Disclosed is a storage water heating system with a heating apparatus external to the storage tank. The external apparatus receives a liquid coming from a lower portion of the tank, heats it, and delivers it to a top portion of the tank, where the hot water outlet is located. In this way, the natural thermocline of temperatures in the storage is maintained, the water delivered is at a greater temperature, efficiency is increased by reducing heat standing losses, and there is greater control over the quantity of energy stored. The external apparatus may be activated in response to a heating demand for the storage or for outlet water, or even in response to a power surplus from photovoltaic equipment and in the absence of withdrawal. A control system may modulate the power of the instantaneous water heater to track the surplus power of the photovoltaic system.

A solar thermal combined heating and power system includes: a solar thermal array; a thermal energy storage unit; a generator unit configured to provide electrical power to the structure; an array-to-storage heat transfer device configured to transfer thermal energy from the solar thermal array to the thermal energy storage unit; a storage-to-generator heat transfer device configured to transfer thermal energy from the thermal energy storage unit to the generator unit; a storage-to-water heat transfer device configured to transfer thermal energy from the thermal energy storage unit to the water reservoir; a storage-to-air heat transfer device configured to transfer thermal energy from the thermal energy storage unit to the interior air of the structure; and a control unit configured to operate the array-to-storage heat transfer device, the storage-to-generator heat transfer device, the storage-to-water heat transfer device, and the storage-to-air heat transfer device.