between $1,000 to $10,000 per pound, are the greatest barrier to the development of SPS. Most SPS proposals require launch costs of about $200 per pound to compete with your local utility company. However, growing demand for electric power could outstrip traditional production capability, driving prices up to the point where SPS would be competitive. If limits on producing electricity by burning coal (in order to reduce pollution) are enacted, SPS could become competitive even earlier.
Four basic steps involved in the conversion of solar energy to electricity and delivery are:
Capture solar energy in space and convert it to electricity
Transform the electricity to radio frequency energy and transmit it to Earth
Receive the radio frequency energy on Earth and convert it back to electricity
Provide the electricity to the utility grid
Using photovoltaic cells does the conversion of solar energy to electric energy. There are different types of photovoltaic cells. The single crystal silicon is one type of photovoltaic cell, which is formed by a doped wafer formed from a slice of single crystal. Though it has good efficiency it is less used due to expense factor, which comes in due to necessity of high grade of silicon. Its follower is poly crystalline silicon with moderate efficiency and reduced cost. Gallium arsenide is but most commonly used due to high efficiency in comparison to all other types. Then there are dynamic cells which use Solar concentrators to concentrate upon a mechanical heat engine (not photovoltaic). But these are expensive and involve higher maintenance. Often not suitable for small applications. But they do have high conversion efficiencies of the range 30% and above.
Developing any substantial source of energy requires the dedication of significant amounts of capital, land, technical skills, etc. The exploitation of Space Solar Power will require all of these plus some that are unique. As noted before, SSP systems will likely operate in geosynchronous orbit. This orbit is at an altitude such that the platform appears to be stationary over a specific point on the surface of the Earth. As a result, this particular orbit is highly desirable for Earth-oriented activities, for example communications, hence international control is exercised over the assignment of positions or "slots" in this orbit.
TRANSMISSION
Solar power from the satellite is sent to Earth using a microwave transmitter. This transmission is transmitted to the relevant position via an antenna. The transmission is transmitted through space and atmosphere and received on earth by an antenna called the rectenna. Recent developments suggest using laser by using recently developed solid state lasers allow efficient transfer of power. A range of 10% to 20% efficiency within a few years can be attained, but further experimentation still required taking into consideration the possible hazards that it could cause to the eyes. In comparison to laser transmission microwave transmission is more developed, has high efficiency up to 85%, beams is far below the lethal levels of concentration even for a prolonged exposure. The microwave transmission designed has the power level well below the international safety standard (Frequency 2.45 GHz microwave beam). The electric current generated from the photovoltaic cells is passed through a magnetron which converts the electric current to electromagnetic waves. This electromagnetic wave is passed through a waveguide which shapes the characteristics of the electromagnetic wave.
Effectiveness of Wireless Power Transmission (WPT) depends on many parameters. Only a part of WPT system is discussed below, which includes radiating and receiving antennas and the environment between them. The wave beam is expanded proportionately to the propagation distance and a flow power density is increased inversely proportional to the square of this distance. However the WPT has some peculiarities, which will be mentioned here. WPT systems require transmitting almost whole power that is radiated by the transmitting side. So, the useful result is the power quantity at the receiving antenna, but not the value of field amplitude as it is usually required. Efficiency of WPT systems is the ratio of energy flow, which is intercepted by receiving antenna to the whole radiating energy.
Field distribution on the receiving antenna usually is uniform because its size is small comparatively to the width of the beam. For WPT systems this distribution isnâ„¢t uniform. It has a taper form and it depends on the field distribution on the transmitting antenna.
For increasing of the energy concentration on the receiving antenna the phase distribution on the radiating antenna has usually a spherical form with the center in the point on crossing of the receiving plate and the radiating axis. Radiating antenna of the WPT systems usually has a taper distribution of the field. This distribution allows to increase the efficiency and to decrease the field out of the receiving antenna.
The efficiency of energy transmission is expressed by the functional 2. To increase the field distribution on radiating aperture is made as a tapered distribution. High value of is supposed to be in the majority of known projects of the WPT systems.
However, the effectiveness of the WPT system is defined not only by the value of . It is also determined by the rectangularity of the field distribution on the radiating aperture, the rectangular distribution factor in the theory of antennas is usually called the surface utilization factor . The meaning of these two parameters and is discrepant because to increase 2 it is necessary to have the field falling down to edges, but to increase it is necessary to have a uniform field.
To increase the effectiveness of WPT system it is necessary to increase the product 2, though the requirements for each of both multipliers are opposite. This product is named a generalize criterion! It is possible to find the way out of this contradiction if the antenna is discontinuous (discrete) one. Let us produce the field distribution in the radiating discrete antenna falling to its edges not by means of creation of non-uniform distribution of the field but with the help of irregular situation of identical sub apertures, each of them having the uniform field distribution. It is supposed that the number of these apertures is sufficiently high in order to admit the approximation of the integral optimum monotonous Gauss distribution by means of step function. The places of sub aperture disposition can be found by the differentiation of this step function. Discrete distribution of sub apertures presents non-equadistant antenna
array consisting of the similar elements. Such optimization is optimal in Chebyshevâ„¢s sense since the maximum error tends to zero while the number of sub apertures is tended to infinity. So the field in the place of observerâ„¢s disposition would be similar to step and the monotonous signal source. The falling to the edge field distribution is typical for the WPT problems. For the discrete-step distributions that means the concentration of sub apertures in the center and their gradual discharge on the edges. Thus all sub apertures are similar and have the uniform distribution of the field with the equal amplitude, which may reach the maximum admissible value.
The dismemberment of continuous apertures and slight moving of them apart in the space when all of apertures are equal and uniformly feed increases their effectiveness (the generalized criterion is increased). The generalized criterion determines the quality of the WPT Systems better than usual criterion. The optimal distribution form may be reached for the large radiating apertures where dismemberment at many parts is easily realized by disposition of sub aperture clots in places, which correspond to high field intensity (first of all it concerns the center of the radiator) and relieving sub aperture density at edges of antenna. This construction allows to approach to unit the value both of coefficients 2 and . As a result the effectiveness of the WPT system will be essentially increased.
For receiving these transmitted waves rectennas are set up at the Earth. 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 and 95% of the beam will fall on the rectenna but the rectenna is around 5km across (3.1 miles). Currently there are two different design types being looked at- Wire mesh reflector and Magic carpet. Wire mesh reflector type rectennas are built on a rigid frame above the ground and are visually transparent so that it would not interfere with plant life whereas in the magic carpet type material pegged to the ground.
CHALLENGES
The development and implementation of any new energy source present major challenges. And it is acknowledged that bringing about the use of Space Solar Power on the Earth may be particularly daunting because it is so different. The major challenges are perceived to be:
(1) The mismatch between the time horizon for the implementation of SSP and that for the expansion of conventional energy resources
(2) The fact that space power is intrinsically global, requiring enterprise models that give every player a suitable stake and adequate safeguards
(3) The potential for concerns over reliability, safety and environmental implications
(4) The need to obtain publicly-allocated resources outside the normal purview of the energy community
(5) The prevailing mind set which tends to view the future energy infrastructure as an extrapolation of the present one.
However great the challenges, it is important to enhance global energy systems so they work for all the people of the Earth. It is asserted that a prudent course would be to give serious attention to all plausible options and prepare to implement several if needed.
It is well understood that something as vast as the global energy system can change only slowly. In fact, it takes from 50 to 75 years for one source to lose dominance and be replaced by another. Even if it is recognized and agreed that a shift to different sources is needed, penetration would be slow.
The time horizon for implementing Space Solar Power will be at least a couple of decades. Current work being carried out in the US by the National Aeronautics and Space Administration (NASA) and in Japan by the Ministry of Economy, Trade and Industry (METI) indicate that demonstrations of space-to-ground transmission of power could come in the current decade and initial commercial power delivery in about 20 years. A significant contribution in terms of global energy would clearly take substantially longer. The challenge presented by this mismatch can be addressed in two ways:
First, governments will need to underwrite, to a major extent, the R&D needed to bring the enabling technologies to maturity. Governments have traditionally
supported R&D efforts as a spur to new economic activity. Examples can be found in the development of rail and air transport systems, computers and, most recently, the internet.
Second, a near-term involvement by the users (the electric utilities and their suppliers) should be promoted. It is very important for these prospective users to keep abreast of progress as the technology matures.
The global scope of Space Solar Power will present another significant challenge in terms of appropriate enterprise models that give every player a suitable stake and adequate safeguards. International cooperation in the energy area is commonplace and indeed the infrastructure for energy is highly interdependent around the world. Energy acquisition, distribution, and utilization tend to involve multiple countries and far-flung networks along which various forms of energy flow. Similarly, international collaboration has been important in major space ventures of which Space Solar Power would certainly be an example.
Briefly, there are several reasons for international collaboration. The most compelling are:
The need for increased energy supplies is a global need
The impact on the environment of present energy practices is a matter of worldwide concern
International coordination in energy provisioning is common today and the interdependence will only grow in the future
The needed technology is widely distributed and no one country has all the capability
The large scale of Space Solar Power will require international financing
International regulations control critical resources, specifically slots in geosynchronous orbit and appropriate transmission frequencies
Recognition of Space Solar Power as a viable and safe approach to energy will require an international consensus.
Space Solar Power is perceived as very different from all other power sources because of its wireless delivery. A significant challenge will be to allay concerns about the safety of this transmission mechanism. A substantial body of theoretical and experimental work exists and this work indicates that, for the power density levels being considered for importation of power from space, there are no troublesome effects to life forms. Since radio frequency power is non-ionizing, the only likely effects are thermal and these should be modest in view of the fact that the intensity of the transmitted beam Space Solar Power is perceived as very different from all other power sources because of its wireless delivery. A significant challenge will be to allay concerns about the safety of this transmission mechanism. A substantial body of theoretical and experimental work exists and this work indicates that, for the power density levels being considered for importation of power from space, there are no troublesome effects to life forms. Since radio frequency power is non-ionizing, the only likely effects are thermal and these should be
modest in view of the fact that the intensity of the transmitted beam.
Developing any substantial source of energy requires the dedication of significant amounts of capital, land, technical skills, etc. The exploitation of Space Solar Power will require all of these plus some that are unique. As noted before, SSP systems will likely operate in geosynchronous orbit. This orbit is at an altitude such that the platform appears to be stationary over a specific point on the surface of the Earth. As a result, this particular orbit is highly desirable for Earth-oriented activities, for example communications, hence international control is exercised over the assignment of positions or "slots" in this orbit.
The changes in dominant source over time were noted in an earlier figure and we see a continuing change. Considering the relative role of the various sources over just the last century, we have seen the prominence of wood vanish and that of coal diminish greatly. At the same time, the contributions of oil and gas rose from virtually nothing to dominance, and nuclear became a significant contributor in a matter of only 25 years.
Considering the changes washing over our world in almost all areas of life and the economy, can we expect anything less dramatic in the energy arena over the 21st century
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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 world’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.
WIRELESS POWER TRANSMISSION (WPT) BACKGROUND
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
INTRODUCTION TO LARGE SPS
Since 1967, Solar Power Satellites (SPS) have proposed to collect solar energy in
space and beam it down to the Earth. With the energy crisis of the early 1970's, SPS
was seriously considered as an alternative to producing electric power from fossil fuels
(during the 1970s, petroleum was used to produce a significant fraction of the U.S.
electric power supply). With worldwide demand for electric power increasing as well as
concern growing over urban smog and the greenhouse effect, SPS is again attracting
mainstream interest.
There are several advantages to SPS. Solar radiation can be more efficiently collected in space, where it is roughly three times stronger than on the surface of the Earth and it can be collected 24 hours per day (since there are no clouds or night in high Earth orbit). SPS does not use up valuable surface area on the Earth and can be beamed to areas with the
highest demand at any particular time. Most of these systems would utilize photovoltaic
(PV) cells similar to those on Earth-based systems (such as those used by home power systems and highway sign panels). Others would utilize reflectors and mechanical
collectors similar to those used in special large-scale solar facilities in France and the
California desert (Barstow). Some PV systems would also use reflective concentrators.
Most of these systems collect solar energy in space and transmit it via a microwave energy beam to an Earth-based rectenna which converts the beam into electricity for use on Earth.
Microwave beams have a fairly low wavelength (lower than visible light) and do not appear to pose any danger to the Earth's atmosphere. In fact, telephone companies have been beaming microwaves through the atmosphere for over thirty years without any known problems. High launch costs, which can run roughly between $1,000 to $10,000 per pound, are the greatest barrier to the development of SPS. Most SPS proposals require launch costs of about $200 per pound to compete with your local utility company. However, growing demand for electric power could outstrip traditional production capability, driving prices up to the point where SPS would be competitive. If limits on producing electricity by burning coal (in order to reduce pollution) are enacted, SPS could become competitive even earlier.
Sir ,
Please give full report of RE: Wireless Power Transmission via Solar Power Satellite .
where i can find matlab simulations of satellite.
[attachment=15078]
1. Theoretical Background
It is known that electromagnetic energy also associated with the propagation of the
electromagnetic waves. We can use theoretically all electromagnetic waves for a wireless power
transmission (WPT). The difference between the WPT and communication systems is only efficiency.
The Maxwell’s Equations indicate that the electromagnetic field and its power diffuse to all
directions. Although we transmit the energy in the communication system, the transmitted energy is
diffused to all directions. Although the received power is enough for a transmission of information,
the efficiency from the transmitter to receiver is quiet low. Therefore, we do not call it the WPT
system.
Typical WPT is a point-to-point power transmission. For the WPT, we had better concentrate
power to receiver. It was proved that the power transmission efficiency can approach close to 100%.
We can more concentrate the transmitted microwave power to the receiver aperture areas with taper
method of the transmitting antenna power distribution. Famous power tapers of the transmitting
antenna are Gaussian taper, Taylor distribution, and Chebychev distribution. These taper of the
transmitting antenna is commonly used for suppression of sidelobes. It corresponds to increase the
power transmission efficiency. Concerning the power transmission efficiency of the WPT, there are
some good optical approaches in Russia[5][6].
Future suitable and largest application of the WPT via microwave is a Space Solar Power
Satellite (SPS). The SPS is a gigantic satellite designed as an electric power plant orbiting in the
Geostationary Earth Orbit (GEO). It consists of mainly three segments; solar energy collector to
convert the solar energy into DC (direct current) electricity, DC-to-microwave converter, and large
antenna array to beam down the microwave power to the ground. The first solar collector can be
either photovoltaic cells or solar thermal turbine. The second DC-to-microwave converter of the SPS
can be either microwave tube system and/or semiconductor system. It may be their combination. The
third segment is a gigantic antenna array. Table 1.1 shows some typical parameters of the
transmitting antenna of the SPS. An amplitude taper on the transmitting antenna is adopted in order
to increase the beam collection efficiency and to decrease sidelobe level in almost all SPS design. A
typical amplitude taper is called 10 dB Gaussian in which the power density in the center of the
transmitting antenna is ten times larger than that on the edge of the transmitting antenna.
The SPS is expected to realize around 2030. Before the realization of the SPS, we can consider the
other application of the WPT. In resent years, mobile devices advance quickly and require
decreasing power consumption. It means that we can use the diffused weak microwave power as a
power source of the mobile devices with low power consumption such as RF-ID. The RF-ID is a
radio IC-tug with wireless power transmission and wireless information. This is a new WPT
application like broadcasting.
