CHOOSING A SOLAR WATER HEATER
Seek expert advice before deciding which solar water heater to buy.
Climate considerations are very important when selecting a solar water heater and your state government advisory centres can provide excellent local advice.
The Australian Consumers’ Association (Choice) provides detailed information to help you choose the best solar water heater for your location and budget.
Manufacturers and retailers may also be able to help with detailed selection guidelines.
Choosing the right size
The best size of storage tanks and solar panels depends on the number of people in the home, how efficiently they use water, the climate and the efficiency of the water heater.
Reducing your hot water demand can reduce the size and cost of the system you need.
Manufacturers or suppliers will advise the best size for your application.
POSITIONING YOUR SOLAR WATER HEATER
For optimum performance throughout Australia solar hot water systems should face solar north. Orientation can deviate up to 45° from north without significant loss of efficiency. Use a compass to check orientation.
For maximum efficiency, ensure that the solar collectors are not shaded by trees or nearby buildings, particularly in winter when the sun is low in the sky.
For best performance, solar collectors need to be installed at an angle to the horizontal. This maximises the annual amount of sunlight falling on the panels. It is usually recommended that the solar collectors are installed at the same angle to the horizontal as the angle of latitude at the installation location. In Australia, this angle varies from 17.5° in Darwin to 53° in Hobart. In some cases, it may be desirable to increase the angle somewhat to improve winter performance and reduce overheating in summer.
In practice, many solar water heaters are installed at the roof pitch angle as it is cheaper and usually more aesthetically pleasing to install solar collectors flush with the roof, rather than use supports to achieve a greater angle. Roof pitch angles in Australia are commonly between 20° and 30°, so this will often reduce performance in winter. In existing homes, the benefits will usually outweigh the costs. In new homes, design of roof areas to accommodate a suitable solar collector angle may be possible.
OTHER INSTALLATION TIPS
A complete thermosiphon system, when full of water, can weigh several hundred kilograms. Most roofs can support a storage tank without reinforcement but you need to check this before installation. Talk to your builder, designer or engineer to find out.
Be sure to insulate all components, including pipes, to get the best performance from your system. This is particularly important for thermosiphon systems where there is a long distance between the tank and the hot water taps. It is critical in cold climates.
Make sure the booster control is in an accessible location and has an indicator light you can see from inside to remind you to turn it off when not required.
OPERATING AND MAINTAINING YOUR SYSTEM
Follow the manufacturer’s maintenance recommendations.
Set the temperature of your booster thermostat to 60°C. A lower setting may allow growth of harmful legionella bacteria.
In favourable climates during summer, water temperatures in a solar water heater can approach boiling point. Heat dissipation devices may be required to prevent water from boiling. It may also be necessary to fit a mixing valve to reduce water temperatures experienced at the tap to safe levels during summer.
Carry out jobs that need hot water early in the day so that the water left in the tank will be reheated by the sun, ready for use at night.
Regularly clean solar panels to remove dust. You can use a broom with some detergent to give them a scrub.
Flush out collectors to remove sludge. Heat pump systems do not require flushing.
Make sure you turn the booster off when going on holidays and consider turning it off during summer if conditions are favourable.