Electricity in the U.S. basics

Electricity in the United States is produced with diverse energy sources and technologies

The United States uses many different energy sources and technologies to generate electricity. The sources and technologies have changed over time and some are used more than others.

The three major categories of energy for electricity generation are fossil fuels (coal, natural gas, and petroleum), nuclear energy, and renewable energy sources. Most electricity is generated with steam turbines using fossil fuels, nuclear, biomass, geothermal, and solar thermal energy. Other major electricity generation technologies include gas turbines, hydro turbines, wind turbines, and solar photovoltaics.

Fossil fuels are the largest sources of energy for electricity generation

Natural gas was the largest source—about 40%—of U.S. utility-scale electricity generation in 2022. Utility-scale are systems with at least 1,000 kilowatts (or 1 megawatt) of electricity generation capacity. Natural gas is used in steam turbines and gas turbines to generate electricity.

Coal was the third-largest energy source for U.S. utility-scale electricity generation in 2022—about 18%. Nearly all coal-fired power plants use steam turbines. A few coal-fired power plants convert coal to a gas for use in a gas turbine to generate electricity.

Petroleum was the source of less than 1% of U.S. utility-scale electricity generation in 2022. Residual fuel oil and petroleum coke are used in steam turbines. Distillate—or diesel—fuel oil is used in diesel-engine generators. Residual fuel oil and distillates can also be burned in gas turbines.

Nuclear energy provides about one-fifth of U.S. electricity

Nuclear energy was the source of about 18% of U.S. utility-scale electricity generation in 2022. Nuclear power plants use steam turbines to produce electricity from nuclear fission.

Renewable energy sources provide nearly 20% of U.S. electricity

A variety of renewable energy sources are used to generate electricity and were the source of about 22% of total U.S. utility-scale electricity generation in 2022.

Wind energy was the source of about 10.2% of total U.S. utility-scale electricity generation and accounted for 47.6% of utility-scale electricity generation from all renewable energy sources in 2022. Wind turbines convert wind energy into electricity.

Hydropower plants produced about 6.2% of total U.S. utility-scale electricity generation and accounted for 28.7% of utility-scale electricity generation from renewable sources in 2022. Hydropower plants use flowing water to spin a turbine connected to a generator.

Solar energy provided about 3.4% of total U.S. utility-scale electricity and accounted for 15.9% of utility-scale electricity generation from renewable sources in 2022. Photovoltaic (PV) and solar-thermal power are the two main types of solar electricity generation technologies. PV conversion produces electricity directly from sunlight in a photovoltaic cell. Most solar-thermal power systems use steam turbines to generate electricity. EIA estimates that about 0.06 trillion kWh of electricity were generated with small-scale solar photovoltaic systems in 2022. Small-scale includes systems with less than 1,000 kilowatts of electricity generation capacity.

Biomasswas the source of about 1.3% of total U.S. utility-scale electricity generation and accounted for 5.9% of electricity generation from renewable sources in 2022. Biomass is burned directly in steam-electric power plants, or it can be converted to a gas that can be burned in steam generators, gas turbines, or internal combustion engine generators.

Geothermal power plants produced about 0.4% of total U.S. utility-scale electricity generation and accounted for 1.9% of electricity generation from renewable sources in 2022. Geothermal power plants use steam turbines to generate electricity.

How electricity gets to your home

The electric power grid

Electricity is generated at power plants and then travels through a complex system, often called the grid. The grid includes electricity substations, transformers, and power lines that connect electricity producers and consumers. Most local grids are interconnected to each other, forming larger, reliable networks that ensure there is always enough electricity to meet demand.

In the United States, the electricity grid is made up of thousands of miles of high-voltage power lines and millions of miles of low-voltage power lines. This network connects thousands of power plants to hundreds of millions of electricity customers across the country.

Electricity sources and types of providers

The source of the electricity you buy varies. Some electric utilities generate all the electricity they sell using their own power plants. Other utilities buy electricity from different utilities, power marketers, independent power producers, or from wholesale markets.

The way electricity is sold to you varies from region to region. The company selling you power may be:

• A not-for-profit municipal electric utility (owned by the city or local government)
• An electric cooperative owned by its members (owned by stockholders, often called an investor-owned utility)
• A private, for-profit electric utility (owned by stockholders, often called an investor-owned utility)

In some states, electric utility customers can buy electricity directly from a power marketer, and a local utility delivers it. A few federally owned power authorities—including the Bonneville Power Administration and the Tennessee Valley Authority, among others—also generate, buy, sell, and distribute power. No matter the electricity’s source, local electric utilities operate the distribution system that connects homes and businesses to the grid.

Delivering electricity

Power plants generate electricity, which they send to customers through transmission and distribution power lines.

• High-voltage transmission lines, such as those hanging between tall metal towers, carry electricity over long distances. Higher-voltage electricity makes long-distance electricity transmission more efficient and less expensive.
• Distribution transmission lines carry the lower-voltage electricity, which is safer to use in homes and businesses, and delivers it to customers.
• Transformers at substations play a crucial role. They either increase (step up) or reduce (step down) voltages to adjust to the different stages of the journey—from the power plant on long-distance transmission lines to the distribution lines that deliver electricity to homes and businesses.

Evolution of the electric power grid

At the beginning of the 20th century, more than 4,000 isolated electric utilities operated in the United States. As the demand for electricity grew, especially after World War II, these lone utilities began to connect their transmission systems to each other. These connections allowed utilities to share the economic benefits of building large and often jointly owned power plants to serve their combined electricity demand at the lowest possible cost. Interconnection also reduced the amount of extra generating capacity each utility had to have available to ensure reliable service during peak demand. Over time, three large, interconnected systems evolved in the United States.

U.S. electrical system interconnections

For the electricity grid to remain stable, the amount of electricity supplied must match electricity demand. To achieve this balance, the different organizations that operate different parts of the grid must work together.

The U.S. electric grid in the Lower 48 states has three main interconnections. These interconnections mostly operate independently from each other and rarely transfer electricity among them:

• The Eastern Interconnection covers the area east of the Rocky Mountains and a part of the Texas panhandle.
• The Western Interconnection covers the area from the Rocky Mountains to the west.
• The Electric Reliability Council of Texas (ERCOT) covers most of Texas.

The Eastern and Western Interconnections are also linked to Canada's power grid. This network structure makes the grid more reliable by providing multiple paths for power to flow and allowing generators to supply electricity to many different areas. This redundancy helps prevent widespread blackouts if a transmission line or power plant fails.

Balancing authorities

The three major grid interconnections describe the physical structure of the grid. The day-to-day operation of the electric system within regions is managed by entities called balancing authorities. They ensure electricity supply constantly matches power demand. Most balancing authorities are electric utilities that have taken on the balancing responsibilities for their part of the power system. All regional transmission organizations in the United States also act as balancing authorities. ERCOT is unique because the balancing authority, interconnection, and regional transmission organization are all the same entity and physical system.

A balancing authority ensures that electricity demand and supply are precisely balanced to keep the grid safe and reliable. If electricity demand and supply fall out of balance, local or even widespread blackouts can happen. Balancing authorities maintain proper operating conditions by ensuring enough electricity is available for expected demand, which includes managing electricity transfers with other balancing authorities.

Electric reliability organizations

Electric utilities are responsible for keeping their systems safe and planning for future power needs. Initially, the electric power industry developed voluntary standards for coordination. Today, utilities have mandatory reliability standards for planning and operating power systems and for addressing security threats to critical electrical infrastructure. The North American Electric Reliability Corporation develops and enforces mandatory grid reliability standards, which are approved by the Federal Energy Regulatory Commission (FERC). Canada has its own regulators that fill this role.

Challenges facing the power grid

Construction of U.S. electricity infrastructure began in the early 1900s, driven by new technologies, central-station generating plants, and growing electricity demand, especially after World War II. Now, some of the older transmission and distribution lines have reached the end of their useful lives and must be replaced or upgraded. New power lines are also needed to maintain overall reliability and to connect to new renewable energy generation resources, such as wind and solar, which are often located far from cities, where electricity demand is highest.

Several challenges exist for improving the grid's infrastructure:

• Siting new transmission lines (getting approval for new routes and acquiring the necessary land can be difficult)
• Determining how to fairly recover the construction costs of a new transmission line built in one state when it also benefits customers in other states
• Addressing uncertainty in federal regulations about who pays for new transmission lines, which affects the ability of private companies to raise money for construction
• Expanding long-distance transmission lines to reach high-quality wind and solar resources, which are often far from population centers
• Protecting the grid from physical and cyber attacks

Electricity & the environment

Although electricity is a clean and relatively safe form of energy when it is used, the generation and transmission of electricity affects the environment. Nearly all types of electric power plants have an effect on the environment, but some power plants have larger effects than others.

The United States has laws that govern the effects that electricity generation and transmission have on the environment. The Clean Air Act regulates air pollutant emissions from most power plants. The U.S. Environmental Protection Agency (EPA) administers the Clean Air Act and sets emissions standards for power plants through various programs such as the Acid Rain Program. The Clean Air Act has helped to substantially reduce emissions of some major air pollutants in the United States.

The effect of power plants on the landscape

All power plants have a physical footprint (the location of the power plant). Some power plants are located inside, on, or next to an existing building, so the footprint is fairly small. Most large power plants require land clearing to build the power plant. Some power plants may also require access roads, railroads, and pipelines for fuel delivery, electricity transmission lines, and cooling water supplies. Power plants that burn solid fuels may have areas to store the combustion ash.

Many power plants are large structures that alter the visual landscape. In general, the larger the structure, the more likely it is that the power plant will affect the visual landscape.

Fossil fuel, biomass, and waste burning power plants

In the United States, about 61% of total electricity generation in 2021 was produced from fossil fuels (coal, natural gas, and petroleum), and about 1.3% was produced from materials that come from plants (biomass), and municipal and industrial wastes. The substances that occur in combustion gases when these fuels are burned include

• Carbon dioxide (CO2)
• Carbon monoxide (CO)
• Sulfur dioxide (SO2)
• Nitrogen oxides (NOx)
• Particulate matter (PM)
• Heavy metals such as mercury

Nearly all combustion byproducts have negative effects on the environment and human health:

• CO2 is a greenhouse gas, which contributes to the greenhouse effect.
• SO2 causes acid rain, which is harmful to plants and to animals that live in water. SO2 also worsens respiratory illnesses and heart diseases, particularly in children and the elderly.
• NOx contribute to ground-level ozone, which irritates and damages the lungs.
• PM results in hazy conditions in cites and scenic areas and coupled with ozone, contributes to asthma and chronic bronchitis, especially in children and the elderly. Very small, or fine PM, is also believed to cause emphysema and lung cancer.
• Heavy metals such as mercury are hazardous to human and animal health.

Power plants reduce air pollution emissions in various ways

Air pollution emission standards limit the amounts of some of the substances that power plants can release into the air. Some of the ways that power plants meet these standards include:

• Burning low-sulfur-content coal to reduce SO2 emissions. Some coal-fired power plants cofire wood chips with coal to reduce SO2 emissions. Pretreating and processing coal can also reduce the level of undesirable compounds in combustion gases.
• Different kinds of particulate emission control devices treat combustion gases before they exit the power plant:
  • Bag-houses are large filters that trap particulates.
  • Electrostatic precipitators use electrically charged plates that attract and pull particulates out of the combustion gas.
  • Wet scrubbers use a liquid solution to remove PM from combustion gas.
• Wet and dry scrubbers mix lime in the fuel (coal) or spray a lime solution into combustion gases to reduce SO2 emissions. Fluidized bed combustion also results in lower SO2 emissions.
• NOx emissions controls include low NOx burners during the combustion phase or selective catalytic and non-catalytic converters during the post combustion phase.

Many U.S. power plants produce CO2 emissions

The electric power sector is a large source of U.S. CO2 emissions. Electric power sector power plants that burned fossil fuels or materials made from fossil fuels, and some geothermal power plants, were the source of about 32% of total U.S. energy-related CO2 emissions in 2021.

Some power plants also produce liquid and solid wastes

Ash is the solid residue that results from burning solid fuels such as coal, biomass, and municipal solid waste. Bottom ash includes the largest particles that collect at the bottom of the combustion chamber of power plant boilers. Fly ash is the smaller and lighter particulates that collect in air emission control devices. Fly ash is usually mixed with bottom ash. The ash contains all the hazardous materials that pollution control devices capture. Many coal-fired power plants store ash sludge (ash mixed with water) in retention ponds. Several of these ponds have burst and caused extensive damage and pollution downstream. Some coal-fired power plants send ash to landfills or sell ash for use in making concrete blocks or asphalt.

Nuclear power plants produce different kinds of waste

Nuclear power plants do not produce greenhouse gases or PM, SO2, or NOx, but they do produce two general types of radioactive waste:

• Low-level waste, such as contaminated protective shoe covers, clothing, wiping rags, mops, filters, reactor water treatment residues, equipment, and tools, is stored at nuclear power plants until the radioactivity in the waste decays to a level safe for disposal as ordinary trash, or it is sent to a low-level radioactive waste disposal site.
• High-level waste, which includes the highly radioactive spent (used) nuclear fuel assemblies, must be stored in specially designed storage containers and facilities (see Interim storage and final disposal in the United States).

Electric power lines and other distribution infrastructure also have a footprint

Electricity transmission lines and the distribution infrastructure that carries electricity from power plants to customers also have environmental effects. Most transmission lines are above ground on large towers. The towers and power lines alter the visual landscape, especially when they pass through undeveloped areas. Vegetation near power lines may be disturbed and may have to be continually managed to keep it away from the power lines. These activities can affect native plant populations and wildlife. Power lines can be placed underground, but it is a more expensive option and usually not done outside of urban areas.