Cluster study: what it is and how it replaced serial processing

A cluster study evaluates every interconnection request that entered a common application window as a single group, against a single base case, rather than evaluating each request individually in queue order. FERC adopted the approach as the default in Order No. 2023, which reformed the pro forma Large Generator Interconnection Procedures.

The change addressed a specific mechanical problem. Under serial processing, each study assumed the projects ahead of it in the queue would be built. When one of them withdrew, the assumptions beneath every study behind it changed and the studies had to be redone. Restudy cascades lengthened timelines across entire regions.

Clustering fixes the base case for the group, so a withdrawal within the cluster is handled through the cluster restudy rules and the cost allocation among remaining members, rather than by restarting the queue behind it. The cluster study produces the identified network upgrades and the allocation of their cost among cluster members. A project that proceeds then moves to the facilities study and, if it continues, to an interconnection agreement.