In this process, solar radiation is converted into heat by means of absorbers. The heat transferred to a liquid is led in forced circulation, first into a heat storage device and then into a water heater. The cooled-down liquid is rercirculated. The storage material used here is paraffin. A measuring and control device is provided to switch from periods with solar radiation to periods where only stored energy is consumed. This device consists of a photocell measuring the incoming sunlight and a temperarure sensor. The control system is put into operation by a combination of the two measured values. The heat accumulator consists of several elements connected in parallel. A control device makes sure that only one accumulator element at a time is part of the circuit. The absorbers, as usual, consists of the absorber plate proper and a cover plate.