Solar Hot Water
Installing a solar hot water system is one of the best ways you can save money on energy bills and reduce your greenhouse gas emissions
Heating water accounts for 30% of an Australian household’s energy use, making it second only to transport as a household’s largest cause of greenhouse gas emissions. However, a solar water heater can reduce your emissions by as much as four tonnes of CO2 or more per year—the equivalent of taking one car off the road—simply by using the sun’s energy to heat water at zero cost.
Depending on the climate you live in, a solar hot water system can provide between 50 to 90% of your hot water needs. The initial purchase price will probably be higher than a similarly sized non-solar water heater but the savings in energy bills will generally pay for this difference in less than 10 years (in as little as four years in some cases). A solar system generally has a longer lifespan than a conventional unit, so financial returns can be considerable over the life of the system.
Rebates
Federal and some state governments are encouraging the use of solar hot water systems with renewable energy certificates (RECs) and rebates. Rebates vary from state to state, but can save you a great deal on the cost of a solar water heater, making them more economically viable.
Flat panel and evacuated tube collectors
Most solar hot water systems use solar collectors (in the form of panels or tubes) to absorb energy from the sun. Water is heated by the sun as it passes through the collectors. It then flows into an insulated storage tank for later use.
The most common form of solar collector is the flat-plate panel. They consist of a dark coloured, metallic absorbing plate to which a network of pipes is bonded. This arrangement is then placed in an air-tight metal box with a glass cover on the top and insulation on the back and sides to reduce heat loss. As the sun shines on the collector panel the water in the pipes becomes hot due to conduction from the collector plate.
In the last few years another type of collector has started to appear on the Australian market. These are known as evacuated tube collectors. They consist of two glass tubes (one inside the other) that are bonded to each other at each end to form a sealed space between them. The surface of the inner tube is coated with a heat-absorbing coating. The space between the two tubes has most of the gas removed from it (hence they are evacuated), which provides a high level of insulation. As solar radiation passes through the outer glass tube and heats the inner tube, it is trapped by the lack of gas, which would otherwise allow heat loss. Evacuated tube collectors are suited to colder climates as they can perform well even on cloudy days.
Collector panels need to be placed on a north-facing roof. Also, ensure the collectors are not shaded by trees or nearby buildings, particularly in winter, when the sun is low in the sky.
Storage tanks
Hot water flows into these tanks either by a passive or active system. In passive systems, the tank is placed above the solar collectors so that cold water sinks into the collectors, where it is warmed by the sun and rises into the tank. A continuous flow of water through the collectors is created without the need for pumps.
In active systems, solar collectors are installed on the roof and the storage tank is located on the ground or another convenient location. Water is pumped through the solar collectors using a small electric pump. This option is good if you want to limit the visual impact of the system on the roof or if your roof can not support the weight of the tank.
The storage tank is usually fitted with an electric, gas or solid fuel booster that heats the water when there is not enough sunlight.
The right fit
So why not start planning now for when you existing hot water system gives up the ghost! Choose one that is best suited to your climate and your lifestyle now and in the future. And remember, by reducing your hot water demand (by taking five-minute showers and washing clothes in cold water) you can reduce the size and cost of the system you need.
More information:
Solar hot water booklet
Solar hot water rebates
www.yourhome.gov.au
