4.5.2 Materials The objective of the materials analysis was to assess potential materials problems by identifying the types and quantities of materials required by the SPS and alternative technologies. Defining materials problems is not simple; many important factors should be included: resources, reserves, production capacity, import dependence, price, and opportunity costs. The possibility of resource and/or reserve constraints depends on market penetration scenarios. Domestic production factors include current capacity, normal growth rate, and required growth rate to meet a given demand level. If domestic supplies of a material are inadequate, the balance must come from foreign markets; consequently, the possibility of cartels and the effects on the U.S. balance of trade must be considered. Since price is influenced by supply and demand, the possible effects of large increases in supply or demand must be investigated. If a material is largely used by a single energy technology, opportunity costs result from the limited use of the resource for other purposes. The possibility of substitute materials becomes an important issue for any materials judged to be a potential problem. This comparative assessment is based on available research. In general, conclusions about materials problems published in the open literature were not based on rigorous considerations of the above-mentioned criteria. Thus there is a lack of uniformity in conclusions from technology to technology because the assessments were done by different researchers. Where possible, an attempt was made to reconcile these differences for this assessment . Sources include environmental impact statements,23,159 system designs, 137,160,161 system descript ions,139,162 federal documents,163, 165 anj comparative studies.^» 166-168 The present comparison focuses on three screening criteria: Import dependence, availability (resources/reserves), and demand. Table 4.37 summarizes potential materials problems, by technology, for the three screening criteria. There are two materials that raise all three flags: gallium and tungsten. Gallium is used for the SPS, and tungsten is used for both coal and the SPS. A number of materials raise the import dependence flag, probably the most important from a national security point of view. Nine SPS materials are indicated for reasons of import dependence. Because of the lack of complete and highly reliable materials data, a scenario perspective was not explicitly attempted for materials. Thus, the assessment has proceeded only to a qualitative side-by-side level. 4.5.3 Energy Objective. The objective of the net energy analysis169 was to provide a comparison of the net energy requirements of the SPS (silicon and GaAlAs solar cells) and alternative energy supply systems (CG/CC, LWR, and TPV with silicon solar cells). Conventional energy systems provide substantially more energy than was required to put them into operation, and so the concept of net
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