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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Solar power plant. History of invention and production
Directory / The history of technology, technology, objects around us A solar power plant is an engineering structure that converts solar radiation into electrical energy. The ways of converting solar radiation are different and depend on the design of the power plant.
Solar radiation is an environmentally friendly and renewable source of energy. The reserves of solar energy are huge. By the beginning of the XNUMXst century, mankind has 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. Among the machine converters, the most famous are steam and gas turbine plants operating at all ground thermal and nuclear power plants. The schematic diagram of a closed gas turbine plant looks like this. Solar radiation, collected by the concentrator on the surface of the solar boiler, heats the working fluid - an inert gas to temperatures of the order of 1200-1500 degrees Kelvin and, under pressure created by the compressor, supplies hot gas to the blades of a gas turbine, which drives an alternating current generator. The gas exhausted in the turbine first enters the regenerator, where it heats the working gas after the compressor. Thus, it facilitates the work of the main heater - the solar boiler. Then the gas is cooled in the cooler-emitter. Tests of a three-kilowatt gas turbine plant, carried out in 1977 on a five-meter faceted parabolic concentrator at the Physical-Technical Institute of the Academy of Sciences of Uzbekistan, showed that plants of this type are very maneuverable. The output to the nominal speed was no more than a minute from the moment the sun spot was pointed at the cavity of the cylindrical boiler. The efficiency of this installation is 11 percent. In a power plant with a steam turbine converter, the solar energy collected by the concentrator heats the working fluid in the solar boiler, which turns into saturated and then into superheated steam, which expands in a turbine connected to an electric generator. After condensation in the cooler-radiator of the steam exhausted in the turbine, its condensate, compressed by the pump, again enters the boiler. Since the supply and removal of heat in this installation is carried out isothermally, the average supply and removal temperatures are higher than in a gas turbine installation, and the specific areas of the radiator and concentrator may turn out to be smaller. Such an installation, operating on an organic working fluid, has an efficiency of 15-20 percent at relatively low temperatures of heat supply - only 600-650 degrees Kelvin. A schematic diagram of a closed gas turbine plant (CGTU) is shown in the figure. Here, solar radiation, collected by concentrator 1 on the surface of solar boiler 2, heats the working fluid - inert gas to temperatures of the order of 1200-1500 K and, under pressure created by compressor 3, supplies hot gas to the blades gas turbine 4, which drives an alternating current generator 5. The gas exhausted in the turbine first enters the regenerator 6, where it heats the working gas after the compressor, thereby facilitating the operation of the main heater - the solar boiler, and then cools in the refrigerator - radiator 7. As shown ground tests of a three-kilowatt gas turbine plant, carried out in 1977 on a five-meter faceted parabolic concentrator at the Physico-Technical Institute of the Academy of Sciences of Uzbekistan, installations of this type are very maneuverable, reaching nominal speed (36000 rpm) took no more than 1 minute from the moment the sunspot was pointed at cavity of a 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. Converting solar radiation into electrical current
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. From many of the shortcomings inherent in machine converters, power plants with so-called machineless converters are free: thermoelectric, thermionic and photovoltaic, which directly convert the energy of solar radiation into electric current. "Thermoelectric generators are based on the thermoelectric effect discovered in 1821 by the German physicist T.I. Seebeck, which consists in the appearance of thermo-EMF at the ends of two dissimilar conductors, if the ends of these conductors are at different temperatures," L.M. writes in the Soros Educational Journal Drabkin - The open effect was originally used in thermometry to measure temperatures. The energy efficiency of such devices - thermocouples, implying the ratio of the electrical power released at the load to the heat supplied, was a fraction of a percent. Only after Academician A.F. Ioffe proposed to use semiconductors instead of metals for the manufacture of thermoelements, the energy use of the thermoelectric effect became possible, and in 1940-1941 the world's first semiconductor thermoelectric generator was created at the Leningrad Institute of Physics and Technology. In the 40s and 50s, the theory of the thermoelectric effect in semiconductors was developed by the works of his school and also very effective (to this day) thermoelectric materials were synthesized. By interconnecting individual thermoelements, it is possible to create sufficiently powerful thermopiles. A 10 GW power plant can weigh up to 200 tons. Reducing the weight of the power plant is directly related to the increase in the efficiency of converting solar energy into electricity. This can be achieved in two ways: by increasing the thermal efficiency of the converter and by reducing irreversible energy losses in all elements of the power plant. In the first case, concentrated radiation makes it possible to obtain very high temperatures. But at the same time, the requirements for the accuracy of solar tracking systems are greatly increased, which is unlikely for concentrating systems of enormous size. Therefore, the efforts of researchers were invariably aimed at reducing irreversible losses. They tried to reduce the flow of heat from hot junctions to cold junctions by conduction. To solve this problem, it was necessary to achieve an increase in the quality factor of semiconductor materials. However, after many years of attempts to synthesize semiconductor materials with a high quality factor, it became clear that the value achieved today is the limit. Then the idea arose to separate the hot and cold junctions with an air gap, like a two-electrode lamp - a diode. If in such a lamp one electrode, the cathode, is heated and at the same time the other electrode, the anode, is cooled, then a direct current will appear in the external electrical circuit. This phenomenon was first observed in 1883 by Thomas Edison. “The phenomenon discovered by Edison was called thermionic emission,” writes L.M. Drabkin. “Like thermoelectricity, it was used for a long time in the technique of low currents. emissions are different, but the expressions for the efficiency are the same. The main components of irreversible losses in the TEC are associated with the non-isothermal nature of the heat supply and removal at the cathode and anode, the heat transfer from the cathode to the anode through the structural elements of the TEC, as well as with ohmic losses in the elements of the series connection of individual modules. To achieve high efficiency of the Carnot cycle, modern TECs are designed for cathode operating temperatures of 1700-1900 K, which, at temperatures of cooled anodes of about 700 K, makes it possible to obtain an efficiency of about 10 percent. Thus, due to the reduction of irreversible losses in the converter itself and with a simultaneous increase in the heat supply temperature, the efficiency of the TEC turns out to be twice as high as that of the TEG described above, but at significantly higher heat supply temperatures.
Now consider the photoelectric method of energy conversion. Solar cells use the phenomenon of an external photoelectric effect, which manifests itself at the pn junction in a semiconductor when it is illuminated with light. A pn (or np) junction is created by introducing an impurity with the opposite sign of conductivity into a single-crystal semiconductor base material. When solar radiation hits the pn junction, the electrons of the valence band are excited and an electric current is generated in the external circuit. The efficiency of modern solar panels reaches 13-15 percent.
Solar power plants have one, but a very significant problem. The atmosphere interferes with obtaining and using "clean" solar energy on the Earth's surface. And what if we place solar power stations in space, in near-Earth orbit. There will be no atmospheric interference, weightlessness will allow you to create multi-kilometer structures that are necessary for "collecting" the energy of the Sun. Such stations have great merit. The transformation of one type of energy into another is inevitably accompanied by the release of heat, and its release into space will prevent dangerous overheating of the earth's atmosphere. Today, it is impossible to say for sure what solar space power plants will actually look like, although designers started designing such power plants back in the late 1960s. Any version of the project of a solar space power plant assumes that this is a colossal structure. Even the smallest space power plant must weigh tens of thousands of tons. And this gigantic mass will need to be launched into an orbit far from the Earth.
Modern launch vehicles are able to deliver the required number of blocks, nodes and panels of solar batteries to a low - reference - orbit. To reduce the mass of huge mirrors that concentrate sunlight, they can be made from the thinnest mirror film, for example, in the form of inflatable structures. The assembled fragments of the solar space power plant must be delivered to high orbit and docked there. And the section of the solar power plant will be able to fly to the "place of work" under its own power, one has only to install low-thrust electric rocket engines on it. But that's in the future. So far, solar panels have been successfully powering space stations. Author: Musskiy S.A.
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