NewTrans3.txt[9/15/2024 8:36:13 PM] SPACE SOLAR POWER PLANTS IN THE GLOBAL ENERGY CONTEXT OF THE NEXT FIFTY YEARS MAURICE CLAVERIE and ALAIN DUPAS National Center for Scientific Research Interdisciplinary Research Program for the Development of Solar Energy 282, Bd Saint Germain — 75007 Paris, France Abstract — Space solar power plants (SSPs) would be high-power units (3 to 5 GW) for baseload electricity production. Their potential market will be that of large baseload power plants (LBHPs) after the year 2000, the earliest date for which a large number of SSPs can be expected to enter service. An assessment of this market based on prospective scenarios from Case Western Reserve University (CWRU) and the World Energy Conference (WEC) suggests very large needs: 548 GCEBs between 2000 and 2025 according to the CWRU scenario, and 394 according to the WEC scenario. GCEBs will eventually compete on the market with three other energy systems: coal-fired power plants, breeder reactors, and thermonuclear fusion reactors. The first two of these systems are technologically very advanced, but may encounter major ecological obstacles. The feasibility of thermonuclear reactors is also not yet proven. GCEBs are undoubtedly technically feasible, and research directly concerning them receives at least as much funding as that devoted to fusion. However, considerable attention should be paid to the environmental problems posed by the transmission of microwave energy between space and Earth. In the very long term, it can be estimated that the use of a renewable energy source, the sun, will be a definite advantage for space solar power plants. I. INTRODUCTION Space solar power plants (SSP) have so far been considered primarily as a space system, and not as an energy system, to be inserted into the global energy context. The spatial aspects of SSP are obviously very important: they are decisive for establishing the feasibility and assessing the cost of the system. However, at equal or similar costs, it is the energy aspects that will decide the choice in favor of SSP or competing technologies. These aspects include the type of energy produced, the scale of production, the adequacy to energy demand, the heat released into the environment and more generally the environmental problems posed by this type of plant. These are the aspects that we propose to consider here. THE NATURE OF THE PRODUCTION OF SPACE SOLAR POWER PLANTS The reference solar power plant considered in the preliminary comparative studies of the US Department of Energy (DOE) and NASA delivers a power of 5000 MW. This power level is not immutable, but it should be noted that its order of magnitude is imposed by the characteristics retained for the microwave beam transmitting the energy between the collector located in space and the receiving antenna located on the ground (rectenna): industrial frequency of 2.45 GHz, and maximum intensity of 200 mW/cm2 at the center of the beam at the level of the ionosphere. The design of a CSS of significantly lower power would require profound changes to the microwave link, and probably the abandonment of this in favor of another technology. We will return to this fundamental point later, but at the current stage of the analyses on CSS, they must be considered as production units with a power in the range of 3 to 5 GW. The form of energy produced is naturally electricity. In addition, CSS have the particularity of producing electricity practically permanently, because their space solar panels are illuminated all year round, with the exception of daily eclipses of less than 74 min duration occurring for about 2 months on either side of the equinoxes. Relatively little attention has been paid to this question of eclipses, which would certainly pose a problem for electricity networks largely using CSS. But if we accept, as most authors do, that this problem will be easily solved, then CSS appear essentially as “baseload” power plants producing nominal power day and night for most of the year. In fact, the power that a CSS can produce varies by about 15% throughout the year (Fig. 1), due to variations affecting two parameters: the Earth-Sun distance and the angle of the photovoltaic panels with the direction of the sun's rays. But it is the power supplied in the most unfavorable conditions that is taken as the nominal value. CSS are therefore ultimately baseload power plants with a capacity of 3 to 5 GW. As an energy system, they are therefore quite comparable to current nuclear power plants, which generally group together 4 reactors of 1000 to 1200 MW.
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