Rapport sur la situation actuelle de la conversion energetique directe de l'energie solaire et apercus futurs

Abstract

The authors stress first the fact that “utilization of solar energy” does not mean the natural applications, only the artificial ones. With regard to the energetic conversion of solar radiation, its interest seems to be considerable, because of the near future depletion of stores of energy carriers, such as fossil and nuclear fuels. The authors start with a short description of the principal conversion processes concentrating on: photovoltaic, thermoelastic, thermoelectric, thermionic and heliochemical processes, to which this paper is devoted. First of all the trapping of solar radiation is studied as the first general step to all kinds of conversion. This collection is mostly done by mirrors made of brilliant aluminium or metallized glass or by metallized epoxy resins. The classical reflectors have a focal zone with one entry. The Laboratoire d'Héliotechnique de la Faculté des Sciences de Marseille has studied vortex type reflectors offering a focal zone with several entries and great advantages for the effective realization of trapping equipments. The authors give a detailed description of the reflector “Héliodyne” with 50 m diameter. Having indicated the optimum conditions for construction of solar water heaters, the authors describe the conversion of solar into electrical energy by thermoelectric, thermionic and photovoltaic generators. Concerning the first method, the authors describe a high power thermoelectric generator utilizing Bi 2Te 3 as thermoelectric material and being now under construction in the authors' laboratory in Marseille. Examining the future of utilizations of solar energy by helioelectric conversion, the authors point to the successful practical application in space technology. The necessity of great reliability has intensified the efforts of industrial laboratories to increase it stepwise. In this way even the terrestrial applications of photovoltaic cells has been facilitated in spite of the low efficiency. In conclusion the author points out the importance of the classical methods of conversion of solar heat and of the construction of a prototype of a large thermal power station.