U.S. Energy Information Administration logo

Electricity

‹ See all Electricity Reports

Electricity Monthly Update

With Data for April 2019  |  Release Date: June 25, 2019  |  Next Release Date: July 24, 2019

Previous Issues

Highlights: April 2019

  • Wholesale natural gas prices dropped considerably in the West after March’s record highs.
  • Many electricity systems set new 12-month daily low demand days during April.
  • After five consecutive month-over-month decreases, U.S. coal stockpiles saw an 11% increase compared to the previous month, now putting total U.S. coal stockpiles at 108 million tons.

Key indicators

Statewide average temperature ranks
Statewide precipitation ranks
Total net generation
Net generation by select fuel sources

Wind and solar capacity factors vary by both season and region

The capacity factor of a power generating facility is a measure of how much energy is produced by a power generating facility compared with its maximum output. It is measured as a percentage, generally by dividing the total energy produced during a given period of time by the amount of energy the plant would have produced if it had ran at full output during that time. In 2018, for example, nuclear generators (93%) and natural gas combined-cycle generators (58%) were on the higher end of the range of capacity factors, while renewables such as wind (37%) and photovoltaic solar (26%) were on the lower end. Geothermal is the one renewable that is at the higher end of the range with a capacity factor of 77%. The main reason for a reduced capacity factor for wind and solar technologies is the availability of the energy source. The local atmospheric conditions of a season and the geographic conditions of a region drive the variability of renewable performance.

U.S. Operating Utility-scale Battery Storage as of February 2019 Source: U.S. Energy Information Administration, Form EIA-923, Power Plant Operations Report; Form EIA-860, Annual Electric Generator Report; and Form EIA-860M, Preliminary Monthly Electric Generator Inventory. Months by season include spring (March, April, and May), summer (June, July, and August), fall (September, October, and November), and winter (December, January, and February).
Note: Data for 2018 and 2019 are preliminary.

On a national basis, wind plant capacity factors tend to be the highest in the spring, with capacity factors dropping about 30% during the summer before ramping up again in mid to late fall and winter. The chart above illustrates the median capacity factor by season for the five-year period from spring 2014 through winter 2019. The median value represents the middle value of all wind plant capacity factors for that period. In other words, 50% of plants have capacity factors higher than the median and 50% of plants have capacity factors lower than the median. In addition, 25% of all wind plants have a capacity factor lower than the first quartile and 25% of all plants have a capacity factor higher than the third quartile value. For the Spring 2014 to Winter 2019 period, the median wind capacity factor ranges from 38.2% in spring and 26.4% in summer to 33.6% in fall and 38.1% in winter.

U.S. Operating Utility-scale Battery Storage as of February 2019 Source: U.S. Energy Information Administration, Form EIA-923, Power Plant Operations Report; Form EIA-860, Annual Electric Generator Report; and Form EIA-860M, Preliminary Monthly Electric Generator Inventory. See census map for census division locations.
Note: Data for 2018 and 2019 are preliminary.

These trends can also be seen at the regional level using census divisions. The national seasonal pattern is well represented by traditional wind generating regions such as the West South Central Division (Texas and Oklahoma), the West North Central Division (Iowa, North Dakotas, and Kansas), and the East North Central Division (Michigan, Illinois, and Indiana). However, not all divisions have the same trend. The Contiguous Pacific Division (California, Oregon, and Washington) has nearly the inverse; wind generation increases during late spring, peaks in June, and gradually decreases through the fall until December. This inverse results from the combination of cold Pacific currents flowing along the coast and the land-sea breeze effect working against the normal west-to-east winds.

U.S. Operating Utility-scale Battery Storage as of February 2019 Source: U.S. Energy Information Administration, Form EIA-923, Power Plant Operations Report; Form EIA-860, Annual Electric Generator Report; and Form EIA-860M, Preliminary Monthly Electric Generator Inventory. See census map for census division locations.
Note: Data for 2018 and 2019 are preliminary.

The West South Central (40.2%) and West North Central (40.7%) Divisions have the two highest median average capacity factors, as well as the narrowest spread between the first and third quartile. This combination of factors would indicate solid and consistent wind resources for these areas. These two regions comprise an emerging area of increasing wind generation stretching from Texas all the way to North Dakota. In contrast, the East North Central Division, the fourth-largest wind generation division, has a wider spread in capacity factors relative to its median. This spread would indicate a fair amount of variance in capacity factors for this region.

U.S. Operating Utility-scale Battery Storage as of February 2019 Source: U.S. Energy Information Administration, Form EIA-923, Power Plant Operations Report; Form EIA-860, Annual Electric Generator Report; and Form EIA-860M, Preliminary Monthly Electric Generator Inventory. Months by season include spring (March, April, and May), summer (June, July, and August), fall (September, October, and November), and winter (December, January, and February).
Note: Data for 2018 and 2019 are preliminary.

In contrast to wind facilities, photovoltaic plant performance peaks in the summer because the days are longer. The median solar capacity factors goes from 27.5% in spring to 30.2% in summer, and it then declines to 22.6% in fall and 16.7% in winter. The trend of average capacity factor for solar is fairly consistent for all regions since it is dependent on the seasonal sun patterns that are universal across all regions. This also makes the spread across seasons consistent and narrow.

U.S. Operating Utility-scale Battery Storage as of February 2019 Source: U.S. Energy Information Administration, Form EIA-923, Power Plant Operations Report; Form EIA-860, Annual Electric Generator Report; and Form EIA-860M, Preliminary Monthly Electric Generator Inventory. See census map for census division locations.
Note: Data for 2018 and 2019 are preliminary.

The top regions for average solar capacity factors are the Pacific Contiguous, Mountain, and West South Central census divisions. All three divisions, like most divisions, have experienced their highest average capacity factors in June, with the Pacific Contiguous at 39.5%, Mountain at 35.5%, and West South Central at 31.3%. At the lower end of the scale is the Middle Atlantic (22.7% for July) and New England (19.3% for June). The Contiguous Pacific, Mountain, and West South Central Divisions have higher average capacity factors because they have more sunshine, and the New England and the Middle Atlantic Divisions have lower average capacity factors because they have more snow, rain, haze and cloud coverage.

U.S. Operating Utility-scale Battery Storage as of February 2019 Source: U.S. Energy Information Administration, Form EIA-923, Power Plant Operations Report; Form EIA-860, Annual Electric Generator Report; and Form EIA-860M, Preliminary Monthly Electric Generator Inventory. See census map for census division locations.
Note: Data for 2018 and 2019 are preliminary.

Looking at the regional level for the Spring 2014 to Winter 2019 period, the Pacific Contiguous (24.4%), Mountain (23.5%), and the South Atlantic (22.2%) have the highest median capacity factors. These figures are consistent with the weather patterns that characterize those areas.


Principal Contributor:

Brady Tyra
(Brady.Tyra@eia.gov)

Print this issue Download the data (csv)

In this Issue:

Highlights

End Use

Resource Use

Regional Wholesale Markets

Coal Stocks

Data Tables

About Electricity Monthly Update

Electricity Monthly Update Explained

Methodology & Documentation

Contact Information & Staff