waters (25 to 28 °C) in tropical zones, and those of the ocean floor (6 to 8 °C) at depths to the order of 600 m off Abidjan, Ivory Coast, by means of a conventional thermal machine, complemented by an adapted working fluid. The only explanation for the low temperature of the seabeds is their reception of permanent supplies from polar waters. George Claude made an endeavour to capture this energy during the 1930’s at Abidjan, but a storm destroyed the installations while still in construction. Various projects are actually being carried out, some of which correspond to realsized installations (several hundred MW-h) on floating platforms. The platforms may well solve the problem of piping the pumped cold waters (which will then be vertical), but they do not provide a solution to the problem of transporting the energy produced. One project aims at producing hydrogen on the spot, to later transport it, in liquid form, to the mainland, by barge. This is solar origin energy. Biomass is undeniably an interesting energy source. But burning wood in a chimney will quickly become an expensive luxury, then a crime, for wood deserves a better end! Biomass potential energy density by m2 is and will remain low; added to conversion problems (organic matter) into CO or CH4 gas or methyl or ethyl alcohol, there is also fundamentally a collection problem, especially as concerns “forest residue,” that is, the substance that grows under a forest hindering its growth — a substance which would therefore be in our interest to collect. A “ripe” forest has reserves totaling 1700 MKj/ha, and an annual growth rate of 11 MKj/ha. This is clearly less than the quantity of energy provided by one hectare of cereals (35 MKj/ha) but biomass’ annual upkeep demands substantially less energy and labour. Energy resulting from biomass is part of the “planting and sowing, growth, harvest, collection and transformation” system and this is the perspective in which actual studies are being developed. Stocking problems are minor. The overall output is in the region of 1% to 3%. This energy is of natural solar origin, (distributed) which, if well exploited, can contribute to maintaining the present biological balance. What remains is direct solar energy, to be exploited either by thermal conversion on the blackest possible body or by photoelectric conversion. On Earth, this energy is modulated according to predictable variations (day/night, seasons) or unpredictable ones (cloud covering). Productivity in both cases, reported during bright periods, reaches approximately 10%. Thanks to the fall out of space problems it is probable that electrical conversion will claim recognition before the year 2000, even for heating facilities. Collecting solar energy in space can provide us with constantly available energy (except for a few hours, by satellite per year). Nevertheless, a certain number of problems remain to be solved. The theme of this symposium is therefore to make a contribution to the following question: Is the production of solar energy by means of geostationary satellites feasible? An answer should be given by 1990. Only then, if the answer is positive, will the real technical problems arise. However, it is not excluded to consider these problems even now, for they promise to be both difficult and numerous: in-space construction of the satellite itself, active control of the structure (it can hardly be conceived as infinitely rigid), energy conversion on board, its transmission, reception on Earth, and link-up with distribution networks. Security problems in case of beam deviation do not seem to present great difficulties, however a few hours annual eclipse is inevitable. Meanwhile, let us take note of the following problems:
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