Capacity Accreditation of Inflexible Resources in New England

Sierra Club
Project completed March 2023

New England's slowest power plants, including old coal and oil resources, struggle to support grid reliability when system conditions change quickly and unexpectedly, but today these operational limitations aren't accounted for in ISO New England's Forward Capacity Market. On behalf of Sierra Club, Synapse analyzed the performance of several of New England's legacy fossil generation units to understand the extent of their operational inflexibility, and evaluated the risk of encountering unpredicted changes in system conditions such as load levels on time scales in which these inflexible resources would be too slow to respond and support reliability. We found that these plants would struggle to support grid reliability in a range of plausible system conditions, and that the limitations of these resources were a major factor in New England's last two capacity scarcity events. Our analysis shows that ISO New England should account for operational limitations when it accredits the capacity value of each resource to improve system reliability and allow new and better-performing technologies to fully compete in the market. We described our findings in a technical report.