Surplus interconnection service uses existing interconnection headroom

Surplus interconnection service allows a new resource to use existing interconnection capacity that the original generator does not use, typically because its capacity factor or operating profile leaves headroom. Because the injection is bounded by the existing agreement, the study burden is far smaller than a new request.

The classic application is storage added at an existing solar or wind site, or at a thermal unit whose output rarely reaches its interconnection limit. The economics are strong precisely because network upgrade exposure is small or nil.

The constraints are contractual as much as technical. The existing interconnection customer controls the headroom, site control must be arranged, and any change to the operating profile of the host resource can compress the available surplus.

For a developer without a viable queue position, this is the most reliable path to energisation on a two- to three-year horizon.

What to watch: transmission provider business practice manuals, which determine how surplus requests are queued relative to standard requests.