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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Solar water heating installations. Economic efficiency of solar heating systems. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Alternative energy sources The optimal values of the parameters of solar heating systems and their areas of use depend to a large extent on capital investments in these systems, which are made up of the costs of individual elements. In solar installations, only the solar collector is a non-standard element, which, according to various estimates, can account for up to 60% of the cost of the entire installation. Therefore, the economic efficiency of using solar energy in heat supply systems is largely determined by the cost of a solar collector, which depends on the scale of production, materials used in the manufacture, design features and area of use. For the manufacture of solar collectors, materials such as steel, aluminum, plastics, and various types of insulation are used. Each of these materials has certain advantages and disadvantages. Recently, for the manufacture of collectors, polymeric materials (fiberglass, polyacrylates, polyvinyl chlorides, polyamides, etc.) have been increasingly used, which are lighter and cheaper than metals, more resistant to corrosion, not subject to destruction during freezing, and provide great opportunities for construction. These materials have sufficient resistance to thermal and atmospheric influences and durability (service life up to 15 years). Research is also underway on the use of extruded rubber and lightweight concrete. Under conditions of experimental production, the specific cost of the collector can vary widely up to 100-300 rubles/m2. In this case, when evaluating the comparative economic efficiency of a solar plant and a traditional source of heat, the comparability of options according to the conditions of equipment production is violated. Therefore, it is of interest to estimate the possible unit cost of a solar collector in serial production based on the existing technology for manufacturing similar equipment (steel heating radiators, plate heat exchangers). The results of evaluating the unit cost of a solar collector under conditions of serial production using various materials are presented in Table. 3.3. As can be seen from the table, the unit cost of a flat-type solar collector, depending on the design and materials used, varies from 10 to 40 rubles/m2. The lowest cost is a solar collector made of plastic, the highest is a collector in an aluminum case with an absorbing aluminum panel. It should be noted the high manufacturability of the collector made of polymeric materials and 1,5-2 times lower labor costs for its manufacture compared to the same characteristics of metal structures (labor costs for the manufacture of flat-type solar collectors, presented in Table 3.3, average 2 -4 person*h/m2). The table shows the masses of solar collectors. The largest mass has a collector made of steel based on a steel heating radiator of the RSG type. Table 3.3. Unit cost of solar collectors
The use of a two-glass coating leads to an increase in the specific cost of the collector within 1-2 rubles/m2 and an increase in the mass of the collector by 7-8 kg/m2 (with a glass thickness of 3 mm). Of great importance is the heat capacity of the collector, which determines the amount of heat used to warm the collector to operating temperature after cooling overnight. The collectors containing plastic elements have the lowest heat capacity. They are also characterized by lower weight and cost. To reduce the amount of heat used to warm up the solar collector and create highly efficient installations, it is necessary to strive to reduce the mass characteristics and use elements from low-heat-capacity materials. In table. 3.4 shows the structure of the unit cost of a flat-type solar collector, calculated according to cost items. Table 3.4. The structure of the unit cost of a flat-type solar collector
In the structure of the unit cost of a solar collector, 40-60% of the cost falls on the cost of an absorbing panel (a larger value applies to a panel made of aluminum), about 10% - on glazing, insulation, assembly, the rest - on the collector body. The thermal efficiency of a solar collector is determined by its efficiency, which can vary widely depending on the design and operating conditions. An increase in the efficiency of the collector, especially at a significant temperature difference between the heated liquid and the environment, as mentioned earlier, can rarely be achieved without complicating its design, which leads to an increase in unit cost. One of the ways to improve the characteristics of flat-plate collectors is the processing of the absorbing surface, the creation of a selective surface in order to reduce its emissivity in the long-wavelength part of the spectrum without a significant decrease in the absorptivity in the short-wavelength range. As selective coatings, oxidized copper, black nickel, black chromium are most often used, the use of which is justified only for collectors operating at temperatures above 333 K. According to some authors, the use of selective coatings causes an increase in the cost of coating the absorbing surface of the collector by 3-4 times , compared to a black ink based coating. Therefore, it can be expected that the use of selective coating based on existing low-cost technologies will lead to an increase in the unit cost of the collector by 2-4 rubles/m2. The use of selective coatings based on black nickel, chromium and other elements can lead to an increase in unit cost by 20-30 rubles/m2. Another way to increase the thermal efficiency of a flat-plate collector is to use evacuated collectors. Using the technology of manufacturing evacuated fluorescent lamps of the LB type with a reflective layer to create such collectors, it can be expected that the specific cost of the collector will be 50–70 rubles/m2 (under serial production conditions). The thermotechnical perfection of the solar collector is determined by the value of the ratio In the future, with the improvement of the manufacturing technology of solar collectors of various types, a decrease in their unit cost and an increase in the closing costs for organic fuel, the areas of economic efficiency of the use of more advanced designs will expand. With a specific collector cost of 18-22 rubles / m2 (this corresponds to the cost level of the most common type of solar collector - based on a DC heating radiator), the cost structure,%, in the solar heat supply system on average for residential buildings is given in Table. 3.5. Table 3.5. Cost structure,%
Note. Numerator - values for hot water installations, denominator - for combined installations (heating and hot water supply). The increase in the cost of a heat supply facility due to the construction of a solar plant can vary for hot water systems within 5-15%, with a lower value for buildings with a higher number of storeys. For combined systems, the average rise in price is 20-30%. The cost of construction works includes the preparation of a territory or a platform on the roof of a building for solar collectors, a boiler room, tanks, heat exchangers, the construction of supporting structures, thermal insulation of equipment and other works. The cost of creating support structures averages 8-15% of the cost of the entire installation and is included in the cost of construction work. In general, about 40-50% of the total cost of solar heating systems is accounted for by construction and plumbing work. This indicates significant reserves for reducing capital costs, which can be realized at the stage of design and installation of solar plant elements. Solar heat supply systems will have the smallest capital investments when solar collectors are combined with the structures of the roofs and walls of the building, the automation system is simplified, communications are reduced when transporting the coolant, etc. Author: Magomedov A.M.
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The smaller this ratio, the higher the efficiency of the collector. However, an increase in efficiency, and therefore a decrease 
most often associated with the complication of the design and the increase in its specific cost.
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