June 21, 2018 by Michael Goggin, Vice President at Grid Strategies LLC
“Grid Shows Improved Resilience” is the headline of the just-released “State of Reliability” report by the North American Electric Reliability Corporation (NERC), the entity tasked by the U.S. government with regulating electric grid reliability.
Across 13 metrics of electric reliability and resilience, NERC found improvements in 11, one was inconclusive, and one was stable or improving for all but two grid operators. The final metric (reserve margins) was addressed in a NERC report released last month, which found that almost all regions have power plant capacity well in excess of what they will need for the foreseeable future, though it did note some concerns for Texas and part of the Midwest.
(Of particular note in last month’s report on reserve margins, NERC found that PJM, the grid operator for many Mid-Atlantic and Great Lakes states and the primary focus of recent arguments about electric reliability and resilience, has the largest excess reserve margin among all power systems in the Eastern U.S. that experience peak demand during the summer. In fact, with a 33% reserve margin, PJM has twice its target level of reserve power plant capacity.)
NERC’s State of Reliability report puts more nails in the coffin of the myth that federal action is needed to prop up uneconomic coal and nuclear power plants to ward off concerns about electric reliability and resilience. As nearly everyone from fossil fuel producers to electricity consumers to environmental advocates have explained, bailing out coal and nuclear plants would only harm electric reliability and resilience by undermining the markets that keep electricity affordable and reliable.
Electric reliability and resilience are increasing
NERC’s report is replete with data showing improving electric reliability and resilience. Emergency events in which customers can lose power have trended steadily downward (page 170), while “the trend over the five years shows improving reliability for the generator fleet,” (page 5). Highlighting the growing importance of new technologies for maintaining electric reliability, the report also finds that the “2013–2017 trend of demand response realization is improving” (page 1).
Another key point is that overall power plant failure rates are declining. If the shift from coal to cleaner resources was causing problems it would show up here as an increase, when in fact the opposite is true.
The report’s top conclusion is that the bulk power system “showed improved resilience” during extreme events last year, most notably during Hurricane Harvey in Texas and Hurricane Irma in Florida. NERC’s report notes how in Florida, “system hardening between the storms increased resiliency and reduced restoration time from 18 days for Wilma [in 2005] to 10 days for Irma.” (page vii)
That finding confirms what several co-authors and I explained last month: efforts to improve electric reliability and resilience should focus on strengthening the electricity transmission and distribution systems that cause around 99% of customer outage hours, not bailing out coal and nuclear generators to address generation-related concerns that account for a fraction of 1% of customer outage hours.
Renewable resources are contributing to electric reliability
Renewable power plants are increasingly providing a range of grid reliability services. Wind and solar plants have advanced power electronics and sophisticated controls that allow them to respond to system reliability needs an order of magnitude faster than conventional power plants.
Data in the report document the positive impact renewable resources are having on system reliability and resilience. NERC found that in Texas, there is a highly significant 0.24 correlation between wind output and the power system’s ability to stabilize system frequency following the loss of large conventional power plants, a key element of resilience (page 139). This makes wind output the third most important factor for the Texas power system’s ability to withstand a frequency disturbance.
In Texas, wind plants typically provide most if not all of the entire power system’s response when system frequency is high, and when curtailed they can increase output to stabilize low system frequency. Adding wind and solar also tends to improve the power system’s frequency response by giving conventional power plants more opportunity to provide that and other reliability services. In Colorado, wind plants are commonly used to regulate frequency, and the California grid operator has demonstrated that solar plants can do so as well.
The power electronics and fast controls inherent in modern wind and solar plants also make them resilient to frequency and voltage disturbances on the power grid, a key aspect of reliability. Since 2005 wind plants have met a rigorous standard for withstanding grid disturbances, one that many conventional power plants cannot meet. Today’s report does note that NERC is working with the solar industry and others to update reliability standards to ensure the capability of solar plants to ride-through grid disturbances is being encouraged, and not discouraged as has been the case in some instances because some standards have failed to keep up with solar’s rapid growth.