ERCOT runs a connect-and-manage interconnection model. Unlike PJM or MISO, projects don't wait for network upgrades to be assigned and built before they can interconnect. That's why developers consistently prefer it. The process is faster - in principle.
In practice, the median timeline for a BESS project from queue entry to operation is now 4.1 years. Three years ago it was 3.5. The queue has grown. The process hasn't scaled with it.
The more important shift is where the delay is accumulating. It's not at construction. It's not at permitting. It's at the Full Interconnection Study: the TSP-led engineering study that sits between queue entry and the Interconnection Agreement.
That's a structural change in where program risk lives on ERCOT projects. And most development teams haven't updated their sequencing to account for it.
For transmission-connected projects -utility solar, BESS, C&I solar at scale, the ERCOT interconnection process runs through three sequential study gates:
1. Security Screening Study, run by ERCOT. It flags sub-synchronous resonance risks, weak or very weak grid conditions, inverter modelling requirements, and post-fault ride-through compliance. Projects flagged here may need to submit a Weak Grid Support Plan before proceeding.
2. Full Interconnection Study, run by the relevant TSP. This is the substantive work: steady-state load flow, short-circuit analysis, stability modelling, facility study. The FIS determines network upgrade requirements and the project's export limit. It's also where the queue has backed up.
3. Quarterly Stability Assessment, conducted every three months. A project needs to be included in a QSA before it's eligible for Initial Energization. Miss a QSA window and you're waiting a minimum of three months. On a compressed program, that's a material schedule event, not an administrative one.
The FIS is the critical path. And the FIS is where submissions are getting held up.
ERCOT doesn't process FIS applications centrally. Each Transmission Service Provider runs its own queue, with its own resourcing and its own backlog:
Processing timelines and information-request turnaround vary between them, and not by a small margin. A site selection process that doesn't account for TSP territory is making program assumptions without the information to support them. Which TSP your project falls under, and what their current FIS queue looks like, belongs in feasibility analysis. If it comes up after the application goes in, it's too late to act on it.
The TSPs processing FIS applications are working through a queue that has grown 40% in three years. They are not resourced to absorb incomplete submissions. When an application comes in with missing dynamic models, incompatible PSS/E or PSCAD file formats, unresolved reactive power capability demonstrations, or protection scheme conflicts, it gets rejected and re-queued.
Re-queuing means starting the FIS clock again. It means missing the next QSA window. On a BESS project where the Interconnection Agreement isn't signed, the financing isn't closing. On a C&I solar project where the export limit scheme isn't resolved, the detailed design can't be finalized.
Where projects once took 1.8 years after signing an IA to reach operation, it now takes 2.5 years. The delay is in the study phase, before the IA is signed.
The queue position isn't controllable once you're in it. The TSP's processing capacity isn't controllable. The QSA schedule isn't controllable. The application quality is.
A clean FIS application: complete dynamic models, correct file formats, resolved protection scheme, documented reactive capability - clears the study on first review. That's where the timeline compression comes from.
The projects clearing the FIS on first review are the ones where HV engineering was done before capital was committed and before the application went in, not revised to catch up with what the study returned.
At Illumine-i, our ERCOT scope covers that sequence: interconnection strategy from feasibility, protection coordination studies, export limit scheme design, and construction-ready HV drawings built to what the FIS will require. If your program is at feasibility or early development and the interconnection sequence isn't locked, that's the conversation to have before the queue makes the decision for you.
It depends on where you are. If your SSS is complete but the FIS hasn't started, there's still a window: complete your dynamic models, resolve protection coordination, and validate your export limit assumptions before the TSP begins the study. If you're already in the FIS, the priority shifts to ensuring your responses to TSP information requests are complete on first submission. An incomplete response triggers the same re-queuing risk as a rejected application.
For projects not yet in the queue, no. The median FIS timeline alone exceeds what's available. For projects past the SSS with a clean FIS in process, it depends on where you are in the QSA cycle and whether your IA can be signed in time. One thing worth noting: the physical work test requires racking installed on site by July 4, not interconnection complete. But if the engineering sequence supporting construction-start has unresolved interconnection dependencies, that needs to be clear now, not at the July deadline.
A minimum of three months, and that assumes everything else in your programme is locked. On a BESS project where financing is contingent on the signed IA, a missed QSA cycle delays the IA, delays financial close, and delays procurement. On programs targeting the ITC construction-start deadline, three months is often the difference between a project that qualifies and one that doesn't.
Yes, materially. Oncor, AEP Texas, CenterPoint, and TNMP run their own processes with different resourcing levels. Oncor covers the largest territory and the densest queue. Know which TSP your site falls under before the application goes in.
If your site is flagged as weak or very weak during the SSS (based on short-circuit ratio at the interconnection point), ERCOT requires a Weak Grid Support Plan before the project can proceed to the FIS. The plan addresses how the project handles grid strength concerns: inverter control settings, reactive power support, synthetic inertia. Projects that haven't assessed grid strength at site selection find out mid-SSS. In some cases it changes the project's technical and commercial viability entirely, which is a bad thing to discover after you've committed to a site.
