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Installing Solar Hot Water Systems
Solar hot water systems are an excellent way of obtaining hot water for household usage, and they are not as complicated as you may think. Also, they’re an excellent way to save money on your electricity bill and they will significantly reduce your greenhouse gas emissions. Read on to learn more.
How Solar Hot Water Works
Solar hot water systems use the power of the sun in order to heat water for household use. Solar panels are used to absorb the sun’s energy and the energy heats water as it flows through the collectors. Once the water is heated, it passes into a storage tank.
In a direct system, the water is heated as it passes through flat, glazed panels which are located on the roof of the house. The hot water is stored in an insulated tank that is usually directly above the collectors. A booster is available when there isn’t enough hot water to meet your needs.
An indirect system uses a heat exchanger and these systems are recommended for areas that are susceptible to frost. Water that has been treated with anti-freeze is run through the solar panels and the heat from the sun is transferred to water that is already in the storage tank.
Solar collectors or panels are usually made up of a blackened metal absorber plate within a glazed and insulated metal box. Water channels through the absorber carry the liquid to be heated. For optimum usage, the collectors should be placed on a north facing roof at an angle between 15 and 50 degrees.
Types of Solar Hot Water Heaters
A thermosiphon hot water system is where both the storage tank and the solar collector panels are mounted on the roof. As this system can weigh several hundred kilograms with water, it is important to ensure that your roof can carry the load, or that you can reinforce the roof if necessary. In this system, the hot water tank is mounted horizontally above the collector panels and the thermosiphon effect (heat naturally rises) is enough to circulate the water from the panel into the tank without a pump. These are great if the area is not frost prone, but, if it is, the water can freeze and destroy the panel, thus requiring a heat-exchange fluid with a freezing point lower than that of water.
If you don’t want to have the storage tank on the roof – either because of the look or the weight – you will want a pumped solar hot water system. This is where just the collector panels are mounted on the roof with the storage tank at ground level. Because the thermosiphon effect cannot circulate the water in this case, an electric pump is required. These systems don’t require a heat-exchange fluid for frost protection as a sensor will turn on the pump when near freezing point is achieved, and warmer water is circulated through the panels.
Solar Hot Water Boosters
Many solar hot water systems are fitted with a booster to increase the supply of hot water when it may otherwise be inadequate. Electric boosters use an electric element inside the storage tank to heat water. A gas booster uses a natural gas burner as a water heating system either inside the storage tank or in a separate unit downstream from the storage tank. A solid fuel booster heats water through a heat exchanger which is commonly known as a wet back system. To reduce greenhouse gas emissions, your best choice is either gas or solid fuel.
The booster can be operated manually or be automatically controlled by a thermostat that comes on when the temperature of the water drops below a set level. A timer can also be used to manage your booster and ensure that you get the maximum benefit of the sunlight.
Frost Protection on Solar Hot Water Systems
If you live in a frost prone area, frost protection is essential. This is because during a frosty period, the water can freeze inside the collector and destroy it. A knock valve (mechanical drain down valve) can be used but they can be problematic as they often jam open and drain the tank or fail to operate altogether. Electric heating elements are an option but they are not failsafe, especially during times of power outage. A closed circuit hot water system, in which the heating fluid is separated from the water, is the best option in frost prone areas as they ensure that water does not flow through the solar collectors.
Maintaining the Solar Hot Water System
When you install your solar hot water system, it is important that you follow the maintenance recommendations that the manufacturer outlines. It is a good idea to set the booster thermostat to around 60 degrees. Setting it lower will save energy but you should stay above 55 degrees in order to stop harmful bacteria from growing. During summer, water in the system can approach boiling point so you may need a heat dissipation device to stop the water from boiling, and you may need a plumber to fit mixing valves to your taps to ensure that the water is a safe temperature to use.
Any tasks that need hot water should be carried out early in the day so the water in the tank can be reheated ready for use at night. Clean solar panels regularly to remove dust. This can be done with a broom and detergent. Flush out the collectors to remove sludge, however, be aware that heat pump systems do not require flushing.
Solar Hot Water Rebates
To offset the cost of the solar hot water system, rebates are available. The Federal government offer rebates of up to $1000 to eligible people to install solar and heat pump hot water systems in order to replace existing electric hot water systems. This is part of their push for energy efficiency as water heating is the singe largest source of greenhouse gas emissions from the average home, accounting for around 28 percent of home energy use.
Your State government may also offer a rebate. For example, in NSW, a rebate of up to $1200 may be available, depending on the amount of RECs (Renewable Energy Certificates) that you have. RECs are an electronic form of currency that was established to promote renewable energy generation. For more information, contact your hot water system supplier.
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