final societal assessment report which attempt to compile the key findings and their implication for SPS. The findings are briefly surveyed below by issue area. Resources Based on an initial understanding of system characteristics, the physical resource requirements most likely to present a potential problem were considered to be land, materials, and energy. Therefore, a preliminary study was commissioned to assess the magnitude and impact of these SPS resource requirements. Since determination of land requirements alone is not as important as knowing where rectenna sites can be located, a second study was conducted to identify locational criteria and make a preliminary determination of areas that were eligible for rectenna sites. On the basis of the preliminary studies, three additional activities were undertaken in the final assessment. First, a general methodology for materials assessment of energy systems was refined and applied to the SPS situation to validate and extend the preliminary findings. Preliminary work in the analysis of energy utilization by SPS indicated that no further work was warranted in this area. The preliminary siting and land-use studies, however, indicated the need for a more sophisticated approach to this problem. Two additional studies were, therefore, set in motion. The first of these was essentially a follow-on to the preliminary work in finding eligible and ineligible areas for rectenna sites. The second examined a specific site in great detail to determine the potential environmental impact of installing an SPS rectenna there. These studies are all essentially complete; results are briefly indicated in the following paragraphs . The preliminary materials analysis compiled a list of required materials for an SPS and then, using a relatively crude screening procedure, evaluated each material in terms of world and domestic supply. Also considered were manufacturing capacity and adequacy of the data base. The refined methodology uses computerized screening of the materials with flags raised at various threshold levels as a function of several parameters: current domestic and world production rates, domestic and world reserves, and so on. Thresholds can be changed and the analysis rapidly run to determine sensitivities. No insurmountable materials problems are evident in either the preliminary or refined analysis. However, materials definition, both quantities and specific kinds, is in a fairly primitive state. Similar analyses will be required as the detailed materials requirements become better defined. Currently, well over half of the elements or compounds required by either design option (silicon or gallium arsenide for the photovoltaic cell material) present no problems. There is a problem in the demand for mercury and tungsten in both options, with silver and gallium becoming problems for the gallium arsenide option. Manufacturing capacity problems are also judged to be more severe for the gallium arsenide option. Net energy analysis has been used in the past to compare alternative energy generating systems in terms of the energy produced by each system per unit of energy required. The preliminary assessment indicated that there have been a few analyses of the SPS using some of the widely varying techniques
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