We come now to the use of the main renewable energy sources. Many potential hydroelectric sites, both small and large, are not yet equipped. This is particularly true for the Andes and Himalayan mountains. Equipping them will have the additional advantage of reducing floods. Biomass (wood and agricultural wastes) can supply fuels like ethanol without increasing the CO2 content of the atmosphere, since new trees or plants can grow where this biomass has been removed for use. These clean motor fuels will compete with hydrogen produced by water electrolysis; hydrogen is the cleanest conceivable fuel and should replace fossil fuels not only in car, plane or ship engines, but also in domestic and factory heating systems. Last, but not least, solar energy must be developed. Thermal conversion is competitive today in some areas for water heating and at some sunny, isolated locations solar photovoltaic is used. Eventually the cost of photovoltaic cells will decrease and large solar power stations will become competitive in such areas as northern Africa or the Middle-East. In parallel we are expecting much from Power From Space. This paper presents a short resume of SPS 91 work. Power from Space History It was in 1968, a mere quarter of a century ago, that Peter Glaser invented the concept of SPS. A decade later, the principle of the conversion of solar energy in space for use on Earth was so well established that the United States Department of Energy was authorized to carry out its SPS Concept Development and Evolution Program (CDEP), 1979 - 1981, which concluded that SPS is technically possible. In 1983, Princeton’s Space Studies Institute carried out an additional study (Moonbased operations option) which concluded that SPS can be profitable. This was followed by the 1989 NASA Lunar Enterprise Case Study Task Force Report: SPS/LPS/3He. In 1991 the SEE (Societe des Electriciens et des Electroniciens) organized the second International SPS Symposium in Paris, resulting in a comprehensive review of world state-of-the-art and a direct exchange of views among principal research personalities from all over the world. And 1992, International Space Year, witnessed both a consensus selection of SPS International Recommendations and the first experimentation on the path to definitive testing, measurement and assessment.
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