NERC’s Energy Reliability Working Group (ERWG), formerly the Energy Reliability Assessment Working Group (ERAWG), is a body of energy experts from multiple sectors within the industry. A primary function of the group is to develop educational materials that describe potential fuel and energy-related risks to reliability of the North American bulk power system, along with possible solutions to these risks.

In March 2023,the group publishedConsiderations for Performing an Energy Reliability Assessment Volume 1, a white paper to guide stakeholders in evaluating and ensuring the reliability of energy systems amid a rapidly evolving power grid. Building upon this work, late last year the ERWG published a technical reference document Considerations for Performing an Energy Reliability Assessment Volume 2 to provide grid planners, operators, and regulators with essential factors to consider when performing an energy reliability assessment (or ERA).

The growing penetration of variable renewable resources, combined with early retirement of conventional generation and electrification trends, has led to the risk of Uncertain Energy Availability across North America and in MRO’s region. This risk is described in detail in MRO’s 2025 Regional Risk Assessment, which identified Uncertain Energy Availability as an extreme risk for the second year in a row.

The second volume published by the ERWG helps to address this risk by encouraging consideration for inputs related to stored fuels, just-in-time-fuels, outage modeling, electricity demand, electricity storage, and transmission during the development of ERAs. Stored fuels discussed in the document include nuclear fissile material, fuel oil, coal, water for hydro units, and natural gas as liquefied natural gas (LNG) or in subsurface storage. Just-in-time fuels include natural gas, run-of-river hydro, solar, and wind generators.

The document describes three different time horizons for completing an ERA: near-term, seasonal, and planning. A near-term ERA begins with a 1-day or 2-day outlook and extends to several days or weeks. Key inputs include existing generation, short-term demand forecast, variable energy resources (VERs) forecast, and planned outages. The seasonal ERA expands the study timeframe to months, but less than a year. The key inputs for a seasonal ERA are the existing and planned generation, assumptions made for VERs output, outage modeling known for generation and transmission, and demand based on historical and projected load growth as load forecasts are typically unavailable or unreliable. A planning ERA looks ahead at the long-term (1- to10-year) time horizon. The planning ERA considers more uncertainty in assumptions made about generation resource additions and retirements, natural gas availability, VERs output, emission constraints on generator operation, historical outage modeling, electricity demand projections based on potential electrification, and the use of transmission upgrades to relieve constraints.

The final chapters provide methods for modeling, sensitivity modeling, study metrics and criteria, and considerations for corrective actions. Based on the modeling methods and study metrics and criteria of the ERA study, corrective action plans can be assembled for any of the ERA studies. In chapter eight, the considerations are grouped by corrective actions and the applicable time horizon. In general, the near-term ERA provides fewer options than a planning ERA, but factors such as public appeal to reduce load, rescheduling outages, strategic fuel replenishment, and demand response programs can be impactful. Corrective action plans for the planning ERA include increasing additional generation and transmission projects, enhancing market structures, and delaying generation retirements.

As the energy landscape continues to shift, ensuring a reliable and resilient bulk power system requires a comprehensive and coordinated approach to conducting ERAs. Volume 2 emphasizes the importance of essential reliability services, resource adequacy, stakeholder coordination, infrastructure planning and environmental compliance. The document also considers energy-related assessment gaps that will be created as the resource mix continues to evolve.

By incorporating these considerations into planning and operations strategies, utilities can better navigate bulk power system changes and maintain reliability and stability of the power grid.

– Brian Giggee, Director of Electric System Operations and Planning, Montana-Dakota Utilities Company (and member of MRO’s Reliability Advisory Council), and Bryan Clark, MRO Director of Reliability Analysis

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