Roof-integrated flat plate collectors,
Figure: Viessmann WerkeA flat plate collector is a metal box with a glazed cover on top and a dark absorber plate on bottom. The sides and bottom are typically insulated to minimize heat loss. A flat plate collector functions when sunlight passes through the glazing and heats up the absorber plate, which then changes the solar energy into heat energy.
Careful consideration is required when a flat plate collector is to be installed in an area where freezing is likely. If pure water is used in the piping, rather than solar antifreeze or a water/antifreeze mix, damage is likely to occur if it is inadequately insulated.
Flat plate collectors have historically been made with metal plates, but special polymers are now also available. One of the best metals to use in a flat plate collector is copper. Because of this, however, the cost can be highly variable depending on world markets. In addition, metal versions of flat plate collectors are more prone to freezing damage than the polymers. On the other hand, extreme heat can actually melt the polymer versions. However, the average lifetime of a flat plate collector is more than 25 years with little maintenance and with the same high performance throughout.
A common alternative to the flat plate collector type of solar thermal panel is the evacuated tube collector. This latter type of collector was first introduced in the 1970s and uses a series of large vacuum tubes with internal absorber plates to gather and convert solar energy.
The Flat Plate Collector - Optimal for Domestic Solar Water Heating
A flat plate collector is generally less expensive to purchase than an evacuated tube collector, but the latter is overall more efficient in operation (Solar Collector Efficiency). The performance difference is particularly notable at lower temperatures. A flat plate collector, however, is better suited to regions that receive large quantities of snow. In these regions, even the smallest amount of light that reaches the collector will help heat the unit and melt the snow.