Capacity accreditation—the determination of the resource adequacy (RA) contribution of individual resources or groups of resources—is used to conduct RA assessments to determine whether there are sufficient resources to serve demand. It is also used for long-range resource expansion planning and within electricity markets.
Capacity accreditation metrics—the values assigned to a resource or resource class to define its contribution—and methods, which are the means to derive those values, differ due to different applications and alternative approaches to RA assessments. Methods are evolving from those that are relatively simple, transparent, deterministic approaches to those probabilistic methods which require more complicated modeling. This change is to accommodate power system evolution (towards greater use of renewables and storage), consider individual or resource-type characteristics, properly assess system risk, and evaluate the probability of loss of load events.
This Technical Brief summarizes and categorizes various capacity accreditation methods and metrics and discusses their strengths, weaknesses, and overarching principles. It addresses complexities involved in evaluations as well as implications of using different methods. It shares insights on how even the same method can show different values with changes to assumptions, modeling features, and data used. It provides a few examples from industry on the use of new capacity accreditation approaches. The Briefing concludes with principles to consider when designing or modifying RA assessments.