In the United States, emission factors (EFs) applied to grid electricity consumption are available by both state and by eGRID subregion. If you are using state level EFs, determining which set of factors to apply is simple – just use factors published for the state in which your site is located. However, in order to use the subregion level EFs that are considered best-practice in GHG accounting, you must first determine which subregion your site is in, and this is not quite as straightforward.

Subregions, unlike states, are defined using the transmission, distribution and utility service territories of power plants and therefore don’t follow traditional geographic state boundaries. For example, the subregion of WECC Northwest includes all or part of the following states: California, Idaho, Montana, Nevada, Oregon, Utah, Washington, and Wyoming. There are 26 such eGRID subregions and each covers a unique area of the country and has its own set of emission factors applicable to grid electricity consumption.

Due to the fact that maps modeling eGRID subregions are approximate, the US Environmental Protection Agency (EPA) provides two support tools to help organizations determine precisely which eGRID subregion their facilities are located in. Both these tools use your facility zip code, a precise geographic locator, as the means to determine the subregion of the facility.

Method 1: Online Power Profiler Tool

Within the Clean Energy section of their website, the EPA has provided a handy web application called the “Power Profiler”. Using this tool is incredibly simple and requires only a couple of steps:

  1. Enter the zip code of your site into the embedded web application
  2. Select the appropriate utility provider. Some zip codes will be associated with only one provider, while others may return several options; you can determine which distributor your company is with by reviewing your utility bills or asking your building manager.
  3. Note the eGRID subregion presented above the “Fuel Mix Comparison” chart, or click on “your region of the power grid” to view your subregion on a map

It’s that easy. The results page of the Power Profiler tool also presents a few other interesting facts related to your subregion, including:

  • The percent fuel mix of sources used to generate electricity in your region alongside a comparison with the national fuel mix
  • A comparison between the average emission output rates in your subregion to the national average rates, in lbs/MWh, for carbon dioxide, methane and nitrous oxide
  • Resources related to energy efficiency and green power purchases

Method 2: Excel Power Profiler Tool

Method 1, described above, is absolutely the way to go if you’re only looking up the eGRID subregion for a couple of facilities. However, if you’re working on a GHG assessment for a company with a slew of sites located all over the United States, this method will quickly become tedious and time-consuming.

Luckily, the EPA has provided the same functionality in a format that is much more conducive to your task – the Power Profiler eGRID Subregion and GHG Emissions Finder Tool. While the name is a bit lengthy and complex, the process is thankfully not.

  1. Download the Excel spreadsheet using the link at the bottom of the Power Profiler webpage
  2. Read the directions on the “TOC” tab carefully
  3. Begin entering your site zip codes into Column B of the “Data Entry” tab. Remember to enter ZIP+4 codes and codes with leading zeroes properly.
  4. The primary eGRID subregion will be presented in Column D. Some zip codes are associated with more than one subregion; therefore, do not assume that just because a facility has the same zip code as another, that the same utility company will provide its power. If a zip code is associated with multiple providers (and thus subregions), the relevant secondary and tertiary subregions will show up in columns E and F, and you will need to visit the Power Profiler online tool to choose the appropriate power provider and determine with certainty the correct subregion for your facility.

Just like the online tool, the Excel version of Power Profiler displays the emission output rate for your primary subregion in columns H, I and J. Output rates for secondary and tertiary subregions, where applicable, are also displayed.

Once you’ve determined which eGRID subregion your facility is located within, you’ll need to record the appropriate emission factors from the EPA and convert your data into the appropriate unit required to apply the researched factors. Or, you can use emissionfactors.com. Up-to-date factors for each subregion are found quickly and easily, and are available converted into any unit you may need.

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