Converting solar radiation into electrical current. Scheme, description

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Converting solar radiation into electrical current. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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By the end of the XNUMXth century, mankind had developed and mastered a number of principles for converting thermal energy into electrical energy. They can be conditionally divided into machine and machineless methods. The latter are often referred to as direct energy conversion methods because they lack the stage of converting thermal energy into mechanical work.

Machine conversion of solar energy into electricity Among machine converters, the most famous are steam and gas turbine plants, which have been operating at all ground thermal and nuclear power plants for a century. They are also suitable for work in space, but in this case a special heat exchanger is needed - an emitter that acts as a steam condenser. At the same time, if in a ground-based steam turbine installation the heat of condensation is removed by circulating water, then in space conditions, heat removal from the steam or gas (if it is a gas turbine) exhausted in the turbine is possible only by radiation. Therefore, the power plant must be closed.

A schematic diagram of a closed gas turbine plant (CGTU) is shown in fig. 1, a. Here, solar radiation, collected by the concentrator 1 on the surface of the solar boiler 2, heats the working fluid - an inert gas to temperatures of the order of 1200-1500 K and, under pressure created by the compressor 3, supplies hot gas to the blades of the gas turbine 4, which drives the alternating current generator 5 The gas exhausted in the turbine first enters the regenerator 6, where it heats up the working gas after the compressor, thereby facilitating the operation of the main heater - the solar boiler, and then cools in the cooler - emitter 7. As shown by ground tests of a three-kilowatt gas turbine installation carried out in 1977 at a five-meter faceted parabolic concentrator at the Physical-Technical Institute of the Academy of Sciences of Uzbekistan, installations of this type are very maneuverable, reaching the nominal speed (36000 rpm) took no more than 1 minute from the moment the sunspot was pointed at the cavity of the cylindrical boiler. The efficiency of this installation was 11%.

It may seem that for solar power plants using free energy, the efficiency is not as significant as for traditional thermal engines running on organic fuel. However, this is not so, because the dimensions and weight of the most bulky and heavy parts of solar space power plants - the concentrator and the refrigerator - emitter - depend primarily on the efficiency of the installation.

It is possible to create a power plant with a steam turbine converter (Fig. 1b).

Converting solar radiation into electrical current
Fig.1. Schematic diagrams of solar gas turbine (a) and steam turbine (b) electrical installations

Here, the solar energy collected by the concentrator 1 heats the working fluid in the solar boiler 2, which turns into saturated and then into superheated steam, which expands in the turbine 4, which connects to the electric generator 5. After condensation in the cooler-radiator 7 of the steam exhausted in the turbine, its condensate, compressed by pump 8, again enters the boiler. Since the supply and removal of heat in this installation are carried out isothermally, the average temperatures of supply and removal turn out to be higher than in a gas turbine plant (at the same heat supply temperatures), and the specific areas of the radiator and concentrator may turn out to be less than in a CCGT.

The American solar steam turbine plant "Sunflower", similar in purpose, had an efficiency of 12% with a specific area of the cooler-emitter of the order of 1 kW/m2. With such characteristics of a 10 GW SCES (this is the power required today by the largest megacities of the world), a refrigerator-emitter with an area of 10 km2 would be required. Relatively less developed experimentally are power plants with reciprocating machines of a closed cycle.

A common disadvantage of all machine converters is the presence of rotating parts in them, which creates problems in maintaining a constant orientation of the station.

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