Solar heating. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Solar water heaters have been used for heating and hot water since the beginning of the XNUMXth century. To date, in a number of countries (USA, Germany, Norway), with state support for energy saving programs, solar collectors made of polymer plastics with glazing installed on roofs or on glazed verandas are widely used.

The device of the solar module-water heater is very simple (Fig. 3.3). A flat screen with pipes welded from below is illuminated by the sun's rays. Pipeless screens are also used, in the form of two plates with a slotted gap between them. The screen is connected by pipes to the upper and lower parts of the storage tank. Natural circulation is established in the circuit: cold water enters the pipes from the lower part of the tank, water heated in the screen pipes with a lower density flows into the upper part of the tank. The top plate of the screen is painted with black matte paint to increase the absorption of radiant energy, and covered with glass or polymer film to protect against precipitation. In regions with negative temperatures, the circuit is filled with an aqueous solution of antifreeze; antifreeze heated by solar radiation gives off heat to the water of the storage tank in a tubular heat exchanger.

Fig.3.3. The simplest solar water heater

Norwegian energy experts estimate that the annual energy savings from solar heating systems in northern Europe is 250.300 kWh per square meter of collector area. The cost of solar collectors in Norway is about 80 euros per square meter, including protective coating when installed on the roof. The payback period at current electricity prices in Norway is about 10 years. At the same time, environmental pollution as a result of fossil fuel combustion in boilers of traditional thermal power plants and boiler houses is excluded.

There are also air (calorifer) solar heating systems in the world. The air heated in the solar collector flows through a heat accumulator - a container filled with crushed stone or pebbles. If it is necessary to heat the room, the room air is driven by a fan through a layer of pebbles. The air solar heating system can also be operated without a heat accumulator. In this case, the fan drives the room air directly through the air solar collector.

A new way of using solar radiation for heating is the use of window glass covered with a polyester film with a metal coating. This glass is transparent to the rays of the light wavelength range, which carry the maximum energy in the solar spectrum, but it reflects infrared radiation from the room and thus provides a "greenhouse effect" in the apartment. Such glasses are increasingly used in Finland.

Solar energy can be used to desalinate sea and polluted water. The simplest solar distiller is a vessel filled with a thin layer of salt water; the sun's rays concentrated on the vessel evaporate the water. The steam condenses on an inclined flat wall, and the condensate flows into the desalinated water collector. Solar refrigeration units have also been developed, in which the refrigerant (ammonia) is evaporated by solar radiation and further participates in the absorption-type refrigeration cycle. Solar thermal equipment (thermal panels, hot heat supply installations, solar distillers) is produced by Mashinostroenie NPO in Reutov, Moscow Region.

Solar energy is also used in small high-temperature installations (Figure 3.4). The sun's rays are focused by a parabolic mirror on a heated object (for example, a melting crucible).

Fig.3.4. solar heater

Compared to heating in furnaces, such installations provide more intense heating and a cleaner process. The same device have "solar kitchens".

Author: Labeish V.G.

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