Pre-heated solar heating system, also called copper coil solar heating system.The water in the water tank only plays the role of heat absorption and heat release. The water capacity in the hot water storage tank is kept constant. The hot water is entered through the coiled cold water in the hot water storage tank, and the cold water is absorbed through the coil. The energy in the hot water tank raises the temperature. Due to the inherent performance of the coil design, the temperature of the water in the coil is close to the temperature of the solar hot water in the tank (temperature difference ≤ 3 ° C). In this way, the pressurized tap water continuously enters the coil to absorb the solar hot water energy and the temperature is raised and used. The water capacity in the hot water storage tank is constant but the water temperature is continuously reduced until there is no heat transfer value with the water temperature in the coil.