Top 5 Things EPCs Need to Know About Power System Studies

As utility-scale solar projects grow in size, complexity, and grid impact, understanding the nuances of power system studies has become essential for engineering, procurement, and construction (EPC) firms. These studies aren't just regulatory hurdles; they directly shape whether and how a project gets connected, what it will cost, and whether it hits key delivery milestones.

At their core, power system studies model how a new solar project will interact with the local grid, ensuring that it won't negatively impact stability, voltage, or reliability. These studies vary in scope but often include load flow, short circuit, protection coordination, and voltage ride-through modeling.

For EPCs, getting these studies right means fewer delays, lower risk, and more confidence when working with developers and utilities. Here’s what to know about them:

1: They’re Not One-Size-Fits-All

No two power system studies are exactly alike, because each utility has its own requirements. Sometimes, even different regional divisions within a utility will have their own processes, expectations, and review timelines for interconnection studies.

For developers, this means that just because a study was completed one way for a project in one region doesn’t mean the same approach will work elsewhere. This lack of standardization creates a high risk of misalignment unless EPCs coordinate closely with engineering partners who understand each utility's preferences.

For instance, one developer we worked with submitted interconnection applications to two different utilities, each of which required a completely different set of studies. One utility required a full suite, including short circuit, protection coordination, arc flash, and load flow studies. The other required only short circuit and voltage drop calculations.

If that developer hadn’t worked with an engineering partner familiar with each utility’s specific requirements, they’d have risked either providing incomplete documentation or wasting valuable time and resources preparing unnecessary paperwork.

Understanding these nuances ahead of time allows EPCs and developers to avoid interconnection delays, cost overruns, and worst-case scenarios like having to redesign the system. It’s why we practice close coordination with utilities from day one.

2: They Can Make or Break Your Project Timeline

Power system studies are often one of the longest lead-time tasks in the development process—and one of the easiest to underestimate. Utilities and ISOs may take several months to review and respond to submissions. If that submission isn’t 100% correct or fails to meet their modeling standards, they may require significant revisions – essentially restarting the clock.

These delays affect permitting and can jeopardize tax credit eligibility, off-taker agreements, and construction sequencing. An incomplete or inaccurate study package can knock a project to the back of the interconnection queue. In areas with high interconnection demand, missing a study milestone might result in losing your queue position completely.

The best way to avoid that is to collaborate early and often with an engineering partner who can do more than produce high-quality deliverables. Your engineering firm should also communicate proactively with the utility, to flag potential issues before they derail your schedule.

3: They Help Prevent Costly Problems Down the Line

Power system studies aren’t just paperwork for utility approval. They’re a tool to identify risks that can dramatically affect project costs, construction timelines, and even safety.

While power system studies are fundamentally about ensuring grid stability, they also assess project viability. Their results determine how much equipment you’ll need to meet voltage ride-through or reactive power requirements—and whether those costs still allow the project to pencil out.

For instance, a short circuit study might reveal that existing equipment can’t handle the fault current a new system could introduce, triggering a need for upgraded switchgear or protection devices. Or a load flow study might show an unexpected voltage drop under certain conditions, alerting engineers to the need for additional conductors or system reconfiguration.

These issues can be addressed relatively easily in the design phase, but if they’re discovered later – during construction or commissioning – they can derail a project. If you find out too late that your system needs additional reactive compensation or a specialized transformer configuration, that might add hundreds of thousands of dollars to the build.

That’s why we conduct many of these studies well before the utility requires them. To us, they’re much more than a compliance task; they help us optimize the project’s economics and long-term performance. It’s part of our proactive, risk-reduction approach designed to help clients avoid surprises and keep their schedules intact.

4: Component Choices Can Impact the Entire Study

One of the biggest misconceptions about power system studies is that you can always finalize equipment choices after interconnection approval. In reality, the equipment you select—especially major components like inverters, transformers, and even PV modules—can significantly affect your study results and ultimately your project's ability to interconnect.

For instance, switching from one solar panel brand to another, even with the same wattage, can change string voltage or current. One type of module may have a slightly higher open circuit voltage, which could push your system past acceptable voltage thresholds. That could ripple through an entire electrical design, requiring re-optimization of stringing configurations or inverter selection. So, a seemingly minor difference between equipment brands can trigger rework—or worse, a failed study submission.

Inverter behavior is another critical variable. Some inverters offer grid support functionality or reactive power compensation. If your study includes a reactive power requirement and your inverter doesn’t support it, you’ll either have to change your design or add reactive compensation equipment—both of which take time and cost.

Avoid invalidating power study results by bringing in your engineering team early, and aligning on equipment choices before studies begin.

5: Choose the Right Partner for Successful Power Studies

Power system studies are one place where the right upfront work, with the right engineering partner, can eliminate downstream headaches.

The earlier you bring in your Engineer of Record, the smoother the process. That allows time to model system behavior accurately, account for key design tradeoffs, and avoid costly surprises from unvetted equipment changes or missed utility requirements. When developers and EPCs collaborate closely with engineers from the start, they set their projects up for faster approvals, fewer redesigns, and better financial outcomes.

At Castillo Engineering, we work closely with utilities, understand the nuances of regional requirements, and ensure every submittal meets the highest standards from the outset. And with Design IQ , our proprietary internal design automation tool, we’re streamlining the process even further.

Design IQ empowers our engineers to deliver faster, higher-quality designs that are more accurate from the start. Our clients get even fewer revisions, faster approvals, and a more predictable path from concept to construction.

Developers and EPCs already have enough moving parts to juggle. If you want a partner who knows how to navigate power system studies with precision—and help you stay ahead in a rapidly evolving market—we’re ready to get to work.

Get in touch with our team to discover how we can streamline your project and ensure long-term success.