Scope 5’s Electricity (Residual mix) library provides residual electricity mix emission factors for 31 European countries and the United States. The Residual mix represents the mix of uncertified electricity within a grid system and removes the impact of claimed renewable energy credits.
As per the Greenhouse Gas Protocol’s Scope 2 Guidance, in the absence of more precise emission factors, residual mix emission factors should be used to calculate market-based Scope 2 emissions.
Table 6.3 from the Scope 2 Guidance describes the hierarchy of emission factors to be used for Scope 2 market-based emission calculations - note residual mix is the second-to-last option in the table:
Where the Numbers Come From
There are two sets of emission factors in the library: the AIB set and the Green-e set.
The Association of Issuing Bodies (AIB) governs the European Energy Certificate System (EECS). The AIB aggregates and publishes national residual mixes for the European Union members, Iceland, Norway, Switzerland and the United Kingdom.
For the 2018 set of emission factors, Scope 5 draws on the “Direct GWP” column in “Table 2: Residual Mixes 2018” from the “European Residual Mixes - Results of the calculation of Residual Mixes for the calendar year 2018” document. The emission factors reflect the direct greenhouse gas emissions in CO2 equivalents (CO2e).
Note on Austria: In 2018, residual mix was not calculated for Austria, as it has an operational full disclosure system, meaning that electricity consumption is fully, explicitly tracked in the country.
For the 2019 set of emission factors, Scope 5 draws on the “CO2 (gCO2/kWh)” column in “Table 2: Residual Mixes 2019” from the “European Residual Mixes Results of the calculation of Residual Mixes for the calendar year 2019” document. Please note that for its 2019 publication the AIB opted to publish only Direct CO2 emissions "due to difficulties in updating the advanced emission factors..."
In order to keep the 2019 set comparable to previous conversion factor sets, Scope 5 completed the CO2 factors with CH4 and N2O factors sourced from the International Energy Agency's "IEA Emission Factors 2020", Tables: "CH4 factors" and "N2O factors" for 2018.
Green-e is a trusted energy certification program created by the Center for Resource Solutions. According to the EPA, Green-e is the only program certifying green energy products in the United States.
In addition to certifying renewable energy, Green-e publishes residual mix CO2 emissions rates. The Scope 5 Green-e CO2 emission factors come from the “Green-e® residual mix emissions rate,” table, column “Adjusted System Mix”. Green-e calculates these emissions rates (factors) by removing all Green-e® Energy certified sales for each Emissions & Generation Resource Integrated Database (eGRID) subregion. As such, the Green-e residual mix emission factor set is aligned with the eGRID subregions.
As per Green-e’s guidance, the Scope 5 library combines the Green-e CO2 emission factors with the CH4 and N2O emission factors provided by eGRID Summary Tables - Table 1, “Total output emission rates”.
For more information about a specific emission factor’s provenance, please refer to the ‘Source’ for the individual conversion factor set, as illustrated in the following example.
Scope 5’s conversion factors are current through the AIB and the Green-e 2020 publications. We expect these authorities to publish updated emission factor sets on a yearly basis. Scope 5 will incorporate new factors as they are released.
Global Warming Potentials (GWPs)
All emissions factors in the AIB library are expressed in units of CO2e; as such GWPs are not explicitly defined.
Following the Greenhouse Gas Protocol recommendation, the Green-e resources use GWPs from the IPCC's Fifth Assessment Report (AR5).
The Scope 5 team is always available to help, whether that means navigating the application, making changes to your account configuration or just answering questions.