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.

£50,000 printed house released by WikiHouse

From: http://www.technology4change.com/page.jsp?id=312

Looking at the details in the PDF, a lot of the ideas are similar to those being used by ecofab for my project:
– see some screen grabs below.

From the article:

WikiHouse has released the design for a £50,000 printed house for the UK that could help tackle problems like urbanisation, climate change and inequality, say creators.

The design is the latest creation from the non-profit project that has been developed to help produce low-cost, high-performance houses that are suited to local needs.

The project, called WikiHouse, is an open source construction system which makes it possible for anyone to design, share, download, adapt and ‘print’ houses.

Users of the system can ‘print’ house parts from a standard sheet material like plywood, and the main structure assembled in about a day without the need for conventional construction skills, say creators.

“The open secret is that in reality almost everything we today call architecture is actually design for the 1%,” said WikiHouse co-designer Alastair Parvin of London-based design studio 00.


“The challenge facing the next generation of architects is how, for the first time, we will make our client not the 1% but the 100% – to radically democratise the production of architecture.”

He added: “We are moving into a future where the factory can be everywhere – and increasingly the design team can be everyone.”

WikiHouse is currently under development, with a growing community of teams and is seeking collaborators and funders.

Wall panel layers:





Assembled wall panel:

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.

Green Roof & PV

From the Winter 2012 copy of Green Building Magazine (volume 22, No3).

Two green roof studies. One, carried out in Berlin, where green roofs had been installed in the 1980’s. They varied the PV arrays to find the most efficient:

  • Over 5 years, PV panels over a green roof Vs a bitumen roof has 6% higher yields.
  • If over a green roof AND on a swivelling stand that tracks the sun, then 10% higher.

So green roofs boost PV productivity AND as they insulate the roof, they decrease the amount of energy needed for heating and cooling.


The second study looked at planting schemes. The most popular current choice is sedum, du to high resistance to draught. Sedum was compared to Stachys byzantian, Hedera hibernica and Bergenia corifolia.

Stachys byzantina (commonly known as Lamb’s Ear) outperformed the other species in terms of leaf surface cooling, cooling the substrate beneath it’s canopy and even the air above it’s canopy during short intervals over hottest periods, when soil moisture was not limited.

The conclusion was to not choose the best plants for a shallow substrate, but those that provide the best all round environmental performance, including bio diversity. This may involve deeper substrates and some form of irrigation.

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.”

Thermodynamic panels WILL or WON’T get the RHI?

Looking at multiple posts on the http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9761&page=1#Item_0, discussion, Thermodynamic panels don’t look likely to be a part of the Renewable Heat Incentive payments that are due to start in 2013.


The 21-09-2012 reply from Jewsons (” the only national builders’ merchant with exclusive rights to the new and innovative Thermodynamic Atmospheric Energy Panels”) to this blog post of theirs, 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.

suggests they believe Thermodynamic Panels will get the RHI


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

  1. DECC held a RHI webchat yesterday and, as part of that, confirmed that thermodynamic panels will not be eligible for RHI until they are MCS accredited.

A users feedback on Thermodynamic Panels

From http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9763

We have been in our house for almost a year now, tried to build to passishaus standards and despite plumber, electrician and MVHR installation problems (see previous discussions if clarification needed), the thermodynamic panel is one piece of kit that i cannot fault. There is a backup immersion fitted and has never been switched on and we have had 60 degree hot water every day without fail. I have seen the panel completely white with frost and still no bother with hot water. I am in no shape or form connected to any company that sells or installs the panels, but I have no problem recommending the technology.

Carbon Neutral Woodstove!

From http://www.houzz.com/ideabooks/4651034/list?utm_source=Houzz&utm_campaign=u176&utm_medium=email&utm_content=gallery20

Some models are carbon neutral. European woodstoves using the Nordic Ecolabelsystem are so efficient that the carbon emitted when they’re used properly is equal to the carbon a tree naturally emits while decomposing in the forest.

Appliances generating the most CO2 by 2016?

I’m not sure I’ve got this right, but I think the http://www.nhbcfoundation.org/Researchpublications/Energyefficientfixedappliances/tabid/518/Default.aspx post means that a 2016 built house (if to the regs !) will have the main areas of CO2 emmissions in order of magnitude as:

  • appliances (49%)
  • space heating (22%)
  • water heating (11%)
  • pumps and fans (10%)
  • lighting (8%)

So I’d better get those best rated appliances and building control systems for the kitchen and elsewhere.