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The amount of carbon emitted from a kWh of fuel
The carbon factor of a fuel is the multiplication factor used to calculate the carbon1 emissions that result from the use of a given quantity of the fuel.
It can be expressed as:
Carbon emissions = carbon factor x fuel use
Each fuel has its own carbon factor, and some of them can change dramatically over time. For example, the carbon factor for grid electricity dropped by nearly 75% between 2014 and 2022 due largely to the reduced use of coal generation.
Looking at the two main fuels used in UK housing, in SAP 10 the carbon factor for grid electricity is 0.136 kg/kWh, and for mains gas is 0.210 kg/kWh. A new feature of SAP 10 is that the carbon factor for grid electricity can change over the course of the year, and this is taken into account in some calculations within SAP. This is due to the different ratio of renewable energy being used to create grid electricity over the course of a year – from a low of 0.111 in July (when there is more solar for instance) to a high of 0.163 kg/kWh in December and January (when there is lower solar and more base load demand).
The housing sector should standardise on the carbon factors given in Tables 12 and 12d of the SAP 10 specification document.
Units: kilograms of carbon dioxide per kilowatt-hour of delivered energy (kg/kWh).
1 Or more strictly, carbon dioxide equivalent, that also includes the global warming impact of CH4 and N2O as well as CO2