UK fuel mix: how clean is your electricity?

The power that comes out of your wall from the national grid comes from a variety of sources: smoke belching coal plants, clean hydroelectric dams, or controversial nuclear reactors.

A smokestack belching smoke

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Different energy companies use a different fuel mix, and as a result the electricity the national grid supplies us differs in how green it is. If we want to be green,where should we get our power from?

Fuel Mix

By law, all UK energy companies have to publish their “fuel mix”. This is the proportion of their power that they get from various sources. From this we can put some actual numbers on how clean the different companies are:

SupplierNuclearGasCoalRenew.OtherCO2 Intensity
CO2 emissions
Cost on bill
External cost
Cost including external
Npower2%55%29%12%2%0.4741565£516.71£63.28£ 579.99
Brit Gas27%50%14%8%2%0.3161042£448.08£38.78£ 486.86
EDF / Sainsbuys69%0%28%3%0%0.253834£488.27£60.60£ 548.87
Eon6%49%30%11%4%0.4761570£499.56£69.23£ 568.79
Southern / Scottish Hydro / Swalec / Atlantic / M&S /Ebico1%49%35%14%1%0.5011653£485.42£71.09£ 556.51
Scottish Power0%40%47%14%0%0.5681874£483.23£88.80£ 572.03
Ecotricity*2%20%12%64%2%0.191630£488.31£28.82£ 517.13
Good Energy0%0%0%100%0%00£485.20£1.82£ 487.02
LoCO20%55%0%45%0%0.198653£ 452.31£7.90£ 460.21
Utility Warehouse2%55%29%12%2%0.4741565£ 436.02£63.28£ 499.30
First Utility6%52%32%5%4%0.5001651£ 564.50£73.76£ 638.26
Ovo*5%39%24%29%3%0.3771244£ 403.79£56.01£ 459.80
Green Energy UK*0%64%0%36%0%0.230760£ 460.44£8.89£ 469.33

*These suppliers also offer a fully green tariff that has the same 100% renewable fuel mix as Good Energy.

This table assumes the average UK domestic electricity consumption of 3300kWh per year. Prices shown are valid for October 2012 or the price rises due in Nov 2012 where applicable. Tariffs compared were the standard online dual fuel rate and do not include any special deals for new customers.

What is the “external cost”?

It’s a way of putting a number on all the damage done by emissions. It includes global warming potential, other environmental damage (such as acid rain), and health problems and deaths from air and water quality. The worst offenders are dirty fossil fuel power stations like coal and oil, but even renewable sources aren’t zero impact (they’re just very low).

When expressed as a monetary value, it represents the amount you’d have to pay extra to offset the actual damage from the emissions. Simply put, the lower the external cost, the cleaner and more sustainable the source. This is a more broad-ranging metric than simple CO2e emissions, which only evaluate global warming potential and none of the other negative impacts.

The actual numbers used (in pence per kWh): coal = 5.4, gas = 0.39, nuclear = 0.48, renewable = 0.055, other = 6.05. (source: Pearce et al 1992). Fuel mix multiplied by this number gives the external cost, and the annual total shown above is for 3300kWh.

But isn’t all power from the national grid the same?

No. While it’s true that even if you’re on a 100% renewables deal the actual electrons that reach you may have come from another source, the fact of an electricity supply contract is that it’s a two-way transaction. Electrons flow to you from the grid, and money flows away from you to your supplier. It doesn’t matter if the electrons you actually consume come from a coal plant at the end of your road, if the money you pay your power company obligates them to purchase the same amount of green energy and feed it into the national grid (possibly at a different time from when you are consuming electricity). The net result is that your consumption has caused the same amount of that type of electricity to be generated and fed into the grid. So there really are “green electrons” and “dirty electrons”, it’s just that the process is abstracted a little by the presence of the national grid.

What stands out?

Even within the Big 6 energy companies (not known for their greenness) there’s a wide variation in the quality of the supply. When you look at just CO2, EDF and British Gas are surprisingly good, getting almost as low as some of the smaller specialist green suppliers. However, EDF only gets so low because of all their nuclear plants, and this shows in the overall impact where they fall back into the pack of dirty offenders. In the long run, the green suppliers like Good Energy, LoCO2, Green Energy UK and Ecotricity all come out well ahead, although British Gas is actually not far off them (and is cheap!).

Npower is the worst of the big six, being both dirty and expensive. But if you want the absolute worst deal in Britain you’ll be heading off to First Utility.

Scotland is a country keen to promote it’s renewable resources but unfortunately the Scottish companies seem to be topping up their decent renewable percentages with a lot of coal, so end up being some of the dirtiest. Oops.

Ovo are the cheapest overall, but LoCO2 only cost £1 more a year and emit about half as much CO2. If you go with Ovo, use their proper green tariff, as their standard one is pretty dirty.


If you want the cleanest electricity available you can’t beat Good Energy, LoCO2, or the green tariffs from Ecotricity, Ovo and Green Energy UK. If you want to go with a major supplier, British Gas is by far the cleanest electricity.

Disclosure: I’m a Good Energy customer, and wholeheartedly recommend them. If you’d like to switch to them and get a £25 bonus for us both, please get in touch.

Pearce, D.W., Bann, C. and Georgiou, S. (1992) The Social Costs of Fuel Cycles, Report to 
the UK Department of Energy,
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This page last updated 22 October 2012