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Will my Immersun qualify for RHI payments?

Posted by Cathy Debenham on 13 August 2013 at 10:58 am

Q: We have recently installed an Immersun to compliment our solar PV. This is using between 4 and 6 Kw hours per day to heat our water. It was simple to install and much cheaper than our solar thermal panel in our last house. Does the Immersun (or equivalent) qualify for a renewable heat incentive (RHI) payment as they do the same job?

A: The short answer to your question is no. PV switches do not qualify for RHI payments. While they are cheaper for the owner of a solar PV system, they are not cheaper in carbon terms. And the Department for Energy and Climate Change's goals for the RHI are to meet the renewables targets and carbon reduction targets.

There is an argument that while installing a PV switch is within the feed-in tariff rules, it is not in the spirit of the scheme. Everyone with solar PV is paid to export half of the electricity they generate, but if they use it to heat water they are not exporting it. 

In addition, by dumping surplus solar generated electricity as heat anyone who normally heats their water using mains gas is increasing their CO2 emissions, and reducing the carbon benefits of their solar PV installation. 

This is explained by the Stuart Elmes, CEO of Viridian Solar (manufacturer of solar PV and solar thermal panels) at thesolarblogger:

"The electricity we use is mostly made by burning gas and coal at a relatively low efficiency in a power station.  A unit of electricity is not only worth more in pence, it also costs more in carbon dioxide emissions than a unit of gas heating.

"If a unit of electricity is exported from your home, it displaces a unit of electricity used somewhere else on the grid, and prevents the emission of 522 grams of carbon dioxide.

"If instead, a gas-heated home installs one of these switching units and heats water instead of exporting that unit of electricity, it is preventing the use of a gas boiler to provide a unit of heat, and saves only 212 grams of carbon dioxide."

He calculates that over a 25 year lifetime a typical solar PV installation that doesn't use a switching unit would save 5.5 tonnes more carbon dioxide emissions than a system with a switching unit.

On those figures, there's no way that the government is going to incentivise solar switching! 

Photo Credit: et_id_der_ikke_findes via Compfight cc

More information about solar switches and the RHI on YouGen

Introduction to the domestic renewable heat incentive

Domestic renewable heat incentive: your questions answered

How to use excess solar electricity for water heating

The benefits of using solar PV energy to power your immersion


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

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5 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 3 September 2013 at 8:15 am

Hi Don, I'm not familiar with the one you mention, but there are a lot of solar switches on the market which all essentially take excess solar generated electricity and use it to heat the immersion.

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Don J

Don JComment left on: 2 September 2013 at 4:22 pm

Can anyone tell me if the Solar immersion switch by Altobo Renewables Ltd does the same job as the Immersun unit?

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Cathy Debenham

Cathy DebenhamComment left on: 15 August 2013 at 10:40 am


Your situation is different from the example that Stuart is talking about in the blog as both the cost and the carbon emissions of Calor gas are higher than those of mains gas - which is what he is talking about.    I wasn't saying don't use an immersun, just why there's absolutely no way that the government is going to include them in the RHI.   I'm interested to hear that your solar thermal doesn't meet you hot water needs in the summer months. We generally turn off the boiler sometime in April and turn it back on at the end of September. We have to do an hour's boost every now and then, but not that often (last summer was an exception to that). But there are only two of us, and it probably wouldn't be the same if we had more people in the house.

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Cathy Debenham

Cathy DebenhamComment left on: 15 August 2013 at 10:28 am

Here's a comment from a reader that would rather remain anonymous:

I found your story about Immersun incredible – as in, hard to believe. We had our Immersun installed in early June and since then it has generated 398 kwH of energy into our heat store. I turned off the boiler some time in June, and apart from the odd day, it has been off ever since.

I have a 500litre thermal store and a solar thermal system (as well as my 2.6Kw solar pv installation). My solar thermal system, despite being designed to cope, has never been enough on its own. I have spent something in the region of £43,000 on renewable systems, internal and external insulation, woodburner with backboiler, double glazing, low energy lighting, heavy curtains, draught-proofing, and just about everything else you can imagine and I can tell you that the best money out of all that was the £575 I spent on our Immersun. It is the final key which makes the whole thing tick – without it, our solar thermal system and our wood burning stove alone or in combination (and obviously I am not using the latter in the summer) would not cope with our hot water ! demands, despite being ‘correctly sized’.

I am ecstatic about our Immersun – to be able to turn off the boiler and no longer have to watch the needle falling on our Calor gas tank and wait with dread as the tanker turns up and empties another £500-600 worth of Siberian gas into our tank is a dream come true. I have no basis on which to question his figures, but does Stuart Elmes seriously believe that I am better off paying for gas imported all the way from Qatar or Siberia than I am diverting electricity to provide my own hot water needs, right here in my own house?? Is he a stooge for the government?? His arguments are based on the carbon footprint alone, and even then I find them dubious. Has he taken the transport mileage into account? There is no logic to it either: is he suggesting that burning one unit of imported gas uses only 212 grams of CO2 whereas one unit of electricity generated creates 522 grams of CO2? On what basis does he assume this??

But here’s a thing. I am not posting this under comments, because I am aware of the fact that my FIT provider, if they knew my identity and the fact that I own an Immersun, could potentially cut my FIT payments on the basis that I am not exporting the electricity that I claim to be (which is true). So basically anyone who owns an Immersun and figures out how great it is, are unable to go public and tell everyone about it because who would prefer to prioritise the common good over the benefits they’re receiving. Not me!! Therefore, please treat this is any way that you wish journalistically but I wish to remain anonymous. It might explain why no-one sticks up for the Immersun in public – they know that they’re onto one of the best ever inventions for renewable users but if they’ve got any sense they’ll keep their head down and remain schtum.

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philwjonesComment left on: 14 August 2013 at 8:51 pm

But while those of us exporting are paid pretty much a pittance per unit compared to what we'd pay if we actually used those units from the grid (and what the units are sold on for), the incentive is there to use whatever power is generated by the panels.

Admittedly, the FIT for some of us is fairly generous, but the export payment needs to be a bit more realistic to stop people wanting to use as much as is generated and not export..

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