The rapid deployment of inverter-based resources like solar and wind is exposing shortcomings in standards and processes relied on for connecting these power plants to the grid and then operating them reliably.
Operational shortfalls have been particularly acute during grid disturbances which have grown in likelihood and magnitude since at least 2015.
Those were key points raised during a technical session held earlier this year by the North American Electric Reliability Corp. (NERC). A meeting summary was released by NERC in late March.
The NERC session emphasized that the challenges surrounding inverter-based resources are not due to technology shortcomings, but rather the “shortcomings of processes and the lack of harmonized comprehensive standards” that can be applied during the interconnection process and then throughout the project’s lifecycle.
“The lack of uniformity, clarity, consistency, enforcement, and detail in interconnection requirements and processes has led to unreliable operation of inverter-based resources that are connected to the bulk power system and the widespread abnormal performance of resources during grid disturbances,” the session summary said.
The summary said that the rapid integration of bulk power system (BPS)-connected inverter-based resources ranks as the most significant grid transformation driver across North America.
It said that a few years ago, when inverter-based resources made up a relatively small share of the generation mix, the approach was that those resources should generate energy during normal operation and then get out of the way during grid disturbances. This strategy is no longer acceptable under rapidly increasing penetrations of inverter-based resources on the North American grid, the summary said.
“It is imperative that these controls be configured in a way that supports grid reliability.”
A security loophole?
Turning to cyber security, the session reported as a top concern the increasing amount of generation that is not subject to NERC Critical Infrastructure Protection (CIP) standards.
Specific concerns included the growing level of DERs that often are connected directly to the internet as well as unregistered inverter-based resources on the grid that are also not subject to the NERC CIP Standards; the introduction of DER aggregators, their control of many DERs across a large footprint, and their lack of applicability to the NERC CIP Standards; the prevalence of vendor or manufacturer remote access and potential cross-border control center operations; and securing the “overall electricity ecosystem for this vastly changing” resource mix.
It said that requirements largely have been left at the functional level without specifying performance clearly and with sufficient detail. In turn, this has led to “ambiguous requirements that are difficult to enforce” as well as inconsistencies and misinterpretations by owner/operators, developers, and equipment manufacturers.
NERC said that the interconnection process currently limits its ability to assure grid reliability to a date no earlier than the facility’s commercial in-service date.
It said that its jurisdiction for assuring grid reliability could be expanded through a “bifurcation of performance requirements” and “facilitation of the interconnection queue.” It said that requirements must be updated to ensure that the interconnection customer complies with performance and modeling requirements throughout the process, or else face “explicit corrective actions.”
A ‘grandfather’ loophole?
The NERC session also said that a lack of equipment standards has challenged the interconnection of inverter-based resources. While IEEE 2800-2022 outlines minimum performance specifications based on inverter-based resource capabilities, the standard by itself is not sufficient to address ongoing reliability risks. And it said that implementing the IEEE standard solely for newly interconnecting resources (in other words, grandfathering existing facilities) would not address systemic risks posed to grid reliability.
The session summary also said that no commissioning requirements currently exist within NERC reliability standards for newly interconnection resources. However, a number of situations have arisen in which the facility as commissioned does not match the model that was used during the interconnection process. These discrepancies leave the system subject to unexpected or abnormal performance issues, and have been illustrated “numerous times” in NERC disturbance reports.
The session called for requirements to ensure that a commissioned facility matches what was studied, and with all discrepancies addressed prior to commercial operation.
Non-compliance with interconnection requirements or NERC standards are generally only identified after a major reportable event occurs rather than proactively through auditing and study practices.
The NERC session also said that industry is increasingly challenged with addressing reliability issues for unregistered inverter-based resources, which are reaching “critical mass” and create local and regional reliability risks. It said this issue is compounded by the growing presence of DERs connected to the distribution system.
The summary said that NERC plans to strengthen its advocacy on this issue, particularly with state regulators and the National Association of Regulatory Utility Commissioners. NERC also submitted a work plan to FERC in a bid to “more comprehensively” address registration of inverter-based resources.
