Page - 82 - in Clean Water Using Solar and Wind - Outside the Power Grid

82 Clean Water Using Solar and Wind: Outside the Power Grid of the solar panel increases the surface area for heat absorption. The heat-transfer liquid is circulated through copper or silicon tubes contained within the flat surface plate. The flat-plate design is slightly less compact and less efficient when compared with an evacuated tube system, but the cost is lower. A flat-plate SWH can work well in all climates and can have a life expectancy of over 25 years. An SWH system contains a storage tank. In a close-coupled system the storage tank is mounted with the collector on the roof. The tank is located above the collectors to take advantage of the principle of thermo-siphoning. This principle utilises collectors to heat the water, which rises to the storage tank. Cold, denser water flows through the collector, is heated up and is then returned to the tank. As the heated water is less dense, it rises to the top of the tank. Roof-mounted flat- plate collectors that utilise thermo-siphoning are extremely popular. Since the system has no moving parts it is easy to maintain and reliability is very high. How about electricity requirement? Yes, electricity may be needed to (1) lift the cold water to a level where it can flow into the storage tank and (2) make sure that the system does not overheat. If the storage tank is filled with hot water, it may overheat and a valve may be closed so that no more hot water is fed into the tank until more cold water is fed into the system. 6.3 FURTHER READING Several practical SSD solutions are demonstrated on www.youtube.com (search for “solar: still distillation”). Kalogirou (2004) presents a survey of the various types of solar thermal collectors and applications. Practical demonstrations as well as academic lectures on solar thermal systems can also be found on www.youtube.com (search for “solar thermal”). Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user