THE POTENTIAL OF SOLAR ENERGY Today, the application of solar energy is recognized as a promising alternative to meeting future energy demands, since the Earth receives prodigious quantities of solar energy (1.7 x 101 4 kW are intercepted by the Earth). However, it, is a widely distributed resource; one square meter of the Earth's surface exposed to direct sunlight receives the energy equivalent of only one kilowatt. Moreover, this energy is not easily convertible and certainly is not “free.” Thus, while solar energy is abundant enough to provide self-sufficiency and clean enough to satisfy the most ardent environmentalists, methods must be found for converting it efficiently and economically into useful forms. One important drawback to the large-scale application of terrestrially based solar-energy conversion is the interruptions of solar radiation during periods of inclement weather or at night. These interruptions lead to a requirement for substantial energy storage capacity. Another drawback to the large-scale application of terrestrially based solar-generated power is that it will be economical in only a few locations. Consequently, terrestrial solar systems probably will be useful only in meeting peak demands. These obstacles can be overcome when the solar energy conversion system is placed in synchronous orbit around the Earth where solar energy is nearly constant 24 hours a day.1 Synchronous orbits are utilized today by communications satellites, and are ideally suited for the large-scale conversion of solar energy in a satellite solar power station (SSPS), see Figure 1,* as presented in hearings before the Committee on Aeronautical and Space Sciences, October 31, 1973. The SSPS has the potential to provide an economically viable and environmentally and socially acceptable option for power generation on a scale substantial enough to meet a significant portion of future world energy demands. The concept of the SSPS is based on the extension of existing technology and on the successful start of the development of an effective space transportation system, as represented by the space shuttle. The SSPS could use solar cells to convert solar energy to electricity on a nearly continuous basis. The electricity would be fed to microwave generators incorporated in a transmitting antenna in the SSPS. The antenna would direct a microwave beam to a receiving antenna located in direct line of sight on Earth, and there the microwave energy would be reconverted safely and efficiently to electricity. Additional SSPS systems can be established to deliver power almost anywhere on Earth. ‘This baseline design 2 represents the present stage of evolution (see Figure 2), which began with a planar array of solar cells. This baseline design utilizes silicon solar cells in combination with solar reflectors to convert solar energy into electricity, and was evolved by the team of Arthur D. Little, Inc., Gruman Aerospace Corporation, Raytheon Company, and Spectrolab, Inc..
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