Hidden Problems That Blow Up Your Project Schedule

The site walk looked clean and the contract is signed, then engineering finds the thing nobody checked. Here is how to catch it before it costs you the deadline.

Featuring John Antonelli, P.E., Vice President of Engineering, SunSmart Engineering. Adapted from the SunSmart Engineering × Clean Energy Help × FlaSEIA panel, Commercial Solar in 2026. Watch the clip: "12 - Hidden Problems That Blow Up Your Project Schedule.mp4".

Most of the surprises that wreck a commercial solar schedule were sitting in plain sight before anyone signed anything. The site walk goes fine, the customer signs, the project drops into the pipeline, and then the plan set lands on an engineer's desk and a problem shows up that nobody priced or scheduled. In 2026 that hurts more than usual. With hard credit deadlines in play (begin construction by July 4, 2026, or be placed in service by December 31, 2027), a few lost weeks can put the tax credit itself at risk. The upside is that these surprises are almost always predictable.

The usual culprits

John Antonelli, P.E., has worked in solar since 2013, and he keeps seeing the same short list of problems take down otherwise healthy projects:

"The usual issues we see involve things like the service voltage for the building, transformer sizing, the actual transformer that feeds the building, and the location or means of interconnection, roof attachment issues, or forgetting to account for fire code setbacks. Those are the things that may delay the project once we get the information and review it up front with the contractor or developer."

That breaks into five recurring offenders. Service voltage, because the electrical configuration at the building dictates what the utility will even allow, and it gets stricter as systems get bigger. Transformer sizing, because the transformer feeding the building has a finite rating and your system has to fit under it. Interconnection location and means, because where and how the system ties into the service is not always obvious, and the available options drive cost and timeline. Roof attachment, meaning how the array fastens to the structure and whether the roof and framing can actually take it. And fire-code setbacks, which eat into usable roof area and can quietly shrink the system size that was sold.

None of this is exotic. These items get missed on a site walk precisely because they live in the electrical service, the structural framing, and the code book, not in anything you can eyeball from the parking lot.

The service-voltage trap on bigger systems

Service voltage is the one that catches people most, and it gets sharper above 100 kilowatts DC. A lot of utilities will only permit a system that size if the building's service is a configuration they are set up to handle. Here is how John put it:

"When I say service voltage, especially for projects larger than 100 kilowatt DC, a lot of utilities are only going to allow that if the service voltage at the building is 120/208 or 277/480Y three-phase."

Utilities want clean, modern three-phase services like 120/208 or 277/480Y because that is what their interconnection rules and equipment are built around. Older buildings are where this bites. Plenty of them were wired with a 240 Delta three-phase service, which does not fit those acceptable categories.

For an older building running 240 Delta, you usually end up with one of two choices: the owner pays the utility to add a new service, or you cap the system under 100 kilowatts. And there is a catch, because some utilities will not even let you do the smaller-system option. It varies utility to utility. A new service can mean real money and a long lead time, and shrinking the system below 100 kW can wreck the project economics that justified the deal. Either way, that is a conversation to have before the contract is final, not after.

Service voltage also ties into the rest of John's electrical list. In Florida, interconnection rules generally limit a system so it does not exceed 90% of the serving utility transformer's rating, measured against a gross power rating equal to 85% of total DC nameplate (module quantity × module watts × 0.85). Same family of constraints. Service, transformer, and means of interconnection all have to line up before a design is real.

The fix is boring: do the homework first

The pattern across all of these is the same. They are cheap to catch early and expensive to find late. John's main lesson is plain:

"One of the main lessons is doing a lot of homework up front and allowing time to adjust the designs."

In practice that means pulling the building's service voltage and transformer information, confirming the interconnection point and method, checking the roof structure and attachment approach, and laying out the fire-code setbacks. Then review all of it with the contractor or developer before the deal closes. When SunSmart gets that information early, the team can flag a 240 Delta service, an undersized transformer, or a setback problem while there is still room to adjust the design, re-quote, or set the customer's expectations honestly.

The alternative is finding out after you have committed a price and a timeline. In a year governed by federal deadlines, lost weeks are not just margin. They can be the credit.

Key takeaways

• The most expensive problems show up after the contract is signed, and they are usually predictable.
• The recurring culprits: service voltage, transformer sizing, interconnection location and means, roof attachment, and fire-code setbacks.
• Above 100 kW DC, many utilities only allow systems on a 120/208 or 277/480Y three-phase service.
• An older 240 Delta three-phase building can force a paid utility service upgrade or a sub-100 kW cap, and some utilities will not permit the smaller system at all.
• In 2026, schedule slips can threaten the tax credit, so front-loading the engineering review is the cheapest insurance you can buy.

How SunSmart Engineering can help

SunSmart Engineering reviews service voltage, transformer capacity, interconnection, roof attachment, and fire-code setbacks up front, before the deal is locked, so the problems that blow up schedules surface while there is still time to adjust the design. As a full-service engineering firm for solar and storage, based in Florida and working nationwide, we help contractors and developers turn a clean site walk into a buildable, code-compliant plan set. Visit sunsmartengineering.com or call 866-786-8655.

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Educational information only, not tax, legal, or engineering advice. Rules referenced (credits, FEOC, safe-harbor litigation, and the July 4, 2026 / December 31, 2027 dates) were current as of the June 2026 webinar and continue to change. Confirm current requirements with a qualified professional before acting.