With these hypotheses and this strategy, world energy supplies are established as indicated in table II. For the northern countries, there would be a very large effort towards energy conservation (4800 Mtoe {million tonnes oil equivalent}), the very rapid fall in the use of fossil fuels, which would be reserved as much as possible in the southern countries. A moderate growth (30%) of nuclear energy would take place until 2020 before its continuous fall until 2100. For renewable energies, there would be an increase in the contribution of biomass to supplies (especially in the form of fuel, sometimes imported from other production zones), the progressive use of the very important hydro-power reserves in the (former) USSR, and a rise in solar and wind energy. All the renewable energy sources would reach significant values after 2060. For the southern countries, there would be a major initial increase in use of fossil fuels, followed by the beginning of a decrease in 2050 and stabilization at approximately 3000 Mtoe in 2100. The nuclear energy supply would remain confined to a few countries in which it is already present before phasing out. An international effort would be made towards equipping the numerous hydro-power sites in Latin America, Asia and Africa. Biomass and solar energy would play, in the long-term, the major role in these countries reaching nearly half of the final supply. Figure 1 illustrates the evolution of the world energy supplies. The NOE scenario's impact on the environment appears in figure 2. The concentration of carbon dioxide in the atmosphere would be stabilized around 470 ppm. The stock of nuclear waste would reach a ceiling at 0.5 million tons before the end of the century. A place in the sun? The above scenario shows the key role of solar energy to the global energy supply, since 2350 Mtoe are required in 2100. Then the questions are: What is the optimum mix of solar technologies for different regions with various needs? Is there any need for Solar Power Satellites (SPS) in that mix of solar technologies? The present technologies are first able to ensure decentralized energy needs for thermal and electrical applications (water and house heating, electrical domestic applications, communications, water pumping and so on). This corresponds to a great number of end-use points, each consuming a small amount of energy, the accumulation of which becomes significant. On the other hand solar thermodynamic power plants have been successfully demonstrated for producing electricity on the grid. In California, nine solar power plants of the cylinder parabolic mirror type from 30 MW to 80 MW installed in the Mojave desert, supply their electricity to the grid. The competitiveness is obtained due to good correlation between electrical needs and sunshine in these regions. A 25% contribution of natural gas is provided to optimize production.
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