The Average Operating Emissions Rate (AOER) is a calculation of the average emissions rate of all the electricity generated on the local grid at a certain time. Average emissions generally are a way to allocate responsibility for emissions evenly, instead of causally. The units of AOER are the amount of pollution per unit of energy (lbs/MWh).

Load shifting using this signal wouldn’t reduce emissions, but many companies find the data helpful for the purpose of attributional emissions accounting. GHG Protocol’s Corporate Standard allows the use of average emissions factors to determine the total annual emissions footprint of the electricity consumption of a company’s assets. The AOER allows this accounting to be done using more recent and frequent emissions factors. Learn more about why marginal emissions are better than average emissions for impact accounting.

The AOER is calculated by summing the total emissions from all generators in a particular hour and grid region, and dividing by the total energy generated (MWh). WattTime performs a simple calculation using publicly available data sources.

Step 1: Determine total generation for each fuel type (e.g. use EIA data or similar).

Step 2: Assign annual emissions factors for each fuel type (e.g. use IEA annual factors by country).

Step 3: For each fuel type, multiply its total generation (MWh) by its annual emissions factor (lbs/MWh) and sum the results to get the total emissions (lbs); then divide total emissions by total generation to get the AOER (lbs/MWh) for the grid.

Note: WattTime’s AOER is specific to generators in a particular grid region and does not reflect imports/exports.