A solar thermal system is formed by a collector absorbing solar energy and an insulated water tank where heat is stored. Two different solar systems exist: natural circulation and forced circulation.
In a forced circulation system the fluid flows through a circulation unit connected to the solar circuit. The system uses electrical sensors (probes) to control circulation. These sensors permit to compare the temperature of the fluid in the collector with the one in the tank (thermocouple). In this system there are less limits for storage tanks location. Usually, the hydraulic circuit connected to the panel is closed and it is separated from the hot water one by a coil in the tank used as heat exchanger