6 Varieties of solar collector

Just as solar space heating systems can have several variants, so can solar collectors. The most common types for low­ temperature use are:

These are most suitable for swimming pool heating, as it’s only necessary for the water temperature to rise by a few degrees above ambient air temperature, so heat losses are relatively unimportant.

Figure 13 Unglazed panel solar collector

These are the mainstay of domestic solar water heating They are usually single glazed but may have an additional second glazing layer, with a more elaborate glazing system a higher temperature difference can be sustained between the absorber and the external air.

Figure 14 Glazed flat plate water collectors

These are not so common as water collectors and are mainly used for applications such as supplying warm air for crop drying.

Figure 15 Flat plate air collectors

The example shown in Figure 17 takes the form of a set of tubes similar to fluorescent tubular lamps. The absorber plate is a metal strip running down the centre of each tube. Heat losses due to convection are suppressed by a vacuum in the tube. The absorber plate uses a special ‘heat pipe’ to carry the collected energy to the water, which circulates along a header pipe at the top of the array. These collectors are generally more expensive than flat plate ones, but they have lower heat losses, allowing a better performance in winter.

Figure 16 Evacuated tube collector

We now move from describing the use of solar energy on individual buildings to looking at its use on a larger scale, such as supplying heat to an entire district.