Energy Intensity Indicators: Terminology and Definitions

The Energy Intensity Indicators website uses the following terms with their associated definitions. The terms related to various definitions of energy are discussed first.

Three separate definitions of energy are used in the system of indicators: 1) delivered, 2) source, and 3) source, adjusted for electricity generation efficiency change. These definitions are discussed below.

Delivered energy is the amount of energy consumed at the point of sale (e.g., that enters the home, building, or establishment) without adjustment for any energy loss in the generation, transmission, and distribution of that energy. As such, it is the sum of fossil and renewable fuels (e.g., biomass or fuel wood) and purchased electricity. Delivered energy is sometimes referred to as "site" energy.

Source energy consumption is defined as delivered energy plus the energy losses associated with the production of electricity by the utility sector (i.e., losses that occur in the generation, transmission, and distribution). These losses are allocated to the end-use sectors in proportion to their direct electricity consumption. The sum of source energy for four end-use sectors (transportation, industrial, residential buildings, and commercial buildings) is equal to the economywide use of energy defined in the system of indicators.

Source energy, adjusted for electricity generation efficiency changes. An issue with the use of source energy is that both improvements in energy efficiency in the consuming sector, as well as improvements in the generation of electricity can affect the trend in energy intensity. To account for changes in electricity generation efficiency an alternative concept of source energy is computed, one that effectively holds the energy intensity in the electric utility sector (ratio of losses to sales to end users) constant (see methodology in the comprehensive 2014 report – Section 2.6). As terminology in the system of intensity indicators, an index consistent with this definition is typically termed an "adjusted source energy intensity index."

For the high-level energy intensity indicators shown on this website, this third definition of energy is employed. In the downloadable spreadsheets available from the site, energy intensity indexes based on delivered and the conventional definition of source energy are included. Energy intensity indexes are also computed separately for total fuels (sum of fossil and renewable) and electricity. A broad comparison of how trends in energy intensity differ with respect to the three alternative definitions of total energy (delivered, source, and adjusted source) is discussed on the website [Sectoral Comparisons].

Important note: The adjustment for electricity generation efficiency is applied to the construction of the intensity index only. To maintain transparency with conventional measures of source energy as published by the Energy Information Administration (EIA), the absolute values of source energy discussed and shown in the graphics on this website are conceptually consistent with the EIA treatment. As such, measures of source energy shown here continue to reflect changes in the underlying ratios of losses to sales exactly as reported by EIA. This avoids any confusion that might be caused in presenting an alternative measure of energy consumption.

Excluded energy. The system of energy intensity indicators considers only that energy that is used as a factor of production of a good or service. Energy used as a material, such as petrochemical feedstocks or asphalt, is not considered here. Other uses, such as fuels used for military aircraft or recreational boating, are also excluded, primarily because there are neither data available, nor any accepted definitions of how to measure the associated activities. As a result, the total energy defined in the system of energy indicators will not necessarily match the end-use consumption estimates published by the Energy Information in its Monthly Energy Review. (In 2011, total U.S. energy consumption employed in the system of energy intensity indicators was 92.0% of the value published by EIA. See Economywide Energy Intensity in Highlights.) For a complete discussion of sources and estimation procedures for historical energy use by sector, see the 2014 comprehensive report.

Energy Efficiency. Energy efficiency can be defined for a component or service as the amount of energy required in the production of that component or service; for example, the amount of steel that can be produced with one billion Btu of energy. Energy efficiency is improved when a given level of service is provided with reduced amounts of energy inputs, or services or products are increased for a given amount of energy input. (See also Efficiency vs. Intensity.)

Energy Intensity. The amount of energy used in producing a given level of output or activity (see also Efficiency vs. Intensity). It is measured by the quantity of energy required to perform a particular activity (service), expressed as energy per unit of output or activity measure of service.

Economywide energy intensity (also referred to as aggregate energy intensity). At the economywide level, energy intensity is measured only in terms of a temporal index (currently relative to the year 1985). Changes in energy intensity by sector are energy-weighted to construct the economywide index.

Sector energy intensity. This is energy intensity calculated at the sector level. When source energy is considered, intensity is calculated for five sectors, the four end-use sectors and the electricity producing sector. When total energy is considered intensity is calculated for the four end-use sectors only.

Subsector energy intensity. This is the energy intensity for subsectors within a given sector (see subsectors). Subsector intensity is energy use divided by the activity of the subsector.

End-use sectors. The four sectors that consume primary energy and electricity: transportation, industry, residential and commercial.

Transportation sector. An end-use sector that consists of all vehicles whose primary purpose is transporting people and/or goods from one physical location to another. Included are automobiles; trucks; buses; motorcycles; trains, subways, and other rail vehicles; aircraft; and ships, barges, and other waterborne vehicles. Vehicles whose primary purpose is not transportation (e.g., construction cranes and bulldozers, farming vehicles, and warehouse tractors and forklifts) are classified in the sector of their primary use (see the EIA glossary).

Industrial sector. An end-use sector that consists of all facilities and equipment used for producing, processing, or assembling goods. The industrial sector, for purposes of the system of energy intensity intensity indicators, is comprised of: manufacturing; agriculture, mining; and construction. Establishments in this sector range from steel mills, to small farms, to companies assembling electronic components. Overall energy use in this sector is largely for process heat and cooling and powering machinery, with lesser amounts used for facility heating, air conditioning, and lighting. Fossil fuels are also used as raw material inputs to manufactured products (see the EIA glossary).

Residential sector. An end-use sector that consists of living quarters for private households in both single-family and multifamily housing units. Common uses of energy associated with this sector include space heating, water heating, air conditioning, lighting, refrigeration, cooking, and running a variety of other appliances. The residential sector excludes institutional living quarters (see the EIA glossary).

Commercial sector. An end-use sector that consists of service-providing facilities and equipment of: businesses; federal, state, and local governments; and other private and public organizations, such as religious, social, or fraternal groups. The commercial sector includes institutional living quarters. Common uses of energy associated with this sector include space heating, water heating, air conditioning, lighting, refrigeration, cooking, and running a wide variety of other equipment in nonresidential buildings. The commercial sector also includes some nonbuilding energy use, such as street lighting, water and sanitary services, and communication equipment (e.g., cell towers). Note: This sector includes generators that produce electricity and/or useful thermal output primarily to support the activities of the above-mentioned commercial establishments (see the EIA glossary).

Electricity sector. An energy consuming sector that generates electricity. Data are organized to separate electricity-only generators from combined heat and power (CHP) generators. The electric-only generators provide power to residences, commercial establishments, and industry within the same harmonized grid through transmission and distribution lines. CHP generators may sell power to the wholesale market, but they also provide heat (usually in the form of steam) to themselves or to other customers. CHP generators are further classified as electric-only, commercial, and industrial, depending on who purchases the power.

Subsectors. A subsector reflects the differentiated level of economic activity within a given sector. There are several various levels of subsector detail. Examples of subsectors used in the national system of indicators on this website:

  • In the transportation sector, the subsectors are first passenger versus freight, but then each of these can be further disaggregated into modes of travel—highway, air, rail, and water.

  • For the industrial sector, the first level of subsector division is between manufacturing and non-manufacturing (agriculture, mining, and construction). Manufacturing is further disaggregated into major industry groups and then into industries at the three-digit level of the North American Industry Classifications System (NAICS).

  • The residential sector is disaggregated by the four major census regions: Northeast, Midwest, South, and West.

  • The commercial sector is not disaggregated in the current system of indicators. No reliable time series data at either the building type or regional level is available.

  • The electricity sector is divided into electric-only producers and producers of combined heat and power (CHP). CHP producers are further divided into electric-only, commercial, and industrial producers.

Output (also referred to as Activity). The major activity that drives economic production for the economy or its sectors and subsectors. At the level of the aggregate economy output is measured by GDP. The output measures for sectors varies for each sector, The output measures for each of the sectors used for the national system of indicators on this website are as follows:

  • The transportation sector uses passenger-miles and freight ton-miles
  • The industry sector uses the value of shipments (i.e., sales)
  • The residential sector uses households and estimates of residential floor space 
  • The commercial sector uses square feet of floor space as the activity measure
  • The electricity sector uses kilowatt hours of electricity produced

Passenger-miles traveled. The total distance traveled by all passengers. It is calculated as the product of the occupancy rate in vehicles and the vehicle miles traveled (see the EIA Energy Efficiency Glossary).

Ton-mile. The product of the distance freight is hauled, measured in miles, and the weight of the cargo being hauled, measured in tons. Thus, moving one ton of freight one mile generates one ton mile (see the EIA Energy Efficiency Glossary).

Other explanatory factors. Other explanatory factors are changes that affect the energy intensity of a sector or subsector that does not reflect changes in the efficiency with which energy is used. It is useful to differentiate these factors into structural changes, behavioral changes, and weather, although these distinctions are not always clear-cut.

Structural change is further defined below; behavioral changes are changes due to changes in consumer preferences that are reflected in choices that effect energy use, but are not directly tied to energy efficiency changes. A third category of factors are other factors over which we have no control; clearly weather dominates this third category, but there may be others.

Structural change. As it affects energy efficiency, structural change is a change in "other explanatory factors" that affects the energy intensity that is unrelated to the efficiency with which energy is used. For example, a change in product or industry mix in the industrial sector could affect energy intensity but a shift in industrial output is unrelated to actual energy efficiency improvements (e.g., a decline in steel production, or an increase in the output of the electronics industry relative to the growth of other industries). A second example of a structural factor is population migration. Migration of population from colder regions to warmer regions would alter the energy intensity of the residential sector, but would not, of itself, change the efficiency of energy use in the residential sector. Another example of structural change is the long-term trend in business activity in the U.S. from goods producing industries to service producing industries. For further discussion, see the section on Efficiency vs. Intensity.