How MISO Determines Capacity Accreditation for Resources

How MISO calculates accredited capacity for different resource types

MISO’s capacity accreditation process varies depending on the type of resource, reflecting the unique characteristics and operational profiles of each. Let’s dive into how MISO handles thermal generation, renewables, demand response, and storage.

Thermal resources: For traditional thermal generators like coal, natural gas, and nuclear plants, MISO calculates Seasonal Accredited Capacity (SAC) based on historical performance during critical hours. These hours are typically the top eight coincident peak hours for each season over the past three years. MISO applies seasonal forced outage rates to the installed capacity (ICAP) of these resources to determine their SAC. This ensures that thermal resources are credited based on their actual availability during peak demand periods, rather than their theoretical maximum output.

Renewable resources: Wind and solar resources are accredited using the Effective Load Carrying Capability (ELCC) methodology. ELCC measures the ability of these intermittent resources to reliably contribute to meeting peak demand. MISO conducts system-wide ELCC studies to determine the seasonal capacity value of wind and solar fleets. For individual resources, MISO uses unit-specific metrics, such as average capacity factors during peak hours, to allocate the system-wide ELCC value. New resources without operational history receive a class average capacity credit until sufficient data is available.

Demand response resources: Demand response (DR) resources, including Behind-the-Meter Generation (BTMG) and other load-modifying resources, are accredited based on their ability to reduce demand during emergencies. MISO evaluates these resources using historical performance data and their compliance with Module E-1 requirements. DR resources must demonstrate their ability to respond during capacity and transmission emergencies to qualify for accreditation.

Storage resources: Electric storage resources (ESRs) are accredited based on their ability to provide energy during peak demand periods. MISO considers factors like the duration of discharge and the resource’s ability to recharge between peak periods. Storage resources must demonstrate they can operate for at least four consecutive hours during MISO’s peak demand periods to qualify for capacity accreditation.

The role of ELCC studies in capacity accreditation

Effective Load Carrying Capability (ELCC) studies are at the heart of MISO’s accreditation process for intermittent resources like wind and solar. These studies use probabilistic and deterministic methods to evaluate how much capacity these resources can reliably contribute to meeting demand.

MISO’s ELCC studies begin with a system-wide analysis, which calculates the seasonal ELCC value for the entire fleet of wind or solar resources. This involves simulating the Loss of Load Expectation (LOLE) under various scenarios to determine the reliability contribution of these resources. Once the system-wide ELCC value is established, MISO allocates it to individual resources based on their historical performance and locational factors. This two-step process ensures that each resource is credited fairly while maintaining overall system reliability.

How capacity accreditation impacts MISO’s capacity auctions and resource adequacy

MISO’s capacity accreditation process directly influences its Planning Resource Auctions (PRAs) and resource adequacy requirements. Accredited capacity values determine how much capacity a resource can offer in the PRA, which is MISO’s primary mechanism for procuring capacity to meet peak demand.

By accurately accrediting resources, MISO ensures that the capacity procured in the auction reflects the actual reliability contribution of each resource. This prevents over-reliance on resources that may not perform as expected during critical periods. For example, the ELCC methodology accounts for the variability of wind and solar, ensuring that their capacity credits align with their ability to deliver during peak demand.

Accurate accreditation also supports MISO’s long-term resource adequacy planning. By understanding the reliable capacity of different resource types, MISO can identify potential shortfalls and guide investment in new resources. This is particularly important as the grid transitions to a cleaner energy mix, with increasing reliance on renewables and storage.

Why MISO’s capacity accreditation matters

MISO’s capacity accreditation process is more than just a technical exercise—it’s a critical tool for ensuring grid reliability and market efficiency. By tailoring accreditation methods to the unique characteristics of each resource type, MISO creates a level playing field that encourages diverse participation in its capacity market.

The use of ELCC studies for renewables and the rigorous evaluation of other resource types ensure that MISO’s capacity auctions procure the right mix of resources to meet demand. This process not only supports reliability but also fosters innovation and investment in new technologies.

As the energy landscape continues to evolve, MISO’s capacity accreditation methods will play a key role in shaping the future of the grid. Whether you’re a market participant, a policymaker, or an energy enthusiast, understanding how MISO accredits capacity is essential for navigating the complexities of today’s energy markets.

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