Environmental Issues: Air

Benchmarking Air Emissions of the 100 Largest Electric Power Producers in the United States - 2006
2008 Data Sources, Methodology and Quality Assurance
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This report examines the air pollutant emissions of the 100 largest electricity generating companies in the United States based on 2008 electricity generation, emissions and ownership data. The report relies on publicly-available information reported by the U.S. Energy Information Administration (EIA), U.S. Environmental Protection Agency (EPA), Securities and Exchange Commission (SEC), state environmental agencies, and company websites.

Data Sources

The following public data sources were used to develop this report:

EPA ACID RAIN PROGRAM DATABASE: EPA's Acid Rain Emissions Reporting Program accounts for almost all of the SO2 and NOx emissions, and approximately three quarters of the CO2 emissions analyzed in this report. These emissions were compiled using EPA's on-line emissions database available at http://camddataandmaps.epa.gov/gdm/.

EPA TOXIC RELEASE INVENTORY (TRI): Power plants and other facilities are required to submit reports on the use and release of certain toxic chemicals to the TRI. The 2008 mercury emissions used in this report are based on TRI reports submitted by facility managers and which are available at http://www.epa.gov/tri/tridata/tri08/national_analysis/index.htm.

EIA FORM 923 POWER PLANT DATABASE (2008): EIA Form 923 provided almost all of the generation data analyzed in this report. EIA Form 923 provides data on the electric generation and heat input by fuel type for utility and non-utility power plants. The heat input data was used to estimate approximately one quarter of the CO2 emissions analyzed in this report. The form is available at http://www.eia.doe.gov/cneaf/electricity/page/eia906_920.html.

EIA FORM 860 ANNUAL ELECTRIC GENERATOR REPORT (2008): EIA Form 860 is a generating unit level data source that includes information about generators at electric power plants, including information about generator ownership. EIA Form 860 was used as the primary source of power plant ownership for this report. The form is available at http://www.eia.doe.gov/cneaf/electricity/page/eia860.html.

EIA FORM 861 ANNUAL ELECTRIC POWER INDUSTRY DATABASE (2008): EIA Form 861 provided all of the electricity sales and delivery data analyzed in this report. The form contains aggregate information about electricity sales, revenue, and customer counts of all electric utilities in the United States. It is available at http://www.eia.doe.gov/cneaf/electricity/page/eia861.html.

EPA U.S. INVENTORY OF GREENHOUSE GAS EMISSIONS AND SINKS (2008): EPA's U.S. Inventory of Greenhouse Gas Emissions and Sinks report provides in Annex 2 heat contents and carbon content coefficients of various fuel types. This data was used in conjunction with EIA Form 923 to estimate approximately 25 percent of the CO2 emissions analyzed in this report. Annex 2 is available at http://www.epa.gov/climatechange/emissions/downloads10/US-GHG-Inventory-2010_Annex2.pdf.

Plant Ownership

This report aims to reflect power plant ownership as of December 31, 2008. Plant ownership data used in this report are primarily based on the EIA-860 database from the year 2008. EIA-860 includes ownership information on generators at electric power plants owned or operated by electric utilities and non-utilities, which include independent power producers, combined heat and power producers, and other industrial organizations. It is published annually by EIA.

For the largest 100 power producers, plant ownership is further checked against self-reported data from the producer's Form 10-K filed with the SEC. If a discrepancy is found, ownership of the plant is updated using data from its 10-K filed with the SEC for the year 2008. Consequently, in a number of instances, ultimate assignment of plant ownership in this report differs from EIA-860's reported ownership. This may happen when the plant in question falls in one or more of the categories listed below:

  1. It is owned by a limited liability partnership shareholders of which are among the 100 largest power producers.


  2. The owner of the plant as listed in EIA-860 is a subsidiary of a company that is among the 100 largest power producers.


  3. It was sold or bought during the year 2008. Because the Form 10-K for a particular year is usually filed by the producer in the first quarter of the following year, this report assumes that ownership as reported in the Form 10-K is more accurate.


In all cases listed above, information reported in the Form 10-K takes precedence over the EIA-860 database. If the partnership or the subsidiary has multiple shareholders, percentage ownership is adjusted accordingly.

Identifying "who owns what" in the dynamic electricity generation industry is probably the single most difficult and complex part of this report. In addition to the categories listed above, shares of power plants are regularly traded and producers merge, reorganize, or cease operations altogether. While considerable effort was expended in ensuring the accuracy of ownership information reflected in this report, there may be inadvertent errors in the assignment of ownership for some plants where public information was either not current or could not be verified.

Generation Data and Cogeneration Facilities

Plant generation data used in this report come from EIA Form 923.

Cogeneration facilities produce both electricity and steam or some other form of useful energy. Because electricity is only a partial output of these plants, their reported emissions data generally overstate the emissions associated with electricity generation. Generation and emissions data included in this report for cogeneration facilities have been adjusted to reflect only their electricity generation. For all such cogeneration facilities emissions data were calculated on the basis of heat input of fuel associated with electricity generation only. Consequently, for all such facilities EIA Form 923, which report a plant's total heat input as well as that which is associated with electricity production only, were used to calculate their emissions.

Note that beginning in 2008 the EIA implemented a new method of allocating fuel consumption between electric power generation and useful thermal output for cogeneration facilities. The new method distributes a plant's losses equally between electricity and thermal outputs. Prior to 2008, useful thermal output was generally assumed to be up to 80 percent efficient assigning all other losses to electric output of a plant. The new method, therefore, results in an increase of electric power production efficiency at cogeneration facilities.

NOx and SO2 Emissions

The EPA Acid Rain Program collects and reports SO2 and NOx emissions data for nearly all major power plants in the U.S. Emissions information reported in the Acid Rain database is collected from continuous emission monitoring (CEM) systems. SO2 and NOx emissions data reported to the Acid Rain Program account for almost all of the SO2 and NOx emissions assigned to the 100 largest power producers in this report.

The Acid Rain database collects and reports SO2 and NOx emissions data by fuel type at the boiler level. This report consolidates that data at the generating unit and plant levels. In the case of jointly owned plants, because joint ownership is determined by producer's share of installed capacity, assignment of SO2 and NOx emissions to the producers on this basis implicitly assumes that emission rates are uniform across the different units. This may cause producers to be assigned emission figures that are slightly higher or lower than their actual shares.

CO2 Emissions

CO2 emissions reported through the EPA Acid Rain Program account for approximately three quarters of the CO2 emissions used in this report. The remaining 25 percent was calculated using heat input data from EIA Form 923 and carbon content coefficients of various fuel types provided by EPA. Table A.1 shows the carbon coefficients used in this procedure. Non-emitting fuel types, whose carbon coefficients are zero, are not shown in the table. EIA Form 923 reports heat input data by fuel type at the prime mover level. This report consolidates that data at the generating unit and plant levels. In the case of jointly owned plants, because joint ownership is determined by producer's share of installed capacity, assignment of CO2 emissions to the producers on this basis implicitly assumes that emission rates are uniform across the different units. This may cause producers to be assigned emission figures that are slightly higher or lower than their actual shares.

Mercury Emissions

Mercury emissions data for coal power plants presented in this report were obtained from EPA's Toxic Release Inventory (TRI). Mercury emissions reported to the TRI are based on emission factors, mass balance calculations or data monitoring. The TRI contains facility-level information on the use and environmental release of chemicals classified as toxic under the Clean Air Act. Because coal plants are the primary source of mercury emissions within the electric industry, the mercury emissions and emission rates presented in this report reflect the emissions associated with each producer's fleet of coal plants only.

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