If you’ve been in the U.S. solar game long enough, you know there’s more to getting a project approved than just having good panels and a sharp crew. One of the first hurdles—especially in permitted jurisdictions—is making sure your plans are stamped by the right professional engineer (PE).
But here’s where many contractors, especially newer ones get tripped up: the difference between structural stamps and electrical stamps. I’ve been working in the U.S. solar engineering space for over a decade, and I’ve seen projects delayed, budgets squeezed, and contractors frustrated simply because they misunderstood what stamp they needed (or thought one could replace the other).
What is a Structural Stamp?
A structural stamp is essentially a licensed structural engineer saying:
This system, as designed, won’t compromise the building’s integrity, and it can handle the loads it’s going to face.
That means the engineer reviews how the racking attaches to the roof or ground, checks load calculations for wind, snow, and seismic conditions, and makes sure the mounting structure complies with local building codes.
For residential rooftop systems, this often includes:
- Roof framing analysis
- Attachment point spacing
- Penetration details
- Load calculations for the specific site
If you skip this step in areas that require it, your permit application can stall indefinitely. Worse, installing without proper review can create liability nightmares if there’s ever a failure.
What is an Electrical Stamp?
An electrical stamp is a licensed electrical engineer’s way of saying:
“This system’s wiring, components, and interconnections are safe, code-compliant, and capable of operating as intended.”
Here, the focus shifts to:
- Conductor sizing and ampacity
- Overcurrent protection
- Grounding and bonding
- Interconnection methods
- Compliance with NEC (National Electrical Code) requirements
It’s not about whether the roof can hold the system—it’s about whether the electrons will behave themselves and not burn the place down.
Why You Might Need Both
Some jurisdictions only require one stamp—usually structural for rooftop installs or electrical for ground mounts. Others require both, especially in commercial or larger residential projects.
For example:
- Structural-only: Small residential rooftop in a rural area with straightforward electrical work.
- Electrical-only: Ground mount on a concrete pad where structural loads are obvious and minimal.
- Both required: Multi-megawatt commercial rooftop in a coastal city with hurricane wind load considerations and complex electrical interconnection.
The Biggest Mistake I See
Contractors often assume:
If I have a structural stamp, that should cover electrical too… right?
Wrong.
These are different disciplines with separate licensing requirements. Your structural PE may not be licensed—or even legally allowed—to sign off on electrical designs, and vice versa.
Practical Advice for Solar Contractors
From my years of dealing with AHJs (Authorities Having Jurisdiction) across dozens of states, here’s my short list of tips:
- Check local requirements first: Some AHJs publish clear guidelines, others… not so much. A quick call to the permitting office can save weeks.
- Build relationships with both types of engineers: Having a go-to structural and electrical PE in your corner makes you faster and more competitive.
- Don’t cut corners: Even if a project might squeak by without one of the stamps, skipping it can expose you to massive risk.
- Factor it into your bid. Too many contractors eat costs because they didn’t account for PE review and stamping up front.
Conclusion
Structural stamps keep your system standing. Electrical stamps keep it running safely. Both keep you out of trouble. As a solar engineer, I’ve seen the frustration when a permit comes back with “missing engineer’s stamp” stamped across it in red ink. Trust me, it’s a headache you can avoid. Know the difference, plan for both when needed, and work with engineers who understand solar.
Because in this business, good engineering isn’t just about passing inspection, it’s about protecting your reputation, your client’s property, and the future of solar itself.
