Reformulating Energy Storage Capacity Accreditation Problem with Marginal Reliability Impact

TL;DR

This paper introduces a new method to calculate energy storage capacity accreditation using Marginal Reliability Impact, improving efficiency and providing practical insights for system operators and policymakers.

Contribution

It reformulates the reliability-based storage dispatch model as an optimization problem to directly compute MRI from Lagrange multipliers, avoiding brute-force methods.

Findings

EUE is a piecewise linear function

Storage MRI remains non-negative across scenarios

Numerical validation with California system confirms findings

Abstract

To enhance the efficiency of capacity markets, many electricity markets in the U.S. are adopting or planning to implement marginal capacity accreditation reforms. This paper provides new insights into energy storage capacity accreditation using Marginal Reliability Impact (MRI). We reformulate the commonly used reliability-based storage dispatch model as an optimization problem, enabling direct calculation of the MRI from the Lagrange multipliers, rather than using brute-force perturbation analysis. The analysis demonstrates that the EUE is a piecewise linear function and the storage MRI retains a non-negative property across various system scenarios. We further explore the influence of qualified capacity (QC), storage dispatch rules, and other key factors on storage accreditation, providing practical insights for system operators. Additionally, comparisons of storage capacity accreditation under different reliability criteria offer valuable guidance for policymakers in setting future standards. Numerical results from a modified California system validate our findings and highlight several important phenomena associated with the MRI-based accreditation scheme.