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How do energy suppliers compare for green energy generated?

Posted by Alex Barrett on 24 May 2016 at 1:45 pm

Q. I am keen to switch energy providers but the one I favour says it cannot tell me how much of its energy is generated from green sources. This is an important criterion for me and I am a little suspicious of this company's supposed ignorance. Is there a definitive information source that states the green energy each energy company generates?

A. All energy companies are required to publish their fuel mix, this is the proportion of the energy they generate from each source; coal, gas, nuclear, renewables and other sources. This information can be found on the websites of the energy companies, but isn’t always easy to find.

Here we’ve compiled the latest figures from the big six energy companies, for the financial year from 1 April 2014 to 31 march 2015. The average fuel mix across all UK energy generation is also shown for comparison. 


% Coal

% Natural Gas

% Nuclear

% Renewables

% Other

British Gas
























Scottish Power












UK Average






These companies also publish figures on the amount of waste that is produced by their energy generation. The table below shows the mass of carbon dioxide emissions and high-level radioactive waste produced by each of these companies during the same period.


CO2 Emissions g/kWh

High-level radioactive waste g/kWh

British Gas












Scottish Power






UK Average



The proportions are quite varied, but it is encouraging to see that renewables have a fairly large share for each company. SSE have the largest proportion of renewables in their fuel mix, at 37%.

The smallest proportion of renewables is at EDF, however they have the largest proportion of nuclear power in their fuel mix. This means that they actually have the lowest CO2 emissions, despite their low share of renewables. The downside of this is that the mass of radioactive waste they produce is much higher than most of their competitors.

Scottish power use the largest proportion of coal at 46.4%, while npower use the largest proportion of natural gas 59%. When considering fossil fuels as a whole npower comes out worst. 80% of their fuel mix is generated from coal and gas.

The lowest proportion of coal is at British Gas, while EDF use the least natural gas in their fuel mix. Overall EDF have the lowest share of fossil fuels, just 28.7% of their fuel mix uses coal and gas. However this is offset with nuclear power rather than renewables, so how green they are may depend on your opinions on nuclear power.

These companies are far from the only options when it comes to sourcing sustainable electricity. Many smaller energy suppliers have much larger proportions of renewable energy, and market themselves as being green alternatives to the big six. Ecotricity and Good Energy both use 100% renewable sources, while Green Star uses 99.8% renewables.  

Some energy companies also offer green tariffs, which allow you to ensure that a certain proportion of the energy you use is being generated by renewable sources. Companies ensure that they have enough renewable generating capacity to cover that used by customers with a green tariff, so choosing one of these options encourages more renewable energy to be generated overall.

While there is not yet enough renewable capacity to cover all of the UK's energy demand it is increasing all the time. On 10 May 2016 all UK electricity was briefly generated without coal for the first time since the industrail revolution. The government hopes to phase out coal fired power stations by 2025, although whether this is yet feasible remains to be seen. As the share of cleaner energy sources grows events like this will hopefully become a more regular occurrence.


British Gas




Scottish Power


Electricity Info: Share of renewables across a wider range of companies, Table of Fuel Mixes for all companies

Ofgem: Latest fuel mix statistics for the UK as a whole

The Energy Saving Trust: Information on green electricity

The Guardian: UK energy from coal hits zero for the first time in over 100 Years

Gizmodo: UK power generation to go coal free by 2025

Also on the blog
Where did green energy tariffs go?


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

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4 comments - read them below or add one

Alex Barrett

Alex Barrett from Comment left on: 1 June 2016 at 12:18 pm

In response to the comment by SolarWind. These numbers are for the UK fuel mix, so only Électricité de France's UK based generation capacity is included. We currently only have a handful of interconnectors to mainland Europe, a 2GW link to France, and a 1GW one to the Netherlands. This means that EDF's French nuclear power stations don't provide much energy to the UK.

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Alex Barrett

Alex Barrett from Comment left on: 31 May 2016 at 9:59 am

Hi Ian,

You are quite correct, in that it is the overall carbon intensity of the whole system which is important. This can be quite a tricky issue due to the way the electricity grid works. We may buy electricity from one energy company or another, but they don’t maintain separate distribution networks. Rather all nearby generators are responsible for providing our electricity, not necessarily the ones operated by our chosen energy companies.

The easiest way to put it is to say that all of the electricity is mixed together when it is distributed. I don’t really like that analogy, as it makes it sound as though electricity is a physical thing, which isn’t really the case.

A better way of looking at it is that each energy company knows how much energy their customers need at any given time, and puts enough energy into the system to meet that demand. This energy is then distributed as electricity, but the energy that customers receive comes from whichever power stations are most convenient, not necessarily the ones that the company in question operates.

When a company says that they use 100% renewable energy they just mean that all of the energy they put into the grid comes from renewable sources, not that the electricity that their customers receive was generated by solar panels or wind farms. If you live right next to a nuclear power station, then it will probably be producing the energy you consume, even if you pick a green tariff.

In this sense trying to work out where the electricity we use “comes from” is largely irrelevant. Electricity in itself is neither carbon intensive nor carbon neutral, it is just a medium through which energy is transmitted. I’d argue that what is important is the overall greenhouse gas emissions of each company’s operations. The more renewables (and arguably nuclear) they use, the less GHGs they will be contributing to our overall emissions. In this respect choosing a green tariff, or a company with a high share or renewables in their fuel mix encourages development of cleaner energy, even if what we ourselves use is anything but.

The Renewable Obligation ensures that all companies have to produce a minimum fraction of energy from renewables. If a company sells on a certificate this essentially means that they are using some of their renewable generating capacity on behalf of another company which wouldn’t otherwise meet its obligations. This doesn’t change the overall fuel mix of either company, it just allows one with more renewables than required to cover for those that don’t have enough. I’d certainly prefer all of the energy companies to meet their obligations by installing more capacity, rather than buying from those with an excess, but I don’t think that this makes the green credentials of the company selling the certificate any worse. If anything the fact that they are exceeding their obligations is encouraging.

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Solar Wind

Solar WindComment left on: 30 May 2016 at 5:47 pm

You need to look on the bright side. EDF stands for Electricity De France, so all the neclear is generated in France and that is where the waste is to.

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Ian Smith

Ian SmithComment left on: 28 May 2016 at 11:16 am

Alex, could you possibly extend this article to cover the implications of the Renewables Obligation?  If, say, utility X claims to generate all its electricity from renewable sources and does not sell on the Renewable Obligation Certificates that it earns from doing this, then one can treat its output as genuinely zero/low carbon.  However, if utility X then sells some of the ROCs to another utility so that that utility can meet its obligations for achieving the minimum level of 'greenness' in its supply, then the physical electricity sold by utility X cannot be as low carbon as if it had not done sold the ROCs.  In fact, it might make sense to treat the carbon intensity of  the electricity representing the proportion of ROCs sold as having an average  intensity for the whole system.  One needs to distinguish between claims that electricity is generated or sourced from renewables and its carbon intensity.  I am interested in the latter in choosing a supplier, not the former.

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