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Chapter 3

Direct Solar Energy

tube, a transparent cover, a frame and insulation (Figure 3.3a). For low-temperature applications, such as the heating of swimming pools, only a single plate is used as an absorber (Figure 3.3b). Flat-plate col- lectors demonstrate a good price/performance ratio, as well as a broad range of mounting possibilities (e.g., on the roof, in the roof itself, or unattached).

Unglazed Solar Collectors

Tube-on-Sheet Collector

Flat Plate Collectors

Single or Double Glazing

Pump Flow

Glazing Frame

Metal Deck

Rubber Grommet

Box

Flow Passages

Serpentine Plastic Pipe Collector

Absorber

Insulation

Plate

Backing

Figure 3.3a | Schematic diagram of thermal solar collectors: Glazed flat-plate.

Typically 1 1/2’’ ABS Pipe

Evacuated-tube collectors are usually made of parallel rows of trans- parent glass tubes, in which the absorbers are enclosed, connected to a header pipe (Figure 3.3c). To reduce heat loss within the frame by convection, the air is pumped out of the collector tubes to generate a vacuum. This makes it possible to achieve high temperatures, useful

Pump Flow

Figure 3.3b | Schematic diagram of thermal solar collectors: Unglazed tube-on-sheet and serpentine plastic pipe.

Evacuated-Tube Collectors

Heated Water

Insulation

Solar Energy

Vapor Rises to Top

Condensed Liquid Returns to Bottom

Heat Transfer

Heat Transfer

Copper Sleeve in Manifold

Aluminium Header Casing

Copper Manifold

Vacuum Indicator

Evacuated Glass Tube

Evacuated Heat Pipe

Figure 3.3c | Schematic diagram of thermal solar collectors: Evacuated-tube collectors.

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