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Electricity Monthly Update

With Data for January 2020  |  Release Date: March 24, 2020  |  Next Release Date: April 24, 2020

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U.S. power interruptions totaled an average of nearly six hours per customer in 2018

Interruptions in electricity service vary in frequency and duration across the nearly 3,000 electric distribution systems in the United States. Power interruptions are caused by many factors including weather, vegetation patterns, and utility practices. In 2018, power interruptions for U.S. electricity customers totaled an average of 5.8 hours (345 minutes) per customer. This total is based on reliability information reported to the U.S. Energy Information Administration (EIA) by utilities who collectively serve 94% of the nation’s 153 million electricity customers.

U.S. system average interruption duration index (SAIDI), in minutes per customer Source: U.S. Energy Information Administration, Form EIA-861, Annual Electric Power Industry Report.

The reliability of electric utilities can be measured using the System Average Interruption Duration Index (SAIDI) metric, which is the total amount of time an average customer experiences a non-momentary interruption during a year. For those utilities that report metrics using IEEE standards (formerly the Institute of Electrical and Electronic Engineers), non-momentary interruptions are defined as interruptions that last longer than five minutes.

Utilities can report SAIDI including all events (referred to as with major events) or after removing the effects of major events (referred to as without major events), or both. (For more information on SAIDI and SAIFI data reporting, please refer to this video about EIA reliability metrics). Since EIA began collecting reliability data in 2013, average annual U.S. SAIDI values have been consistently less than two hours per customer when major events are removed (106 minutes¬–118 minutes). The past two years of data show that interruptions classified as major events were the primary cause of increases in total SAIDI. In 2017, SAIDI with major events was the highest since EIA began collecting reliability data in 2013, doubling from the levels of previous years. This increase was a result, in part, of high levels of hurricanes, wildfires, and severe storms.

Average U.S. system average interruption duration index (SAIDI), in minutes per customer Source: U.S. Energy Information Administration, Form EIA-861, Annual Electric Power Industry Report.

The three main types of electric distribution utilities are investor-owned utilities (IOU), which are owned by shareholders; cooperative energy utilities (co-ops), which are owned by members of the cooperative; and public utilities, which are owned by government entities, such as municipalities, regional authorities, states, etc. Publicly owned utility customers experienced on average the highest reliability, averaging about one hour of interrupted electric service annually since 2013. Meanwhile, IOU customers averaged just under two hours of interrupted service excluding major events, and cooperative customers averaged about two and half hours of interrupted service excluding major events. This same reliability ranking also generally prevails when major events are included.

Average U.S. system average interruption duration index (SAIDI), in minutes per customer Source: U.S. Energy Information Administration, Form EIA-861, Annual Electric Power Industry Report.

From 2013 to 2018, Arizona, Nevada, North Dakota, the District of Columbia, and Iowa had the lowest cumulative SAIDI; year-average SAIDI values ranged from 58 minutes (District of Columbia in 2017) to 165 minutes (Iowa in 2014). North Carolina, Vermont, West Virginia, Maine, and South Carolina on average had the highest cumulative SAIDI, well above the U.S. average. In each of these states, the high SAIDI values were caused by major events such as winter storms or hurricanes. The average SAIDI for these five states from 2013 to 2018 ranged from about 10 hours in Vermont to 16 hours in Maine per year.


Principal Contributors:

David Darling
(David.Darling@eia.gov)

Sara Hoff
(Sara.Hoff@eia.gov)

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