U.S. Energy Information Administration logo
Skip to sub-navigation

Frequently Asked Questions (FAQs)

This page has no sub-navigation. Skip to page content.

What is the difference between electricity generation capacity and electricity generation?

Electricity generation capacity is the maximum electric output an electricity generator can produce under specific conditions. Nameplate generator capacity is determined by the generator's manufacturer and indicates the maximum output of electricity a generator can produce without exceeding design thermal limits.

Net summer electricity generation capacity and net winter electricity generation capacity are typically determined by a performance test and indicate the maximum electricity load a generator can support at the point of interconnection with the electricity transmission and distribution system during the respective season. Two primary factors affect or determine the difference in capacity between summer and winter months:

  • The temperature of cooling water for thermal power plants or the temperature of the ambient air for combustion turbines
  • The water flow and reservoir storage characteristics for hydropower plants

Electricity generation is the amount of electricity a generator produces during a specific period of time. For example, a generator with 1 megawatt (MW) capacity that operates at that capacity consistently for one hour will produce 1 megawatthour (MWh) of electricity. If the generator operates at only half that capacity for one hour, it will produce 0.5 MWh of electricity. Many generators do not operate at their full capacity all the time. A generator's output may vary according to conditions at the power plant, fuel costs, and/or as instructed by the electric power grid operator.

Electricity net generation is the amount of gross electricity generation a generator produces minus the electricity used to operate the power plant. These electricity uses include fuel handling equipment, water pumps, combustion and cooling air fans, pollution control equipment, and other electricity needs.

Capacity factor of electricity generation is a measure (expressed as a percentage) of how often an electricity generator operates during a specific period of time using a ratio of the actual output to the maximum possible output during that time period.

Learn more:
Energy Explained: Electricity in the United States
Data on electric power plants generating capacity
Data on electricity generation and thermal output
Existing nameplate and net summer capacity by state, type of producer, and energy source (historical data file from1990 to most recent year available)
Net generation by state, type of producer, and energy source (historical data file from1990 to most recent year available)
Electric Power Monthly: includes monthly and annual data on electricity generation, generation capacity, and capacity factors; the Technical notes include a formula for calculating capacity factor on page 21
Electricity Monthly Update
Today in Energy articles on electricity

Last updated: February 11, 2021

Other FAQs about Electricity