Types of solar thermal collector The flat plate collector

These units are, as the name indicates, flat plates tilted to receive maximum solar radiation. Behind the plate are pipes which carry the heat extraction medium. There are two types of heat absorbing medium, air and water. Water containing an anti-freeze solution is the most common and is circulated behind an absorber plate to extract and transfer its heat. In the UK they are usually limited to providing domestic hot water, mainly in the summer months. To exploit their efficiency to the full there should be a heat storage facility which accepts excess heat during the summer to top up heating needs the rest of the year. However, the size of both the collectors and storage tanks makes this an uneconomic proposition in most cases.

There are four main components to the design:

• transparent cover plate;

• heat absorber plate;

• a pipe circuit to absorb and transport the heat;

• insulation behind the plate and pipes (Figures 5.10 and 5.12).

Transparent cover plate —i

Absorber plate

Transparent cover plate —i

Absorber plate

Flow passages

Figure 5.10 Flat plate collector

Flow passages

A more sophisticated version was devised for the Freiburg Solar House. The collector is placed within a semi-circular reflector. The reflected radiation means that the collector receives heat on both sides, nearly doubling its efficiency. Coupled with insulated water storage this system was able to supply all the domestic hot water for the whole year (Figure 5.11).

Figure 5.10 Flat plate collector

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