Terms that are important to understand when learning about electricity production and consumption include:
- Generation is a measure of electricity produced over time. Most electric power plants use some of the electricity they produce to operate the power plant. Net generation excludes electricity use for power plant operations.
- Capacity is the maximum level of electric power (electricity) that a power plant can supply at a specific point in time under certain conditions.
- Sales includes the amount of electricity sold to customers over a period of time, and they account for most U.S. electricity consumption.
More electricity is generated than sold because some energy is lost (as heat) in electricity transmission and distribution. In addition, some electricity consumers generate electricity and use most or all of it, and the amount they use is called direct use. These consumers include industrial, commercial, and institutional facilities, as well as homeowners who have their own electricity generators. The United States also exports and imports some electricity to and from Canada and Mexico. Total U.S. electricity consumption by end-use consumers is equal to U.S. retail sales of electricity plus direct use of electricity.
The U.S. Energy Information Administration (EIA) publishes data on two general types of electricity generation and electricity generation-capacity:
- Utility scale includes electricity generation and capacity of electric power plants with at least 1,000 kilowatts, or 1 megawatt (MW), of total electricity-generation capacity.
- Small scale includes generators with less than 1 MW of generating capacity and that are usually located at or near where the electricity is consumed. Most solar photovoltaic systems installed on building rooftops are small-scale systems.
A standard unit for measuring electricity is the kilowatt (kW), which is equal to 1,000 Watts. A Watt is a measure of energy named after the Scottish engineer James Watt. One kW of electricity generated or used for one hour is a kilowatthour (kWh). Other units for measuring electricity capacity and electricity generation and consumption are:
- Megawatt (MW) = 1,000 kW; megawatthour (MWh) = 1,000 kWh
- Gigawatt (GW) = 1,000 MW; gigawatthour (GWH) = 1,000 MWh
In 2022, net generation of electricity from utility-scale generators in the United States was about 4,243 billion kilowatthours (kWh) (or about 4.24 trillion kWh). EIA estimates that an additional 58.51 billion kWh (or about 0.06 trillion kWh) were generated with small-scale solar photovoltaic (PV) systems.
In 2022, about 60% of U.S. utility-scale electricity generation was produced from fossil fuels (coal, natural gas, and petroleum), about 18% was from nuclear energy, and about 22% was from renewable energy sources.
- The percentage shares of utility-scale electricity generation by major energy sources in 2022 were:
- natural gas39.8%
- renewables (total)21.5%
- nonhydroelectric renewables15.3%
- petroleum and other0.9%
To ensure a steady supply of electricity to consumers, operators of the electric power system, or grid, call on electric power plants to produce and place the right amount of electricity on the grid at every moment to instantaneously meet and balance electricity demand.
In general, power plants do not generate electricity at their full capacities at every hour of the day. Three major types of generating units vary by intended usage:
- Base load generating units normally supply all or part of the minimum, or base, demand (load) on the electric power grid. A base load generating unit runs continuously, producing electricity at a nearly constant rate throughout most of the day. Nuclear power plants generally operate as base load service because of their low fuel costs and the technical limitations on load responsive operation. Geothermal and biomass units are also often operated in base load because of their low fuel costs. Many of the large hydro facilities, several coal plants, and an increasing number of natural gas-fired generators, particularly those in combined power applications, also supply base load power.
- Peak load generating units help to meet electricity demand when demand is at its highest, or peak, such as in the late afternoon when electricity use for air conditioning increases during hot weather. These so-called peaking units are generally natural gas- or petroleum-fueled generators. In general, these generators are relatively inefficient and are costly to operate but provide high- value service during peak demand periods. In some cases, pumped storage hydropower and conventional hydropower units also support grid operations by providing power during peak demand.
- Intermediate load generating units make up the largest generating sector and provide load responsive operation between base load and peaking service. The demand profile varies over time and intermediate sources are in general technically and economically suited for following the changes in demand. Many energy sources and technologies are used in intermediate operation. Natural gas-fired combined-cycle units, which currently provide more generation than any other technology, generally operate as intermediate sources.
Additional categories of electricity generators include:
- Intermittent renewable resource generators include wind and solar energy power plants, which generate electricity only when wind and solar energy resources are available. When these generators are operating, they tend to reduce the amount of electricity required from other generators to supply the electric power grid.
- Energy storage systems for electricity generation for electricity generation use electricity (or some other energy source, such as solar-thermal energy) to charge an energy storage system or device, which is discharged to supply (generate) electricity when needed at desired levels and quality. ESSs provide a variety of services to support electric power grids. In some cases, ESSs may be paired or co-located with other generation resources to improve the economic efficiency of one or both systems.
- Distributed generators are connected to the electricity grid, but they primarily supply some or all of the electricity demand of individual buildings or facilities. Sometimes, these systems may generate more electricity than the facility consumes, in which case the surplus electricity is sent to the grid. Most small-scale solar photovoltaic systems are distributed generators.
Some types of power plants may actually use more electricity to operate than they generate, and therefore, may have negative net generation on a monthly or annual basis. For example, peak-load generating units may be idle for relatively long periods of time. However, they require power from the power plant that they are part of, or from the electric power grid, to be in operable condition when called upon to supply power. Over an entire month or year, their electric generation may be less than the power they used while they were waiting to be dispatched. Power plant maintenance or repair activities may also take generators off-line for extended periods of time, which may result in negative net generation for the facility. Energy storage facilities for electricity generation (generally) use more electricity than they generate and have negative generation.
At the end of 2022, the United States had 1,160,169 MW—or about 1.16 billion kW—of total utility-scale electricity-generation capacity and about 39,486 MW—or nearly 0.04 billion kW—of small-scale solar photovoltaic electricity-generation capacity.
Generating units fueled primarily with natural gas account for the largest share of utility-scale electricity-generation capacity in the United States.
- The percentage shares of total U.S. utility-scale electricity-generation capacity by primary energy source in 2022 were:
- natural gas43%
- renewables (total)29%
- other sources0.3%
The U.S. Energy Information publishes data for three categories of electricity-generation capacity. Nameplate capacity, determined by the generator's manufacturer, is the generating unit's maximum output of electricity without exceeding specified thermal limits. Net summer capacity and net winter capacity are the maximum instantaneous electricity load a generator can support during the summer or winter, respectively. These values may differ because of seasonal variations in the temperature of generator cooling fluid (water or ambient air). EIA reports electric generation capacity as net summer capacity in most of its electricity data reports.
Energy sources for U.S. electricity generation
The mix of energy sources for U.S. electricity generation in the United States has changed over time, especially in recent years. Natural gas and renewable energy sources account for an increasing share of U.S. electricity generation, and coal-fired electricity generation has declined. In 1990, coal-fired power plants accounted for about 42% of total U.S. utility-scale electricity-generation capacity and about 52% of total electricity generation. By the end of 2022, coal's share of electricity-generation capacity was 17% and coal accounted for about 20% of total utility-scale electricity generation. During the same period, the share of natural gas-fired electricity-generation capacity increased from 17% in 1990 to 43% in 2022, and its share of electricity generation more than tripled from 12% in 1990 to 40% in 2022.
Most U.S. nuclear and hydropower plants were built before 1990. Nuclear energy's share of total annual U.S. electricity generation has held steady at about 20% since 1990. Electricity generation from hydropower, historically the leading source of total annual utility-scale renewable electricity generation (until 2014), fluctuates from year to year because of precipitation patterns.
Electricity generation from nonhydro renewables
Renewable electricity generation from sources other than hydropower has steadily increased in recent years, mainly because of additions to wind and solar generating capacity. Since 2013, total annual electricity generation from utility-scale nonhydro renewable sources has been greater than total annual hydropower generation.
Wind energy's share of total utility-scale electricity- generation capacity in the United States grew from 0.2% in 1990 to about 12% in 2022, and its share of total annual utility-scale electricity generation grew from less than 1% in 1990 to about 10% in 2022.
Although relatively small in terms of its share of total U.S. electricity-generation capacity and generation, solar electricity-generation capacity and generation have grown significantly in recent years. Utility-scale solar electricity-generation capacity rose from about 314 MW—or 314,000 kW—in 1990 to about 72,108 MW—about 72 million kW—at the end of 2022. About 98% was solar photovoltaic systems and 2% was solar thermal-electric systems. Solar energy's share of total U.S. utility-scale electricity generation in 2022 was about 3.4%, up from less than 0.1% in 1990. In addition, EIA estimates that at the end of 2022, the United States had 39,487 MW of small-scale solar photovoltaic-generation capacity, and electricity generation from small-scale photovoltaic systems was about 59 billion kWh.
The number of small-scale solar photovoltaic (PV) systems, such as those on rooftops, has grown significantly in the United States over the past several years. Estimates of small-scale solar PV capacity and generation by state and sector are included in the Electric Power Monthly. As of the end of 2022, almost 36% of total U.S. small-scale solar PV electricity-generation capacity was in California.
Factors that affect the mix of energy sources for electricity generation
The major factors that have contributed to changes in the U.S. electricity generation mix in recent years include:
- The combined effect of several years of low natural gas prices and the performance advantages of new natural gas technologies, particularly highly efficient combined cycle generators
- Generally decreasing costs for deploying wind and solar generators
- State requirements to use more renewable energy sources
- Availability of government and other financial incentives for building new renewable capacity
- Federal air pollution emission regulations for power plants
- Slowing growth in electricity demand
A general decline in the price of natural gas for electric power producers has been a major factor in the rise of natural gas-fired electricity generation and the decline of coal-fired electricity generation since 2008. When natural gas prices are relatively low, high-efficiency, natural gas-fired combined-cycle generators can supply electricity at a lower cost than coal-fired generators. Coal-fired power plants then operate less often and earn less revenue, which decreases their profitability and reduces the incentive to invest in new coal-fired generation capacity. Sustained low natural gas prices encourage development of new natural-gas fired capacity. Unlike coal-fired generators, natural gas-fired-generators:
- Can be added in smaller increments to meet grid generating capacity requirements
- Can respond more quickly to changes in hourly electricity demand
- Generally have lower compliance costs for environmental regulations
Retail electricity sales
U.S. retail electricity sales to end-use customers was about 3,909 billion kWh—or about 3.9 trillion kWh—in 2022, an increase of about 103 billion kWh from 2021. Retail sales include net imports (imports minus exports) of electricity from Canada and Mexico.
- The sales of electricity to major types of U.S. retail customers and percentage shares of total sales in 2022 were:
- residential1,522 billion kWh39%
- commercial1,373 billion kWh35%
- industrial1,008 billion kWh26%
- transportation7 billion kWh0.2%
Electricity is sold by different types of providers
Electricity providers can be grouped into full-service providers, which sell bundled electricity services—energy (electricity) and delivery—to end users and other providers.
Full-service providers may generate electricity from power plants that they own and sell the electricity to their customers, and they may sell some of it to other types of providers. They may also, in turn, purchase electricity from other full-service providers or from independent power producers, which these providers sell to their customers. Full-service providers include:
- Investor-owned utilities are electric utilities whose stock is publicly traded.
- Public entities include municipalities, state power agencies, and municipal marketing authorities.
- Federal entities are either owned or financed by the federal government.
- Cooperatives are electric utilities owned by and operated for the benefit of the members of the cooperative.
Other providers market and sell electricity to the customers of full-service providers or provide only electricity delivery services to consumers. They mostly include electricity marketers that operate in states that have customer choice for selecting electricity providers. Full-service providers deliver the electricity for the electricity marketers to consumers. Direct electricity transactions also occur from independent power producers to (usually large) electricity consumers.
- The percentage shares of electricity sales by type of provider in 2021 were:
- investor-owned utilities57%
- public and federal entities16%
- other providers15%
In addition to sales to end-use customers, electricity is also often traded on wholesale markets or through bilateral contracts.
Last updated: June 30, 2023, with data from the February 2023 edition of the Electric Power Monthly; data for 2022 are preliminary.