Petersburg Physics and Technology Institute of the Russian Academy of Sciences under the guidance of academician Zh. LAlferov and by the Scientific Production Amalgamation Kvant under the guidance of A.M.Rzhevsky. PV improvement in the CIS is being carried out the following main directions: • directed improvement of semiconductor structure specifications by its optimum alloying and creation of built-in electric fields; • transition from homogeneous to heterogeneous and various semiconductor structures; • creation of cascade PVs made of specially matched width of the "forbidden" band semiconductors that allow in every cascade to transform the emission passed through the previous and others, (i.e. creation of multijunction solar cells) We consider the use of concentrating systems to be the further step to improvement of PVs. Their application will allow both cost reduction due to the smaller area occupied by PVs and increase its resistance to cosmic radiation owing to screen effect of concentrators. However the solar array with concentrators has an essential shortcoming - the necessity of accuracy in orientation to the Sun. The degree of solar radiation concentration for silicon PVs reaches several dozens, and several hundreds for PVs made of gallium arsenide. Solar Power Systems with Heat Engines In converting heat to electricity in existing space power satellites Brayton, Rankine and Stirling thermodynamic cycles are used. A number of technological difficulties which we come across at present made the scientists in our countries develop power systems using Brayton and Stirling cycles. The development of dynamic conversion for generating electricity is stimulated by a number of its virtues, the main of which are: • higher efficiency in comparison with other solar energy converters • possibility of easy transition to high values of on board voltage when constructing high power systems; • possibility to provide both electrical and heating needs; • presence of tested in other industries separate construction elements (compressors, turbines, bearings etc.) of such installations; • possibility of power control according to the given power consumption schedule. Due to specific requirements to space power, turbine driven generators having appeared recently, gained one more advantage, the relative invulnerability to particle flow, to electromagnetic radiation and other outer space factors. A mixture of noble gases (He + Xe) is more frequently used as an operating gas in such plants. This operating gas is heated in a heat receiver. The heat receiver can be either combined or not with a heat accumulator. The presence of the heat accumulator
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