Executive Summary
FERC Order 901, issued October 19, 2023, represents the most significant regulatory expansion affecting inverter-based resources (IBRs) since FERC Order 2222 opened wholesale markets to distributed resources. The order directs NERC to develop and implement reliability standards addressing the unique performance characteristics of IBRs—solar, wind, and battery storage facilities that use power electronic inverters rather than synchronous generators.
This memorandum provides a comprehensive analysis of Order 901's requirements, the resulting NERC standards development process, and the staggered compliance timeline extending through November 2026 and beyond. The analysis examines four key areas: data sharing requirements, model validation standards, planning study enhancements, and performance requirements during grid disturbances.
For IBR owners and operators, Order 901 creates new compliance obligations that require significant preparation. Facilities previously exempt from NERC registration may now face mandatory registration and compliance with reliability standards. Even currently registered facilities face enhanced requirements for ride-through capability, model accuracy, and data provision.
The compliance timeline is staggered across multiple filing dates, with performance requirements (November 2024), data and model validation requirements (November 2025), and planning study requirements (November 2026) phased in over three years. Prudent facility owners should begin preparation immediately, as the technical work required—particularly EMT model development and validation—can take 12-18 months.
1. Background and Regulatory Context
1.1 The Events That Prompted Order 901
FERC Order 901 did not emerge in a regulatory vacuum. The order represents FERC's response to a series of grid disturbances where IBRs performed unexpectedly, contributing to or exacerbating reliability events rather than supporting grid stability.
The most significant events include:
Blue Cut Fire (August 16, 2016): During a wildfire-induced fault in Southern California, approximately 1,178 MW of solar generation tripped offline within a 6-minute window. Investigation revealed that inverter protective settings caused generation to disconnect during voltage disturbances that should have been ridden through.
Canyon 2 Fire (October 9, 2017): A similar event saw 900 MW of solar generation trip during a fault, with inverter control systems contributing to oscillatory behavior before disconnection.
San Fernando Disturbance (July 2020): During a transmission fault, 1,000 MW of solar generation entered "momentary cessation"—a state where inverters stop injecting current but remain connected—exacerbating the voltage depression and causing a cascading loss of additional generation.
Odessa Disturbance Events (May and June 2021): Two separate events in the ERCOT system saw significant solar generation trip during transmission faults. The June event resulted in the loss of approximately 1,100 MW within seconds.
These events shared common characteristics: IBR facilities responding to grid disturbances in ways that differed from their modeled behavior, inadequate ride-through capability, and controls that prioritized equipment protection over grid support.
1.2 FERC's Regulatory Authority
FERC's authority over bulk power system reliability stems from Section 215 of the Federal Power Act, added by the Energy Policy Act of 2005. This section authorizes FERC to certify an Electric Reliability Organization (ERO)—NERC—and approve reliability standards developed by that organization.
Order 901 exercises this authority by directing NERC to address identified reliability gaps. While FERC cannot directly write reliability standards, it can direct NERC to develop standards addressing specific issues and reject proposed standards that fail to adequately address reliability concerns.
The order specifically directs NERC to:
- Develop registration criteria for IBRs not currently subject to NERC reliability standards
- Establish data sharing requirements enabling accurate IBR modeling
- Create model validation standards ensuring models reflect actual facility performance
- Develop planning study requirements incorporating IBR-specific reliability considerations
- Establish performance requirements for IBR behavior during grid disturbances
1.3 Relationship to Other Orders
Order 901 operates alongside several other FERC directives affecting IBRs:
Order 2023 (Interconnection Reform): Establishes new pro forma interconnection procedures, including enhanced study requirements for IBRs and cluster study processes designed to reduce interconnection queue backlogs.
Order 2222 (DER Market Participation): Opens wholesale markets to distributed energy resource aggregations, creating new categories of IBR participants.
Order 881 (Transmission Line Ratings): Requires transmission providers to use ambient-adjusted line ratings, affecting available transmission capacity for IBR generation.
Together, these orders represent FERC's comprehensive approach to integrating IBRs into the bulk power system while maintaining reliability.
2. Order 901's Four Pillars
2.1 Data Sharing Requirements
Order 901 recognizes that grid operators and planners cannot ensure reliability without accurate information about IBR capabilities and limitations. The order directs NERC to develop standards requiring IBR owners to provide:
Equipment Specifications: Detailed technical data about inverter characteristics, including current injection capabilities, fault current contribution, voltage and frequency operating ranges, and control system architectures.
Operational Parameters: Real-time and historical data about facility performance, including active and reactive power output, voltage regulation performance, and responses to grid events.
Control System Information: Documentation of inverter control modes, protective settings, and the logic governing responses to grid disturbances.
Model Parameters: The specific parameters required to accurately represent facility behavior in planning models, including both positive-sequence and electromagnetic transient (EMT) model data.
The resulting NERC standard development has focused on modifications to MOD-031 (Demand and Energy Data) and new data reporting requirements under the Facility Ratings, System Operating Limits, and Transfer Capability (FAC) family of standards.
2.2 Model Validation Requirements
Perhaps the most technically demanding aspect of Order 901 involves model validation. The disturbance events described in Section 1.1 revealed a consistent pattern: IBR facilities did not behave as their planning models predicted. This discrepancy undermined the reliability studies that grid operators depend upon.
Order 901 directs NERC to require:
Model Accuracy Standards: Quantitative requirements for how closely models must match actual facility performance, with specific accuracy thresholds for active power, reactive power, and current injection during disturbances.
Validation Testing: Procedures for testing models against actual facility behavior, either through staged tests or comparison with disturbance recordings.
Periodic Revalidation: Requirements for ongoing model validation as facilities age, control systems are updated, or performance changes are observed.
EMT Model Requirements: For facilities in areas with high IBR penetration or where EMT phenomena affect reliability, requirements for electromagnetic transient models in addition to traditional positive-sequence models.
The model validation requirements are implemented primarily through revisions to MOD-026 (Verification of Models and Data for Generator Excitation Control System or Plant Volt/Var Control Functions) and MOD-027 (Verification of Models and Data for Turbine/Governor and Load Control or Active Power/Frequency Control Functions), which are being consolidated into MOD-026-2.
2.3 Planning Study Requirements
Order 901 addresses gaps in how IBRs are incorporated into reliability planning studies. Traditional planning approaches, developed for systems dominated by synchronous generation, may not adequately capture IBR-specific reliability considerations.
The order directs NERC to require:
IBR-Specific Study Scenarios: Planning cases that specifically stress IBR performance, including low-inertia conditions, high IBR penetration scenarios, and events that challenge ride-through capability.
EMT Study Requirements: For regions where positive-sequence models are insufficient, requirements for electromagnetic transient studies that can capture fast-acting IBR control dynamics.
Sensitivity Analysis: Studies examining how reliability outcomes change based on IBR model assumptions, identifying conditions where modeling uncertainty creates reliability risk.
Coordination Requirements: Enhanced coordination between Transmission Planners, Planning Coordinators, and IBR owners to ensure study assumptions reflect actual facility capabilities.
These requirements are being implemented through modifications to TPL-001 (Transmission System Planning Performance Requirements) and associated planning standards.
2.4 Performance Requirements
The final pillar of Order 901 addresses the core issue revealed by disturbance events: IBRs must ride through grid disturbances rather than tripping or entering momentary cessation. The order directs NERC to establish:
Voltage Ride-Through Requirements: IBRs must remain connected and continue operating during voltage disturbances within defined envelopes. The requirements specify how long facilities must ride through disturbances at various voltage levels.
Frequency Ride-Through Requirements: Similar requirements for frequency excursions, ensuring IBRs remain connected during under-frequency and over-frequency events.
Momentary Cessation Limits: Restrictions on when and how long IBRs may enter momentary cessation (reducing output to zero while remaining connected), addressing the phenomenon that exacerbated the 2020 San Fernando disturbance.
Current Injection Requirements: Requirements for IBRs to inject reactive current during voltage disturbances, supporting grid voltage recovery rather than simply riding through passively.
These performance requirements are implemented through PRC-024-4 (Frequency and Voltage Protection Coordination for Generating Resources) and the new PRC-029-1 (Inverter-Based Resource Performance).
3. Compliance Timeline
3.1 Staggered Implementation
Order 901 recognizes that the required standards cannot be developed, approved, and implemented simultaneously. FERC established a staggered timeline:
| Filing Category | NERC Filing Deadline | Compliance Effective |
|---|---|---|
| Performance Requirements | November 2024 | ~24 months post-approval |
| Data/Model Validation | November 2025 | ~24 months post-approval |
| Planning Studies | November 2026 | ~24 months post-approval |
| Registration Criteria | Ongoing | May 2026 (Category 2) |
3.2 Performance Requirements Timeline (November 2024)
NERC filed the performance-related standards—PRC-024-4 and PRC-029-1—in November 2024. FERC approved these standards in July 2025, establishing:
PRC-024-4: Revised frequency and voltage protection coordination requirements, including updated ride-through curves and explicit requirements for IBRs.
PRC-029-1: New standard establishing mandatory ride-through and performance requirements specifically for IBRs, including momentary cessation limitations and current injection requirements.
For existing registered facilities, compliance with these standards becomes mandatory approximately 24 months after FERC approval, targeting mid-2027. However, new facilities seeking interconnection must demonstrate compliance with performance requirements as a condition of interconnection.
3.3 Data and Model Validation Timeline (November 2025)
The November 2025 filing deadline covers data sharing and model validation requirements:
MOD-026-2: Consolidates MOD-026-1 and MOD-027-1 into a unified model verification standard. The standard requires facility owners to validate models against actual performance data and provide updated models when validation reveals discrepancies.
Data Reporting Requirements: Enhanced requirements for IBR owners to provide equipment specifications, operational data, and model parameters to their Planning Coordinators and Reliability Coordinators.
FERC is expected to act on these standards in 2026, with compliance obligations beginning approximately 24 months later. Full compliance with MOD-026-2 is required by April 1, 2030, with interim milestones for initial model submission and validation.
3.4 Planning Study Timeline (November 2026)
The final tranche of standards addresses planning study requirements:
TPL-001 Modifications: Enhanced requirements for incorporating IBR-specific scenarios and EMT studies into transmission planning assessments.
FAC Standard Modifications: Requirements for how IBR capabilities are represented in facility ratings and system operating limits.
These standards, once approved, will establish how grid planners must study systems with high IBR penetration, ensuring that reliability assessments reflect actual IBR capabilities and limitations.
4. Regional Implementation Considerations
4.1 ERCOT
ERCOT presents a unique implementation challenge. As a non-FERC-jurisdictional system, ERCOT is not directly subject to Order 901. However, Texas RE (the Regional Entity for ERCOT) implements comparable requirements, and ERCOT's own Operating Guides increasingly align with NERC standards.
ERCOT's experience with IBR disturbances—particularly the 2021 Odessa events—has made the region a leader in IBR performance requirements. ERCOT's Operating Guides already include ride-through requirements that in some cases exceed NERC standard minimums.
For IBR owners in ERCOT, the practical impact of Order 901 is indirect but significant. Equipment meeting NERC PRC-024-4 and PRC-029-1 requirements will generally satisfy ERCOT requirements, but facility owners should verify compliance with both frameworks.
4.2 Western Interconnection
WECC has extensive experience with IBR integration, particularly in California where solar penetration levels frequently exceed 50% of demand. CAISO's planning processes already incorporate many Order 901 concepts, including EMT study requirements and stringent model validation procedures.
However, Order 901 creates uniform minimum requirements that may exceed current practices in some Western areas. Facilities in the broader WECC region outside CAISO should expect enhanced requirements as Order 901 standards are implemented.
4.3 Eastern Interconnection
The Eastern Interconnection encompasses multiple RTOs/ISOs (PJM, MISO, SPP, ISO-NE, NYISO) and non-RTO regions. Implementation consistency across this diverse landscape presents challenges.
PJM has been particularly aggressive in requiring EMT models for IBR interconnection studies, creating a de facto requirement that precedes formal Order 901 standards. MISO and SPP, with rapidly growing wind and solar portfolios, are enhancing their IBR study capabilities.
Facility owners in the Eastern Interconnection should expect regional variations in how Order 901 requirements are implemented, with RTOs potentially imposing requirements that exceed NERC minimums.
5. Implications for IBR Owners
5.1 Registration Impacts
The most immediate impact for many IBR owners is the expansion of NERC registration requirements. Facilities previously exempt from registration based on size or interconnection characteristics may now face mandatory registration under the Category 2 criteria:
- Connected at 60kV or above
- Aggregate capacity of 20 MVA or greater at a single point of interconnection
Registration brings with it compliance obligations under applicable NERC standards. The May 2026 deadline for Category 2 registration requires immediate action—registration applications should be submitted by early 2026 to allow processing time.
5.2 Technical Preparation
Order 901 creates substantial technical work for IBR owners:
Model Development: Facilities must provide accurate positive-sequence and (increasingly) EMT models. For existing facilities without validated models, development can take 6-12 months and require engagement with inverter OEMs.
Model Validation: Once models exist, validation against actual performance data—either from commissioning tests or disturbance recordings—requires engineering analysis and may reveal needed model updates.
Protective Relay Coordination: Ensuring protective relay settings align with PRC-024-4 ride-through curves may require coordination studies and, potentially, relay setting changes.
Control System Updates: Facilities that enter momentary cessation or fail to provide adequate ride-through may require inverter firmware updates or control system modifications.
5.3 Compliance Program Development
For newly registered facilities, Order 901 requires establishing NERC compliance programs encompassing:
- Designation of compliance responsibility
- Documentation and evidence retention
- Internal compliance monitoring
- Preparation for NERC audits and spot checks
- Self-reporting of potential violations
Facilities without existing compliance infrastructure should budget 6-12 months for program development.
6. Conclusions and Recommendations
FERC Order 901 represents a watershed moment in IBR regulation. The order's comprehensive approach—addressing data, models, planning, and performance—reflects the reality that IBRs are fundamentally different from the synchronous generation the grid was designed around.
For IBR owners, the path forward requires immediate action:
First, assess registration status. Facilities meeting Category 2 criteria face a May 2026 deadline that leaves limited time for preparation.
Second, engage with model development. EMT models are increasingly required across all regions, and lead times for model development from OEMs can extend to 12 months or longer.
Third, review protective relay settings. The ride-through requirements in PRC-024-4 and PRC-029-1 set specific curves that protective settings must respect.
Fourth, plan for compliance infrastructure. Newly registered facilities need compliance programs, documentation systems, and trained personnel.
The reliability events that prompted Order 901 demonstrated real risks from inadequately integrated IBRs. The standards being developed address these risks, but only if facility owners take compliance seriously. The staggered timeline provides opportunity for preparation—but the time for preparation is now.
Select Citations
- (FERC): Reliability Standards to Address Inverter-Based Resources, Order No. 901
- (NERC): Inverter-Based Resource Performance: Issues and Recommendations
- (NERC): Odessa Disturbance Event Reports
- (FERC/NERC): Joint Staff Technical Conference on Inverter-Based Resources, Docket No. AD22-9-000
- (NERC): IBR Registration Initiative Program Updates
