Study: frequency of power outages in US stable, but total minutes without power increasing over time
In the most comprehensive analysis of electricity reliability trends in the United States, researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and Stanford University have found that, while, on average, the frequency of power outages has not changed in recent years, the total number of minutes customers are without power each year has been increasing over time.
The researchers pinpointed what utilities and their regulators refer to as “major events,” or events generally related to severe weather, as the principal driver for this trend. The finding suggests that increasingly severe weather events are linked to a 5-10% increase in the total number of minutes customers are without power each year, said Berkeley Lab Research Scientist and Stanford PhD candidate, Peter Larsen, the lead author of the report.
The researchers analyzed reports for a large cross-section of utilities representing nearly 70% of US electricity customers spanning 13 years from 2000 to 2012.
Although a 2013 White House report noted that major power outages and severe weather events are increasing, this study is the first of its kind to use econometric analysis techniques to statistically correlate these events with electricity reliability. Most studies of reliability have relied on information that reflects only the largest power outages. Yet, over the course of any given year, the largest events typically account for no more than 10% of all power outages. This study, by relying on information for all power outages, both large and small, conclusively identifies a trend that is linked directly to these larger events.
We find statistically significant correlations between the average number of power interruptions experienced annually by a customer and a number of explanatory variables including wind speed, precipitation, lightning strikes, and the number of customers per line mile. We also find statistically significant correlations between the average total duration of power interruptions experienced annually by a customer and wind speed, precipitation, cooling degree‐days, the percentage share of underground transmission and distribution lines. In addition, we find a statistically significant trend in the duration of power interruptions over time—especially when major events are included. This finding suggests that increased severity of major events over time has been the principal contributor to the observed trend.—“Assessing Changes in the Reliability of the US Electric Power System”
One surprise was that the study did not find a consistent link between reliability and utility transmission and distribution (T&D) expenditures.
This work was funded by the Office of Electricity Delivery and Energy Reliability, National Electricity Delivery Division of the US Department of Energy. Other co-authors were Kristina H. LaCommare of Berkeley Lab and James L. Sweeney of Stanford.