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Definitions of Technologies for Data Used

This page in the Summary of Trends section outlines the data used in the State of the States analysis and the limitations of the data. The renewable energy trends in the states (shown in the tables under the Renewable Energy Generation by Resource page) are based on 2007 renewable energy generation. The definition of renewable energy for this analysis includes biomass, geothermal, hydroelectric, solar (central), and wind, as defined and tracked by the U. S. Department of Energy's Energy Information Administration (EIA). Also included in some tables, as noted, are distributed solar capacity data as tracked by the Interstate Renewable Energy Council, and wind capacity as tracked by the American Wind Energy Association. Note that the definition of renewable energy and renewable energy types are broad and differ depending on analysis and data needs.

For the purposes here, renewable energy is defined as:

  • Biomass: agricultural crops and residues; dedicated energy crops (herbaceous and tree species); forestry products and residues; residues and byproducts from food, feed, fiber, wood, and materials processing plants [sawdust from sawmills, black liquor (a byproduct of paper making), cheese whey (a byproduct of cheese-making processes), and animal manure]; post-consumer residues and wastes, such as fats, greases, oils, construction and demolition wood debris and other urban wood waste, municipal solid wastes and wastewater, and landfill gases. The specific EIA definition includes landfill gas/MSW biogenic, wood, and derived fuels.

  • Geothermal: electricity produced centrally from heat in the earth.

  • Conventional Hydroelectric: comes from the movement of water. The EIA defines a conventional plant as one in that, "all of the power is produced from natural streamflow as regulated by available storage." Pumped storage is not collected and reported under this definition because the EIA considers it to use nonrenewable resources for operation. In this report, low-impact and distributed hydro, which may have a large potential for electricity production is not included as a result of data limitations.

  • Solar (central): the radiant heat from the sun, which can be converted into electricity on the large scale, such as through concentrated solar power, concentrated PV, or similar technologies.

  • Solar (distributed): on- and off-grid distributed solar electric noncentral electricity generation resources, including residential, commercial, and industrial applications. Primary technology is photovoltaics (PV).

  • Wind: the extraction of kinetic energy from the wind for conversion into electricity.

Due to the unique context in each state, the data are normalized for three parameters to aid in comparison among states: percentage of total electricity generation, state population, and gross state product. Population data for the states are from the U.S. Department of Commerce Census Bureau. State GSP data are compiled from the U.S. Bureau of Economic Analysis. Due to the recent rapid growth in wind energy development, total renewable energy growth during the past five years is skewed when all technologies are grouped together, resulting in a distortion of growth trends. To remedy this and show the growth of major renewable energy technologies in each state, growth rankings measuring growth from 2001-2007 and 2006-2007 are presented. These rankings are separated into technology and then normalized for comparisons between technologies and states.

Data and Methodology Limitations

(Note: All references for this section are available in the full report "State of the States 2009: Renewable Energy Development and the Role of Policy" (PDF 4.2 KB). Download Adobe Reader.)

  • In general, the EIA dataset is considered the most comprehensive source for electricity generation information in the United States, and it is the primary source for trends information in this analysis (with noted exceptions). There are a number of challenges in collecting renewable electricity generation at the state level, but those are not the focus here. Instead, the strength of the dataset as a nationwide comparable source in terms of definitions and data collection techniques are the reasons for its use.

  • Data for distributed solar electricity resource development are limited by lack of collection by EIA.

  • Data on renewable-based electricity generation in the U.S. territories is limited. EIA data were supplemented with direct contact to territory energy offices, but no additional data were received by the authors.

  • Most recent data are from 2007. Significant market changes between 2007 and 2009 are expected to have an impact on renewable energy generation and will be reported in later versions of this analysis.

  • "Growth" rankings provide information on the largest growth rates between 2001 and 2007 and between 2006 and 2007, leading to heavier weighting of states that began the development of the particular renewable resource in each of those timeframes. The purpose is to acknowledge the challenge of early-stage development. Alternative and additional methods are under consideration for future reports.