answer to these questions. It will certainly not be possible to make a definite statement concerning the safety, environmental and economic aspects of the SPS until the major design options, material and operational aspects have been defined in much greater detail. The experience with the development of other potentially significant energy sources, e.g., light water nuclear reactors, fast-breeder reactors, thermonuclear fusion reactors, or terrestrial solar energy conversion, shows that usually several thousand million dollars must be invested in technology development and health and safety studies before sufficient data on technical, economical, health, and safety aspects are available to really assess the viability of a new energy source. A major question which is always asked is whether the SPS concept will be able to compete with other potential future energy sources. A comparative assessment of the SPS has been started in the United States in an attempt to establish the answer. So far, two general observations have emerged from this study: • At present prices, centralised electrical power plants, based on fossil fuels or nuclear reactors, can produce electrical energy more cheaply than all alternatives based on the use of inexhaustible energy sources. However, the supplies of fossil fuels and uranium are limited and may become exhausted in the foreseeable future; as a consequence, it is very difficult to predict the evolution of fuel prices. • The uncertainty in the design, performance, safety, or cost of all major alternatives for producing electrical energy, e.g., fast-breeder reactors, terrestrial solar-energy conversion, thermonuclear fusion, satellite power systems, is so great that it is not possible at present to assess the relative advantages in a rational manner. All these systems have one aspect in common, however. Apparently, they do not depend on exhaustible resources, and the price of the electrical energy generated will be more dependent on the capital investment needed for exploitation than on the price of scarce base commodities. Considering the present lack of “hard facts” on which to base a choice between various potential energy sources for the future, there appears to be little choice than to continue to investigate a number of alternatives in parallel. The question still remains, however, whether Europe could have reasons to include the SPS in the alternatives to be investigated, in addition to the support already given to the development of fast-breeder systems, nuclear fusion, advanced coal utilisation, or, at a lower scale, terrestrial solar energy conversion. Any decision concerning a significant European effort in assessing the viability of the SPS concept must be political, considering the magnitude of the SPS concept and the size of the potential impact of either a negative or positive decision. As an input to the decision process, this paper addresses three questions which appear to be important in assessing the potential impact of the SPS on Europe and which are not affected by the present lack of technical definition of the SPS: • Would Europe really need the SPS as an additional energy source in the next century if its technical and economic feasibility can be demonstrated? • What could be the economic effect of an SPS programme in Europe? • What would be the impact of the technology development associated with an SPS programme? 2. THE ENERGY SUPPLY AND DEMAND BALANCE IN EUROPE The Western European countries have only half of the per capita energy consumption of the United States but they nevertheless consume approximately 20% of
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