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Solar Hot Water

By Lauriston Muirhead     Lauriston is chair of WATCH (Wodonga Albury Towards Climate Health)

It wasn’t just Lady Chatterly’s greenhouses that got hot. Greenhouses also get hot because light enters easily through the glass, but when it bounces around in the greenhouse some of the light changes to heat which does not travel so well back out through the glass.  The trapped heat warms the greenhouse.  A solar hot water panel is just a flat “greenhouse” on the roof with water running through it.  When the sun shines, the water heats up and is stored in an insulated tank. 

Approximately 25% of the average household energy bill is paid simply to heat water.  The sun can do much of this heating for free.

In the simplest solar hot water systems, the hot water tank is above the panel on the roof.  Hot water rises so it circulates through the panel by “thermosyphon” (no pump required.)  Alternatively, panels can be on the roof but the hot water tank can be at ground level.  Some people prefer this look.  More practically, it makes for easier maintenance access (but it does need a small electric pump to circulate the water.)

Cloudy days mean an electric or gas boost is needed occasionally.  Mains gas is best.  The sun heats the water which then flows through a gas heater.  If the water is heated enough by the sun, the gas does not turn on but if the water is not hot enough, the gas automatically turns on and completes the heating.  This system will not run out of hot water.  If mains gas is unavailable, bottled gas can be used but is more expensive.  An electric boost is not as “instant” as a gas boost and if there is a sudden high demand, the hot water can “run out” until the electric boost (usually on “off peak” night rates) or the sun, heats it up again.

There are many solar hot water systems available and the technology is well tried and tested.  Talk to your local suppliers or green plumber to ensure you get an appropriately designed and sized system for your circumstances.  Most systems will pay for themselves in a few years, especially with current government incentives.  Those who have already made the change enjoy largely free hot water, those who don’t will continue to pay ever increasing electricity prices.  Remember the ancient Chinese proverb – “Only a fool does not install a solar hot water system.”