Published: August 9, 2024
By: Concentric Staff Writer
Extreme weather has developed into the primary reliability threat to the Bulk Power System (BPS), although there were minimal severe weather threats to the grid last year, national reliability officials say.
Other than severe weather, other reliability threats pointed out by the North American Electric Reliability Corporation (NERC) are increased demand, problems with inverter-based resources (IBRs) such as solar and wind, and a rise in forced-outage rates for generation resources.
NERC recently issued a set of “actionable recommendations” from workshops held in March 2024 in conjunction with the National Academy of Engineering regarding electric reliability criteria for planning resource and transmission adequacy. Resource and transmission planning will be increasingly important as the grid transforms to cleaner, but more intermittent, renewable generation, the organization said.
NERC said there is a need for additional criteria, actionable short- and long-term recommendations, and next steps. The workshop concentrated on two broad topics: capacity vs. energy and planning the evolving transmission grid, the organization said in a report, entitled Evolving Planning Criteria for a Sustainable Power Grid.
Planning needs to evolve past the traditional loss-of-load standard of one day in ten years, which focuses on peak load, because this approach does not account for the growing risk in all hours that results from the increased variability and uncertainty caused by renewable generation, as well as increasing demand levels, NERC said.
NERC suggested that other methods, such as the Regional Energy Shortfall Threshold (REST), are being explored by the Independent System Operator New England, which reflects the region’s risk tolerance in regard to energy shortfalls during extreme weather. This is particularly relevant during extreme weather when impacted areas are highly reliant on long-distance transfers from other areas that have greater fuel diversity and sufficient resources to serve demand, NERC said.
The organization said extreme weather events are disrupting electricity supplies at “unacceptable levels,” citing the 2020 heat dome in California and Mexico, Winter Storm Uri in 2021, and Winter Storm Elliott in 2022.
“Given that electricity plays an essential role in modern society, energy adequacy is a critical complementary consideration of resource adequacy to ensure overall system reliability,” NERC said in the report.
A major factor affecting reliability is the growth of data centers and cryptocurrency mining, which NERC said can have a significant effect on demand and resource projections as well as system operation. Cryptocurrency mining refers to the way cryptocurrency coins are created and how transactions are verified. The process involves blockchain and a decentralized ledger to verify that a sender has adequate funds and is not “double-spending” coins. Cryptocurrency mining requires solving complex mathematical puzzles and is designed to require substantial computational effort, which increases as more miners join the network. Miners need to run their computers 24-7, creating massive energy demand.
The Electric Reliability Council of Texas (ERCOT), for instance, has a huge number of interconnection requests from cryptocurrency miners, with nine gigawatts (GW) worth of approved planning studies and 41 GW of studies currently requested, NERC said in its 2023 Long-Term Reliability Assessment.
“This new category of large flexible loads is leading some areas to update load forecasting methods to capture the flexibility and price-responsiveness of cryptocurrency mining operations,” NERC said in the assessment. “In anticipation of further growth in large flexible loads, ERCOT and its stakeholders are assessing further operational issues that could emerge, such as the effect on system frequency of sudden changes in large flexible loads.”
In another report, the 2024 State of Reliability Overview, NERC noted that the Texas Interconnection has improved greatly in reliability by using battery energy storage to support system frequency. Texas can no longer meet summer and winter peak demand with only conventional generation “and has demonstrated how these challenges can be successfully managed while at the same time encountering new ones.”
California has been adding an unprecedented amount of energy storage to its grid, helping it to meet peak summer demand. The California Independent System Operator said that the amount of energy storage is approaching 10 GW, which has helped it manage the grid this summer.
Coal unit retirements and the impact of IBRs such as solar and wind continue to impact the BPS; for example, disturbances to battery energy storage in California (March and April 2022) and solar in Utah (April 2023). Disturbances in IBRs are no longer limited to solar generation, the organization said in the State of Reliability Overview.
As a result, the Federal Energy Regulatory Commission in October 2023 directed NERC to develop new reliability standards for IBRs, saying they will help the reliability of the grid by accommodating the rapid growth in solar photovoltaic, wind, fuel cell, and battery storage that is due to form a large proportion of new generation resources coming online over the next 10 years.
“Over the past several years, a handful of extreme weather events has increasingly been the largest challenge to BPS reliability, and the unprecedented magnitude of these events has dominated reliability trends,” NERC said in the State of Reliability Overview.
However, in 2023, the weather was less extreme, although there were still incidents such as flooding in California in January through March, winter storms and cold waves in the Northeast in February, Hurricane Idalia on the Gulf Coast in March, as well as tornadoes, heat storms and drought in various regions of the county. There were also record-setting wildfires in Canada that caused short-term outages on the transmission system.
Overall, Severity Risk Index days decreased in 2023, illustrating the ability of the BPS to withstand severe weather and the importance of advanced preparation, active management of the grid during extreme weather, and rapid response to events, NERC said.
Forced outages of generation units on the U.S. grid were at historic highs in 2023, exceeding rates for all years prior to 2021. Forced outages refer to unexpected events that disrupt the normal output of the unit, such as failures due to mechanical, electrical, or control systems, as well as natural events.
Despite no occurrence of major events comparable to Winter Storms Uri (February 2021) or Elliott (December 2022), the weighted equivalent of forced-outage rates for coal and cycled natural gas units remained high in 2023, NERC said. Forced-outage rates for hydroelectric units were also high, but this generation remains a much smaller portion of the fleet. NERC found that the decreasing reliability of coal generation, along with an increase in variable generation, will necessitate larger reserve margins going forward.
There is a correlation between the forced-outage rates for coal generation and the overall forced-outage rate for all types of generation, NERC said. The correlation includes the age of coal units and their outage rates, but the outage rate for coal units is affected more by an increase in needed maintenance and a reduction in service hours as these units age and face retirement. As coal units retire, they are increasingly being replaced by IBRs such as solar, NERC said.
Forced outages also continue to increase for wind generation, rising to 18.9 percent in 2023, compared with 18.1 percent in 2022, NERC said. While there is not an exact comparison to outage rates for conventional generation units, “the continued increase is of concern given the growth in wind generation over recent years,” the report says. New, expanded reporting requirements for both conventional and renewable generation went into effect in 2024, which will allow for expanded analysis of the performance of both IBRs and conventional generation in future years, NERC said.
Other emerging issues for the grid include the state of blackstart resources—specialized power plants that can start without any external electricity supply—that are critical in cases of outages. They often use auxiliary power sources such as batteries or diesel generation. Recent extreme winter weather events have exposed vulnerability to generating units and fuel sources that are not adapted to low temperatures, which raises issues regarding blackstart unit readiness, NERC said.
“The changing resource mix is cause for additional awareness of blackstart capabilities. Currently, few IBRs on the system are capable of grid forming control, one of the necessary components for blackstart resources”, NERC said in the Long-Term Reliability Assessment.
Another rising problem is that distribution transformers are in short supply nationally, with manufacturers unable to keep up with demand. Lead times for transformers are often longer than two years, and low inventories of replacement resources and lack of skilled labor have the potential to slow restoration efforts following hurricanes and other severe weather events. Access to grain-oriented electrical steel used in power transformers is another constraint, and new efficiency standards for distribution transformers proposed by the U.S. Department of Energy could worsen the challenges because they set up requirements that manufacturers are not set up to handle, NERC said.
Finally, local load growth is occurring, including industrial and commercial development, which includes data centers, smelters, manufacturing centers, hydrogen electrolyzers, and port electrification. New load being added to the system, such as data centers, require more heating and cooling than other commercial buildings, creating challenges in load forecasting and localized transmission development, NERC said.
The NERC reports provide a window into the challenges facing the grid, including weather, growing load, and other factors that ensure grid planners will have their hands full in meeting demand in coming years.
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All views expressed by the author are solely the author’s current views and do not reflect the views of Concentric Energy Advisors, Inc., its affiliates, subsidiaries, related companies, or clients. The author’s views are based upon information the author considers reliable at the time of publication. However, neither Concentric Energy Advisors, Inc., nor its affiliates, subsidiaries, and related companies warrant the information’s completeness or accuracy, and it should not be relied upon as such.