By Richard Schlottmann, NERC Senior Reliability Compliance Specialist
The Joint NERC and Texas RE Staff Report regarding the Texas events of May 9 and June 26 evaluates the first disturbance involving a widespread reduction of solar photovoltaic (PV) resource power output observed in the Texas Interconnection. Per the NERC report, “The event involved solar PV facilities across a large geographic area of up to 200 miles away from the location of the initiating event. The Electric Reliability Council of Texas (ERCOT) provided Texas RE and NERC with a brief report as the disturbance was categorized as a Category 1i event.1” Analysis of the disturbance provides key findings and recommendations for industry.
- Across all regions, industry is not sufficiently implementing recommendations from NERC Reliability Guidelines. The GO/GOP is usually aware of the recommendations but is not implementing them. The TO, TP and PC entities are only adopting some of the recommendations.
- Significant updates and improvements need to be made to Interconnection Agreements with respect to performance-based metrics to ensure reliable performance of inverter-based resources.
- Improvements to NERC Reliability Standards to address systemic issues with inverter-based resources are needed as PV solar facilities continue to have abnormal performance. Of particular note are facilities with settings in compliance with PRC-024 which encounter issues performing accordingly during grid events.
- Performance assessment and mitigation, due to lack of performance-based standards and no authority from RCs, TOPs or BAs to assess the performance of inverter-based resources makes it difficult for entities to establish performance requirements. Subsequently , this leads to large scale and widespread events where resources tripped when they should not have done so.
- PRC-024-3 and Ride-Through concerns arise when the standard is not effectively nor efficiently addressing systemic reliability concerns with inverter-based resources. (Yes, the settings are compliant but that is only part of the compliance.) Hidden protections within the inverter that trip for inverter terminal conditions and POI conditions is an ongoing issue that needs to be addressed. There are numerous other protections that will trip equipment that is not solely based upon voltages and frequency levels; therefore, NERC is recommending a comprehensive Ride-Through standard be developed.
- A suggested change is to start treating abnormal conditions for inverter-based resources like PRC-004 and report them to the RC, BA and TOP based upon an agreed upon MVA threshold. Investigations similar to misoperations reporting should follow.
- Current modeling is ineffective and needs to utilize electromagnetic transient modeling to more accurately reflect inverter-based resource behaviors during events.
The report in its entirety can be found HERE.