The principle is straight forward. When the sun is shining, water is pumped through the solar panel and is heated by solar energy. This heated water then flows through a heat exchanger, warming the water stored in the hot water cylinder. The hot water in the cylinder can then be used for washing and bathing as required, with your boiler providing backup heating. In the summer the water in the cylinder can reach a temperature of 80 deg C within half a day, and the insulation on the cylinder will keep the water warm for the next day. Typically the solar hot water system will reduce your domestic hot water bill by 50%.