could be derived from other research programs; microwave bioeffects, space transportation, laser, and photovoltaic development appear to be the most critical technical issues. However, it is unlikely that such “generic” research programs by themselves would answer adequately all of the high priority questions upon which SPS development decisions depend. If a dedicated SPS research effort is started now, the level of effort chosen would, to a large degree, determine the time it takes to obtain the information needed for a development decision. An effort set at $5 to $10 million per year could be sufficient to gather the minimum necessary information while minimizing the risk of insufficient or untimely information. A $20 to $30 million per year effort could gain the maximum information at the earliest possible time. It reduces the risk of not generating information in time to make an adequate development decision. Whatever the level, if a research program were instituted, it should investigate those areas most critical to SPS economic, technical, and environmental feasibility. Particular attention should be given to studying and comparing the various technical alternatives; but the feasibility of SPS also ultimately depends on its social, political and institutional viability. Thus, a research program should continue to explore these aspects of SPS development and deployment as well (see Table 1). ENERGY CONTEXT Even if it were needed and work began now, because of the many uncertainties and the long lead time needed for testing and demonstration, a commercial SPS is unlikely to be available before 2005-2015. Therefore, SPS could not be expected to constitute a significant part of electricity supply before 2015-2025. By that time, the U.S. will be importing very little foreign oil. Consequently, SPS cannot reduce our dependence on imported oil in this century. However, if efficient electric vehicles or other electric end-use technologies are developed by about 2010, electricity from SPS or other sources could substitute for synthetic liquid fuels generated from coal or biomass. Along with other electricity generating technologies, SPS has the potential to supply several hundred gigawatts of baseload electrical power to the U.S. grid by the mid 21st century. However, the ultimate need for SPS as well as its rate of development will depend on the rate of increase in demand for electricity, and the ability of other energy supply options to meet demand more competitively. SPS would be needed most if coal andlor conventional nuclear power are constrained and if demand for electricity is high.
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