Severe Weather Linked To Increasingly Longer Lasting Power Outages In US
A new study being hailed as the most comprehensive analysis of electricity reliability trends in the US sees severe weather as driving increasingly longer power outages in the US.
The study, which was conducted by researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and Stanford University, found that while the average frequency of power outages in the US has not changed in recent years, the total number of minutes that customers are without power, i.e. the length of these power outages, have been increasing over time.
The authors of the report note that “recent catastrophic weather events, existing and prospective federal and state policies, and growing investments in smart grid technologies have drawn renewed attention to the reliability of the US electric power system.” Therefore, the study examined “the statistical relationship between annual changes in electricity reliability” with “a broad set of potential explanatory variables including various measures of weather and utility characteristics.” This is in direct contrast to previous studies which have only focused on “the very largest events” which, “anecdotally … are thought by many to represent no more than 10% of the power interruptions experienced annually by electricity customers.”
The authors of the report found that severe weather acted as the principal driver for the increase in extended power outages.
“This 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 idea that a constant increase in severe weather events is impacting on the US electricity system is not a new one, as a 2013 White House report coming to similar conclusions. However, this new report for the first time makes use of “econometric analysis techniques to statistically correlate these events with electricity reliability.”
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Further findings reached by the analysis — which was itself based on “up to 13 years of information on the annual duration and frequency of power interruptions for a large cross-section of US electricity distribution utilities,” representing nearly 70% of US electricity customers between 2000 and 2012 — included several “statistically significant relationships”:
- A 10% increase in annual precipitation—above the long‐term (generally, 13‐year) average—is correlated with a 10% increase in System Average Interruption Duration Index (SAIDI)
- A 10% increase in the number of cooling degree‐days (i.e., warmer weather)—above the long‐term (generally,13‐year) average—is correlated with a 8% decrease in SAIDI
- A 5% increase in annual average wind speed—above the long‐term (generally, 13‐year) average—is correlated with a 56% increase SAIDI; a 10% increase in annual average wind speed is correlated with a 75% increase in SAIDI
- A 10% increase in the percentage share of underground line miles is correlated with a 14% decrease in SAIDI
- Independent of the above factors, each successive year over the analysis period is also correlated with a nearly 10% increase in SAIDI
“We find a statistically significant trend in increasing annual average duration of power interruptions over time,” the authors write. “The trend is larger when major events are included, which suggests that increases in the severity of major events over time has been the principal contributor to the observed trend.”
Interestingly, however, the authors also found that an increase in transmission and distribution (T&D) expenditures did not correlate to any statistically relevant improvement in reliability in the following year. “We expected to find that increased spending on T&D would lead to improved reliability, but it is possible that a combination of proactive versus reactive utility maintenance policies may be off-setting this effect on reliability,” explained Larsen, the lead author of the report.
The relationship between proactive and reactive T&D spending and deployment is also one of the primary improvements the authors note should be made in any future studies of US electricity reliability. They also note that “there may be more appropriate annual weather parameters available to more accurately capture the impact of major events” that they did not have access to, or include in their report.
“We hope the findings from the study will provide a more solid basis upon which to ground future private and public decisions on the long-term reliability of the US electric power system,” said co-author and Berkeley Lab Staff Scientist Joseph Eto.
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