Solar thermal systems are widely used to provide heating and hot water for residential, commercial or industrial applications. Since their use took off in the 1970s as a result of the high oil prices, several million units for the production of hot water have been installed worldwide. In Tokyo alone there are 1.5 million buildings equipped with solar water heaters . Some small countries such as Israel are also widely using solar thermal energy for homes and other installations . They are the most widespread and easiest way to utilize solar power, as only moderate temperatures are needed and the technology is simple. Solar heating systems are composed of a collector in which a liquid, generally water, is heated, and a pump to transfer the heat to living spaces or a storage tank for later use. In the thermal collector, mounted on the roof facing the sun, a fluid running through polymer or copper tubing is heated by sunlight. For some applications, solar water heating systems have been especially popular: as an example, in the Western United States, heating of swimming pools accounted for more than 90% of the demand in 1999 . Although governmental incentives and further cost reductions are still desirable, the technology is mature and already considered to be competitive in an increasing number of countries. On the other hand, solar heating and cooling of buildings is not yet competitive with conventional energy sources, and therefore generally still rare.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.