PV > House use = Water Heating

There seems to be a new entrant to the market for setting it up so that if your house solar panels (PV) are generating more electricity than the house is using, this gets auto diverted to an immersion heater to heat up your water.

So you use the water tank as an energy battery of sorts.

In the UK, you get paid via the Feed-In Tarriff system if you export to the grid or not. Plus a rate for what you do export, but that is a lot less than the rate at which you buy electricity if you need to. So these systems are said to save around £300 a year.

Thermodynamic Panels :: Happy Irish Customers

The Irish firm LVP Renewables have been installing Thermodynamic Panel systems in Ireland for a while. Their site has a big list of happy Thermodynamic Panel customer testimonials including:

We are a family of six-two adults and four children ranging in age from 13 to 21 years …. Having now had the system in for 10 months we are delighted with it and there have been no problems to date. We are never in need of hot water as we have had a constant flow since the systems installation in October 2011

Their FAQ page has a few interesting items:

Does this system need a back-up heating system during the winter?

No, this is the only solar panel heating system that will provide you with 100% of your hot water. Also our cylinders come with a mini-emersion inside that can be turned on manually if needed. However if you would like to incorporate a back-up heating system there is a provision for a secondary heating coil in most of the systems we provide (call for specific information on tanks). If you decided that you wanted the secondary coil in the tank then we would advise you to put a manual leaver on the system and only use it if necessary.

What is the difference between an Energie Solar Panel System and Solar Tubes or Plates?

Unlike traditional solar panels (tubes and flat plates) the Energie system offers:

  • No unnecessary annual maintenance checks. In order to maintain the maximum efficiency of tubes and plates they must be serviced annually.
  • LVP panels are lightweight (weighing only 8kg) and roof structures do not need to be reinforced. Conventional solar panels are heavy-weighing anything from 40-300kg
  • Energie Solar Panels absorb heat from both sides unlike traditional panels which only capture radiation on one side
  • One Energie panel (80cmx200cm) will provide a family of up to 6 people with all of their hot water needs. With traditional solar a large amount of panels is needed to provide similar quantities of water
  • Energie panels need no back up from oil or gas. Other solar panels need an auxiliary energy source when the sun isn’t shining or when in high demand
Is the system provided with any device to treat bacteria such as Legionella?

Yes. In accordance with current legislation, it is provided with a circuit to rise the temperature up to 70 Degrees, which is manually activated and automatically disconnected

What happens if we install 2 panels on the roof?

The heating time will be reduced by half

Thermodynamic Panel Case Study :: Cork (Ireland) water and space heating

Their site also has case studies including one for a central heating and domestic hot water system in Cork (so SE Ireland).

Most are about water heating only (no heating) with positive comments.

The Cork water and space heating was for:

  • 235 sq m 2 storey stone cottage with a large extension that has:
    – 4 bedrooms, 3 bathroom (1 en suite), 1 kitchen, 2 sitting rooms, 1 large hallway, 1 utility.
    The Silver Spray property is 281 sq m (4 bedrooms ….
  • Radiators (not under floor heating)
    – average water temp to the radiator circuit 45 degrees C input, 35 degrees average return temp.
    – the radiators give the property a 1000 litre water buffer !
  • 300 litre water tank.
  • I can’t work out what the figures mean !


Thermodynamic panel :: A happy user

One of the long GreenBuildingForum threads on Thermodynamic Panels has had some comments from somebody that installed one on their property in Northern Ireland, 18 months ago:

  • “I have had a thermodynamic panel installed for 18 months now and so far I can’t find fault with it.”
  • “It provides all the hot water requirements that is asked if it.”
  • “I have never switched on the built in immersion even when it has been -10 degrees outside and the panel has had an inch of ice on it.”
  • “I couldn’t justify solar as lets face it who wants something that only works well 7-8 months out of 12 then you need an additional piece of kit as back up, or pay £3000 per bole hole for a ground source heat pump when you don’t have enough land for slinkies or have their own personnel forest to supply a log boiler.”

Installed System

  • £4,100
  • Panel
  • 280 litre cylinder
  • pump and fittings
  • County Down, Northern Ireland
  • “Currently there are 4 showers every morning, plumbed to dishwasher and washing machine, and and usual washing in the sink when items don’t fit in the dishwasher.”

Beware of Thermodynamic Panels ?

I’ve been sent a scan of a one page article in the Clean Slate publication by the Centre for Alternative Technology (CAT, www.cat.org.uk) that has the title:

Think Twice about thermodynamic panels

Compared to an air source heat pump, a Thermodynamic panels is a heat pump connected to a flat panel instead of the heat exchange unit.

The article is concerned that:

  • Panel collectors might work well in some conditions, but badly in others.
  • That air flow can be poor around them,
  • That they can ice up.
  • That there are no studies on year round performance to back up marketing claims.*
  • They don’t qualify for the Microgeneration Certifciation Scheme (MCS). So, pending any updated clarification as what they are (heat pump?) they won’t qualify for the Renewable Heat Incentive (RHI).

* I’ll have to check, but a few companies and Internet sources do seem to have put their year round data on-line. OK these aren’t independent studies, but there is data about.

If the panel is running at low efficiency, then you have a low or zero coefficient of performance or COP. The article points out that consequent running costs at such times could be more expensive than gas (or even oil).

The report quotes an “Energie” thermodynamic system consuming 4.1 kWh of electricity to heat 250 litres of water from 10°C to 55°C with 15°C ambient temp. The 2.7 COP is “no better, financially or environmentally, than a modern gas boiler).

They say a conventional solar water heating system would use less energy and so cost less. The report references the Energy Saving Trust field trial ( I Google found the link).

The reports concern is that:

  • In winter a boiler would be more cost effective.
  • In summer a conventional solar water heating system will be better.

A conventional solar hot water heating system uses almost no fuel.

The CAT advice sheet on conventional solar water heating systems is here.

Confused Conclusion for Silver Spray Water Heating

The end solution for Silver Spray isn’t clear.

  • No mains gas.
  • Next to the sea (so an air source unit will fail and need major component repairs and replacement within 5 years.)
  • Cliff top and narrow plot, plus slope etc means ground source by buried pipes or vertical drilled holes both seem unrealistic.


  • There are going to to solar elec PV panels.
  • The house is going to be highly insulated and sealed, so there will be a low space heating requirement.

So if Thermodynamic panels can have a good chunk of their winter electricity from the PV panels, they could still be the best solution.

Thermal Store

This is part grabbing historical Thermal Store notes to one page, and part adding new notes.

Click here for notes on Thermal storage – pros & cons.

Looking at the Akvaterm thermal stores (which can go up to 5,000 litres !!)

From www.stovesonline.co.uk/wood_burning_stoves/Akvaterm-Geo-Thermal-Stores.html:

  • have a stratification baffle plate about a third of the way down the tank. (see photo below). This can be optionally upgraded to an insulated baffle to further improve performance but the added benefit is not huge as it is very good already.
  • Once the water above the baffle has been heated to a high temperature by the heat pump (50ºC-60ºC) it then shifts to heating the bottom two thirds of the tank to a much lower temperature suitable for underfloor heating (around 40ºC).
  • OR if / when the heat pump is generating lower temp water (often more efficient COP) it only targets the bottom section.
  • larger than normal lower domestic hot water coil. This is to ensure that the incoming mains water picks up as much heat from the bottom of the tank which holds the ‘cheaper’ heat produced at a high C.O.P.

From www.ecoangus.co.uk/Akvaterm_Solar_Plus_Accumulator_Tanks.html:

The AKVAir Solar Plus is available from 300-2000 litres and is 3 bar pressure rated. The tank has 4 coils, two for solar input and two for domestic hot water (DHW) and is divided by a baffle plate, approximately 60% below and 40% above the baffle. Each section contains one solar and one DHW coil and all coils are positioned vertically.

The AKVAir Solar is available from 300-2000 litres and is 3 bar pressure rated. The tank has 3 coils, one for solar input and two for domestic hot water (DHW).

From www.accumulatortanks.co.uk/Solarplus.htm:

Akva Solar plus coils diagram   Akva Solar diagram key

Akva Solar Plus coils + baffle plate     Akva Solar Plus coils


From www.akvaterm.fi/eng/Accumulators/AKVA_SOLAR.41.html:



From www.akvaterm.fi/eng/Accumulators/AKVA_GEO.206.html:

  • AKVA GEO is suited to all heat sources (others seem to be solar or something specific).
  • example layout:



From www.navitron.org.uk/forum/index.php?topic=14183.0:

Heating System Schematic

Dual Cylinders?

From www.chelmerheating.co.uk/dual_cylinder_thermal_store_systems.html:

  • For larger domestic and commercial projects, our dedicated heating buffer cylinders are used in conjunction with our high-gain unvented cylinders to allow greater variation between heating and hot water demand.
  • The separate low-temperature heating buffer allows the small, infrequent heating demands of a property that is “up to temperature” to be met by stored renewable energy before activating the heat pump/boiler to reduce wasteful on/off cycling.

Thermodynamic Hot Water – Comparing Running Costs

A great article on Energie Solar Thermodynamic Hot Water – Comparing Running Costs.

Also look at this post about how they see the systems working, being installed etc.

Looking at the The Energie ECO 200is:

on a really good day (sunny and warm) it will supply at most 4.55 kW of energy and will consume 595W. On a bad day (cold night) it will supply 2.8 kW and consume 890 W – so the coefficient of performance would vary from 3.14 to 7.64 – so for every unit (kWh) of electricity you consume you would return between 3.14 and  7.64 kWh of heat for hot water.

As of February 2012 average gas prices were 4.1p per kWh and electricity averaged 13.7p per kWh. Gas (and oil) boilers have a small level of inefficiency (at best they are 90% efficient over the year)  and thus the cost per kWh of “heat to the water” would be 4.56p. With the Energie system the cost would average at 2.54p (13.7p divided by 5.39).

Annual running cost per kWh:
–  Energie 200is, £0.28
– Gas boiler, £0.51
– Oil boiler, £0.77

Thermodynamic Panels from Jewsons?

I first saw the Thermodynamic panels on the Jewson stand at Eco Expo in London in early 2012.  They now have more info on them, on their Website:

Jewson is the only national builders’ merchant with exclusive rights to the new and innovative Thermodynamic Atmospheric Energy Panels, which can generate 100% of hot water and heating requirements all year round.

In terms of getting them installed:

Trade professionals should be aware that to be able to install the panels, they will need to be F-Gas registered and to have attended an official installation course. Both of these courses will shortly be offered at our Greenworks Training Academy.

The Jewsons blog implies they will be eligible for the RHI (Renewable Heat Incentive).

  • See the comments at the bottom of http://blog.jewson.co.uk/2225/were-all-going-thermodynamic
    “You can find further information at http://www.greenworks.co.uk/. Also, although independent test data is available from Europe and has Solar key mark so is eligible for Renewable heat incentive in the UK, the product is currently gaining independent testing through the BRE in the UK and the data will be available shortly.” 21-09-2012

BUT (10 Nov 2012) update to this post

From http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9761&page=1#Item_22:

  1. I called into my local Jewsons this morning to ask about the panels and what information they had.the guy on the front desk was a waste of time, did’nt know they did solar panels of any description, so I explained what it was I wanted and the guy in the office chipped to say they had been discontinued. Suggested they neededto update the web site and was told where to get off!!! Great customer service!

Thermodynamic Panel Installation Cost

This http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9762&page=1#Item_3 thread on how much should they cost:

I have had two quotes ranging from 6k-9k and I am not sure how much these are and how to compare the two?

I’ve asked a couple of people in the trade what they should cost, and have been told c. £5,500 for one panel and a 250l cylinder

certainly don’t pay over £5k for a single panel and 250l tank fully installed.

TBH I don’t really see why it should need to cost more than around £3.5-4k if you deal with an installation company instead of a sales company, …… with the commission structure.

One thing though is I think there’s probably a temporary shortage of people with FGas certificates along with the other qualifications, for installing this in line with the regulations, which is probably keeping some competition out of the market. If you need a hot water solution now then fair enough, if not then it’s probably better to wait a few months for the dust to settle.

Thermodynamic Hot Water Payback Period and Running Costs Compared to Fossil Fuels

A fantastic article comparing the cost of a Thermodaynamic panel heat exchange system with fossil fuel systems to heat water.


For the Silver Spray  site, we do not have mains gas, so the Vs oil option.

It’s key to note, that at the moment, it is not expected that Thermodynamic panels will qualify for the RHI (Renewable Heat Incentive Payment). Indeed Pete at cernunnos-homes.co.uk dropped me an email to say that “that the system is suspended from the MCS scheme as of the 18th November.”