Contents

Summary

The AMEE category at /business/energy/electricity/defra/uk provides a dataset and a calculation methodology for greenhouse gas emissions associated with the consumption of grid electricity in the United Kingdom. The data is sourced from the UK government department DEFRA.


The methodology

Emissions model

Emissions are calculated, according to this methodology, on the basis on emissions factors which relate a quantity of grid electricity electricity with an associated quantity of greenhouse gas emissions. These emissions factors are based on the average annual emissions intensity of grid electricity in each country (or other region), as specified on a per kWh basis. By multiplying a quantity of electricity by the appropriate factor, the total quantity of emissions are calculated.

Model data

The comprehensive dataset included within methodology differentiates several aspects of electricity-associated emissions, including: (1) the activities of generation, transmission and consumption; (2) direct, indirect and life cycle emissions; (3) historical (raw annual or annual rolling average) data.

Activity type: Separate data are available for greenhouse gas emissions attributable to electricity generation, electricity transmission and distribution, and electricity consumption. All greenhouse gas emissions are ultimately associated with the generation phase, being a consequence of fuel/energy consumption (direct emissions) and related activities (indirect: e.g. fuel sourcing, transport) at the power plant. However, since there are usually losses associated with the distribution and transmission of electricity, the quantity of emissions per unit of electricity generated (e.g. kWh) usually differs from the corresponding per unit emissions at the point of consumption. The DEFRA dataset provides values for greenhouse gas quantities which are attributable to the intermediate transmission phase, although these should be understood to be an accounting convenience reflecting transmission (in)efficiency rather than actual emissions caused during this phase. The emissions associated with electricity consumption are simply the sum of those attributable to generation and transmission. In most cases - i.e. those in which the final, end-point of electricity usage is under consideration - the values for consumption should be used.

Emission type: The DEFRA dataset differentiates between direct and indirect greenhouse gas emissions. 'Direct' emissions are limited to those associated with activities at the power plant, while 'indirect' emissions refer to those which derive from other stages in the production chain such as raw material extraction and fuel delivery. The combination of these two types of emission represents full life cycle emissions for electricity. The importance of these emissions types will vary depending on how the user attributes the various portions of the life cycle emissions to the various agents involved (e.g. supplier, producer, consumer). It is most common to use direct emissions only when considering electricity consumption. Direct emissions are additionally differentiated by the specific greenhouse gases CO2, CH4 and N2O, the latter two quantities being expressed in terms of CO2e. Indirect and life cycle emissions are expressed in terms of CO2e.

Historical values: The greenhouse gas emissions produced per unit of electricity generated/consumed varies through time as the mix of fuels used by power stations supplying a national or regional grid changes. These changes may reflect variations in electricity demand or the relative prices of different fuel types. DEFRA publishes annual emissions factors based on the average quantity of emissions per unit of electricity across the grid during each calendar year starting from 1990. In addition to the raw annual values, DEFRA provides 'rolling average' emissions factors which represent the average of the previous 5 years for each given year. These are suggested as being more suitable for inter-annual comparisons by DEFRA.


Activity data required

Emissions are calculated on the basis of the type of activity::

  • electricity generation
  • electricity distribution and transmission
  • electricity consumption

For most cases - i.e. considering everyday electricity usage - 'electricity consumption' is the most appropriate selection. Emissions are also calculated on the basis of the emission type:

  • direct
  • indirect
  • life cycle (direct + indirect)

Users can also select the basis of the emission factor:

  • annual
  • rolling average

The annual data values are applicable only to direct emissions calculations. The emissions are directly proportional to the energy consumed, i.e. the amount of electricity, so this must be provided by the user.

The quantity of electricity under consideration is specified by setting the energyConsumed profile item value. If users specify start- and end-dates in association with their electricity consumption, AMEE will use its data item value history functionality to apply the appropriate emissions factor(s). If no profile dates are set, the most recent data are used.

Calculation and results

In the case of direct emissions, four quantities are returned, as follows:

  • CO2: CO2 emissions
  • methaneCO2e: CH4 emissions
  • nitrousOxideCO2e: N2O emissions
  • totalCO2e: total direct CO2e emissions (all gases combined)

Note that each of these values - including the separated CH4 and N2O emissions - are expressed in terms of carbon-dioxide-equivalent (CO2e) emissions.

For indirect and life cycle emissions, just the totalCO2e quantity is returned which represents total CO2e emissions for the indirect and life-cycle perspectives respectively. All quantities represent greenhouse gas (CO2e) emissions associated with the energy quantity (and dates) specified.


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