Installed inside the house, the vertical tank is dissociated from the flat plate collector. The circulation circuit (for forced circulation systems) takes the fluid from the collectors to the tank through the pipes. The fluid then goes back to the collectors in order to “reload”. Depending on the water heater type and the conditions of use, a controller and an electric pump can be included in the circuit. Low sunshine periods are compensated for by an electric heating backup, similar to classic water heaters.