Note: This page applies to the newly released recommended 2019 version of emission factors. To switch to the recommended version of emission factors (2019 version), please go to the calculation sources and methods page. To see the scope 2 methodology for the outdated 2017 and 2018 version of emission factors, see this page.
Important updates for the 2019 version of emission factors
Location-based approach: eGrid factors are now current through 2018
Market-based approach: Residual mix emission factors are now available by eGrid region. For more information, please see this page about why residual emission factors changed from NERC regions to eGrid regions.
Overview of Scope 2 calculation methods
According the GHG Protocol Scope 2 guidance from the World Resources Institute, there are two recommended methods for calculating your purchased electricity footprint: Location-based and market-based.
|Method||Equation||Emissions factors||Renewable energy purchases/sales||Regions|
|Location-based||(Total Purchased kWh) x (eGrid emissions factor)||eGrid (through 2018)||Not accounted for||eGrid|
|Market-based||(Total Purchased kWh +/- Renewable kWh) x (Supplier-specific OR Residual emissions factor)||Residual (2015-2017) and eGrid (prior to 2015)||Accounted for||eGrid*|
*This is an important update for the 2019 version of emission factors: Residual emission factors are now available by eGrid regions. They were previously only available by the more aggregated NERC regions.
Below, please find more information about these two recommended methods. A third purchased electricity method (custom fuel mix) is no longer recommended as a best practice, but it is still an option in SIMAP for historical consistency with the CCC.
The “Location-based” method takes the total amount of power purchased from the grid and multiplies it by your regional eGrid factor. Your eGrid region can be selected on the calculation sources and methods form on the Data Mgmt tab. The equation is:
(Total Purchased kWh) x (eGrid emissions factor) = Carbon or nitrogen scope 2 footprint
There are two important factors to note for the location-based method:
- Renewable energy purchase/sales NOT accounted for: The location-based method does NOT account for any renewable energy purchase/sales. This is because the location-based method does not include any market transactions (e.g., RECs and other grid-metered renewable energy purchases). To include renewable energy purchase/sales in your scope 2 electricity calculations, please see the market-based method below. However, the location-based method does include any renewable energy that is part of the grid in the regional emissions factors.
- eGrid regions: The location-based method uses eGrid subregions, shown below.
- Emission factors current through 2018: The recommended 2019 version of emission factors includes the recent eGrid update that has emission factors current through 2018. Select your emission factor version on the calculation sources and methods form.
The “Market-based” method does take your renewable energy purchase/sales into account, and it uses a different set of emissions factors that account for market transactions (residual mix emissions factors) from 2015 through present. The calculation is:
(Total Purchased kWh +/- Renewable kWh) x (Supplier-specific OR Residual emissions factor) = Carbon or nitrogen scope 2 footprint
There are several important considerations for the market-based approach:
- Renewable energy: The market-based method does account for renewable energy purchase/sales.
- Supplier-specific emissions factor definition: Using a supplier-specific emissions factor is the best practice for scope 2 according to the GHG Protocol. The supplier-specific emissions factor is one that is reported by your utility as an emissions factor (e.g., kg CO2/kwh), and it should ideally be published publicly. This factor can be entered as a custom supplier-specific emissions factor on the utility emissions factors page. Note: This is different from a custom fuel mix, which is calculated as a weighted average in SIMAP based on your fuel mix and is not a recommended best practice.
- Residual emission factor definition: If a supplier-specific emissions factor is not entered, then the default for the market-based calculation is the residual emissions factor. The residual emissions factors are factors that exclude electricity generation from ALL voluntary renewable energy transactions. Since those renewables are being subtracted from users’ utility consumption data, it is important not to double-count those avoided emissions.
- eGrid regions: The residual emissions factors (2015-present) are now available by eGrid region. This is a change from previously available residual emission factors, which were available by the more aggregated NERC regions (see figure below). This methodology improvement may result in changes to your scope 2 methods. However, these changes will provide a more accurate estimate of your purchased electricity emissions from your grid.
- Years available for residual emission factors: Available for 2015 - 2017. Because residual mix emissions factors are not available in the US before 2015, the market-based method uses the eGrid location-based eGrid emissions factors for your purchased electricity footprint prior to 2015. Note: Residual mix emission factors are available by NERC region for 2013 and 2014, but those are no longer used in SIMAP due to the inconsistency in regions and system bounds.
- Residual emission factors only available for CO2: Residual mix emissions factors are only available for carbon dioxide. The other parts of your carbon and nitrogen footprints (methane, nitrous oxide, nitrogen oxides) will still be calculated using eGrid location-based emissions factors when you select the market-based method.
- Methodology change from CCC: A change from the CCC methodology is that the SIMAP calculation accounts for renewable energy purchase/sales directly in your scope 2 net kwh calculation. In the CCC, the emissions associated with renewable energy purchase/sales were subtracted/added to your total footprint. Now, in SIMAP, the net kwh purchased is first calculated (based on purchased kwh and the purchase/sale of renewable energy), and then the emissions factors are applied. This means that you will not see the emissions associated with renewable energy purchases calculated separately in your footprint results. This change is based on updated guidance from the GHG Protocol.
For more information on the Green-e energy residual mix emission rates, see this page for 2017 emission factors. Green-e will soon be posting the 2015 and 2016 versions of residual mix emission rates that are by eGrid region online. Previously available versions were by NERC region.
Notice of important scope 2 calculation update [April 2018]
Until recently, the GHG Protocol guidance was to use the eGrid factors used for the location-based method in place of the residual factors needed for the market-based method. This was because residual emissions factors were not yet available for the United States. However, Green-E now offers more accurate residual factors for the United States and Canada for years 2015 and later, which we incorporated into SIMAP in April 2018. Residual factors come from the same data source (EPA’s eGrid program) as the default eGrid factors, but the two calculations differ as follows:
eGrid EF = (Total CO2 emissions) / (Total MWh)
Residuals EF = (Total CO2 emissions – CO2 from renewables) / (Total MWh – MWh from renewable energy transactions)
The way that residual factors are calculated can result in dramatic annual changes. Those are due to the following:
- Residual EF calculations are now available by eGrid [February 2019]. This emission rates were previously available by the more aggregated NERC regions.
- The residual EFs change from year to year due to both changes in fuel mix AND market changes for renewables (more or less renewable energy sales). Because the renewable market is still very dynamic and growing and changing rapidly, the impact on regional emissions factors can also be dramatic.
In sum, you may see significant shifts and variability in your market-based scope 2 totals for the years 2015 onward; this is a reflection of the changing grid and energy markets (and is not an error.)