A solar hot water system works by circulating the solar fluid between the collectors on the roof and the basement. In the basement, the heat from the solar fluid heats the cold water supply line to the building's boiler.
On a sunny day, when there is excess heat, the surplus is used to heat the fluid in the heat storage tank. That way, heat is available not just during the day, but at night as well. Heat can then be drawn off the storage tank to provide heat for showers, dishwashing and laundry at any time.