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NERC: Poor models, studies to blame for renewable energy reliability issues

NERC: Poor models, studies to blame for renewable energy reliability issues
(Image by Como una Reina from Pixabay )

Poor models and study practices are among the factors to blame for escalating issues with renewable energy and battery storage reliability, according to a recent alert from North America’s grid reliability monitor.

The North American Electric Reliability Corporation (NERC) issued an alert on June 4 to generation owners and transmission planners concerning resources — like solar, wind, and batteries — that use inverters to connect to the grid. These assets are increasingly the subject of reliability concerns because of their inability to withstand grid disturbances.

NERC found that 10 large-scale grid disturbances on the bulk power system since 2016 involved the “widespread and unexpected” reduction of nearly 15,000 MW of inverter-based resource output, including 10,000 MW in the past four years. Performing dynamic simulations of the bulk power system, in addition to improved interconnection and system studies, could solve the problem, they said.

“The significantly higher complexity and software-based nature of IBR modeling when compared to synchronous machine modeling necessitates an improvement in the fundamental principles of dynamic modeling to accurately capture the performance of IBR plants,” the NERC alert said.

Episode 67 of the Factor This! podcast features Ryan Quint, who oversees engineering and security integration for the North American Electric Reliability Corporation, which oversees the reliability of the bulk power system. Subscribe wherever you get your podcasts.

NERC aims to gather responses from generation owners and transmission planners to eight proposed recommendations.

“When we have a normal grid event like that and we lose power from dozens of solar PV facilities, hundreds, or maybe even a thousand, inverters all at the same moment in time, that’s a potential recipe for a catastrophically bad day,” Ryan Quint, formerly NERC’s director of engineering and security integration, said on the Factor This! podcast in 2023.

NERC has issued more than a dozen reports in recent years diagnosing the shortfalls of IBRs. Some incidents are what the grid watchdog identifies as “faint signals” of broader implications. Others have teetered on complete grid collapse. 

The root causes of these disturbances typically involve a resource tripping offline due to a normal grid event: a tree falls on a powerline, a squirrel climbs on a substation bus, and so on. And these grid events happen every day. Due to the volume of grid disturbances, NERC’s postmortems are taking on a sterner tone. 

In its 2023 Southeast Utah Disturbance, which detailed the loss of 921 MW of solar generation from nine large-scale solar projects due to a normally-cleared fault on a faraway transmission circuit, NERC, in no uncertain terms, called out inverter original equipment manufacturers and generator owners for failing to address persistent, and previously identified, reliability issues.

Generator owners “are often not addressing performance issues that latently exist within the existing fleet,” NERC wrote, adding that in “all of the causes of abnormal performance in this event have been previously documented by NERC in past reports; however, actions were not taken.”

The disturbances have not, to this point, caused blackouts on their own. But that’s due to IBRs playing a relatively still-small role in the power system. As renewable energy rapidly displaces fossil-fueled, synchronous sources, those “faint signals” may lead to systemic failures if the industry does not remain vigilant in addressing these underlying reliability risks.

Efforts are underway to enhance the NERC reliability standards specifically related to IBR risks. The Federal Energy Regulatory Commission issued Order 901, which directed NERC to develop new or modified reliability standards. NERC is developing a comprehensive work plan regarding standards development activities to meet this directive, and is also making changes to its registration criteria and process to bring smaller projects on the bulk power system under NERC jurisdiction per a separate FERC directive. 

Originally published in POWERGRID International.