The present disclosure provides a water heating system for efficient heating of water for immediate use that fits either to industrial applications or household applications. The water heating system is suitable to be combined with a solar heating unit and it can be operated on electric power or on gas-based heating units for providing hot water to multiple consumers for household or industrial utilization. Furthermore, the system can be stand-alone, operating without any additional water heating system and can provide an immediate stream of hot water, e.g. it can be installed within a water supplying appliance. The water can operate in two modes: (1) heating for immediate use of hot water; and (2) heating water to be contained in a reservoir for later use. The system uses a two (bi) directional flow valve.

A hot water heating system of a dwelling includes a storage tank and a hot water pipe that collects water from a relative upper portion of the storage tank. This water is fed towards a hot water distribution network of the dwelling. The hot water heating system includes in addition a cross-connection pipe that is activated during an emergency mode of the system to direct water from a relative lower portion of the storage tank to be supplied to occupants of the dwelling via the hot water distribution network of the dwelling.

A solar photovoltaic (PV) water heating system includes a tank including at least a first heating unit having at least first and second heating elements, at least one of which is switchable; a PV solar collector; an inverter adapted to convert the output from the PV collector to an alternating power supply; a modulator to modulate the alternating power supply from the inverter; a controller adapted to control the modulator and the switching of the or each switchable heating element; wherein the controller is adapted to control the modulator and the switchable heating elements to maximize the energy drawn from the PV collector.