One of the most influencing constraints is caused by possible changes in climate due to the greenhouse effect of increasing CO2 concentration in the atmosphere. It will veiy probably lead to restrictions on fossil fuel use in a global scale. Presently it is not clear how severe these restrictions might be. However, they should be taken into consideration and some scenarios with decreasing use of fossil fuels especially coal (whose resources are abundant) must be investigated. Another important constraint may be imposed on nuclear energy development depending on the possibility of creation of sufficiently safe reactors and acceptable fuel cycle. There are opposite opinions on this topic and both situations (scenarios) with and without use of nuclear energy should be taken into account. Restrictions on the use of fossil fuels and nuclear energy can drastically increase the role of renewable energy sources (RES). Large scale use of RES is certainly desirable from the environmental view point. But it requires the development of appropriate technologies (and even systems) which are very expensive at present. The increase in the RES share in the global energy balance to 40-50% will require huge financial and material expenditures comparable with the world total military expenses. Among possible ways of extensive use of RES solar space power systems [2], particularly the Lunar power system can be pointed out. Possible achievements in technological progress are vital for the future energy development. It concerns environmentally friendly technologies based on fossil fuels, new types of safe nuclear .reactors, a large variety of technologies for the utilization of RES, development of fusion reactors, etc. The most important renewable sources are terrestrial and space installations or systems for large- scale use of solar energy. Depending on the results of technological progress the centralized and decentralized energy supply will play different roles. The trend towards the decentralized energy supply on the base of RES will certainly be enhanced in the next century. However, it is not acceptable for large industrial centers and towns. Therefore, the centralized energy supply should receive further extension, if such broad-scale technologies as safe nuclear reactors, Lunar power system, etc. are successfully developed. In this case, formation of large energy systems at the regional and world levels will proceed. It is obvious that international cooperation becomes vitally necessary for development and commercialization of new energy technologies and creation of energy systems themselves. Concept of the world energy system The trend towards formation of specialized energy systems at the continental and global levels can clearly be seen in the development of centralized energy supply. They spread over the territory comprising big countries, regions and continents. The existing oil supply system is of the global nature already. Power and gas supply systems have actually become regional ones in some parts of the globe (in Europe, North America,
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