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Solar, wood, insulation: a case study of a home energy-saving retrofit

Posted by Tasha Kosviner on 20 January 2014 at 9:28 am

Heather Hullah and Jenny Barnes are not your average pensioners. Where other 60-somethings might be thinking about winding down, these two are more likely to be found wielding chainsaws and humping logs in their 2.5 hectare woodland.

But then Heather and Jenny’s ex-council house is no longer your typical three-bed semi either. With solar thermal, solar PV, a woodburner and underfloor heating, this 1950s home is a prime example of how, with a little research, cash and hard work, it is possible to turn even the most unpromising of structures into a beacon of energy efficiency and sustainability. 

Heather and Jenny bought their home in 2000, when, like most houses of its style and age, all it boasted in terms of energy efficiency was a bit of roof insulation, some aging double glazing and a decrepit hot water storage system linked to a 20-year old gas boiler in need of some serious TLC.

The first thing the pair did was take up an offer through their energy supplier to get cavity wall insulation and improved roof insulation up to a thickness of 50cm.

While they didn’t have a record of what energy consumption in the house was like beforehand, they estimate that the extra insulation, combined with £5,000 spent on new windows and doors, reduced the home’s energy requirements by 30 per cent. 

In 2008, with energy efficiency in the old part of the house taken care of, plans for a downstairs extension gave the couple the chance to experiment with heating via renewable energy. The brand new, heavily insulated garden room and adjacent utility room were furnished with underfloor heating, supplied from the existing hot water storage tank, which was then linked to solar thermal panels. When the sun isn't shining, the heat is topped up by the boiler, now a brand new condensing boiler.

Not content with a more efficient heating system, in 2011 they turned their focus to energy generation. A 1.9kWp solar PV system with a typical annual output of 1.5mWh was installed, consisting of eight Sharp ND 235Wp panels and a Sunnyboy SB1700 inverter. The panels reduced the home’s reliance on the grid from 4MWh/year to around three. The remaining 0.5mWh which they are unable to use as it is generated, is fed back into the grid. 

The final piece in the renewable puzzle came in the form of Jenny and Heather’s favourite innovation to date: a Westfire 15 woodburning stove, now fuelled through wood they harvest themselves from their own piece of sustainably managed woodland. The stove is rated at 5kW with an efficiency rating of 82 per cent. Heather and Jenny burn around five cubic metres of wood a year, generating 9mWh of heat.

“The stove effectively replaced our radiator central heating system, as the open plan layout of the house means that heat generated in the living room flows to the upstairs part as well,” Jenny reports. “It creates a very cosy, homely atmosphere and now we have our own wood supply, the fuel is effectively ‘free’.”

While not everybody has the privilege – or responsibility – of owning their own woodland, Jenny still maintains that the running costs of the stove is comparable to that of heating with gas, as the price for kWh of delivered wood and gas is similar. Consequently, the stove halved the couple’s dependency on gas, with no change in their monthly outgoings.

They were also delighted to be able to cook a casserole on the stovetop during a recent power cut.

Financial implications of Heather and Jenny’s super-green home?

While they installed the solar thermals too early to be eligible for the renewable heat incentive (only post 15 July 2009 installations qualify), they do receive feed-in tariffs (FITs) of around £800 a year for the solar PV. 

In terms of bills, the replacement boiler and solar thermal meant that bills remained much the same even after the extension, which increased the ground floor footprint by 50 per cent. 

What would they do differently?

With the benefit of hindsight, Heather and Jenny feel that the installation of the solar thermal panels was a mistake and that the roof space would have been better used by installing two more PV panels. This would have given them another £200 a year in FITs and saved them the higher cost of solar thermal installation over solar PV. 

“The underfloor heating and hot water could then have been provided by a combi boiler, which could also have run the central heating when we were not using the woodburner,” says Jenny. 

Their advice for people considering a retrofit:

  1. Insulate walls and lofts and double glaze first – there’s no point in installing expensive energy and heat generating technologies if your house itself wastes heat and power.
  2. If possible insulate under the floors for the same reason
  3. If you are on the gas grid, consider maximising solar pv rather than mixing it with solar thermal. Not only will you qualify for feed-in tariffs, you may also help save more carbon by feeding back unused power into the grid, displacing power generated from less ‘green’ sources. 
  4. Make sure your wood is well seasoned before burning. If possible, buy and store in bulk in the spring, when it’s cheapest, season through the summer and burn through the winter. 
  5. Only choose a woodburner if you’re fit and healthy – it takes a lot of energy to stack wood in a store and ferry baskets into the house each day. 
  6. Select a stove with a external air intake rather than an air brick: it's only slightly more invasive to install but it avoids the problems of a draughty air brick.

More information

YouGen guide to renewable heat incentive

YouGen guide to feed in tariffs

YouGen guide to solar PV

YouGen guide to solar thermal

YouGen guide to insulation

YouGen guide to woodburning stoves

From the blog

Is solar PV suitable for my home? (October 2010)

Can solar PV and solar thermal panels be successfully combined? (February 2011)

What to look for when buying a woodburning stove (April 2012)

Six tips for finding the best log supplier (April 2011)

Wood co-ops offer access to free logs (August 2011)

How to make the most of bio-energy (September 2013)

Solar thermal: 7 things to check before you install (October 2010)

Thermodynamic panels: your questions answered (January 2013)

Can I use solar thermal panels to heat my house? (December 2010)

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

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1 comments - read them below or add one


PaulTNCComment left on: 21 January 2014 at 5:09 pm

Well done, sounds excellent.

You might like to consider joining, a group of about 200 similarly converted homes, just as we have done. See here:


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