The Emissions & Generation Resource Integrated Database (eGRID), published by the US Environmental Protection Agency, is the preeminent source of emissions data for the electric power sector in the United States.
In May 2011, Version 1.1 was published, representing the calendar year of 2007 and incorporating earlier versions covering 2004 and 2005. AMEE represents part of this dataset, enabling the calculation emissions associated with electricity supplied to, and consumed from, the grid systems of the US.
eGRID is based on available plant-specific data for all generating plants that provide power to the electric grid, aggregated at several geographic levels, and descriptive of numerous aspects of the electricity production and consumption process. The full dataset includes absolute values for annual power and heat output and annual emissions, differentiated by fuel type (or other source), as well as by individual plants and geographic regions. Also included, however, is a rich set of emissions intensity data (i.e. emissions 'factors') which enables a spectrum of emissions calculation scenarios to be supported.
Generated versus consumed electricity
The delivery of generated electricity via a grid network is associated with 'distribution and transmission losses'. Therefore, the emissions intensity of electricity consumed by an end-user of the grid is typically higher than that of the same quantity of electricity supplied to the grid. The basic emissions factors provided in the eGRID dataset represent the emissions intensity (i.e. per unit of energy) of electricity supplied to the grid, rather than consumed from the grid by an end-user. EPA publish data on transmission losses for the main 'parent' grid regions of the United States and therefore converting between generated and consumed emissions intensities is achieved by dividing the emissions factor for generation by the appropriate transmission loss quantity (%), as follows:
emissions factorconsumption = emissions factorgeneration / (1 - (transmission loss% / 100))
Emissions intensity data (i.e. emissions 'factors') are provided for the following greenhouse gases and pollutants:
- carbon dioxide (CO2)
- methane (CH4)
- nitrous oxide (N2O)
- other nitrogen oxides (NOx)
- sulphur dioxide (SO2)
- mercury (Hg)
Total versus non-baseload
The eGRID dataset differentiates between 'total' emissions and 'non-baseload' emissions. Non-baseload emissions factors represent the aggregated emissions intensities of power plant generation which is not considered to contribute to the grid baseload (i.e. the minimum level of output supplied to the grid). These emission factors are considered to be useful for estimating the effects of reducing grid electricity consumption, since baseload generation is largely unaffected by such measures.
eGRID aggregates emissions data (i.e. from the data on individual power plants) at several geographic levels:
- US state
- eGRID subregions
- North American Electric Reliability Corporation (NERC) subregions
- Power Control Areas