Here’s an explanation of how we calculated Lifecycle Carbon Emissions
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.
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 technology such as onshore wind, off shore wind, solar photovoltaic etc.
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 Defra1 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 renewables 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 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 type||Lifecycle Emission g/CO2 kWh||Data source|
|Natural gas||369||Ricardo-AEA for Committee On Climate Change (2013)|
|Nuclear||5||Parliamentary Office of Science and Technology (2006)|
|Renewables General (estimated as a mix on/off wind)||33.4||Average of UK REGOs in 2014/15. Proportion of REGOs against emissions factors per technology gives average figure for renewables of 33.4g|
|Renewable - Onshore Wind||8.5||Ricardo-AEA for Committee On Climate Change (2013)|
|Renewable - Offshore Wind||5.6||Ricardo-AEA for Committee On Climate Change (2013)|
|Renewable - Biomass||122||Drax Biomass Supply Report – Feb 2015 ( page 5).|
|Renewable - Solar||54||Ricardo-AEA for Committee On Climate Change (2013)|
|Renewable - Hydro||5||Parliamentary Office of Science and Technology (2006)|
|Renewable - Biogen||11||Anaerobic Digestion & Biogas Association (2012)|
|Renewable - Ocean||25||Parliamentary Office of Science and Technology (2006)|
|Other||369||Fossil fuel generation such as oil, emissions factor of gas used.|
Once we know the proportion of a suppliers 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