Monday, August 31, 2009


Last week I did an analysis of my energy bills for the last year. The results in terms of average power consumption over the past year are:-

Gas: 205 watts, 4.9 kilowatt-hours per day
Electricity: 99 watts, 2.4 kilowatt-hours per day
Total: 305 watts, 7.3 kilowatt-hours per day

These figures are adjusted to take into account the time I am away from the flat, when no gas is used and very little electricity.

According to my calculations, the UK average for total domestic energy consumption per person in 2008 was 992 watts or 23.8 kWh per day. That makes my consumption about 31% of the national average per person when I am in my London flat.

It is tempting to think that if my figures became the national average and similar savings were made in the non-domestic sectors (eg transport, industry and commerce), then the UK could achieve a 69% reduction in its carbon emissions without any switch to renewables. However, there are some special factors.

Firstly, my flat is only about 2 km from the centre of London. With the urban heat-island effect, this means that I must be living in one of the warmest parts of the UK.

Secondly, last winter I was probably "free-riding" on my neighbours' heating. I used my central heating very sparingly - not at all for many weeks - and aimed only to keep the temperature in my living room at or above 15C, often resorting to a body warmer over my sweater. I have three exterior walls and I am largely isolated by a staircase from the next-door flat but I have a flat above and below me. If the occupants of these two flats kept their living-room temperatures at a more normal 20C, say, then they will have been paying their heating bills partly to keep me warm. Serves them right for not being eco, but if they adopted my practice of living at 15C, I would probably need to use more gas to keep up to that temperature. All in all, 69% probably overstates the amount by which domestic energy consumption could be reduced if people adopted my lifestyle - but by how much I don't know.

A few boring details - for enthusiasts only

The exterior walls of the flat are 11 inch cavity walls, both leaves of which are dense brick, with internal plastering. The cavity is filled with rockwool. Additional wall insulation would cost me a lot of floorspace. The windows are double glazed, the frames being UPVC over aluminium, and in my living room, where I spend most of my indoor waking hours, there is secondary glazing in addition, giving me triple glazing in effect. Practically all my light bulbs are compact fluorescent. My boiler is nine years old and not a condensing boiler, so further economies are possible there. I have a fridge but not freezer and use my television and hi-fi very little. The main calls on my electricity are fridge, lighting, computer and an electric kettle.

My calculation of the national average domestic energy consumption is as follows:-

Total domestic energy consumption in 2008: 45,985 thousands of tonnes of oil equivalent (Source: Office for National Statistics, Monthly Digest of Statistics, July 2009, Table 8.2)
Multiply by 11,630 x 1,000 to convert to kilowatt-hours (kWh) - the conversion factor of 11,360 is given in Department for Business, Enterprise and Regulatory Reform, Digest of United Kingdom Energy Statistics 2008, p17
Divide by 366 (2008 was a leap-year) to give consumption per day
Divide by 61,383,000 - 2008 mid-year estimate for UK population (Source:, accessed 31 August 2009)

Daily energy consumption = 45,985 x 11,630 x 1,000 / 366 / 61,383,000 = 23.8 kWh / day
Multiply by 1000/24 to give power consumption in watts = 23.8 x 1000 / 24 = 992 watts