The basic natural processes used in solar heating are the thermal energy flows associated with radiation, conduction and convection. When sunlight shines on a solar collector, the collector absorbs the biggest part of solar radiation. These basic responses to solar heat influence the design of the solar collector, material choices and the placement of the collector to provide hot water for a home.

Heat flows from a hotter to a cooler media by radiation, conduction or convection. Sunlight heats the plate absorber by radiation; at the same time the air layer between the plate absorber and the glass cover of the collector does this by convection whilst heat is transferred through the copper pipe to the water by conduction.

A less common type of solar water collector is based on the use of two concentric tubes. The outer tube is evacuated and a semi-circular silver mirror is used to focus the sunlight falling on its surface and directed onto the absorber tube which contains the solar (or working) fluid. To prevent freezing during the winter, water is mixed with an amount of anti freeze. This solution cannot be used directly and so its heat is transferred to the hot water supply through a coil in the hot water tank.

criteria	economics
installation	advice