Abstract: A water heating solar module designed for being connected to a boiler of a water heating system, the module comprises a vessel having a water inlet and a water outlet, a first heating element installed in the vessel, and a power supply for feeding the first heating element with electric power produced from solar energy. The module is arranged as follows: the vessel is positioned near the boiler, so that the vessel's bottom portion is placed not higher than the boiler's bottom portion; the water inlet is provided at the vessel's bottom portion and is adapted for receiving water from the boiler; the water outlet is provided at the vessel's top portion and is adapted for delivering water from the vessel to the boiler; the power supply is electrically connectable to a photoelectric device for receiving electric energy there-from, and to the first heating element, for heating water in the vessel.