Daily wholesale electricity prices were highest in the West, reaching $312/MWh in the Southwest (Palo Verde) and $300/MWh in the Northwest.
Daily peak demand was lower on eight of the nine selected electricity systems in September, with California (CAISO) the only system recording a higher daily peak in September than in August.
Total U.S. coal stockpiles had a month-over-month decrease of 4.8%, reaching 80 million tons in September 2021. This is now the lowest level of total U.S. coal stockpiles recorded for the month since these data were collected using the power plant operations report beginning in 2001.
On average, U.S. electricity customers experienced just over eight hours of electric power interruptions in 2020, the most since we began collecting electricity reliability data in 2013. The average U.S. electricity customer experienced nearly 20 more minutes of power interruptions in 2020 than in 2017, the year with second-longest duration of interruptions in our records. When major events are excluded, the average duration of interruptions customers experienced annually from 2013 to 2020 was consistently around two hours.
Different factors cause power interruptions, including weather, vegetation patterns, and utility practices. Utilities can report interruption duration values with major events (including snowstorms, wildfires, and hurricanes), without major events, or both.
One metric used to measure the reliability of U.S. electric utilities is the System Average Interruption Duration Index (SAIDI), which measures the total time an average customer experiences a non-momentary power interruption in a one-year period. SAIDI is often paired with the System Average Interruption Frequency Index (SAIFI), which measures the frequency of interruptions. Electricity reliability metrics are explained further in our video guide on SAIDI and SAIFI and are available in our Annual Electric Power Industry Report.
Electricity customers in the District of Columbia, Arizona, Nevada, North Dakota, and South Dakota had the shortest total time of electric power interruptions in 2020, ranging from 44 minutes in the District of Columbia to 101 minutes in South Dakota.
Customers in Alabama, Iowa, Connecticut, Oklahoma, and Louisiana experienced the most time with interrupted power in 2020, ranging from almost 29 hours in Alabama to 60 hours in Louisiana. The long interruptions were largely because of major weather events. The United States experienced 14 hurricanes in 2020 and 11 major storms, making for an extremely disruptive Atlantic weather season.
Louisiana experienced the most active storm season in the state’s history, including Hurricane Laura, which was the state’s second-most costly storm after Hurricane Rita in 2005. Alabama was also hit with several hurricanes. Tropical Storm Isaias severely affected Connecticut, leaving about 750,000 electricity customers without power, some for over a week.
A derecho affected Iowa and other parts of the Midwest, causing widespread power interruptions and damaging grid infrastructure. Damages from the derecho resulted in the early retirement of Iowa’s only nuclear power plant, the Duane Arnold Energy Center, ahead of the plant’s scheduled October 2020 decommissioning. In Oklahoma, an ice storm in October 2020 resulted in widespread power interruptions.
In addition to power interruption duration, reliability can also be measured in terms of the frequency of power interruptions. Maine, which historically has the most frequent electric power interruptions (averaging 3.1 interruptions annually from 2013 through 2020—the most in the nation), is a heavily forested state where power interruptions resulting from falling tree branches are common. In 2020, Maine saw the highest average number of power interruptions per customer (3.9 interruptions). West Virginia, another heavily forested state with a history of frequent interruptions (averaging 2.5 interruptions per year since 2013—the second most in the nation), experienced 2.4 interruptions per customer in 2020. The Gulf States of Louisiana (3.2 interruptions), Mississippi (2.5 interruptions), and Alabama (2.4 interruptions) also experienced a higher-than-average number of interruptions per customer, largely due to major events. In contrast, the District of Columbia (0.4 interruptions), Nevada (0.7 interruptions), Nebraska (0.8 interruptions), Arizona (0.8 interruptions), and Wisconsin (0.8 interruptions) where well below the U.S. average of 1.4 power interruptions per customer.