6.0 DEVELOPMENT OF SPS TRADEOFF AND EVALUATION CRITERIA AND SIMULATION PROGRAMS 6.1 SPS TRADEOFF AND EVALUATION CRITERIA Most of the trade studies that have been conducted to date were performed to obtain an understanding of the advantages and disadvantages of various schemes rather than to eliminate options. The results of many of these studies have indicated very slight differences in one approach versus another, and with further study and increased understanding, some conclusions could actually change. In most cases where one scheme appears better, the less favorable options were not eliminated from consideration but less effort may have been devoted to their further study. Most tradeoffs were accomplished to minimize the mass and cost of the SPS program. However, there are some limiting constraints that are not as tangible as mass and cost that had to be considered. Many environmental issues had to be considered, such as operational environment, microwave beam, vehicle emissions, and other terrestrial impacts resulting from the nature and magnitude of the SPS program. For example, the power density level at which microwave beam-ionosphere interactions are expected to occur was used as an upper limit with a resulting effect on the size of the microwave transmission system. Material properties, such as thermal limitations on the microwave structure, were considered. The lifetime and reliability of materials and equipment were important parameters that had to be studied. Other factors such as the outage time for maintenance on turbomachines were considered in the tradeoffs. Factors such as program risks because of uncertainties in technological forecast were examined. The availability of resources was considered also. Tungsten was eliminated as a choice for radiators in the solar thermal concept because of the limited reserves of tungsten. Safety was also an important item for consideration. Finally, comparisons were made of the various SPS concepts such as photovoltaic, thermal, and nuclear; and, of course, the SPS program itself was compared to alternate conventional and future power systems. 6. 2 SIMULATION PROGRAMS 6. 2 1 SYSTEMS DESIGN ANALYSIS MODELS System design analysis models have been developed for both the photovoltaic and thermal SPS concepts for use in trade studies, sensitivity analyses, and to assure consistent and compatible designs. This has been
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