Solar hot water systems

Last updated: 19 August 2021

A solar hot water system uses the sun's energy to heat water.

When there isn’t enough sunshine to fully heat the water, a gas or electric booster will kick in as a back-up.

Solar hot water systems only heat water and don’t generate electricity.

Read about solar photovoltaic (or PV) systems that generate electricity.

Installing solar collectors

The solar collectors (or panels) of the solar water heater need to be installed on a section of north-facing roof, no more than 45° east or west of true north. They should be sloping at an angle of between 15° and 50°, a standard roof pitch of around 20° should be sufficient. To maximise their exposure to the sun throughout the year, make sure they’re unshaded.

Other roof orientations may also be suitable, provided the unit is mounted on a frame to face north.

Types of systems

There are 2 types of solar hot water systems:

  • close-coupled systems
  • pumped systems.

These systems come with an electric or gas booster as a back-up when there’s not enough sun to fully heat the water.

Close-coupled systems

Close-coupled systems have solar collectors on the roof, and a horizontally mounted storage cylinder located above. The water is heated as is passes through the collectors when the sun is shining.

The system can heat water directly or indirectly.

In a direct system, heated water naturally rises through the solar collectors into the storage cylinder. When this happens, it draws cooler water at the base of the storage cylinder down to the bottom of the collectors, where it rises through the collectors as it is heated. This “thermosyphon” cycle is repeated while the sun is shining, gradually heating water in the cylinder.

In an indirect system, the water that flows through the collectors is treated with an anti-freeze, such as glycol, and it is kept separate from the water in the cylinder. The heated water-glycol mixture passes through a heat exchanger coil to heat the water in the cylinder, and is then drawn back to the bottom of the collectors. These systems are used in frost prone locations, to prevent damage to the collectors caused by water freezing and expanding when the outside temperatures are very low.

Indirect systems are more expensive to buy, but can be worthwhile in areas that are susceptible to frost.

Pumped systems

The system includes solar collectors (or panels) mounted on the roof to absorb sunlight. A storage cylinder is located on the ground like a conventional hot water system. A pump circulates water from the cylinder to the collectors for heating, and back.

The pumps use a small amount of electricity.

This system can be used when the roof structure isn’t strong enough to support the weight of the storage cylinder of a close-coupled system.

Boosters

When there’s not enough sunshine to fully heat the water, an auxiliary heater will boost the water temperature.

Boosters can be electric or gas.

An electric-boosted system has a booster element in the storage cylinder. It’s usually possible to run these on the cheaper off-peak electricity tariff.

It’s best to use hot water in the morning, so that the solar energy from the sun re-heats the water in the cylinder throughout the day.

A gas-boosted system uses a gas (natural or LPG) booster. This can be in the storage cylinder. It’s more common to use a gas-instantaneous water heater located on an outside wall (close-coupled systems) or on the storage cylinder (some pumped systems) to provide any necessary boosting when the hot water is being used.

Systems that use solid fuel boosting are also available.

Frost protection

It’s sensible in Victoria to consider some form of frost protection for your solar hot water system.

Some ways to prevent frost include using:

  • an indirect heating system with a heat exchanger
  • frost protection valves.

Valves are cheaper but less reliable.

Another way to prevent frost is by using pumps to circulate water through collectors when the temperature drops below a certain point. This can be risky in areas where power supply is unreliable.

Talk to your supplier about frost protection when getting a quote.

Choose the right-sized system

The following table can be used as a guide to choose the right-sized solar system for your home.

Talk to your supplier for specific size recommendations.

Number of people Storage capacity (litres) Solar collector size (square metres)
1 to 2 160 to 200 2
3 to 4 300 to 370 4

Running costs

Although a solar hot water system will be more expensive to buy, it can use at least 60% less energy than a conventional gas or electric system.

Compare running costs of hot water systems.

Get a discount on solar hot water systems

If you’re replacing your electric or gas hot water system with a solar hot water system, you may be eligible for a discount under the following Government incentive programs: