In last month’s article, I said that solar water heating was an excellent idea. I lied! Well, maybe not completely but I have to tell you a longer story.

Seventeen years ago I connected solar water heating panels to our electrically heated off-peak hot water service. It’s still working – that’s the good news. The not-so-good news? Before the installation we used 4300kWh per annum for water heating, since then 2800kWh. This is a reduction of 35%. Why is it so modest?

Competition!

The big problem is that the solar and the electric booster compete with each other. If it is a cloudy day, then overnight, electricity heats the water. If the following day is sunny, the solar has not much to do.

The temptation of course is to turn off the electric heater altogether and go 100% solar. This often works quite well for a while a time in the summer months. Then the inevitable happens – you run out – and you are the bad guy – the greenie!

Here is a graph of my home electricity use for domestic water heating. Obviously 1989 was the year we installed the solar panels. What about the years 1986 – 1996? Why was it always climbing? The answer: Teenagers! We had two boys.

By 1997 they had started to behave more responsibly. By about 2003 they had both moved out, as you can see from the graph. In fact you can almost read the history of the family through the hot water service!

The map below shows the proportion of solar contribution you can expect across Australia. As you can see, you need to live in Cairns, Brisbane, Perth or Darwin to get more than 75% from solar. That last bit boosted by electricity is the unfortunate part.

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