Page - 81 - in Clean Water Using Solar and Wind - Outside the Power Grid

Solar thermal desalination and solar water heating 81 water heating, even if electrification of the heating process is possible. Solar thermal collectors can be installed on roofs and work well in climate zones all over the world. In sunny regions in Africa and Asia they will naturally be an important complement to solar PV systems. Active solar heating systems use a collector and a fluid that absorbs solar radiation. Fans or pumps circulate air or heat-absorbing liquids through collectors and then transfer the heated fluid directly to a room or to a heat storage system. Active water heating systems usually have a tank for storing solar heated water. Solar systems for heating water or air usually have non-concentrating collectors. This means that the collector area (the area that intercepts the solar radiation) is the same as the absorber area (the area absorbing the radiation). Flat-plate collectors are the most common type of non-concentrating collectors and can produce water with a temperature of more than 90°C. The surface of the absorber determines the efficiency of solar water heaters. It has to combine high absorbance (percentage of incoming energy that a material can absorb) and low emittance (percentage of energy that a material radiates away) of the solar radiation. At the top and bottom of the metal absorbing plate, thicker copper pipes, known as headers, assist in the removal of heated water and the arrival of colder water to be heated. The principles of operation for flat-plate collectors are fairly consistent, but significant improvements in the design of systems, particularly absorber plates, have occurred. The major types of thermal collectors are: • Evacuated tube solar thermal system: this is one of the most popular solar thermal systems in operation. The collector itself is made up of rows of insulated glass tubes that contain copper pipes at their core. Water is heated in the collector and is then sent through the pipes to the water tank. This type of collector is the most efficient, but also the most expensive. • Flat-plate solar thermal system: this is a type of device that has been in use since the 1950s. The main components of a flat-plate panel are a dark coloured flat-plate absorber with an insulated cover, a heat-transferring liquid to transfer heat from the absorber to the water tank and an insulated backing. The flat-plate feature Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user