Summary: The Federal Energy Regulatory Commission (FERC) has proposed new mandatory reliability standards for inverter-based resources (IBRs) to ensure wind, solar, and battery storage don’t threaten grid reliability.

 

A colloquial definition of electric reliability is “having power when it is needed.” NERC’s reliability standards are meant to ensure an Adequate Level of Reliability (ALR) for the bulk power system during normal operating conditions and following localized disturbances such as lightning strikes. According to US Energy Information Administration (EIA), combined generation from wind and utility-scale solar sources increased from 1% of total electricity generation in 2008 to 13% of total electricity generation in 2021.

Renewable energy resources are also called inverter-based resources because they use power electronic devices (inverters) to change direct current (DC) power, produced by generators, to alternating current (AC) power, to be transmitted on the bulk-power system. As the use of this technology grows, it is important to ensure that IBRs do not adversely impact the technical reliability of the grid.

“FERC’s most solemn responsibility is protecting the reliability of the bulk power system. And that includes ensuring that promising new technologies, like IBRs, are configured and operated in a manner that enhances, not weakens, grid reliability. Today’s orders set us on that course,” FERC Chairman Rich Glick said.

To ensure that IBR resources operate reliably well, FERC ordered three IBR-focused actions:

  • An order directing NERC to develop a plan to register the entities that own and operate them
  • A Notice of Proposed Rulemaking to direct NERC to develop reliability standards for IBRs that cover data sharing, model validation, planning, and operational studies, and performance requirements
  • An order approving reliability standards that are related to IBRs, which NERC proposed earlier this year

The need for new reliability standards

Until recently, the Bulk-Power System generation fleet was composed almost exclusively of synchronous generation resources that convert mechanical energy into electric energy through electromagnetic induction. Instead, IBRs predominantly use inverters, which rely on sensed information from the grid (e.g., a voltage waveform) to produce the desired AC real and reactive power output. IBR scans track grid state parameters (e.g., voltage angle) on the order of milliseconds and reacts nearly instantaneously to changing grid conditions.

Some IBRs, however, are not configured or programmed to support grid voltage and frequency and, as a result, will reduce power, exhibit momentary cessation, or trip in response to variations in system voltage or frequency. In other words, under certain conditions, some IBRs cease to provide power to the Bulk-Power System due to how they are configured and programmed.

Since IBRs are well dispersed across the Bulk-Power System, IBR issues must be identified, studied, and mitigated to preserve Bulk-Power System reliability, because they present new opportunities to support the grid and respond to abnormal grid conditions. For Bulk-Power System operators to harness the unique performance and control capabilities of IBRs, these resources must be properly configured and programmed.

To help address the issue, FERC directed NERC to develop new or modified standards to eliminate four reliability gaps related to IBRs, namely data sharing, model validation, planning and operational studies, and performance requirements, such as IBRs’ ability to function during system disturbances.

The need for registering IBRs

The commission gave NERC 90 days to submit a plan describing how it plans to identify and register the owners and operators of IBRs connected to the bulk-power system that are not currently required to register with the organization, referred to as “unregistered IBRs”.

Reports demonstrate that the potential for IBRs to have a material impact on the Bulk-Power System is not limited to larger inverter-based resources that are typically required to register with NERC or to the IBRs within an individual balancing authority area. Additionally, simulations indicate that aggregate IBRs experiencing momentary cessation can lead to instability, uncontrolled separation, and voltage collapse.

Therefore, it is necessary to ensure that unregistered IBRs that may have an aggregate material impact on the reliable operation of the Bulk-Power System are required to register with NERC and comply with NERC Reliability Standards.

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