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Can I connect solar PV to my storage heaters?

Posted by Chris Rudge on 16 August 2012 at 8:37 am

Q: Can I connect my solar power to my storage heaters, and what are the pros and cons?

A: I would strongly advise that unless you have a large (10kwP) solar PV system, having a diversion unit installed to re-direct excess power to a storage heater during the day will not be economic, mainly as you really will only want that heater working during the winter. Unfortunately your 4kwp system will not provide the required 3kwp during the winter months.

However, there are a number of devices either out on the market now, or will be soon, that work as a low cost EMMA unit, that will send all of your excess power to either an immersion heater or one storage heater. I would advise you to check around this month, as there should be a good selection coming on the market [Chris will review them in due course - Ed]. I'd advise diverting the power to an immersion heater, as you tend to use hot water all year, but space heating only gets used in the winter (when there's less sun).

Product reviews

Review of IntellyGreen PV kit

Review of Amelec intelligent solar switch

Review of Immersun: using solar electricity to heat hot water

More information about re-directing and storage excess solar-generated power from YouGen


Auto control enables the use of solar PV for an immersion heater

Using solar PV to heat your domestic hot water

How easy is it to use renewable energy 'off grid'?

Solar PV information page


About the author: Chris Rudge is a qualified electrician who specialises in renewable energy.

If you have a question about anything in the above blog, please ask it in the comments section below.

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17 comments - read them below or add one

Rudge Energy

Rudge EnergyComment left on: 18 September 2016 at 9:31 am

Hi Jezzer

Yes, this blog has been around for a long time and things have moved on a lot.

Though EMMA have a small domestic offering, the 4G, the included features are not really needed for simply running a storage heater. You could look at the Solic200 from which is really simple to fit if you are wiring the storage heater on its own circuit from the consumer unit. Cost is less than £200. 

Though to keep wiring through the house at a minimum, the Solar iBoost from will enable your storage heater to be connected anywhere in the house to a local ring main circuit if needed through a fused spur. The iBoost will need to be installed by the heater, but the sensor clip is wireless, so can be simply clipped onto your incoming mains tails either by the fuse box or even in the outside meter box if you want. The iBoost is around £280, but for non electricians, (and even electricians), offers a far more versatile installation option.

Chris Rudge (Rudge Energy)

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JezzerComment left on: 16 September 2016 at 9:51 am

This thread is now 4 years old. Can anyone comment on whether the latest equipment on the market would make a solar-powered storage heater feasible as background heating for a conservatory? I don't care too much if it doesn't make it habitable in the depths of winter, but if it extended the use of the conservatory by a month or two either side of summer, that would be worth considering.

Some pointers towards suitable compatible equipment (available in the UK) would be really helpful too.

Thanks in anticipation!


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andyteeComment left on: 23 April 2015 at 2:12 pm

Gary - I've looked into this since i too have an Immersun and wish to make use of excess solar. I disagree  with the posters who say that it is not worthwhile since you don't generate enough power in winter to store. As you rightly point out there is a period in Spring and Autumn where heating is still required AND your solar panels are performing really well.

I emailed Immersun and they stated that "Any storage heater up to a maximum of 3.2 kW can be used but it must be of the simple resistive load type with a mechanical thermostat and no electronics integral to it or in line. Dimplex XL,  believe are compatible.". The Immersun 2 manual states this as well as giving wiring diagrams.

Looking at the XL model range, they are reasonably good looking but not portable due to their weight. The weight of the units is from the thermal bricks which accept a large amount of "charge" and hence have to possess large thermal mass. The XL12 model accepts 11.9kwh of charge and the XL18 model accepts 17.85kwh. With a 4kwp pv system it's debatable wether you'd need any larger than the XL12, especially if you are charging a water cylinder as well.

In terms of oil filled radiators, I don't think that would work very well unless you have a very well insulated room. The benefit of storage heaters is their delayed output. I'm also not aware of any alternatives to standard storage heaters like the Dimplex XL range. Remember that the unit must not have any electronics in it and must be able to accept a variable load such as the Immersun delivers.

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GaryComment left on: 22 April 2014 at 8:35 pm

I thought I would add a question here related to the issue of using storage heaters.

My original system was 3.5kWp on a WSW-facing roof, fitted June 2013 along with an Immersun. This performed really well and enabled me to turn the gas water heating off from installation day to early October, and added some pre-heat over the winter. So far (91/2 months in) the Immersun has pumped 380kWh into the immersion heater. So far so good.

However, the generation from my roof is only about 100-400W until midday when it literally jumps to its maximum within 30 minutes and stays there until sunset. I therefore bit the bullet and added another 1.75kWp on our SSE-facing roof in March 2014. So far this is exceeding expectations. Output on the new system rises quickly to about 1.5kW and sits there all day (apart from the TV aerial shadow knocking production in the afternoon - it will just have to be moved!)

On a normally sunny day the water is now up to full temperature by about 11:00 and after midday production can peak at 5kW on a good day in April, so summer should see some good results.  Over these sunny days in April I have been generating in excess of 25kWh per day. Great for washing machine, dishwasher etc etc but also means that a lot is sent back to the grid on "non wash days".

So, the idea of storage springs to mind. The Immersun (mk1) can run a second resistive load via its multi-function relay. This means that once the immersion is hot excess PV can be sent to device two. The Immersun then checks back to see if device one is "hungry" every 15 minutes.  But what to attach?

Batteries are still too expensive and probably would not suit attaching to the Immersun anyway, so some sort of storage heating comes to mind to facilitate turning the gas heating off a month or so earlier in the spring and on again a month or so later. Excess PV in the summer would then still flow to the grid of course...

I have been looking around the web without real success. Storage heaters are out there but they are generally ugly beasts and not portable; oil-filled radiators might be an option to heat the room in late afternoon, so that by bedtime it is still a couple of degrees warmer than it would otherwise have been but whether that would work is not really known as I don't know how long they retain heat after being turned off, nor how long the heat would stay in the fabric of the room...

What I would ideally like is a storage heater that looks good and is portable, or, even better, a storage heater that looks like and fits into the fireplace like a wood burner stove or whatever.

Does anyone have any ideas, thoughts etc on what is available and why I should or shoúld not bother?


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michaelmaloneyComment left on: 10 March 2014 at 7:19 am

I’m seeing a lot of people getting a little iffy with solar power because of the lack of options for storage. There is a new thread which suggests that there are finally people who are up and noticing the demand from people who want to keep the energy they produced for themselves. And why not! Would be great to heat more about the pros and cons of doing so and when the best time to switch from one to the other would be.

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4eco LimitedComment left on: 21 November 2012 at 5:01 pm

Please refer to for information about a low cost modulator which redirects any energy which you would be exporting to your immersion heater or alternative heat source (storage heater, underfloor heating, panel heaters).

Using a single CT Clamp, the immerSUN is easy to fit and keeps you informed of how much electricity you have directed to you heater/immersion.  It does also have a relay which allows you to connect to a second heat source once the first is up to temperature.

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edward50Comment left on: 28 September 2012 at 1:45 pm

Very interesting comment by Solstice Energy - well worth looking on the other thread.

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Solstice Energy Ltd

Solstice Energy LtdComment left on: 28 September 2012 at 12:51 pm

I've just posted something on this question of immersion switches at;

We can't see the benefits, but a lot of installers seem to like them. Am I missing something?!

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Cathy Debenham

Cathy DebenhamComment left on: 28 September 2012 at 8:27 am

Hi Edward

Our solar PV expert Chris Rudge is testing a variety of the products right now, and I'm expecting his reviews soon. I think there may be a patent row going on between EMMA and Engensa. This is something that's on my list to investigate further. I hope to find out more next week at Solar Power UK and will report back.

In the meantime, this blog gives a good outline of the different levels of intervention available.

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edward50Comment left on: 27 September 2012 at 5:26 pm

What update is there, please, on devices that automatically divert excess electricity (but only excess electricity) to an immersion heater? My solar installer rang me today to let me know they are now offering 4eco's Immersun at a starting cost of £540 inc VAT and fitting. Engensa emailed me in early August to say that their Solar24 was now available at £345 plus VAT and excluding fitting, but it's hard to find anything about it on their website. Both these appear to do what EMMA does, i.e. divert to an immersion heater only the electricity that would otherwise be exported. Are there any others?

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Rudge Energy

Rudge EnergyComment left on: 28 August 2012 at 8:47 pm


Hang on before buying an EMMA!.. Though the EMMA works well, there are far cheaper and just as effective alternatives available.. Check back in a few weeks to get a report on some testing  we have been carrying out.


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Rudge Energy

Rudge EnergyComment left on: 28 August 2012 at 8:44 pm

Hi Mark Energeno

We are testing a bunch of immersion switches right now, (check back to YouGen in a week or so for results)... This is the way to go for using excess power, even when your power company uses Smart Meters.

Chris :) 

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Rudge Energy

Rudge EnergyComment left on: 28 August 2012 at 8:40 pm

Hi Alan C

As indicated in the original post, using a standard domestic PV system to run storage heaters is really not a good option, no matter how it gets connected. If you do have a big PV or wind turbine system though, get in contact with me at and let me know what your set up is so we can work something out.

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Alan_CComment left on: 26 August 2012 at 10:55 am

Hi Chris,

This is an interesting post for me as my main source of heating is storage heaters.  My heaters are on a completely separate supply controlled through a timeswitch and with a separate meter and consumer unit.   At the moment I guess my excess power (which is connected in to the standard domestic consumer unit) is feeding the grid and then I am buying it back for my heaters! Is there a way of connecting the inverter output to the off-peak supply?

Thanks, Alan 

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James@JojuComment left on: 18 August 2012 at 8:45 pm

Tokenpom should also note that many SMA inverters (and no doubt others) can be set for a lower maximum power out (and no it won't overheat!)

Regarding water heating etc many newer inverters already have an output to switch a contactor when the power reaches x. We recently used this to heat a small swimming pool at one installation.



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Mark Energeno

Mark EnergenoComment left on: 16 August 2012 at 1:11 pm

We at Energeno are one of the companies launching Variable Power Immersion switches, together with smart plugs for excess electricity.  We hope to have the product in Australia later this year. 

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tokenpomComment left on: 16 August 2012 at 9:11 am

Hi, I live in Australia, and have a 3kw solar array on my roof.

I am limited to exporting 3kw because of our low quality grid connection, but would fitting an EMMA allow me to add additional Panels, to allow me to export my 3kw for more of the day, by disposing of any excess power into a heatsink (such as a water heater) ?

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