Note that the Solar Radiation is 800 W/m2 – good sunlight - and the Ambient Air Temperature is 0°C or 32°F. When the average water temperature in the collectors is the same as the air temperature, the efficiencies of both collectors are similar. As the temperature in the collector rises above the air temperature, the efficiency of the flat plate collector seriously falls away. This illustrates why the Thermomax Evacuated Tube Collectors are ideal for high temperature applications like DHW and heat storage. Thermomax can add heat even when temperatures get really high.