Middlebury College currently calculates electricity emissions by analyzing the specific energy sources and suppliers that provide its electricity. However, the EPA uses a different methodology that calculates constants for each electric grid region based on total emissions divided by electricity generated. While the EPA method accounts for transmission losses, Middlebury's method allows it to choose suppliers based on environmental factors since it knows the exact energy sources. To create the most comprehensive data, Middlebury should use the EPA formula to estimate transmission losses while keeping its source-based analysis to account for its use of renewable energy.

1. Electricity Emissions Calculation Methodology Analysis
Introduction/Current Methodology
Middlebury College’s electricity purchase emissions calculations are derived from a
breakdown of energy suppliers and the respective sources from which these suppliers generate
electricity. This breakdown is comprised of co-generated electricity through biomass/natural gas
burned at Middlebury in addition to purchased electricity produced by suppliers in the New
England grid. The main supplier of college electricity within this grid is Green Mountain Power
(GMP), which, besides producing a majority of its own electricity (56%), sources from ISO-New
England (44%), an external non-profit energy supplier/manager.
The emissions calculations are done from a source perspective, where electricity from
each source (natural gas, coal, solar, wind etc.) from every supplier is accounted for in terms of
its greenhouse gas output. Standard conversion factors are used to calculate CO2, N2O, and CH4
from every electricity source used by the suppliers and through co-generation and added up in
terms of their CO2 equivalency.
This method of emissions calculation serves the purpose of the sustainability policies
pursued by Middlebury College because it allows the institution to view every source of
electricity used, and analyze where it can invest or divest to work towards carbon neutrality.
Through this methodology, the institution knows exactly what kind of energy it is funding, and
that knowledge is an essential piece in lowering carbon emissions.
EPA eGRID Methodology1
The EPA’s eGrid emission calculation methodology differs significantly from the one
used by the college because, rather than breaking down suppliers and energy sources, it utilizes a
series of constants that can be multiplied by the total amount of pollution. These constants, as
shown in the table below, differ per grid because they are calculated based on the total emissions
per pollutant of a region divided by the MWh generated by that region multiplied by a
conversion factor. The table below shows these constants for three main pollutants (CO2, N2O,
and CH4) which can be multiplied by any amount of MWh to get an emissions rate per pollutant
in that grid.
This method of emissions calculation shows pollution relative to an entire grid rather than
through individual sources. This is beneficial because it allows an easy calculation of
transmission losses because all energy consumers function under the same grid, allowing the
EPA to utilize the pollution constants and a grid loss factor (figure 3) to analyze how much
greenhouse gas is produced through energy transportation. The formula developed by the EPA is
shown in figure 2.
1 Diem, Art, and Cristina Quiroz. How to Use eGRID for Carbon Footprinting Electricity Purchases in Greenhouse
Gas Emission Inventories. Rep. The Environmental Protection Agency.Washington D.C.: n.p., 2012. 1-22. Print.

2. Table 1: eGrid total emissions output rate for CO2, CH4, and N2O. The red box displays the New England NPCC’s emissions
rates utilizes by Middlebury College.
Figure 1: Line loss emission rate formula developed by the EPA to calculate greenhouse gas emission rates for each grid. ERg is
displayed in the table above and FFL is displayed in the figure below.

3. Conclusion
Our current methodology aligns with the goals of the carbon neutrality policy because it
allows us to analyze individual sources of energy along with their suppliers, allowing the college
to choose energy options based on environmental consciousness. Despite this, the EPA’s
methodology provides an avenue to estimate emissions through transmission losses, a factor that
Middlebury does not take into consideration. To account for this, the institution should utilize the
eGrid formula to estimate transmission losses while preserving the energy purchase source
analysis in order to create the most comprehensive emissions data. It should be noted that the
EPA calculations account for all sources of electricity within a grid, including non-renewable
ones, causing emission calculations to be much higher than reality for an institution like
Middlebury, which is incredibly environmentally selective in its energy source portfolio.
Utilizing eGrid calculations would give the grid standard emission rates for the electricity
produced at Middlebury without taking the institution’s substantial renewable energy utilization
into account, generating emission rates that are higher than actuality.
Figure 2: eGrid loss factors utilized to calculate grid loss rate through the formula above. The red box displays the grid
Middlebury utilizes.