Solar Hot Water – a hint

Solar hot water systems usually have an electric back-up heater on a thermostat, for times of prolonged overcast weather. How crazy if this is set to default, heating your water every night so you hardly need to use solar!

This is a bit of a bug-bear I have. When we were deciding which system to buy, we walked around our local area asking neighbours about their solar hot water and whether they were happy with their choice. We also got quotes from all the distributors and heard their ‘spiel’. It was a bit of a shock to realise that many people are underutilizing their solar collectors and quite unaware.
Some systems don’t even have a manual switch, so the booster is always ready to kick in automatically. In my opinion, these are the brands to avoid.
Where there is a switch, I gather many people follow the seller’s advice. The sales reps recommend to leave the booster heater on and forget about it. Of course, then they have happy customers who report, “We never run out of hot water!”
However, if your peak demand for hot water is in the evening, for washing up and showers, the thermostat in the hot water system will register a drop in temperature and trigger the booster heater to come on and  heat the water overnight. When the sun comes out next morning the water is still hot so the solar collectors are hardly used!
Instead it is more efficient to leave the booster off and switch it on manually only on grey days if required. When it has been raining all day and you run the tap and find the water isn’t very hot, then turn on the switch. Ours takes about half an hour to heat enough.

3 thoughts on “Solar Hot Water – a hint”

  1. more comments found in forums on www:

    “Solar assisted” can mean all sorts of things in practice. There are some truly shocking systems around that are “solar assisted”. In particular, the ones that add solar panels to a gas-heated storage tank. Trouble is, as soon as you use some hot water, the gas burner starts up as does the solar pump. End result is you won’t save much gas and the solar doesn’t do much in practice apart from adding hugely to the cost of the system.

    Any solar hot water system should be either (1) boosted only by something that doesn’t turn on when during the day (eg off-peak electricity night only rate (the cheapest electricity rate)) or alternatively use the booster to heat only part of the tank (usually the top 30 – 50% but you can go higher without problems if it’s off-peak night only boost). An inline gas (or electric) booster is another option that works fine.

  2. Here are some more things to think about:

    Obviously solar hot water efficiency varies a lot depending what time of day each household needs the hot water. Sometimes it is worth thinking about changing to morning showers, so the system reheats with sunshine.

    Another factor to consider is whether the booster is connected to off-peak power or peak power. If connected to off-peak it means when you turn it on, it doesn’t necessarily come on until some random time in the night, whenever the power company decides.

    Our solar installer recommended connecting it to the full peak power (this is for Queensland) so we can switch on the booster for half an hour when we need it (on a grey day). It means we are completely disconnected from the off-peak system. It also has an advantage of avoiding the administration fee of about $60 a year. Providing you mainly keep the booster heater turned off, the full peak boosting will probably cost less than the $60 administration fee payable for the off-peak connection.

    It’s also worth having a bypass of the heat tempering valve for the kitchen sink (although the heat tempering is mandatory for bathrooms now).

    Note: when your solar hot water system booster is on peak rate, then any use of the booster is disguised among all the other usual uses of mains power that contribute to the total on the bill – so you lose the ability to monitor it and know what’s going on (whereas when it is on the off peak rate you can check it, which is useful for confirming the booster usage agrees with expected).

  3. The minute I saw your speil on solar hotwater last night, I rushed out to check ours, and low and behold, no off swtich. We have solar hotwater and a 2.5 kilowatt solar electricity thing happening. The weird thing to me is that since we got the solar panels for electricity, the off peak water seems to have gone up? I’ve been thinking that somewhere along the line, the new panels being installed have unplugged the hot water??? Maybe it is as you said though and the booster is kicking in more oftern than it should.

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