ECONOMIC POTENTIAL OF SPS Orlando E. Johnson Boeing Aerospace Company The Solar Power Satellite concept is a very simple solar power collection scheme in principle. However, it does require two large independent power processing stations. At the space-based station are solar cells which generate 0.8 Watts of power each. Aggregating enough of these cells by simple seriesparallel electrical interconnections to be able to drive klystrons is basically all that is required. Each klystron requires about 80 KW of power (output of cells) in order to deliver nearly 70 KW of microwave power to the section of antenna that it drives. The second power processing station is on the Earth and it resembles the first station. Here, small dipoles (instead of solar cells) intercept the incoming microwave energy. They deliver 0.5 Watts of power each on average. The power from these dipoles must be aggregated, again by simple series-parallel electrical interconnections, to attain high enough levels to process efficiently and transmit to a utility company to sell. The largest single element of cost in an SPS (Figure 1) is the cost of providing the extensive ground structures and equipment that are required for the receiving antenna. For example, 2.7 Million, 9 x 30 foot panels supported on concrete posts are required. These are projected to cost $0.6B. The 10 billion stamped metal dipoles (@ 5(^), 7 billion diodes (0 4<£)» wiring, switching and conventional power processing equipment come to $2.2B. Adding all other costs, plus a liberal contingency allowance, brings total ground-based costs to $4.IB. The klystrons and power processing equipment that must be transported to space come to $0.9B. This equipment plus the transportation itself are projected to cost $3.4B. $3.3B is allowed for solar cells, space structures and space assembly activities. Only this last amount, which is less than 30% of the total expected SPS cost, is for SPS elements that are largely new developments - in scale if not technology. Would an SPS be competitive with conventional power? It depends highly on the assessment criteria adopted. For example, in the year 2,000, SPS systems are expected to cost $5B more than comparable coal-fired plants. However, each SPS would eliminate over its 40-year lifetime the spending of $40 to $250 Billion for coal. If a comparative analysis is done in which the cost of fuel is highly discounted or fuel cost is excluded because it is an operating expense, not a capital cost, then the higher capital cost of the SPS will dominate the comparison. The SPS may then be rated as a less attractive investment in the eyes of an investor. However, as the coal plant is operated over its 40-year lifetime, the U.S. must forego $25 to $240 Billion in other consumption in order to provide the coal consumed. This means a lower U.S. standard of living and a diversion of several thousand U.S. workers from higher order employment into coal mining. These latter aspects of the SPS have not been clearly understood or
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