Low Wattage Immersion Heater

PockPower · Post by **PockPower** » 22 May 2011, 23:06

To try and use a bit more "free" electricity, a couple of months ago I fitted a timer switch to my immersion heater. As my 3.7KWp system rarely exceeds the 3KW my immersion consumes, I've been trying to find a suitable low wattage replacement, and finally last week I found one!

There are lots of 11" immersions available intended for marine use, but 27" ones are illusive. Eventually I came across a firm in the Isle of Wight that sells them http://www.surecal.co.uk/Product/ImmersionHeaters.aspx .

For £55 including next day delivery I bought a 1.25KW 27" direct replacement for my standard one, and yesterday I fitted it.

I have set the thermostat slightly hotter than the one controlling the boiler, and the timer for 4 hours during my peak production, with the hope that the following morning the boiler will be needed less.....

Just one thing to note, almost all British screw-in immersions are 2.25" BSP fittings, this measurement refers to the bore of the pipe this thread would be on the outside of, and therefore the diameter across the thread is actually slightly more than 2.5"!

I'm not really sure this will ever pay-back, but it makes me feel good, using a bit more of the free electricity.

biffvernon · Post by **biffvernon** » 23 May 2011, 07:38

That's a useful post, PockPower. We have a similar situation. We have our 3kW heater timed to come on at night during the cheap rate electricity hours and I manually switch it on when I notice we're generating over 3kW. It would be much better if we had a low wattage heater. I suppose one day we'll have a clever controller that switches the immersion on whenever our generation exceeds our use, dumping the spare power to water heating before exporting to the grid.

goslow · Post by **goslow** » 23 May 2011, 09:39

be interested to hear how well the 1 KW does in heating a tank of water. I could be interested in this approach maybe as an alternative to solar hot water if I get the free solar PV deal.

Post by **adam2** » 23 May 2011, 10:44

Presuming that the tank is well insulated, 1KW water heater will be fine, it will simply take 3 times as long to heat the same amount of water to the same temperature.

Ideally, 2 similar elements should be installed, one at the top and one at the bottom of the tank.
Initialy only the top one should be used, then when the top of the tank is hot, the top element be automaticly turned off and the botton one turned on.
This has the merit of producing a smaller amount of properly heated water in a relatively short time, rather than a large amount of lukewarm water.

goslow · Post by **goslow** » 23 May 2011, 11:33

Thanks. Actually I realised in "UK carbon emissions terms" its better to heat the water with gas (and better still with solar HW). Due to the fact I'm exporting less solar generated electricity so "everyone else" needs more grid electicity, per KWh more CO2 intensive than a gas boiler.

On the other hand, this way I save money compared to burning gas or installing solar HW!

An Inspector Calls · Post by **An Inspector Calls** » 24 May 2011, 10:52

Dumping your PV output to heat water is OK, but don't forget that if you're buying your water heating off peak, or from gas heating, then what you 'pay' yourself for this generation should be be priced appropriately.

There must be better solutions than this. For starters, a better load to aim for would be fridges and freezers since during the day (when PV is 'on') these loads are bound to require full-price electrcity. So a load diverter to these devices would be a good idea.

For micro-hydro, they have developed many controllers for dumping spare output to various local loads (as part of the mechanism of governing the micro turbine).

e.g.

http://www.google.co.uk/search?source=i ... r&meta=lr=

There was/is a small group at Glasgow University doing a lot of work on these lines.

If I had a PV system (very unlikely) I'd be building something like that.

goslow · Post by **goslow** » 24 May 2011, 11:48

Yes, its only a question of "we have spare PV electricity that we are exporting to the grid and not getting paid for so lets find a way to use it and save more money".

Since my boiler gas is about half the carbon emissions per KWh than grid electricity, on carbon emissions grounds I would not get good marks for doing this. My PV electricity if exported helps displace fossil-generated electricity, so I should ideally use it for appliances depending on grid electricity. That calculation could change in the future if for example the carbon intensity of the grid is reduced by 50% (maybe eventually...).

However, another point is that actually we don't use a lot of hot water as we have an electric shower and cold fill appliances (yeah I know totally on-grid!). So it could be not too bad an idea to fill the space on my roof that would be occupied by solar HW with additional PV, use any spare to warm my hot water tank and avoid some of the ongoing costs/hassle of running solar HW. I suppose as well as the capital cost, solar HW has more servicing costs. However, I suppose we would also gain through RHI on the solar HW so maybe it does not make much difference financially.

In fact we stand to do quite well on the "free solar" idea as we occupy the house during the day and run quite a lot of appliances while the panels would be generating.

RenewableCandy · Post by **RenewableCandy** » 24 May 2011, 15:25

There was/is a small group at Glasgow University doing a lot of work on these lines.

That wouldn't be Tim Miller's SPEED lab would it

??

An Inspector Calls · Post by **An Inspector Calls** » 24 May 2011, 17:23

An Inspector Calls wrote:There was/is a small group at Glasgow University doing a lot of work on these lines.

If I had a PV system (very unlikely) I'd be building something like that.

I've remembered now. It was D S Henderson of Napier (close, but no cigar). The last time I met him was at a conference in Aix (it was hell) when he was describing an ELC for a small hydro plant connected to a woollen mill. CV here:
http://www.d-henderson.co.uk/documents/ ... 8-6-10.pdf

Note he seems to be working on solar generation now. It might be worth exploring to see if he's done any work on electronic load control.

matt_warby · Post by **matt_warby** » 10 Jun 2011, 22:19

(New to site). I've managed to get my immersion heater to come on automatically by sensing when I'm generating excess energy. I sense by looking at the LED from my meter which illuminates when I'm exporting. If this changes Eg kettle is on then it switches off and I don't then rely on peak electricity to run my immersion. Simply switches back on when the kettle switches off. I had to down grade to a 1kW immersion (at 11") as the switch can only cope with 5amps. Works well so that I don't have the gas heating the water. Reducing to 1kw means I can easily switch it on as I can get 3.7kW peak and can run washing machine or dishwasher at the same time. I'm hoping to piggy back the sensing element so I can use a 1KW oil filled heater in winter to further reduce bills. I'll need to wait for that as I'm not sure what I will be producing. I had done a fair bit of looking for an automatic system but could only come across the EMMA system at £1500. This serves the same function for a fraction of the cost.

emordnilap · Post by **emordnilap** » 11 Jun 2011, 16:54

Welcome matt_warby

Sounds like you have a good bit of technical know-how! What's generating your electricity?

matt_warby · Post by **matt_warby** » 11 Jun 2011, 18:35

I'm using solar panels. 16 x 245W Sharp panels. To date have produce 330 kWhrs (installed only for a couple of weeks). I wouldn't say I have a lot of technical know how but in researching installers I found out a lot. (especially that there are a few cowboys out there). I was certainly surprised that nobody had thought how to harness the most of the energy made in an efficient manner, rather than giving it back to the grid. The sales folk only seem to look at the feed in tariff as a money maker and not how you manage the energy produced.

Glyn81 · Post by **Glyn81** » 25 Jun 2011, 09:24

Hi Matt,
Who did you have to install yours? How much?
How did you set up the sensor to switch the immersion heater on and off as I will be interested in this as well as I am looking at ways to save as much as possible.
I am current looking at getting a similar system to yourself although I will have 9 panels on a west roof and 7 on a east with a company called solar essence. Really looking for a immersion heater around 1-1.5kw that can slowly heat my water up with the spare electricity.

I will be grateful on any suggestions or help anyone can give.

Many Thanks
Glyn

Location South Wales UK

matt_warby wrote:I'm using solar panels. 16 x 245W Sharp panels. To date have produce 330 kWhrs (installed only for a couple of weeks). I wouldn't say I have a lot of technical know how but in researching installers I found out a lot. (especially that there are a few cowboys out there). I was certainly surprised that nobody had thought how to harness the most of the energy made in an efficient manner, rather than giving it back to the grid. The sales folk only seem to look at the feed in tariff as a money maker and not how you manage the energy produced.

kernow-sun · Post by **kernow-sun** » 30 Jun 2011, 13:39

(Another new to site). I was really interested in reading your post (see quote) as I have just had a new solar PV system fitted. As I live in a rural setting I have to use oil for the heating system, with an immersion heater being used overnight for hot water. Your system looks to be just the job in maximising the energy created. What is the system and is it available commercially ?

matt_warby wrote:(New to site). I've managed to get my immersion heater to come on automatically by sensing when I'm generating excess energy. I sense by looking at the LED from my meter which illuminates when I'm exporting. If this changes Eg kettle is on then it switches off and I don't then rely on peak electricity to run my immersion. Simply switches back on when the kettle switches off. I had to down grade to a 1kW immersion (at 11") as the switch can only cope with 5amps. Works well so that I don't have the gas heating the water. Reducing to 1kw means I can easily switch it on as I can get 3.7kW peak and can run washing machine or dishwasher at the same time. I'm hoping to piggy back the sensing element so I can use a 1KW oil filled heater in winter to further reduce bills. I'll need to wait for that as I'm not sure what I will be producing. I had done a fair bit of looking for an automatic system but could only come across the EMMA system at £1500. This serves the same function for a fraction of the cost.

emordnilap · Post by **emordnilap** » 30 Jun 2011, 13:54

Welcome kernow-sun.

Keep us posted on your system.

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Low Wattage Immersion Heater

Low Wattage Immersion Heater

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