Sighting in capacity mechanisms to better approach the target: reliability metrics and firm supply calculation

Abstract

Capacity mechanisms are now considered a regulatory pillar of the decarbonisation process that liberalised power systems are undergoing. Remuneration in these mechanisms depends on the so-called firm supply (or capacity credit, calculated through any sort of de-rating method), which is supposed to reflect the expected contribution of each resource to the adequacy of the system in the long term. The determination of the firm supply has always been seen as a system-dependent challenging task, with significant implications for the efficiency of the entire capacity mechanism. Nowadays, however, this task is growing in complexity in decarbonized power systems, due to the further development of new resources such as demand response and storage, the role of correlations among resources, the increasing need for flexibility and likelihood of extreme weather events. This article reviews long-term reliability metrics and methodologies to calculate the firm supply, focusing on state-of-the-art best practices that are consistent to the new challenging scenarios that decarbonising power systems have to face.