The Power Sector Carbon Index is calculated as the ratio between the direct emissions generated from all electricity generation sources from the U.S. electricity sector, and the total net electricity generation.

We use hourly measured CO₂ emissions from the U.S. EPA Continuous Emissions Monitoring Systems (CEMS) data compiled as part the Air Markets Program Data. The EPA collects emissions information from all U.S. Electric Generating Units (EGUs) which combust coal, natural gas, fuel oil, wood or other refuse, and have a nameplate capacity greater than 25 MW. The emissions data is aggregated to monthly, quarterly, and annual levels to compute the monthly, quarterly, and annual Power Sector Carbon Index.

The net electricity generation data comes from the U.S. EIA Power Plant Operations Report (EIA-923). EIA-923 includes information on monthly fuel consumption and net electrical energy generation for every facility in the U.S. with a capacity of 1 MW or greater that is connected to the electric utility grid. Electricity technologies are classified into five broad categories: coal, natural gas, nuclear, renewables (wind, utility-scale solar photovoltaic (PV), distributed solar PV, solar thermal, wood and wood-derived fuels, landfill gas, biogenic municipal solid waste, other waste biomass, conventional hydroelectric, and geothermal plants), and other (all petroleum liquids, petroleum coke, other oils and gases, tires, municipal solid waste, waste heat, purchased steam or electricity, and any other categories that EIA reports as "Other").

Detailed information and data sources on how the Power Sector Carbon Index was calculated is available in this report.

The analysis code for the Power Sector Carbon Index is available on GitHub.