Heating water with the immersion and solar panels?

[Deleted User]

Our solar panels will be installed soon.

We currently use the gas boiler to heat water twice a day - 15 mins each time.

If we put the immersion on a timer to run during daylight for about the same length of time or less - as we don't use much hot water anyway - and we added an extra jacket to the immersion cylinder - would this work out cheaper than using the boiler the way we currently do?

albyota

What size PV arrary are you having?

Using Gas as you do at the moment is by far the cheapest.

We are moving into the winter so your PV system won't be producing very much before next March / April.

Only on the brightest days when the sun is directly on your panels (between 11am & 2pm, assuming South facing) would you be able to match? the consumption of the Immersion heaters 3kW element. so it may be worth considering in the summer months, but I wouldn't let it rule your life.

Cardew

A complicated issue with no clear answer - but on balance for the majority of the time the best course will be to use gas.

It has been discussed at length in other threads; but the simple answer is:

1. An immersion heater uses 3kW.

2. Even if you have the largest 4kWp PV system it will be only be producing 3kW around midday in summer.

3. For much of the year, even around midday it will be producing a lot less than 3kW, and that can vary wildly with each passing cloud.

4. Any electricity shortfall from the 3kW required will be taken from the main electricity at a price that is approx 3 to 4 times that of gas. Some days your panels will not be producing enough to run the 'background' electricity let alone enough to powe,r or contribute to powering, the immersion heater.

5. So IMO the only time to use the immersion is when you are home, and you are sure that at the time the immersion is on, your panels are producing at least 2.5kW.

[Deleted User]

Finally found the info - the solar array will be 3.7kwp on a south facing roof, no shading. We are often at home during the day but we can put the immersion on a timer if needs be. Having said that, in the view of the above answers it may be best leaving it with the gas?

orrery

Deleted_User wrote: »

Finally found the info - the solar array will be 3.7kwp on a south facing roof, no shading. We are often at home during the day but we can put the immersion on a timer if needs be. Having said that, in the view of the above answers it may be best leaving it with the gas?

A timer that may turn on when you don't want would be a very bad idea, but there are 'countdown' timers for immersions that will run for 30m/1h/2h so you could set it to run when you have a clear sky. I have a small electric rad (150W) in my downstairs loo, with a switch outside, and I plan to fit one for that so it can't be left on.

tomny

Regarding using immersion heaters. Is it possible to get them lower rated, say 1kw?

I have an unwired 3 kw one in my gas heated tank. It is not wired in and just screws out.

If there is such a thing as a 1 kw heater that could simply be screwed in as a replacement, then this would be useful.

Do I understand that a 3kw immersion heater would need its own supply? Could a 1kw one simple be fitted with a plug?

Apologies if this is old ground but I'm looking at ways to maximise the benefit of my soon to be installed system (3.12kw).

I like the idea of small electric heaters. I workk from home so I could take advantage of this during the day.

Thanks to all for all these intersting and helpful discussions.

BornAtTheRightTime

Yes you can get lower power elements for immersion heaters. Check out marine sites for them. I also came across a website referring to a manufacturer that will make them to size and power requirements for £60-£80, I think the link was on somewhere on the first few pages on this thread at electricians forums. This will reduce, but not eliminate, the issue Cardew mentions regarding drawing power from the grid during low solar PV generation.

That thread also includes a lot of discussion and information about creating your own control system to auto-divert and manage power to an immersion heater. Whilst this can completely eliminate the problem with over-drawing power, it is definitely one for the electronics expert or serious hobbyist (and probably requires Part P sign-off too).

orrery

tomny wrote: »

If there is such a thing as a 1 kw heater that could simply be screwed in as a replacement, then this would be useful.

There are dual element immersions - effectively 2 in one. Provided the two elements are completely isolated (the one I looked at was) then they could be wired in series to half the power. You'd need to check that with your electrician.

HappyMJ

Normally you would fit a solar water heating system with a solar panel then the electricity that is generated would run a pump that moves the fluid from the roof panels around the tank to heat the water. If there is no sun then there is no need to run the pump and then the electric immersion or gas boiler can be timed to come on at the end of the day or during the night to top it up.

BornAtTheRightTime

HappyMJ wrote: »

Normally you would fit a solar water heating system with a solar panel then the electricity that is generated would run a pump that moves the fluid from the roof panels around the tank to heat the water. If there is no sun then there is no need to run the pump and then the electric immersion or gas boiler can be timed to come on at the end of the day or during the night to top it up.

This is a discussion about using electricity generated by solar PV panels, not solar hot water heating. Two rather different systems!