Net energy analysis shows that the payback period for most of the technologies studied is small (less than 1.5 years). The SPS GaAlAs option, coal, and nuclear options are about one year, with the SPS Si option being about 6 and TPV (silicon cells) 20 years. Thus, the GaAlAs design affords SPS with an option that compares favorably with conventional technologies on a net energy basis. Macroeconomic analyses included the calculation of changes in GNP for the year 2000 and, in qualitative terms, the effect on inflation due to deployment of SPS. Using a target GNP of 3.7 trillion dollars (all figures in 1978 dollars) for the year 2000, deployment of 10 GW of SPS power will require 20 to 50 billion dollars of excess investment compared to the least expensive (coal) option. This is 10 to 25% of 200 billion dollars, the amount available for financing economic growth of about 2.3% per annum. Compounded to the year 2030, such a reduction would result in a $200 to $500 billion reduction in the target GNP of $7 trillion. If uranium and coal fuel supplies are much more contrained than presently envisioned, then deployment of SPS would reduce consumption of these scarce items and possibly reduce their prices. This could in turn reduce total energy expenditures, as indicated in Table 2. For the UH and UI scenarios, SPS energy costs of about 40-50 milIs/kWh would result in a breakeven from a total energy expenditures point of view. The institutional analysis focussed on the regulatory aspects of electricity generation by coal, nuclear, and SPS. The technologies were characterized relative to each other. Justifications for regulation, the level of governmental responsibility, and the cost of regulation were considered. Studies estimate that the annual cost of regulating the nuclear industry is about $6 billion, versus about $3.4 billion for coal. In view of the changing regulatory environment (e.g., the decentralization movement and the growth of power on a local scale), it is possible that SPS regulatory costs may look more like nuclear regulatory costs than coal regulatory costs, due in part to the international regulatory aspects of SPS. If this is true, regulatory costs for SPS could be significant compared to SPS investment costs, particularly in a low deployment rate (3.3 GW/yr) scenario. Conclusions may be stated in the form of important tradeoffs identified in the comparative assessment. In the resources area, the water requirements of coal and nuclear technologies are balanced by the land requirements of solar technologies; materials and net energy issues appear to be of secondary importance, and not significantly different between technologies. Macro- economic tradeoffs involve the use of scarce (or supply-constrained due to regulations) fuels by coal and nuclear technologies (which tends to be inflationary) versus deployment of capital-intensive SPS technology (which siphons off investment funds earmarked for economic growth, resulting in reduced GNP unless there are offsetting factors) which utilizes direct solar energy. Finally in the institutional area, choices involve the known and anticipated regulations of coal and nuclear technologies versus the unknown regulations for SPS (which has an international regulatory dimension).
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