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Electricity Monthly Update

With Data for September 2018  |  Release Date: Nov. 27, 2018  |  Next Release Date: Dec. 26, 2018

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Highlights: September 2018

  • Wholesale electricity prices were much lower across the country compared to July and August.
  • Electricity system demand in the Northeast neared 12-month highs early in the month and neared 12-month lows late in the month as temperatures cooled considerably throughout September.
  • U.S. coal stockpiles were down to 101 million tons in September 2018, which is the lowest observed level of total U.S. coal stockpiles since 2005.

Key indicators

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

The average U.S. electricity customer experienced double the minutes of interruptions in 2017 than in the previous year

In 2017, electric utilities reported annual reliability metrics that accounted for 94% of U.S. electric customers. Reporting has slowly increased from 90% of customers in 2013, when EIA first started collecting this data. By state, these values range from 72% of customers in North and South Dakota to 99% of customers in California, Connecticut, Florida, Hawaii, Maryland, Rhode Island, West Virginia and the District of Columbia. Furthermore, of the reported data, 78% of customers received service from a utility that reported data using standards developed by the Institute of Electrical and Electronics Engineers (IEEE), a professional trade association for electric and information technologies and related fields.

Coverage for electricity reliability statistics Source: U.S. Energy Information Administration, Annual Electric Power Industry Report, Form EIA-861 data file

Reliability of electricity supply systems is usually measured using two metrics that show the average customer duration and frequency of sustained interruption events—the System Average Interruption Duration Index (SAIDI) and the System Average Interruption Frequency Index (SAIFI). For utilities using the IEEE standard, sustained events are interruptions that last longer than five minutes and momentary events are interruptions that last five minutes or less.

Utilities that report SAIDI and SAIFI data to EIA have several options to report this data. Most utilities report all sustained interruptions, and some utilities can also provide data that exclude events categorized as major events. For utilities using IEEE standards, a major event is an interruption that exceeds the calculated value based on the utilities past five years of data. Utilities that do not use these standards may have a different threshold for which interruptions they report.

Average U.S. customer interruptions and hours interrupted Source: U.S. Energy Information Administration, Annual Electric Power Industry Report, Form EIA-861 data file

The average U.S. electric customer was out of power for 7.8 hours (470 minutes) in 2017, which was almost double the amount of time in 2016. This increase resulted from major events. When excluding major events, the average duration of interruptions customers experienced was almost identical in 2016 and 2017. In 2017, the average customer experienced 1.4 interruptions when including major events and 1.0 interruption when excluding major events.

Average U.S. customer interruptions and hours interrupted Source: U.S. Energy Information Administration, Annual Electric Power Industry Report, Form EIA-861 data file

The five states with the lowest average customer minutes interrupted in 2017 were the District of Columbia, New Jersey, North Dakota, Arizona, and South Dakota. These states’ average customer interrupted minutes ranged from 58 minutes (Washington, DC) to 95 minutes (South Dakota). Utilities in these states did not experience very many major events such as hurricanes, blizzards, or tornados. The states that had the greatest average customer minutes interrupted in 2017 were Maine, Florida, New Hampshire, Georgia, and Vermont. In early 2017, Maine, New Hampshire, and Vermont experienced several winter storms. Florida and Georgia experienced long interruptions from Hurricane Irma in September 2017. (Puerto Rico experienced the longest U.S. blackout in history from Hurricane Maria; however, the data in this analysis does not include Puerto Rico). The average customer interruption time in these five states ranged from 14.6 hours (874 minutes) to 41.5 hours (2,493 minutes).

You can find more information on SAIDI and SAIFI reporting in our short YouTube video guide.


Principal Contributor:

David Darling
(David.Darling@eia.gov)

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