Skip to main content
Observer Ethical awards Winners 2011

YouGen Blog

Thermodynamic panels: your questions answered

Posted by Cathy Debenham on 11 January 2013 at 9:12 am

This blog was updated in February 2014, 6 November 2014 and 10 March 2015.

If someone told you that there's a new solar panel that could heat your hot water 24 hours a day, 365 days a year come rain, shine or snow, would you believe them? It sounds too good to be true, and that always makes me suspicious, but that's what the evangelists for thermodynamic panels say.

So what are thermodynamic panels?

Despite being panels, they are closer to an air source heat pump than they are to a solar thermal panel. They are basically a freezer in reverse. Refrigerant enters the panel and as it passes through it absorbs heat from the atmosphere and becomes a gas.

The gas then passes through a compressor which increases the temperature and finally through a heat exchange coil inside the hot water cylinder. This heats the water in the cylinder to 55 degrees. It is estimated that about a quarter of the energy absorbed by a panel comes from solar irradiation, the rest from air and rain.

How much hot water do they produce?

They claim to provide 100% of the hot water requirements for domestic and commercial premises, swimming pools, underfloor heating and can make a contribution to traditional central heating. They come with a built in immersion which uses electricity to boost the water to 60 degrees every so often to avoid any risk of legionella.

How do they compare with solar thermal?

Solar thermal panels heat water in the panels, where thermodynamic ones heat a refrigerant. This allows them to harvest heat from the atmosphere, where solar panels depend on heat from the sun. The refrigerant enters the panel at -22 degrees C, so even on cold winter days they can absorb relative warmth from the air.

Solar thermal panels perform best on roofs that face between south east and south west. Thermodynamic panels can be placed on a wall, or on the roof. It's best not to have them facing north or north west, but they don't have to face south.

Are thermodynamic systems more like air source heat pumps?

Air source heat pumps have a fan running continually, which requires more electricity than the compressor in a thermodynamic system. As a result the thermodynamic manufacturers claim a much higher coefficient of performance (COP) of 3.5 to 4 - that's three and a half to four units of heat generated for each unit of electricity put into the system.

An employee of the Northern Ireland distributor for Energie (dpaddym1), writing on the Green Building Forum, said that his system had a COP of just over 3 in the eight months from January to August last year. A UK distributor of Energie panels has measured coefficients of performance ranging from 2.1 when the outside temperature was -6 degrees and the panel had snow on it, to 5.2 in July. It has measured an average seasonal performance factor of 3.5 to 4. There are no independently verified performance figures for UK-based systems yet.

Are thermodynamic systems designed for use in the UK?

The two main manufacturers are based in Portugal and Spain. The systems they manufacture have not been designed for the UK market. However, I understand that there are companies aiming to bring UK-specific products to the market this year. [Nov 14: there is now at least one company manufacturing in the UK for the UK climate.] 

Have they been independently tested in the UK?

In January 2014 the National Renewable Energy Centre started the first UK test of thermodynamic panels. Their early results can be examined here

How many panels would I need for a domestic installation?

A four person household would need one panel and a 250 litre cylinder. It would cost around £5,500 to install.

Is it worth it if I'm on mains gas?

It depends whether you are looking at it from a financial point of view. Heating with gas is cheaper than with electricity. However, if you are worried about energy security or carbon emissions, then it might make sense.

I saw an ad saying thermodynamic panels produce "free hot water", is that true?

No. There is a cost involved as electricity is used to run the compressor. I've seen estimates of costs around £8 to £10 per month for a domestic system.

Will thermodynamic systems be eligible for the renewable heat incentive (RHI)?

The Department of Energy and Climate Change says it is: "gathering information on performance and on the establishment of standards for these products. At present there is not an established methodology to test and demonstrate their performance and so they are not currently supported under the RHI. ... There are no immediate plans to bring in support under the RHI until demonstrable performance standards are established." 

MCS has now (March 2015) agreed standards for thermodynamic systems, and manufacturers are applying for accreditation. At time of writing (10 March 2015) none have been accredited. However, there still don't seem to be any plans to include thermodynamic panels in the RHI - although that's not what some of the manufacturers are telling their customers. 

Prior to November 2012 thermodynamic panels were eligible for the renewable heat premium payments due to their Solar Keymark accreditation. However, on 5 November Gemserve, the body responsible for the MCS scheme (Microgeneration Certification Scheme) suspended the registration of solar thermodynamic products within the MCS database.

This was for two main reasons:

1. The products tested and certified through Solar Keymark used water and glycol (as do solar panels). However, the products being sold in the UK use a refrigerant F Gas for the heat transfer.

2. Heat pumps have particular requirements under MCS concerning the co-efficient of performance and energy costs of running them, and it's not clear yet whether thermodynamic panels meet the standards. In addition, it is a MCS requirement that estimated performance is calculated using SAP, but these hybrid type systems are not fully covered in the SAP methodology.

MCS is working with a number of manufacturers to develop the required standards.

Should I invest in thermodynamic panels now?

The MCS says: "To be completely clear, this decision does not mean that the product cannot be installed in the UK, simply that they cannot be registered within the MCS database." However,until they are registered in the MCS database they will not be eligible for the renewable heat incentive.

Views differ on the product:  An installer I spoke to has some very happy customers. He has been in the renewables business for 10 years, and rates the Energie solar thermodynamic system as "the best heat-producing product" that he's worked with.

A consultant is less enthusiastic: "The idea behind the technology is almost right, but it is designed for another climate." He cites as an example of one of the resulting pitfalls an installation where ice built up on the panel to such an extent that the panel mountings collapsed under the build up. "It can be dangerous. I'm not such a fan as I used to be."

He also asks why anyone would buy products that are outside the renewable heat incentive and the green deal. His advice for anyone who wants to go ahead is: "go and look at no less than three systems that the installer has done and talk to the owners."

Having heard quite a few outrageous claims made for these panels at trade shows last year, my advice would be for buyers to be wary of investing at this stage, until there has been some testing in the UK, and standards for performance are set by MCS.

Treat any claims by installers that thermodynamic systems installed prior to accreditation by MCS will be eligible for the renewable heat incentive with considerable scepticism. There is no guarantee untill standards are known. If the RHI is a deal breaker for you, then wait for an announcement from DECC that thermodynamic panels are an eligible technology.

See this blog for results of the first independent test of thermodynamic panels in the UK.

More information about renewable heating options from YouGen

YouGen guide to heat pumps

YouGen guide to solar thermal

YouGen guide to biomass boilers

YouGen guide to the renewable heat incentive

YouGen guide to heating and hot water


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

Like this blog? Keep up to date with our free monthly newsletter


20 comments - read them below or add one


sumanrajputComment left on: 29 August 2020 at 11:28 am

I conceded your article to my accomplice and I imagine that individuals will like your article and give great data. 

Jaipur Escorts Service

report abuse


simonLComment left on: 4 May 2016 at 9:37 pm

We are about to rip out Energie Thermodynamic system out - it doesnt work well and any repairs are a rip off (£2000 last time, could have got a new boiler installed for that! I would strongly recommend you dont use ABV solar as they will rip you off). As there is no RHI, the Energie system may look good on a website, it it not great in your home or to your wallet.

report abuse


chorisiaComment left on: 16 October 2015 at 11:20 am

Recent visit from an Energie salesman who said two panels and a 300 litre tank would provide all the hot water for a large house with three bathrooms and three kitchens my flat and five bedsits. I dont believe him. Energy Saving Trust advice ,no independant verification,no microgeneration certificate,so dont buy this technology until there is. Very little user feedback which was not the case for PV when we put in PV panels,I figured if the robust PV technology works on Mars it will work here, five years since installation, it does; but only makes economic sense because of the feedback tariff which is a case of the poor who cannot afford the installation paying  for those of us who can. We have two Brittony multipoint hot water heaters , 7 balanced flue gas wall heaters mostly redundant since dry lining this victorian semi. With utility bills of £1200 a year i am somewhat disappointed that I cannot justify changing our 'outdated' system in spite of having capital languishing in the bank at current interest rates.

report abuse


simonLComment left on: 15 October 2015 at 4:16 pm

Hi all


We have had a Energie Thermodynamic system for a year now and it has been nothing but problematic - STEER CLEAR

There is no support, no RHI and my electric bill has gone through the roof (live in London)


this product is a complete waste of money


report abuse


LozzarkComment left on: 27 June 2015 at 6:22 pm

Please Help.  I had an Energie Hot water system fitted, powered by a thermodynamic panel.  It has worked well enough, but last winter the panel was covered in ice presumably because it was on a North facing roof and it stopped working.  When the ice was gone, the system seemed to work again.  At some point the pressure release valve operated and blew out some water.  The exit pipe was fitted at the front of the house and dripped water onto main window, causing a repetative drips. Strangely it eventually abated on its own.  In the recent past something happended to cause the ouput pressure to fall.  Basically water comes out at gravety fed rate only.   I tried changing the valve with a meter to 2 bar, but it makes no difference.  That's when my problem started, the pressure safety valve started to drip again.   The company that installed the system has ceased trading.  I don't understand the system enough to know whats gone wrong and I've no idea how to find some one who will come and fix it.  

Getting a service engineer is a big issue because although they say no maintenance is necessary, one is supposed to inspect the magnesium rod yearly. No hope of me doing that, and anyway what do I do if it needs a new one.  Also there is a filter on the valve I was talking about needing to be cleaned every 2 years.  No chance of me doing that either.

One big problem is the time it akes for hot water to arrive.  My takn is about 20ft high and about 30 meters from the main hot tap in the kitcken.  It takes 60 seconds for hot water to arrive.  

So does any one know where I find a suitable engineer?  I live in South Cheshire.

I thought I'd update you.  

I found a plumber willing to have a go at the "peripheral" parts of the system.

He confirmed the exit valve from the Energie system had blown out and the drip was caused by debris preventing the valve from seating again.  A few blasts from the relief screw eventually cleared the debris.

The second fault he found was that the expansion vessel was devoid of air.  He pumped it up to 52 psi. (3.5 bar).  He said that was what caused the blowout, but we did not know why there was no air in the expansion vessel. The plumber said the air can deplete with time and I needed to monitor it.  

The third fault he found was that the input pressure reduction valve was only allowing 1 bar.  He replaced that with one that adjusted and set it to 3 bar.  3 bar is what should have been.

All worked well for a little while, but we went on holiday and on return the system spurted out through the pressure relief valve.  The plumber came again, and confirmed the expansion vessel was depleted of air again.  I thought I'd have to replace it, but when the plumber had pumped it up again, as he was screwing on the valves dust cover, he heard a hissing noise.  We think the cover was letting the air out slowly.  The cover was left loose and I am monitoring the vessel to check it was the problem.

In the mean time, with the system at 3 bar, hot water comes out at mains pressure.  The difference is amazing: it has now become a great system to use.  The hot water arrives in a few seconds at high pressure and somehow feels hotter than it was doing.  

While this was going on, I managed to contact Energie in Portugal.  The wanted to see all the paper-work, and then put me in contact with a trained engineer in the UK.  He rang me the other day, but he was 300 miles away in the SE, but a least I have someone I can contact should I need to. He explained how to remove the magnesium rod and check it, and said he could post me a new one (£125) if needs be.  He said it starts at 1.5 in in diameter and if it gets to  0.5 it needs replacing.  The instructions say check at least once every years.

I still have the potential problem of the panel icing up in the winter.  I could fix it by moving the panel, but in fact it is only a couple of weeks a year, and the unit does have a back-up immersion heater for emergencies.  

Would I recommend the system?  It depends. The running is very efficient and for every 5p of energy you put in, you get 35p worth of hot water out.  I didn't realise until all this happened, I could convert my electric showers to mixer showers and save on electricity for the showers, but then there is the showers up front cost.  I have solar panels, so for at least half of the year I'm getting virtually free hot water.  If you have a big house with a big family the investment may be wort it, but it would still take a long time to recover the up front investment costs.  My system was £4k to install 2 years ago, it may cost £5.5k now.  I have a feeling it takes over 20 years to break even.  On a new build, the investment may be worthwhile.  It is certainly an excellent system when working properly. 

report abuse


Richy_WhiteComment left on: 30 April 2014 at 3:58 pm

Hi Sidney - our thermodynamic panel system is set to 'let the water out' at 2.25 bar.   When a tap is put on full this drops to 1.75.   We have a mixer shower which would benefit from a bit more pressure in the 2 coldest winter months but the pressure is adequate in warmer months when the incoming cold water is a wee bit warmer than the liquid ice we get in Dec and Jan!   We have a good head of water where we live and so our system is holding back the mains pressure.

Sounds like you need a wee limiting valve added on your shower feed ... but if there's only a cold feed to your shower then it's not the thermodynamic system at fault. 

report abuse

Cathy Debenham

Cathy DebenhamComment left on: 10 April 2014 at 4:29 pm

Interesting to see that two complaints to the Advertising Standards Authority have been upheld against claims made by Magic Thermodynamic Box for its heating management system.

report abuse


SydneyComment left on: 10 April 2014 at 10:34 am


does anyone have information about the water pressure that is provided by a thermodynamic water heating system? 

We have had a thermodynamic water heating system installed. Three months later our power shower seals burst. The power shower takes water pressure of one bar. 

Now I need to know whether to repair the power shower (which I should do if it can cope with the new water pressure) or replace it with a flow-through sytem (which I should do if the new water pressure is higher than 1 bar). 

The problem is that I have been unable to find out from the installer what the new pressure from our new thermodynamic water heating system is (1 bar? mains pressure? higher than the old immersion heater? lower? ) 

Can anyone help / provide information? Many thanks.


report abuse

Cathy Debenham

Cathy DebenhamComment left on: 11 February 2014 at 9:14 am

Hi Chris

This company had a stand at SolarEnergyUK last year and I had a longish chat with the Irish man that invented it. I don't feel qualified to say whether or not it works. However, there are three reasons why I'd be wary of buying one:

- they couldn't refer me to any significant independent testing into its effectiveness

- I was given a trade price of  £2,000 (plus installation costs), so it would have to make some pretty hefty savings to pay for itself

- there was considerable scepticism about it from solar engineers that I talked to.

report abuse


chris1Comment left on: 10 February 2014 at 8:38 pm

Hi, hoping somebody can help me. I have been approached by a company selling something called the little magic thermodynamic box. It seems like a very good system which can apparently save me a fortune on heating my water. I have been told that a thermodynamic water heating system can be fitted to any existing boiler (with added cylinder). Can anybody tell me if there is any substance to this, as I have seen various people say that thermodynamics aren't particularly beneficial if you are already heating water via a combi boiler.

Thanks in advance

report abuse


kaihoraComment left on: 15 November 2013 at 9:17 pm

Lack of data on UK-based installations:
I have looked wide and far online in the UK and Ireland over recent weeks. There are, so far, not that many installations - or rather not that many installations that are instrumented so that complete performance/consumption/generation data can be collected.

Narec are in the process of setting up a test and, no doubt, more data will become available over the next few months from other sources, too. See here for a few interesting sites (not only on the Energie panel system):

Little Magic Thermodynamic Box Research & Development
Note, this test was not for the Energie system discussed in this post but it does show the results for a similar system. The results are not terribly good (COP between 1.39 and 2.56, if I have got my maths right). I wonder whether this is because there was no air circulation or solar radiation in the test chamber. The test conditions were therefore a "bad case" scenario, such as on a very still night. Interesting all the same.

 LVP Renewables Solar Panel Case Studies
(as far as I can see these are thermodynamic and not solar panels)

National Renewable Energy Centre

I hope this is of interest.


report abuse


kaihoraComment left on: 15 November 2013 at 8:59 pm

I am looking at these thermodynamic panel systems for my own home at present. Key intention is to provide hot water but I have got further ideas:

The panel system may only produce 1-2 kW, not enough to heat a whole house to comfortable temperatures in winter time. However, this should be enough to keep a home frost-free when unoccupied or heat one room in the colder seasons to a comfortable level.
My kitchen radiator can produce around 1 kW. If that comes from the thermodynamic panel system powered mostly from my PV panels then I won't need any fossil fuel heating, even when I am at home all day in winter time.

Practically, it should be quite straightforward to implement this using the Energie SolarBox with the hot water feed from the heat pump fed into the central heating system instead of to the (secondary) cylinder coil - pretty much the same as a gas boiler would be connected.

This type of setup makes perfect sense for Scotland, I think, (even for sunny Dundee) where summer temperatures are often low enough to want a little bit of heating on occasionally. Nothing a jumper can't fix but if I can get that bit of heat for free then why not do it  ?

It will be later in 2014 when I get to install this, so won't be able to give any updates for a while.

report abuse


kaihoraComment left on: 15 November 2013 at 8:48 pm

In response to Jeff B's comment below:

The Energie thermodynamic panel system can be supplied with a so-called "SolarBox", see their website for further details. It contains a heat exchanger and controls and delivers a feed of hot water. This can then be plumbed to the heat exchanger coil of a hot water cylinder. Note, that "normal" indirect hot water cylinders have only one coil that is usually connected to a gas or oil fired boiler.

To be able to use this as well as the panel system you would need a cylinder with a second coil. These are usually called "solar" or "dual coil cylinder". However, as the Energie system is based on a heat pump you really need a dual coil cylinder designed for heat pumps. The key difference to a solar cylinder is that the second coil has a much increased surface area (Energie stated to me that 2 square metre should work fine). Heat pump output is cooler than solar panel output so a larger heat exchanger surface is required to transfer the heat into the cylinder.

I am in the process of picking through the details for my own home, where a new hot water cylinder is required in the near future. So buying one with a heat pump coil now for future installation of a thermodynamic panel system makes sense.

report abuse


likyComment left on: 14 October 2013 at 2:07 am

I found a new version of thermodynamic panel,which size is 1700X800mm.As the web introduce that the 2nd gereration panel is more effective. Is there anyone who are using this panel? 

report abuse


ScotsplumComment left on: 13 September 2013 at 2:17 pm

Hello I had one of these systems fitted in my house in December 2012 originally my hot water was supplied via a combi, I have found a number of  plus' in the installation and only one drawback so far. Plus # 1 My gas bill has decreased substantially (mind you no hot water demand using gas helps), plus # 2 system works even when its cold, raining or at night (despite being sold as a solar system). Plus # 3 Time delay of hot water at taps substantially reduced (that is due to usage of 22mm pipes for supply) plus # 4 definite increase in water pressure for shower (due to usage of mains pressure. The cost of Electricity to run the compressor and boost the water temp once a week appears to be 30p - 50p per week (and that is not bad for 30 gallons of hot water water at 55 C entigrade delivered every day) The biggest drawbacks I have seen is if the system needs repair finding someone qualified to repair it. (its a refrigerant so needs an F gas engineer, unvented cylinder so needs a certified installer and its a plumbing installation so needs someone competent. Another drawback is the Panel fitted outside the house cannot be hidden easily so any resale of the house could be difficult.

report abuse


andallComment left on: 22 May 2013 at 9:10 am

Has anyone had any experience of thermodynamic panels for central heating through radiators in a house that's 30+ years old, ie: not built to the current super-insulated new-build standards? I wouldn't buy them right now, but there's no reason why they shouldn't work.

report abuse


Richy_WhiteComment left on: 13 May 2013 at 12:07 pm

We installed a 200 litre system in January - set it to operate only when our PV panels were generating well so CoP is off the chart (simple plug timer 6 hrs per day).   Put a meter on to see how much electricity it uses - usage has dropped from 22units PER WEEK to 16 units per week now the outside temp is higher and temp of cold mains water is warmer.   We are not on gas grid so oil fired combi boiler now no longer switched on - all hot water supplied by the Energie system.   Simple mess free install.   Very happy with system so far.  Cautious but tech is pretty simple so it should be reasonably durable.   Tank supplied by installer is good quality.   See video of our experience here.

report abuse

Jeff B

Jeff BComment left on: 26 January 2013 at 10:37 pm

As I understand it, the Energie thermodynamic panel system requires you to purchase a special hot water cylinder which couples with the heat exchanger i.e you cannot use an existing DHW cylinder with it. Unless someone comes up with a system which will bolt on to my existing cylinder then I would not be interested. Obviously in addition I would be looking for such equipment to be MCS certified and eligible for RHI payments!

All-in-all I think it has to be a "wait and see" policy with regards these systems.


report abuse

Ben Whittle

Ben WhittleComment left on: 13 January 2013 at 10:50 pm

I guess the most important comparison with Solar thermal is that ST can operate at a COP closer to 15:1 (assuming low energy variable speed pumps are used), which knocks Thermodynamic panels into a cocked hat...

These are basically just heat pumps, and calling them anything else is just misleading. They are without doubt being mis-sold already. Which is not to say that a COP ratio of 3 is pointless, but I expect they will end up with the same reputation as air source heat pumps did for the last 5 years while companies try and overcome the bad press generated by dodgy sales techniques and poor installation quality.

report abuse

Cathy Debenham

Cathy DebenhamComment left on: 11 January 2013 at 4:58 pm

Here's a few comments on this blog from Linked-In:

"Designed for dry atmospheres in Southern Europe - minimum operating temperature is 5 degrees. No defrost cycle for cold and damp countries - that's the UK out! Mis-selling is a huge issue ... numerous complaints regarding the ridiculous claims being made." - Paul Hind, Secon Solar Ltd

"This is another product that will be heavily mis-sold and is already being done so by numerous companies. It does work but will one panel really provide you 100% of your heating and hot water requirements and if so at what COP?" - Gary Fuller, WINAICO UK LTD

"Very good idea in principle but I would like to see more UK specific information and research on them." Shaun Ackerley, Parsec

report abuse

Leave a comment

You must log in to make a comment. If you haven't already registered, please sign up as a company or an individual, then come back and have your say.