Lifecycle carbon emissions

Here’s an explanation of how we calculated Lifecycle Carbon Emissions

Step 1

First, for each supplier, we have to find out what proportion of their electricity comes from the various different generation sources such as coal, gas and nuclear. This is the easy part because all suppliers have to publish this information annually as part of their Fuel Mix Disclosure data. This is a requirement of our industry regulator – Ofgem.

Step 2

The Fuel Mix Disclosure only gives us a breakdown of the major brown fuel types and nuclear, but lumps all of the green info together and simply calls it “Renewable”. Luckily the Ofgem website has the Renewables and CHP Register. This is a database that allows anyone to search for all of the Renewable Energy Guarantees of Origin (REGOs – certificates of greenness) held by suppliers. It’s the REGOs that make up the renewable proportion of a supplier’s Fuel Mix. The data available from the Renewables and CHP Register is broken down into different types of renewable energy technology such as onshore wind, off shore wind, solar photovoltaic etc.

Step 3

Next we have to work out the environmental impact of each companies supply. We do this based on the lifecycle carbon emissions associated with each generation type. This is a common method used to compare products on an environmental basis and is recommended by bodies such as Defra (the Department for Environment Food and Rural Affairs) as it considers the full impact of each technology by considering the emissions associated with it from cradle to grave, not just the period where it's generating electricity.

There are a lot of numbers out there available for lifecycle assessments but it’s not surprising to find that fossil fuels, such as gas and coal, give much larger emissions than cleaner renewable energy sources which don’t involve burning a carbon rich fuel to generate electricity. The figures that we’ve chosen to use have largely been selected from government papers wherever possible (as you can see from the list below). We’ve selected values from the lower end of the published range so that we can’t be accused of penalising brown energy suppliers by using a particularly high emissions factor for the coal or gas proportion of their supply. For instance, the range of emissions factors for coal generation varies by as much as nearly 300g CO2 per kWh whereas the range seen in renewable technologies, especially wind generation is much more defined, e.g. onshore wind ranges by around 12g CO2 per kWh:

Energy typeLifecycle Emissions g/CO2 kWhData source
Coal837DECC (2013)
Natural gas369Ricardo-AEA for Committee On Climate Change (2013)
Nuclear5Parliamentary Office of Science and Technology (2006)
Renewables General (estimated as a mix on/off wind)33.4Average of UK REGOs in 2014/15. Proportion of REGOs against emissions factors per technology gives average figure for renewables of 33.4g
Renewable – Onshore Wind8.5Ricardo-AEA for Committee On Climate Change (2013)
Renewable – Offshore Wind5.6Ricardo-AEA for Committee On Climate Change (2013)
Renewable – Biomass122Drax Biomass Supply Report – Feb 2015
Renewable – Solar54Ricardo-AEA for Committee On Climate Change (2013)
Renewable – Hydro5Parliamentary Office of Science and Technology (2006)
Renewable – Biogen11Anaerobic Digestion & Biogas Association (2012)
Renewable – Ocean25Parliamentary Office of Science and Technology (2006)
Other369Fossil fuel generation such as oil, emissions factor of gas used.

Step 4

Once we know the proportion of a supplier's electricity that is generated by each method and we also have a lifecycle emissions factor for each form of generation it’s simply a matter of combining the two to give us a final easy to compare figure for each supplier.

Last updated: March 2016

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