Recent trends in power system reliability and implications for evaluating future investments in resiliency

Abstract

This study examines the relationship between annual changes in electricity reliability reported by a large cross-section of U.S. electricity distribution utilities over a period of 13 years and a broad set of potential explanatory variables, including weather and utility characteristics. We find statistically significant correlations between the average number of power interruptions experienced annually and above average wind speeds, precipitation, lightning strikes, and a measure of population density: customers per line mile. We also find significant relationships between the average number of minutes of power interruptions experienced and above average wind speeds, precipitation, cooling degree-days, and one strategy used to mitigate the impacts of severe weather: the amount of underground transmission and distribution line miles. Perhaps most importantly, we find a significant time trend of increasing annual average number of minutes of power interruptions over time-especially when interruptions associated with extreme weather are included. The research method described in this analysis can provide a basis for future efforts to project long-term trends in reliability and the associated benefits of strategies to improve grid resiliency to severe weather-both in the U.S. and abroad.

Improving the estimated cost of sustained power interruptions to electricity customers

“…• Updating the reliability data (SAIDI and SAIFI) in our step-by-step process increased the cost of sustained power interruptions to $75 billion (Case 3b) from $30 billion (Case 3a). This is a finding consistent with the conclusions of the [5] study that reliability is getting worse over time. • Accounting for customers who take extra measures to shelter themselves from power interruptions by installing backup generators reduces the estimated cost of sustained power interruptions by 18% from Case 3b to $62 billion (Case 3b).…”

“…Table 8 and Figure 5 summarize the cases. Looking at what happened in each step reveals that the estimated cost of power interruptions declined as a result of updating the CDFs, decreased, and then increased when correcting for the reclassification of customer classes by EIA and accounting for changes from 2001-2015, decreased when accounting for those customers that take extra precautions to prevent power interruptions, and noticeably increased when applying updated reliability metric information, which is consistent with the trend of worsening reliability described in [5].…”

“…This approach uses a distribution to account for differences in the costs of various outage durations, which also accounts for the fact that outage durations are not uniformly distributed and that the relationship between cost and duration is nonlinear. We then applied these costs to the 2012 reliability information from [5]. Table 6 shows the estimated weighted average cost per sustained outage using annual electricity usage, annual partitioning of time of day and year, and the distribution of interruption durations.…”

“…Berkeley Lab also issued a 2016 update of our 2012 assessment of electricity reliability trends. This update found that reliability is worsening, especially when major events are included, and that this worsening trend is likely a result of an increase in severe weather events [5].…”

“…Recent reports have highlighted severe weather as the leading cause of power outages in the United States [5][6]. With more frequent severe or catastrophic U.S. weather events such as Hurricane Harvey, Irma, or Maria occurring, many electricity customers are focused on the issue of electricity reliability.…”