Power installations on solar energy. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power installations on solar energy. 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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The use of solar energy today is reduced mainly to the production of low-grade solar heat using the simplest flat-plate solar collectors. For example, in the United States in 1990, out of 3,6 million GJ of energy produced from solar radiation, 3,5 million GJ is low-grade heat used for hot water supply, heating water in swimming pools and, to a lesser extent, for heating. Israel has about 800 solar collectors installed under a law requiring every home to have a solar water heater, producing about 000 million GJ of energy and providing 15% of the population with hot water.

In modern flat plate solar collectors, the absorber most often has a selective coating layer with an absorption coefficient for solar radiation of 0,94 - 0,96 and an emissivity at the absorber temperature of 0,09 - 0,12. In newly built houses, attempts are being made to combine collectors with elements of the roof of the house, which makes installation easier and cheaper. A complete water-heating installation includes, in addition to collectors, a heat-insulated tank - an accumulator, in which a backup electric heater is built in, the necessary fittings and automation. The collector is usually installed motionless at an angle to the horizon approximately equal to the latitude of the area. On an individual house with an area of about 100 m2, 1-2 collectors are usually installed, with an absorber area of 1-1,5 m2 each and a storage tank with a capacity of about 150 liters. Such an installation in the Western market today costs about 500 USD/m2 of collector area.

The heat output of such an installation significantly depends on insolation, ambient temperature and other climatic parameters. Depending on the latitude of the area and climatic conditions, the annual arrival of solar energy per 1 m2 of surface varies greatly. For latitudes around 30° it can be 8-10 GJ/(m2 year), while for latitudes 50-60° it drops to 2-4 GJ/(m2 year).

The efficiency of a solar collector is determined by its optical characteristics, the quality of thermal insulation, insolation and temperatures of the coolant and ambient air. In most existing installations, the average annual operational efficiency of the collector is at the level of 40-50%. This means that for latitudes of about 30°, 1 m2 of collector can produce 3–5 GJ of heat per year with a temperature of 60–70°C. The cost of this heat with such indicators and a plant lifetime of 30 years turns out to be at the level of 3-4 USD/GJ, which makes these plants attractive to consumers. For higher latitudes, solar water heaters are more preferable as seasonal ones.

Along with collectors, passive methods based on the optimization of architectural and planning solutions are used to use solar heat for home heating. In addition, it is of interest to develop the so-called transparent insulation for the walls of houses, selective films for windows, etc.

Electricity through the use of solar energy can be obtained either in thermal power plants, in which the heat from fuel combustion is replaced by a stream of concentrated solar radiation, or in direct energy conversion plants based on the use of semiconductor photoelectric converters (PVCs).

An interesting project developed in Australia. The Olympic Committee decided to make the Games "green", for which, in particular, a solar thermal power plant with a thermodynamic conversion cycle was built in the Olympic Complex. The project is based on linear concentrators made of flat or slightly curved mirrors and concentrating solar radiation (concentration degree 10-15) on a receiver made of evacuated tubes, inside which there is a thin-walled absorber tube equipped with a heat-receiving fin and covered with a very perfect selective coating. From the absorber, the heat is transferred by heat pipes to the steam generator, where water vapor is produced. Superheating of the steam to a temperature of 330°C is carried out by burning a certain amount of natural gas. The heat from the turbine is used to heat the Olympic pool and other facilities.

Another variety is a solar power plant with a paraboloid concentrator (PC) that follows the sun along two axes. The paraboloid concentrator is theoretically the best concentrating device, allowing for a concentration of several thousand suns, and hence very high heating temperatures. However, PCs, in contrast to tower and SPPs with PCC, due to design considerations, do not allow having large unit capacities in one module. Therefore, the scope of application of SES with a PC is relatively small, not exceeding several tens of kilowatts, mostly autonomous installations. In this case, such plants should compete not with large thermal power plants, but with diesel plants of small and medium capacity, which produce electricity at a cost 2-3 times higher.

In a modular design, the focus of the PC is most often placed directly on the engine, which converts heat into mechanical and then electrical energy. Until recently, only the Stirling engine was used for this purpose, today a gas turbine is also being considered.

Recently, the world has increased interest in installations that directly convert solar radiation into electricity using photovoltaic cells. The cost of electricity generated by photovoltaic installations (PMT) today is several times higher than thermal cycle solar power plants. Nevertheless, PMTs are being actively implemented in both developed and developing countries. In this case, two opposite trends can be observed.

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