The Interconnection Review Process, Explained 

A clean energy customer’s excitement can fade fast if their project hits a roadblock. One day they’re signing a contract, the next they’re asking you why nothing has happened. The answer is often interconnection.

If you work in a customer-facing role, you probably know the steps for interconnection. What can be hard to explain is why they exist. Here’s a breakdown of how utility interconnection review actually works, and why it’s built the way it is.

Why the process exists

When a customer wants to connect a solar system or battery to the grid, the utility needs to verify that the addition won’t compromise safety or grid reliability for everyone else on that circuit. That’s the core purpose of interconnection review.

The rules governing that review process come from state regulatory commissions, not the utility itself. In most states, those rules live inside lengthy administrative documents written in legal language. They’re not designed for customers. They’re designed for enforceability. Understanding that distinction is critical. The utility’s interconnection process is meant to implement state rules, and those rules exist to hold both the utility and the customer accountable.

Three pathways

Most interconnection procedures offer three review pathways, and which one a project lands in depends largely on its size and the existing conditions on the circuit it’s connecting to.

Simplified review is the fastest pathway, typically for smaller systems – often up to 20–25 kW in more modern state rules, though older rules can cap it as low as 10 kW. The key screen is the penetration screen: if the total solar and storage export on a circuit doesn’t exceed the minimum load on that circuit, the project is generally safe to approve without deep engineering study. Pass the screens, get an interconnection agreement.

Fast track review covers larger projects – typically up to 5 megawatts (depending on the state). It includes additional screens beyond what simplified review checks, and if a project passes, the utility evaluates whether any system upgrades are needed. Minor upgrades (like replacing a fuse or reprogramming protection equipment) don’t derail the process. Major ones (like replacing conductors) can push a project into a facility study, which costs thousands of dollars and takes significantly longer. At that point, some customers choose to withdraw and redesign.

Detailed study is the full engineering process – system impact study, facility study, potentially significant costs and timelines. This pathway makes sense for large commercial or community solar projects (a 5 MW community solar project, for example) where the economics can absorb the cost of study. For a residential rooftop system that costs $25,000 installed, a $25,000 study process doesn’t pencil out.

What happens when a project fails the screens

Failing a simplified or fast track screen doesn’t automatically mean the project is dead or headed for a full engineering study. Most modern interconnection procedures include a supplemental review step, sometimes called an “engineering light” study. This might be a power flow study or an effective grounding review, something more detailed than a flat screen, but far less intensive than a full system impact study. Costs typically range from a few hundred to a couple thousand dollars.

The supplemental review exists because the screens are intentionally conservative. They’re designed to catch potential issues early, not to be the final word on every project. Utilities have limited engineering capacity, and customers have limited budgets. Supplemental review is the process’s attempt to find the middle ground, giving projects that push against the screen thresholds a fair shot before committing everyone to an expensive, time-consuming study.

If a project fails supplemental review, it either moves to a detailed study or the customer withdraws.

What this means if you’re supporting customers

Understanding the logic behind these steps changes how you can show up for customers. When someone’s project gets flagged for supplemental review, you can explain why that step exists and what it’s actually evaluating, rather than delivering vague news about delays. When a project fails a screen, you can look at the utility’s required disclosure and use that information to evaluate whether a redesign makes sense.

While it may seem like it, the interconnection process is not a black box. It has a structure, and that structure reflects real engineering and regulatory reasoning. The professionals who understand it are the ones who can successfully navigate it on behalf of their customers. That’s a real competitive advantage.

Go deeper with Vaughan Woodruff

Vaughan Woodruff has spent years working at the intersection of DER policy and project execution. His new course, Owning the Customer Interconnection Experience, is built for customer service reps, interconnection specialists, and project managers who want to move from fumbling through the process to actually understanding it.

Enroll in Owning the Customer Interconnection Experience today!