Solar hot water systems are storage systems and, depending on your climate, can provide up to 90 per cent of your hot water for free using the sun’s energy. Solar hot water systems cost more to buy and install than other hot water systems but can save energy and reduce your bills. Seek expert advice to help you choose the most cost-effective solar water heater for your needs. Be sure to consider the energy source for boosting (gas or electricity), energy tariffs, ease of installation and product cost.
To provide hot water on cloudy days or when demand exceeds supply, most solar water heaters come with a gas or electric booster. A gas booster usually produces less greenhouse gas emissions. Booster systems located inside the storage tank can be inefficient – cutting in and pre-empting the sun.
Override switches and timers can correct this problem if well managed. An increasingly popular approach is to use an inline gas booster that works as an instantaneous water heater – it guarantees a suitable temperature while maximizing the solar contribution. The solar collector and storage tank is generally located on the roof of your home, facing north. The storage tank can also be located inside the roof or at ground level.
Natural gas water heaters generate far fewer greenhouse gas emissions than electric storage systems using mainland grid electricity. Using gas directly in the home also avoids the energy losses associated with the generation and distribution of electricity.
Natural gas water heaters generate far fewer greenhouse gas emissions than standard electric storage systems. Gas storage systems have quicker heat recovery times and generally use a smaller tank than a comparable electric storage system. This improves efficiency and makes indoor installation easier. Systems installed inside the house need a flue that leads outside to vent exhaust gas. Instantaneous hot water systems usually use natural gas as it is cheaper for this application than LPG and electricity. To compare the energy use of gas storage and instantaneous gas water heaters, check the star rating label.
Electricity can be used for standard storage water heaters, for heat pump systems or for boosting solar systems. Expensive three-phase electricity supply is usually needed for instantaneous systems. Electric heat pumps are an efficient type of electric storage water heater that extracts heat from the environment (air, water or ground) to heat water. Like solar water heaters, they cost more to purchase and install but can save energy and reduce your energy bills. Seek expert advice to help you choose the most cost-effective heat pump and electricity tariff for your needs.
Heat pumps that draw heat from the air using only about one quarter to one half of the energy of a standard electric storage system. They operate as a refrigerator but in reverse. The ambient air is used to heat a refrigerant, which converts to a gas. The gas is then compressed, generating heat, which is transferred to the water. The refrigerant is expanded back to a liquid and the cycle repeats. Electricity is not used to directly heat the water but to move the refrigerant around the system.
This is why electricity use is much less than for storage systems. Heat pumps work most efficiently in warm, humid climates. They are not suited for installation outdoors in cold climates and where regular freezing or very cold and dry conditions are experienced. Some heat pumps are manufactured to work more effectively during brief frost conditions but they will cost more to run in these conditions and are not recommended for use in prolonged cold periods.
Note that some heat pumps may require an electric booster element if operated in regions where it is cold. The cost of running a heat pump may increase if it is required to boost during the day when electricity tariffs may be high. Electricity tariffs differ across the states and territories. For further information talk to your plumber or electrician, ask your supplier about the heating specifications of the product you are considering and contact your energy retailer to find out what tariffs may apply.
Ground source (or geothermal) heat pumps use a water body, shallow trench or deep bore instead of the air as a heat source. They usually provide both space heating and water heating. Electricity is used to pump water
around a loop buried in the ground or immersed in a water body. The enclosed water absorbs heat from the surroundings. Geothermal heat pumps can produce more than four units of heat energy for every unit of electrical energy used. They are best suited to multi-residential applications, where plenty of space is available.
Heat pumps can be located and designed to utilize waste heat from air conditioners and refrigerators.
Electric storage water heaters – Standard electric storage water heaters use a heating element inside the tank to heat the water, just like an electric kettle. Emissions from electric storage water heaters can be greatly reduced by using GreenPower or other renewable energy to run the water heater. Electric storage water heaters of less than about 150L usually use peak electricity and are the most expensive of all to run.
Larger electric storage water heaters generally use cheaper off-peak electricity tariffs, where available, heating water at restricted times (usually overnight). To reduce the chance of running out of hot water, tanks are often oversized and overheated, increasing energy consumption and greenhouse gas emissions. An electric storage water heater can indirectly produce as much carbon dioxide each year as the average family car.
While an electric storage water heater may be cheap to buy, it may be expensive to run and this should be taken into account when deciding which water heater to buy.