UTILITIES VIEW OF SPS J. Patmore and J. Bohn Systems Control, Inc. - Palo Alto, California BACKGROUND: The U. S. Department of Energy (DOE) and National Aeronautics and Space Administration (NASA) are currently conducting an evaluation of a solar satellite power system (SPS). The SPS would convert solar energy to microwaves and beam the energy to collecting antennas on the ground for conversion to electricity. The overall system, envisioned as being initiated about 2000 and completed about 2030, would consist of 60 geosynchronous satellites each delivering 5 GW of pwer to conventional utility networks. The cost of the overall system is estimated to be between 0.6 and 1.2 trillion dollars.* To date, about $20 million have been spent analyzing and refining the designs of major subsystems. A limited effort has been expended on studying the SPS/utility interface. This note summarizes the results of a study commissioned by the Electric Power Research Institute, of the problems to be encountered in utility integration of a single 5 GW SPS. This study had two primary objectives: • to identify for the electric utility industry those characteristics of the SPS that will be most significant in implementing the interface with a conventional utility power system. • to indicate to the SPS community the technical and economic concerns of the electric utility industry regarding the development of the SPS concept. SPS could be an important means of tapping solar energy, however, there are many technical, economic, social, and political problems that must be solved before the SPS could be built. If the SPS is implemented, its unique features will pose unique problems for the conventional utility network into which it feeds its power. ECLIPSE AND LOAD FOLLOWING: The spring and fall eclipse periods which the SPS undergoes create some unique problems for the utility system. The onset and retreat of the eclipse periods is very rapid — it takes the SPS a few minutes (2-4) to go from full sunlight to full shadow and the same to emerge. But it takes additional time to shut down and restart the SPS — about 5 minutes to shut the SPS down and 16 to 60 minutes to restart, depending on the length of the down period. However, the load following capability of the utility system may well impose a more serious constraint. The maximum response capability of conventional units range from 1-5%/minute, whereas the SPS can be shut down at the rate of 20%/minute and restarted at the rate of 2-7%/minute. Thus, it is likely that the capability of conventional units will be the limiting factor, not the SPS system. A large number of gas turbines designed for fast start-up may be desirable or even required in a system utilizing the SPS. One negative impact of SPS eclipses would be the increased cycling duty of conventional units which would cause increased 0&M costs and forced outage rate for these units. *A11 costs cited in the text are in constant 1977 dollars.
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