The latest IBRWG (Inverter-Based Resource Working Group) meeting delved into several critical topics surrounding Battery Energy Storage Systems (BESS), HRL (High Resource Limit) definitions, and industry best practices. The discussions aimed to improve integration and operations of inverter-based resources within grid systems. Below is a breakdown of the key discussions and outcomes from the meeting.
Key Topics and Discussions: NOGRR272 and PGRR121
NOGRR272 and PGRR121 Updates: The meeting started with an update on NOGRR272 and PGRR121, which remain tabled at ROS (Reliability Operations Services) and are pending submission of NPRR (New Protocol Revision Request) for market implementation. These items are expected to return to the IBRWG after the next ROS meeting once they are submitted.
BESS Ride-Through Issues in WECC: Curtis Holland from WECC (Western Electricity Coordinating Council) provided an in-depth update on the performance of BESS in the Western Interconnection. He highlighted several key issues and disturbances caused by inverter-based resources (IBRs), including BESS failures to ride through faults, which mirrors issues faced by other inverter-based technologies like solar and wind.
- BESS Growth and Deployment: The capacity for BESS is growing rapidly in California and ERCOT, with further increases expected in the coming years. By 2024, ERCOT anticipates over 10,000 MW of battery storage.
- Systemic Performance Issues: The tripping incidents in the Western Interconnection were discussed, emphasizing that BESS should be treated similarly to other inverter-based resources in terms of performance expectations and fault ride-through capability.
- Event Analysis: It was noted that some recent events involving BESS included faults that were cleared within a few cycles but still resulted in partial plant trips. These faults were often due to inverter protection settings failing to meet the expected performance under system disturbances.
HRL of a Single Resource vs. Aggregated HRL for IRR Groups: The discussion from a previous meeting regarding the HRL definition for solar plants with multiple units was brought up. Acciona Energy had proposed that a single HRL value be applied to units within an IRR (Inverter Resource Group) rather than separate HRLs for each unit.
Key Discussion Points:
- Self-Limiting Facilities: Participants referred to ERCOT’s Nodal Protocol Section 3.8.7, which applies to self-limiting facilities, meaning facilities that exceed the power injection or withdrawal limits set by their interconnection agreement. The protocol ensures that these facilities operate within the agreed-upon limits at the point of interconnection (POI).
- Proposed Change to HRL Definition: The internal discussions at ERCOT considered the proposed change, acknowledging the limitations of current definitions but also recognizing the complexities of aggregating HRLs for multiple units. It was emphasized that further discussions would be held offline with Acciona Energy to refine the proposal and address site-specific details.
Solar Plant Performance and HRL Limitations: Acciona Energy representatives, shared additional insights into the HRL concerns specific to solar plants. They explained that, often, solar plants are designed with more solar panels than what is needed for their AC capacity to account for varying sunlight conditions throughout the day.
Key Insights:
- Capacity Mismatch: It was pointed out that solar plants in ERCOT often have 125% of their AC capacity in solar panels to account for changing sun radiation, yet they are limited by the HRL set at the transformer level. This mismatch leads to lost potential energy injection during peak periods.
- Proposal for Adjusting HRL Limitations: Acciona Energy emphasized that relaxing HRL limitations could allow solar plants to inject more energy into the grid, especially during peak demand periods in the summer, when solar generation is highest.
Review of Droop Settings for Battery Energy Storage Systems
Representatives from Acciona Energy raised concerns regarding the droop settings for Primary Frequency Response (PFR) in BESS. It was highlighted that some battery operators were setting droop too aggressively, which led to unnecessary depletion of battery charge during frequency events.
Recommendations:
- Adjusting Droop Settings: Battery owners were advised to revisit their droop settings to ensure they are within ERCOT’s 5% maximum requirement unless the batteries are providing RSPFR (Responsive Primary Frequency Response). By adjusting these settings, battery systems would avoid rapid discharges and better manage state of charge.
Other Industry Updates and Announcements
Several industry updates, including upcoming events and milestones were provided:
- Grid-Forming Batteries in Great Britain: The first grid-forming battery in Great Britain has gone operational. The Black Heloc battery is a 200 MVA system, part of a broader trend of increasing grid-forming battery installations in the UK.
- Grid-Forming Batteries Study: ERCOT also shared a study on the benefits of grid-forming batteries, particularly in MISO’s footprint, looking at how they can help stabilize weak grid areas and their potential adverse effects in stronger grids.
Conclusion and Next Steps
The meeting concluded with a reminder for attendees to send any suggestions for the next meeting’s agenda. ERCOT will continue working on refining the HRL definitions for solar plants, exploring solutions for the aggregation of HRLs in IRR groups, and addressing BESS performance challenges.
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