ERCOT

ERCOT IBRWG 12.19.25: Reactive Capability at 0 MW, AGS BESS, and NERC Alignment

January 5, 2026

ERCOT IBRWG 12.19.25: Reactive Capability at 0 MW, AGS BESS, and NERC Alignment

The ERCOT Inverter-Based Resource Working Group (IBRWG) met on December 19 to address a set of increasingly practical and consequential issues, such as reactive capability, related to inverter-based resource (IBR) performance, modeling scope, and regulatory alignment. As inverter penetration continues to rise across the ERCOT system—driven by utility-scale solar, wind, and battery energy storage—ERCOT’s focus is shifting from establishing baseline compliance toward actively leveraging inverter capabilities to support grid stability and reliability.

The discussion reflected a broader transition underway within ERCOT planning and operations. Rather than treating inverter-based resources as passive participants that merely meet minimum technical standards, ERCOT is increasingly examining how these assets can and should behave under stressed system conditions, weak-grid scenarios, and evolving reliability criteria. The agenda centered on reactive capability at zero real power output, the potential role of advanced grid-support battery energy storage systems, and ongoing alignment with evolving North American Electric Reliability Corporation (NERC) standards.

Reactive Capability at Zero Real Power

One of the most notable discussions focused on the potential inclusion of “reactive at 0 MW” capability within ERCOT’s reactive study scope. Many inverter-based resources—particularly battery energy storage systems (BESS)—are technically capable of providing reactive power and voltage support even when they are not injecting or absorbing real power. Historically, however, interconnection studies and planning assumptions have not consistently accounted for this capability.

ERCOT staff and stakeholders discussed whether formalizing reactive capability at zero real power would better reflect actual system behavior and unlock additional voltage support during periods of low generation or curtailed output. Doing so would have meaningful implications for interconnection requirements, plant controller logic, and model validation processes. It could also influence how ERCOT evaluates voltage stability margins, particularly in areas with high inverter penetration and limited synchronous generation.

Stakeholders noted that while enabling reactive capability at zero megawatts may offer reliability benefits, it also introduces complexity. Clear expectations would be required around control modes, prioritization between real and reactive power, and performance verification. ERCOT emphasized that any expansion of study scope would need to be accompanied by enforceable modeling standards and validation mechanisms to ensure that modeled behavior accurately reflects field performance.

AGS BESS for Weak-Grid Areas

The working group also explored a potential case study examining the use of Advanced Grid Support (AGS) BESS to improve system stability in weak-grid areas. ERCOT framed this discussion as exploratory rather than prescriptive, but the implications were significant. Rather than viewing storage purely as a market-facing resource optimized for arbitrage or ancillary services, ERCOT highlighted its potential role as a fast-responding stabilizing asset.

Advanced grid-support batteries can provide rapid voltage regulation, frequency response, and oscillation damping, particularly in electrically weak regions where traditional resources are sparse. Participants discussed how such capabilities could be modeled, validated, and potentially incorporated into planning and operational frameworks. Questions were raised around performance obligations, availability during stressed conditions, and how AGS functionality would be coordinated with existing protection and control schemes.

While no formal proposals were advanced, the discussion signaled ERCOT’s growing interest in treating certain inverter-based resources as reliability assets rather than solely as market participants. This perspective has implications for future interconnection requirements, operational expectations, and potential cost recovery mechanisms if AGS capabilities are explicitly relied upon for system stability.

NERC Alignment and Compliance Convergence

ERCOT also provided updates on ongoing NERC alignment standards development related to inverter-based resources. Topics included ride-through requirements, electromagnetic transient (EMT) modeling expectations, disturbance and event reporting, and alignment between planning and operational studies. These efforts reflect an accelerating convergence between modeling accuracy, real-world performance, and enforceable compliance obligations.

Stakeholders noted that the historical separation between planning models and operational reality is narrowing. Inaccurate or outdated models are no longer just a planning inconvenience—they increasingly represent compliance risk. As NERC standards evolve, asset owners may face greater scrutiny regarding whether their registered models, control settings, and observed performance remain consistent over time.

ERCOT emphasized that improved alignment with NERC standards is intended to reduce ambiguity and improve system-wide reliability, but it also places a higher burden on resource owners to maintain disciplined model governance throughout the asset lifecycle.

Implications for Asset Owners and Developers

The December IBRWG discussion underscored a clear message for asset owners and developers: inverter performance is no longer evaluated solely at interconnection approval. Ongoing alignment between study models, plant controls, and operational behavior is becoming a baseline expectation.

Reactive capability assumptions, AGS functionality, and NERC-aligned modeling all require tighter internal coordination between engineering, controls vendors, and compliance teams. Poorly maintained models or undocumented control changes now pose both reliability and regulatory exposure. Developers entering ERCOT must increasingly consider not just how their assets interconnect, but how they will perform—and be verified—under a wide range of system conditions.

Zero Emission Grid supports inverter-based resource owners as ERCOT tightens modeling, performance, and compliance expectations. From dynamic model validation and EMT readiness to control strategy assessment and interconnection study support, ZEG helps ensure that asset behavior, documentation, and planning assumptions remain aligned throughout development and operation.

As ERCOT continues to evolve from minimum compliance toward performance-driven reliability, proactive preparation will be critical for inverter-based resources seeking to operate successfully in the ERCOT market. Contact us to be your helping hand navigating ERCOT’s grid.