IB7»012 UPDATE—09/12/79 ISSUE DEFINITION In the quest for new, inexhaustible sources of energy, solar energy has become a promising contender, because the Sun's energy is not expected to be depleted for six billion years. Several factors prevent solar energy from falling freeiy onto the Earth's surface, however, leading to the concept of building electric power plants which utilize solar energy in Earth orbit. Electricity generated by these stations would be beamed down in the form of microwaves to receiving antennas located on the planet's surface. This concept is referred to as satellite power stations (SPS). Through the authorization and appropriation process, Congress has demonstrated a consistent interest in pursuing feasibility studies of an SPS program. The Executive branch has appeared less enthusiastic about the concept, and a 1976 Office of Management and Budget decision transferred responsibility for the program to the Energy Research and Development Administration (now part of the Department of Energy) from the national Aeronautics and Space Administration, which had previously performed the feasibility studies. This transfer of responsibility was viewed in some quarters as a downgrading of the program, especially when ERDA did not request any funding for SPS in its FI77 budget. In the 95th and 96th Congresses, specific legislation has been introduced to increase funding for determining the technical, economic, and environmental feasibility of the concept. BACKGROUND AMD POLICY ANALYSIS Solar energy is receiving increasing attention as an electrical power source, either through direct conversion of sunlight into electricity (photovoltaics) or by using the energy to heat working fluids which operate conventional turbines (solar thermal). Solar energy, however, is prevented from failing freely onto the Earth's surface by inclement weather, the diurnal cycle, and the screening effects of the atmosphere (on a clear day, the amount of sunlight reaching the ground is about 65* of that above the atmosphere). Solar energy systems on the surface of the planet would therefore require storage systems for those times when solar energy is not available, making then less attractive as a base load power source. Alternatively, these power plants could be placed in orbit around the Earth where sunlight is both continuously available and more intense. Called satellite power stations (SPS), they would be placed in geosynchronous orbit where an object maintains the same position relative to a given point on the globe. Although the SPS would be eclipsed by the Earth's shadow for varying periods of time each day, the eclipse time would never exceed 72 minutes, meaning the system could theoretically operate for 99% of the year, an attractive feature for a base load power source. Because of the need for periodic maintenance, however, plant factors of 80% - 92% have been estimated. Tne electricity would be produced at the orbital station and converted into microwaves, then beamed down to receiving and rectifying antennas (called rectennas) on the planet's surface where the microwaves would be reconverted into electricty. At the present time, the SPS concept is still in the feasibility determination stage, making judgments about it difficult to render. NASA and
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