Replacing an electric storage tank with a solar hot water system can reduce electricity consumption, running costs and environmental impact by 2/3rds.

40% of a typical household electricity use is for water heating.  Therefore a solar water heater can reduce the overall electricity use by 25%.

Solar hot water systems do not provide the whole years hot water but can provide most, if not all of the energy required in Summer and warmer times.  The most common selection results in solar energy collecting around 2/3 of the energy required to heat the water (yearly average).  The electric or gas booster contributes the remaining energy, mainly in Winter.

Solar gain is available during the day throughout the year.  Even cloudy days can deliver some solar gain.

A clear winter day may sometimes deliver more solar energy than a cloudy Summer day.

Clear and sunny                          High solar contribution

Clear and cold                              Reasonable solar contribution

Overcast and warm                  Reasonable solar contribution

Overcast and cold                      Low solar contribution

Close coupled systems have the storage cylinder above the solar collectors all located together on the roof.  Close coupled systems rely on thermosyphon to operate – that is, cold water from the bottom of the tank falls to the inlet at the bottom of the solar collectors.  The water is heated by the sun, rising up through the solar collector and back into the middle and top of the tank. 

Generally speaking, close coupled systems are considered more efficient than the equivalent split system, as indicated by STCs awarded.

Split systems have the storage cylinder located on the ground and the solar collectors located on the roof.  Split systems use a solar controller and pump to transfer cold water from the tank to the solar collectors to be heated and returned to the middle or top of the tank.  The solar controller compares the temperature of the water in the solar collector to that in the tank.  When the collector is hotter than the tank the pump is switched on, transferring the solar heated water to the tank.

In cold weather, and depending on the system design, to solar controller can also turn the pump on to move through the collectors, reducing the risk of frost damage.  The correct solar collector to match the frost risk must be fitted as frost protection is combination of the collector and solar controller.

The Australian Government lists solar water heaters that are eligible for STCs and are therefore eligible to receive a rebate based on the number of STCs.

An STC is a calculation of how much energy is expected to be saved over ten years when using a solar water heater compared to the electricity consumption of an equivalent electric water heater.

1 x STC is 1 x MWh of electricity saved over 10 years = 100 kWh saved in a year

Performance calculations take into account geographic location, solar radiation, the angle of the sun, the efficiency of the solar collector, tank heat loss, cold water temperatures, the quantity of hot water used and hot water usage patterns.

Solar savings between different models and brands can easily be compared – the higher the number of STCs, the higher the energy savings.  To accurately compare systems, select the same tank size, number of solar collectors and booster type.

Gas boosted solar hot water systems offer the best solution to saving electricity, as electricity consumption is very low.

A booster is required to deliver hot water in times of low solar contribution or times of excessive hot water consumption.

The following table is applicable to Equinox solar hot water systems to provide frost protection:

NSW and Victoria have had frost zones defined by postcode.  Refer to the warranty conditions document when selecting the required solar collector.

TANKS

There are two mainstream types of materials that are used to fabricate solar hot water storage tanks:

1. Stainless steel, and
2. Vitreous enamel lined mild steel

Stainless steel refers to the actual tank that holds the water.  Surrounding that tank is insulation and an outer case that is not usually made of stainless steel.  Stainless steel resists corrosion, hence the term stainless, resulting in a long service life.

Vitreous enamel tanks are a mild steel tank that has the inside coated with a ceramic product that is heated in a kiln to solidify into a glass like skin, called vitreous enamel, on the inside of the tank.  This protects the mild steel from corrosion.  A sacrificial anode is used to protest the mild steel from any corrosion that may occur in small areas where mild steel is in the contact with water.