Electric Power Sector Basics

Across the United States, over 11,000 utility-scale power plants generate electricity that is transmitted to customers via the nation's electric power grid. Learn how the power sector has changed over time, how power sector emissions affect human health and the environment, and how EPA’s programs reduce emissions.

Learn more about the U.S. Electric Power Sector:

How Is Electricity Generated?

A range of technologies generate electricity in the U.S. The power sector consists of electricity generators operating in interconnected grid systems, usually regional in scale (in the lower 48 states).

Power plants generate electricity through various technologies that use fossil fuels, nuclear fuels, or renewable energy. Power plants that burn fuels generally use steam boilers, combustion turbines, or both.

Steam boilers burn fuel to heat water and produce steam. This steam is then channeled through a turbine, where it turns the blades and generates electricity.

Combustion turbines burn fuels to create exhaust gases, which spin the turbine to generate electricity. Some combustion turbines use waste heat from fuel combustion to produce steam to turn the blades of another turbine to generate electricity. These types of power plants are referred to as combined cycle power plants and are more efficient than steam boilers or combustion turbines alone.

Many power plants do not burn any fuel to generate electricity. Nuclear power plants are like steam boilers, but the steam is produced from nuclear reactions rather than from fuel combustion. Wind turbines and hydropower use wind or flowing water, respectively, to spin turbine blades that are connected to electricity generators. Solar thermal power plants are like steam boilers, but the steam is produced from concentrated solar energy instead of fuel combustion. Solar photovoltaic (PV) panels absorb light energy from the sun, charging electrons to generate electricity.

How is Electricity Delivered?

After electricity is generated, electrical equipment such as high voltage lines, substations, and transformers safely transmit electricity from its point of generation to the area where it is finally distributed to customers. This process requires careful planning and coordination among grid operators to ensure successful delivery of electricity and is affected by new power generation and storage sources connecting to the grid. Interact with the diagram below by clicking each component and visit U.S. Energy Information Agency’s “Electricity explained: How electricity is delivered to customers” for more information.

Electric utilities and grid operators need to ensure that enough power will be generated to meet demand. As the name implies, "baseload” power plants, such as large nuclear and fossil fuel power plants, operate without much interruption throughout the year. Intermediate, or load-following power plants, adjust their electricity output as demand for electricity fluctuates throughout the day. During times of peak electricity demand, "peaker plants" (power plants that only operate during peak demand) can supplement electricity to meet demand. When electricity supply is greater than demand, excess electricity can be stored for later use. As more renewable energy power plants are connected to the electric power grid, energy storage technologies (e.g., batteries, pumped storage) play a more important role in the electricity system as it helps align renewable energy generation produced in off-peak hours with period of higher electricity demand. Generation is often measured in kilowatt-hours (kWh), megawatt-hours (MWh), or gigawatt-hours (1 GWh = 1 million kWh).

How Is Electricity Used?

Electricity is integral to modern life – used for residential, commercial, industrial, and transportation purposes. Today, there are approximately 11,000 utility-scale electric power plants in the U.S., providing electricity through over 160,000 miles of high voltage lines. Users rely on electricity for lighting, heating, cooling, refrigeration, vehicle charging, manufacturing, and for operating appliances, computers, and electronics.

The following chart is interactive. Click to see each sector's respective electricity consumption.

What Are Fuel Sources for Electricity?

Energy sources range from emissions-intensive (e.g., coal) to zero-emitting (e.g., nuclear, solar, wind, and hydro). The use of coal and natural gas to produce electricity is the key driver of the power sector’s overall pollution emission levels.

In 2022, fossil fuels remained the most common fuel type for electricity production in the U.S. The primary fuel type was natural gas, accounting for about 39.8% of total energy production nationwide. Coal was the second most common fuel type, accounting for 19.7% of electricity production. Nuclear was third at 18.2%. Zip code-level electricity mix data are available on Power Profiler.

What Are the Public Health and Environmental Impacts of Electricity Generation?

Fossil fuel-fired power plants remain a leading source of air pollution. Each fossil fuel has unique impacts on the environment. For example, coal combustion is the largest single source of sulfur dioxide (SO₂) emissions and the second largest source of nitrogen oxides (NO_X), which together form fine particulate matter (PM).  NO_X emissions also lead to the formation of ground-level ozone. Fossil fuel combustion also produces significantly more greenhouse gas emissions, such as carbon dioxide, per unit of energy produced. Toxic heavy metals such as mercury (Hg) are also a byproduct of fossil fuel combustion, threatening the environment and human health.

In addition, SO₂ and NO_X emissions and resulting atmospheric deposition of pollution cause acid rain, which damages lakes, streams, forests, grasslands, and other ecosystems in the U.S. NO_X emissions are a large source of atmospherically deposited nitrogen, which contributes to nutrient enrichment of aquatic and terrestrial ecosystems. This increased nitrogen pollution reduces plant biodiversity, causes eutrophication of freshwater waterbodies and coastal estuaries, and may lead to harmful algal blooms.

Mining, drilling, and extraction of fossil fuels also adversely impact the surrounding water, soil, and air. More information and resources on the air quality and health impacts of SO₂, NO_X, and greenhouse gas emissions can be found in the human health impacts webpage.

How Can Power Plants Reduce Emissions?

There are various technological, operational, and management options for power plants that burn fossil fuels to reduce their emissions.

Pollution control technologies such as:

• Fluidized gas desulfurization (FGD) to reduce SO₂ and PM
• Selective catalytic and non-catalytic reduction (SCR and SNCR) and combustion controls such as low NO_X burners and overfire air to reduce NO_X
• Bag houses and electrostatic precipitators to reduce PM
• Activated carbon injection and dry sorbent injection technologies to reduce mercury
• Carbon capture utilization and storage (CCUS) to reduce CO₂ emissions
• Improved efficiency (heat rate) lowers fuel use and corresponding emissions per unit of electricity
• Fuel switching from higher to lower emitting fuels also lowers the environmental footprint from a fleet perspective

For more information on the U.S. electricity system, see the U.S. Energy Information Agency’s "Electricity Explained" webpage and the EPA's "About the U.S. Electricity System and its Impact on the Environment" webpage.

The Green Power Markets web area has series of webpages that explore the history and operations of the U.S. green power market.

The electric power sector is rapidly transforming, and use of renewable energy sources in the grid is expanding rapidly, along with increased electricity storage capability. Learn more about how the electric power sector has evolved over time ►

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