Solar energy and its use

Active use of solar energy

The active use of solar energy is carried out using solar collectors and solar systems.

Solar collectors and their types The basis of many solar energy systems is the use of solar collectors. The collector absorbs the light energy of the Sun and converts it into heat, which is transferred to the heat carrier (liquid or air) and then used to heat buildings, heat water, produce electricity, dry agricultural produce or cook food. Solar collectors can be used in almost all processes that use heat. The technology for manufacturing solar collectors reached almost modern level in 1908, when William Bailey from the American Carnegie Steel Company invented a collector with a thermally insulated body and copper tubes. This collector looked very much like a modern thermosiphon system. By the end of World War I, Bailey had sold 4,000 such collectors, and a businessman from Florida who had bought a patent from him sold nearly 60,000 collectors by 1941.

A typical solar collector collects solar energy in the modules of tubes and metal plates, painted in black, installed on the roof of the building for maximum absorption of radiation. They are enclosed in a glass or plastic case and are tilted to the south to capture maximum sunlight. Thus, the collector is a miniature greenhouse that collects heat under a glass panel. Since solar radiation is distributed over the surface, the collector should have a large area. There are solar collectors of various sizes and designs depending on their application. They can provide hot water for washing, washing and cooking, or can be used to pre-heat water for existing water heaters. Currently, the market offers many different models of collectors. Integrated collector The simplest type of solar collector is a “capacitive” or “thermosiphon collector”, which received this name because the collector is also a heat storage tank in which a “disposable” portion of water is heated and stored. Such collectors are used to pre-heat water, which is then heated to the desired temperature in traditional installations, for example, in gas columns. In household conditions, pre-heated water enters the storage tank. Due to this, energy consumption for its subsequent heating is reduced. Such a collector is an inexpensive alternative to an active solar water heating system that does not use moving parts (pumps), requiring minimal maintenance, with zero operating costs.

Flat collectors Flat collectors are the most common type of solar collectors used in domestic water heating and heating systems. Usually this collector is a thermally insulated metal box with a glass or plastic lid, in which is placed a black-colored plate of the absorber (absorber). Glazing can be transparent or matte. Flat collectors typically use frosted, light-transmitting, low-iron glass (it transmits a significant portion of the sunlight entering the collector). Sunlight falls on the heat-receiving plate, and thanks to the glazing, heat loss is reduced. The bottom and side walls of the collector are covered with insulating material, which further reduces heat loss.

Solar systems

Solar Hot Water Systems

Hot water is the most common direct application of solar energy. A typical installation consists of one or more collectors in which the liquid is heated in the sun, as well as a tank for storing hot water heated by means of a heat-transfer fluid. Even in regions with relatively little solar radiation, such as northern Europe, the solar system can provide 50–70% of the demand for hot water. It is impossible to get more, except with the help of seasonal regulation. In southern Europe, the solar collector can provide 70–90% of the hot water consumed. Heating water using solar energy is a very practical and economical way. While photovoltaic systems achieve an efficiency of 10–15%, thermal solar systems show an efficiency of 50–90%. In combination with wood burning stoves, the domestic need for hot water can be satisfied almost all year round without the use of fossil fuels.

Thermosiphon Solar Systems

Thermosiphon are called solar water heating systems with natural circulation (convection) of coolant, which are used in warm winters (in the absence of frost). In general, these are not the most efficient of solar power systems, but they have many advantages in terms of housing construction. Thermosiphon circulation of the coolant occurs due to a change in the density of water with a change in its temperature. The thermosiphon system is divided into three main parts: - flat collector (absorber); - pipelines; - Storage tank for hot water (boiler). When the water in the collector (usually flat) is heated, it rises along the riser and enters the storage tank; in its place, cold water flows into the collector from the bottom of the storage tank. Therefore, it is necessary to position the collector below the storage tank and insulate the connecting pipes.

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