How is it all performing?

The total cost of running our home, before it was extended by about 50 percent, was largely dictated by the cost of oil but we also used electricity for the usual household appliances and cooking. Our first prediction of the annual cost of energy for the extended property was approximately 45 percent of the previous amount for the smaller house. The first THREE year's results are now in!  The total energy used in the year ending 28 February 2010 was 42.93% of the average over the previous 3 years.  The savings are even better than we previously thought.  Year 2 ended on 28 February 2011 with our energy costs 36.5% of the previous 3 year average when oil prices were lower.  With oil costs today of 62p per litre we would have been paying around £2600 per annum for oil alone and a further £550 approx for electricity - this for the house before extending it by around 50%. This gives a percentage comparative cost of 32.8%!  Insulation accounts for much of this, plus the efficiency of the GSHP and underfloor heating.  The solar PV and solar thermal panels on the house have also played a useful part in reducing our need to import as much electrical energy from the national grid. Year 3 ending 29 February 2012 was similar to Year 2 in energy cost at 36.6% on the same basis but the energy used was reduced over the full year and the increase in electricity price per kWh resulted in a very similar overall result.

For the 365 days from 1 March 2009 to 28 February 2010 it cost an average of £3.27 per day to run everything, heating, hot water, cooking, washing machine, dishwasher, televisions etc.  In Year 1 we saved over £1600 per year on the energy to run our home and further savings of more than £200 on servicing and insurance as explained below the first chart. In Years 2 and 3 we have saved even more, the cost of all our energy has fallen to £1033.20. The FIT returns and savings approximately cover the cost of running the house.   The average cost per day over the past 561 days to 12 September 2012 has been £2.44.

The improvements in insulation and in the heating/hot water systems have resulted in the Energy Performance Certificate (EPC) for the house producing ratings of C (77) for Energy Efficiency and C (78) for Environmental impact.

If the government had included existing, pioneering solar PV systems in its feed-in tariff (FIT) proposals, as natural justice would suggest, then each kWh of electricity generated would have earned 41.3p for systems retro-fitted to existing dwellings.  NB the rates were increased for qualifying installations from April 2011 to 43.3p/kWh and 3.1p/kWh for any exported (usually assumed to be 50% of the units generated). The FIT started on 1 April 2010 and is paid even if the electricity is used on site.  In addition there is a small amount extra paid for any electricity which is exported to the grid, 3p per kWh (3.1p/kWh from April 2011).  This FIT will significantly influence the "pay back time" of the solar PV.  As a guide, the 2120.0 kWh of energy generated by the solar PV panels from 10 Feb 09 to 31 Mar 10 would have earned £907.36 in cash back (half the energy being deemed to be exported and earning the extra 3p/kWh).  Because the energy generated has reduced the need to import electricity there would be an additional saving of over £100.

The latest FIT for the Garden Room array, which qualifies for the full FIT payment, is 45.4p per kWh generated plus 3.2p extra for half the generation which is deemed to be exported.  These rates have increased roughly in line with the Retail Price Index (RPI), as promised, from 1 April 2012.

 A similar Renewable Heat Incentive (RHI) is proposed which will apply to microgeneration of heat from GSHPs and solar thermal panels, for example.  An announcement of some of the details of the RHI has now been made and has started for commercial premises, but the final details for households have been postponed to 2013.  A limited trial is now in operation but there is still a great deal of uncertainty about the outcomes.  As stated below, if it were me, I would await the results of the trial and take a decision when the final document is published, especially the returns for each kWh of heat generated from renewable sources .  Cynical, yes, but the Pioneers of PV were badly treated by the government(s) over the Feed-in Tariff.

It might be wise to see what happens to existing PV systems, now the cash back has started, to see if they continue to be excluded from the FIT, before installing thermal based equipment or you too could be penalised for trying to lead the way in promoting renewable energy.   Present information seems to indicate that those who have already installed renewable energy systems and are actively promoting the reduction of their own carbon emissions, and those of the country, are going to continue to be excluded from the full FIT rates, at best, or totally excluded from any benefits at worst.  The coalition government may eventually treat the "pioneers" more fairly and, in response, they will act as free ambassadors for renewable energy out in the country reducing the need for expensive advertising campaigns and the need to "police" the system as people try to get around the rules. An opportunity has been missed in the recent review of FIT tariffs, when the pioneers could have been moved to the new 21p/kWh rate.

The commercial scale PV farms which benefit hedge funds and wealthy investors have been excluded from the full FIT rates from September 2011, in favour of the fixed "pot" being used to encourage the installation of PV arrays on house roofs and SME buildings.  This would have been an appropriate time to include the "pioneers" at the same rate as the late adopters, but so far the government has not gone down the "fair" route promised before the election.  I live in hope!

This table shows the energy generated each month by the solar PV panels on the house (only 18 days in February 09 after installation and data up to 12 September 2012) and the average energy generated per day so far.  Garden Room solar PV is now shown in the second chart below and will be included in the table eventually.


Energy Generated kWh

Average Energy generated per day  kWh/day

February 2009

61.0 3.39
March 165.9 5.35
April 211.5 7.05
May 246.8 7.96
June 252.7 8.42
July 247.9 8.00


218.7 7.05


171.3 5.71



November 80.7 2.69
December 68.6 2.21
January 2010 47.4 1.53
February 65.1 2.33
March 167.0 5.39
April 223.8 7.46
May    266.3 8.59


259.1 8.64
July 235.9 7.61
August 198.3 6.40
September 161.9 5.40
October    125.2 4.04
November 76.4 2.55
December 47.3 1.53
January 2011 54.4 1.75
February 57.0 2.04
March 148.5 4.79
April 249.5 8.32
May 254.4 8.21
June 253.5 8.45
July 228.9 7.38
August 203.0 6.55
September 191.9 6.40
October 130.3 4.20
November 54.6 1.82
December 56.3 1.82
January 2012 67.1 2.16
February 95.8 3.30
March 193.5 6.24
April 158.2 5.27
May 239.1 7.71
June 193.5 6.45
July 206.1 6.65
August 199.6 6.44
September (to 11 Sept 2012) 89.5 8.14
TOTAL 7038.9
CO2 saved


Using ghg conversion factor from DUKES (Digest of UK Energy Statistics) 


Garden Room PV chart


Other savings include over £100 per year on boiler servicing and the same on boiler breakdown insurance.  The GSHP requires no service, being a large fridge working in reverse. When did you last have your fridge serviced? There is very little to go wrong with any of the systems but it may be necessary to replace a pump at some stage, although these are easily changed and not expensive. The solar PV panels are guaranteed to work at least 80 percent as well as new after 25 years and all that is required for maintenance is an occasional clean.  Our window cleaners,, use a high tech carbon fibre pole system alongside traditional methods and so all the solar panels are easily cleaned every few weeks.

The chart above shows the net weekly energy use of the house, to Saturday 8 September 2012, in kilowatt.hours.  One kilowatt hour (1kWh) is one unit of electricity as shown by your electricity meter and this costs around 8 to15 pence depending on your electricity provider.  Some electricity companies offer tariffs which supply their electricity from renewable sources such as wind and hydro and, by opting to use these, it is possible to reduce your carbon footprint to much lower levels.   Up to 14 January 2010, we were paying an average of 8.61 pence for every unit we used and electricity is our only energy import since we have no gas, no LPG and no longer use any oil.  From 15 January 2010 our electricity supplier, EDF, increased our tariffs and so from February we changed to a better deal with the same supplier.  We paid an average of 7.31p per kWh over a one year period.  Yet another tariff increase occurred on 1 Jan 2011, with us paying an average of 7.89p/kWh. The latest price rise in July 2011 was to an average of 9.91p/kWh. 

Unfortunately the changes in available tariffs offered by EDF from January 2012 discriminated against large users of electrical energy ie totally electric homes (off the gas grid). Their best tariff would have meant our average cost per kWh would have risen by a massive 58% over a 12 month period!  We therefore moved to OVO energy which not only gives us a better average rate per kWh, of 10.13p, but also is highly rated for customer service by Which? members.

Previous visitors to the website may miss (probably not!) my ramblings about the changing weather conditions which explain the above chart on net energy use of the house.  I feel it was getting too long and not of sufficient interest for most people so it has gone!  I do seem to be starting again on page 2 however, sorry!

Fifteen digital thermostats automatically control the underfloor heating in various areas of the house.  In colder months, some rooms which are not being used can be set to a low temperature, and the door kept closed, whilst others such as the lounge, for example, can be heated to 22 degrees C in the evening for greater comfort.  Each thermostat can be programmed with 4 different temperatures during each day and each one can have its own unique timing for switching temperatures. 

The Underfloor Central Heating downstairs is above 100mm of solid insulation and then covered with screed (a sand and cement mix).  This means the floor has a large thermal mass and does not heat up or cool down rapidly like a radiator does.  The upstairs UFCH is also insulated underneath and then has flooring boards over it plus special Heatflow underlay and fitted carpet, except in the wet rooms which are tiled.  Therefore the upstairs responds more quickly to requests for large temperature changes owing to the floor's lower thermal mass.  Since the whole house is controlled by room thermostats, and any programmed temperature changes are small, a pleasant temperature is maintained throughout the 24 hours with small changes when required.  For example, the kitchen and dining room are increased in temperature ready for breakfast and the lounge is raised by 2 degrees for the evenings.

If you are interested in learning more about generating your own energy, its suitability for your home and guidance on the cost of installing renewable energy then you may like to visit the Energy Savings Trust website.

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