Solar collectors. How much energy can you get? Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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The amount of energy a solar heater can provide depends on the amount of solar radiation and the efficiency of the system. The amount of solar radiation is very different in different regions of the world, while being the most important indicator for the operation of the solar system. The efficiency of a solar installation as a whole depends on the efficiency of the collector and on the losses in the hot water circulation system. Since the latter are affected by a variety of specific parameters, we will focus on the efficiency of solar collectors.

Efficiency is the ratio between the amount of energy produced and the amount of solar energy reaching the collector. This indicator is different for different types of collectors and depends on the intensity of solar radiation, on thermal and optical losses: the greater the loss, the lower the efficiency. Heat losses are minimal if the temperature of the water used in the installation is equal to the ambient air temperature. Thus, a simple absorber without a glass cover, used to heat water in the pool, reaches the highest efficiency - up to 90%.

However, when providing domestic hot water, when the water temperature is 40°C above the air temperature, the efficiency of the collectors is usually less than 20%. In such cases, it is most expedient to use flat-plate collectors with a selective coating and evacuated tubular collectors, the most suitable for this purpose. For heating water to even higher temperatures (for example, for space heating), evacuated collectors are best - but they are also the most expensive.

Efficiency of solar collectors under conditions of moderate solar radiation in Central Europe in summer at noon (800 W/m2)

* Values ​​for low solar radiation in early spring (400 W/m2).

The low efficiency of an evacuated collector in low-temperature regions is explained by high optical losses on the curved glass surface.

Taking into account the fact that different types of collectors differ sharply in price, it becomes obvious that the decisive criterion when choosing a collector is the purpose of its application. Comparative characteristics of collectors from an economic point of view are given in the table below.

Typical characteristics of different types of solar collectors in Germany

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