How Solar Hot Water Works

How Solar Hot Water Works

The Thermosiphon Principle

All solar hot water systems, where the tank is roof-mounted, use the Thermosiphon principle to collect heat from the sun and transfer it to your hot water. The Thermosiphon principle is based on two naturally occurring phenomena:

  • Dark objects absorb heat
  • Hot fluid rises

Solar collector panels are coated with a dark, heat-absorbent surface. This coating absorbs the sun’s rays and heats the fluid in the collector panel. As the fluid heats, it rises to the top of the collector panel and into the tank where it displaces cooler fluid which flows in to the bottom of the collector panel where the process is repeated. This method of water heating requires no electric circulating pump or complex electronic components to heat the stored water. It is a naturally occurring heat transfer process.

The greater the temperature difference between the fluid in the solar collector panels and the water in the tank, the faster the flow between them.

In open circuit systems the fluid in the collector panel is water while in closed circuit systems a special antifreeze fluid is used.

In this way solar water heaters constantly soak up the sun’s energy to maximise your energy savings.

With a thermosiphon solar hot water heating system you can choose from a range of boosters including in-tank electric or gas boosters to ensure you always have hot water on tap even on cloudy days.

Pumped Solar Systems

Pumped solar hot water systems generally have a ground mounted storage tank containing potable water or heat exchange fluid, depending on whether the system is  open (water based) or closed circuit (antifreeze fluid).  The system has either flat plate solar collectors or evacuated tubes on the roof which are connected to the ground mounted tank via insulated copper pipework.   The water or fluid is circulated from the tank at ground level through the solar collectors by an electric pump called a ‘circulator’ absorbing the thermal energy collected by the solar collectors, then transferring the heated water or fluid back to the storage tank.

This continuous cycle repeats itself when a controller on the tank senses an 8°C differential in temperature between the top of the solar collectors and the bottom of the tank, the circulator is activated until the temperature differential falls to 2°C. This ensures the optimum use of the sun’s free energy.

In closed circuit split systems, which are recommended for frost prone and poor water chemistry situations, antifreeze fluid is used to circulate through the collectors. The heat harvested from the collectors is transferred from the fluid to the water in the tank by a heat exchanger.

With a solar hot water split system you can choose from a range of boosters including in-tank electric or in-line gas continuous flow boosting to ensure you always have hot water on tap even on cloudy days.