A solar hot water system uses the sun to preheat water, resulting in less fossil fuel use for public and private facilities. A solar hot water system connects to a buildings existing hot water heating system, providing a supplemental source of heat for all hot water needs. Solar water heating systems are a proven technology that works well even in cold climates. A solar hot water system can provide 40 -70 percent of a buildings annual hot water needs. The amount of contribution varies based on the size of the system and the hot water demand.