22-03-2011, 11:07 AM
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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.
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.
