Solar Hot Water Heating Flat Plate Collectors work well when there is a high ambient air temperature Flat plate panels have been used for around 40 years and are commonly installed in Australia.
Solarhart a Western Australian company first introduced a solar hot water system way back in 1953. They used the technology of flat plate in their systems.They operate at maximum efficiency when the sun is directly overhead at midday but are less efficient at other times of the day when the sun's rays hit the panels at different angles. Flat Plate Collectors consist of a blackened metal absorber plate within a glazed and insulated metal box (flat-plate collector). Pipes attached to the absorber plate carry liquid that is heated by the sun. In a direct heating system, water is heated as it circulates through the flat, glazed panels.
Flat plate panels have no vacuum or real thermal insulation and the heat absorber breaths air. They may require a special anti-freeze fluid for very low temperatures. Flat plate collectors are very efficient it the correct location they are no as efficient as evacuated tubes. However this may not be such a bad thing, as they require a lot less ongoing maintenance because they do not run continually at extreme temperatures.