SOLAR COLLECTORS

02/03/2014 - 16:19
Renewable Energy Development Institute - REDI
SOLAR COLLECTORS

Solar collector is an exceptional device that transform solar energy into thermal energy. In comparison with solar panels it is used to heat water and buildings. The first solar collector was built in 1767 by a Swiss botanist Horace de Saussure. Since then it has been developed and become a complete unit reducing up to 60% energy demand.

At present, the most common types of solar collectors are flat plate and vacuum collectors. The most important task of solar systems is the absorption of solar energy, which is then converted into thermal energy. Collectors are an essential and integral component of solar systems.

Efficiency of the system depends on the number of collectors installed, absorption surface, installation place and hydraulic system connection. In water heating systems, solar panels are connected to the water tank battery which accumulate heat.

To ensure a proper operation of the entire system, there is a need to choose an appropriate elements such as: water tank, a group of control and pump, insulation, and last but not least, proper installation.

Flat-plate collectors are characterized by simplicity and reliability of the structure. On average, the operating time of solar collector is about 20 years. The majority of producers of flat plate collectors use similar technology. Collectors are usually constructed of:

- light casing
- transparent insulation (made from solar glass, translucent sunlight)
- copper absorber
- fastening elements and insulation

Collector casing are usually made of aluminum frame. In order to reduce the weight of the panel the rear wall is produced from light metal or plastic. Number of the ribs placed in the frame, confer structural rigidity. The front wall is made of a special solar glass, transmits light and solar energy. Solar glass has a low iron content. The lower content of iron in the manufacture of solar glass applies the producer, the more infrared transmittance obtained in the solar spectrum, and thus a higher efficiency of the collector. Some solar energy is lost as a result of light reflection from the glass surface, and the solar energy absorbed by the material of the panel. The efficiency of the collector is at a level of about 50%. Installation of flat plate collectors is recommended mainly in areas characterized by a mild climate and warmer winters.

Vacuum tube collectors are made up of tubes filled in vacuum. In the center of each tube there is positioned flat absorber which is responsible for the absorption of solar energy. Vaccum which is best insulation than ever discovered protect tube from lose of energy. Therefore, the loss of energy is almost reduced to 0%. Collector structure allows to obtain high efficiency even in diffuse sunlight (during cloudy days) and in low air temperatures conditions. Research shows that vacuum tube collectors maintain a 30-40% higher efficiency compared with other collectors on average during the year.

An appropriate constructure of vacuum tube collectors allows the sun falling on the absorber into account angles. This reduces the amount of reflected light and increases the energy yield. What is more, even on cloudy and rainy days, the system provides heating and hot water distribution in the building. Tubes are made of durable and hail resistant safety glass. The design allows the free fall of snow and rain between the tubular elements of the collector, and therefore, these devices are successfully installed in areas with higher rainfall and stronger winds. In addition, mechanical damage to the pipe does not suspend operation of the system. A special system of „dry connection” provides safety and easy servicing. High reliability and durability of the system provide free heat and hot water for many years of use.

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