SPACE SOLAR POWER: Technology Description

Space solar power (SSP) and earth-based solar power are the two renewable technologies which clearly have the physical potential to meet all the world’s energy needs. SSP is a complex family of alternative designs, all of which entail using sunlight in earth orbit to generate energy, which is then beamed to the earth by microwave or by light. SSP power is essentially base-load, 24-hours-per-day electricity. Microwave receiving antennas do not block light and are thus more compatible with agricultural land use than earth based solar.

System Concepts

· SSP in low earth orbit (LEO) was proposed for early tests and for boosting communication satellites and other space activities. But for large-scale energy production, the focus is on geosynchronous orbit (GEO).

· The current best “conventional” design is a “modified sandwich design,” using light-weight mirrors to reflect light onto extremely high-efficiency hybrid photoelectric/thermoelectric/electronics panels, which send power to a microwave power transmitter or to an electricity-to-light laser.

· There is great interest in laser-based “constellation” designs, which can be scaled up gradually as new lasers are added to a constellation, exploiting the ability of lasers to concentrate power into smaller areas on earth and thereby avoid the need to start out with a huge initial power station. New designs have been developed for high-power light-to-light lasers, which convert sunlight directly to laser light, avoiding the inefficiencies and heat loads of using electricity as an intermediate.

· There is a hope for very deep cost reduction using a new hybrid design, in which a light-to-light laser is used to ignite nuclear fusion in small pellets containing deuterium. In space-based deuterium-deuterium fusion, ninety percent of the energy comes out directly in the form of electrical current (i.e., proton velocity), which can be transformed to a more usable voltage and beamed to earth without the cost and bulk of the thermal reaction chambers used in nuclear reactors on earth. In effect, the small fusion chamber amplifies the power from the laser by a factor of more than 100, thereby reducing generation cents per kwh by 100.

· Many researchers are highly enthusiastic about the hope of avoiding the costs of transport from earth to orbit by using materials from the moon or the asteroids. This makes sense in terms of physics, but has not been studied as thoroughly as it merits because of limited budgets and psychological barriers.

Representative Technologies

· Mass produced low cost inflatable mirrors for initial harvesting of solar energy in orbit.

· High Power Fiber Lasers (HPFL) using photonic band gap materials for beaming energy to earth or space.

· Light enhanced chemical reactions to directly dissociate sea water into H₂ and O₂ , for direct use or combined with carbon or nitrogen into fuels like ammonia or methanol.

· “Teleautonomous” robotic technology and novel structural concepts to minimize assembly costs.

· Deuterium pellet design for light-induced fusion without a need for large magnetic bottles.

· Beaming power to earth, estimated to cost 4 cents per kwh with proven technology but with room for reduction.

· Very high concentration solar arrays, using many layers and thermoelectric coupling to achieve high efficiency, along with novel heat dissipation technology.

· “Upper stage” rockets using electromagnetic acceleration to reduce costs of LEO- to-GEO transport.

Technology Status/Applications

· Low cost inflatable mirrors have been developed and deployed successfully.

· High power fiber lasers have been developed and are now approaching 1K Watt average power and are being bundled.

· In lab tests under NASA’s SERT program, revisiting SSP in light of current technology, numerous problems were discovered in earlier SSP designs. Circa 2000, new designs were developed which overcame those problems and appear highly credible (though in need of demonstration) on technical and environmental grounds. But projected costs were too high (circa 15 cents/kwh) assuming $200/lb earth-to-LEO transportation costs.

Current Research, Development, and Deployment

RD&D Goals

· Develop inflatable mirror satellites to harvest solar energy in space (100 meter diameter).

· Develop rapid deployment system for inflatable mirrors.

· Develop bundled high power fiber lasers that are sufficient to allow inertial confinement fusion.

· Develop beamed energy techniques to directly dissociate sea water into Hydrogen and Oxygen.

· Develop chemistry of conversion of H and O with N and C to obtain alternative fuels like ammonia.

· Develop efficient direct solar to laser energy conversion technology.

· Fully explore the potential of the four new design approaches described above. Perform first-pass integrated configuration and cost analysis, similar to what was done with the year 2000 designs, in order to identify priorities and options for continued design and subsystem improvement.

· Keep the door open as wide as possible to new design options.

· Reduced cost earth receiving systems, microwave or laser.

RD&D Challenges

· See above. Given the high-risk, high-potential nature of the area, it will be critical to maintain a combination of large lab-based efforts to start to mature critical components, alongside a wide open competition to universities and small businesses to explore new designs either for the system as a whole or for critical subsystems.

RD&D Activities and Federal Expenditures

· The last dedicated investment by the US government in this area was in fiscal year 2002, when NASA and the National Science Foundation (in partnership with the Electric Power Research Institute) split 50-50 the cost and management of an open solicitation. (Search on JIETSSP at www.nsf.gov for details.) Of about 100 proposals received, strict peer review panels recommended that half be funded, worth $21 million. Due to budget constraints, 12 projects were funded at $3.1 million total, extending over two or three years of work. Some new funding is requested in the Administration FY04 budget for the NASA side.

· Laser work at the NASA Jet Propulsion Laboratory and D-D pellet work at Lawrence Livermore Laboratory are crucial to progress in this area, along with extensions of NASA work related to SERT.

· Peer review panels also uncovered very serious options to get earth-to-LEO transportation costs down to the required $200/pound relatively soon, requiring more creative interagency cooperation to be supported at the highest levels.

Recent Progress

· See above. The most important new development has been the development of new design configurations with the potential to be cost-competitive or lower cost than traditional carbon-free sources of baseload electricity. NASA has also filed patents on many new technologies related to the above.

Commercialization and Deployment Activities

· Too early for real large-scale deployment. Component technologies, such as modern wireless technology for power beaming, are being tested in a variety places. For example, Prof. Frank Little of Texas A&M University is doing power beaming tests to verify that it is possible to avoid interference with ground-based wireless communication systems.

Potential Benefits

Carbon Reductions

· Zero carbon dioxide and zero nuclear proliferation in all of the configurations.

Market

· Especially easy to deploy in areas like developing nations, where carbon dioxide problems, electricity shortages and nuclear proliferation problems are especially severe. Probably easier to connect to the US power grid, from remote sites where coal and nuclear plants are also required to be located, than are other renewables, because of the baseload nature of the power. The government of Japan has done an extensive on-site survey of suitable receiving sites in the developing world, where there is enthusiasm for receiving energy from this source.

Key Technology Challenges

· See above. Demonstration and evaluation under limited budgets are the main problem at present.