What exactly do solar installers need to document for the tax credit bonus?
If you locked a project into safe harbor before the July 4 begin-construction deadline, you're probably in the part of the job nobody enjoys: proving the project actually earned the domestic content bonus so you can claim it at filing. The bonus is a real adder on the federal solar tax credit, but it only counts if the paperwork holds up under an audit years later.
This is a documentation problem, not a tax-strategy problem, and it's squarely the installer's to solve. Here's what you actually need to collect, component by component. The credit math and the filing itself belong with your tax advisor. What follows is the hardware and paperwork side, which is the part you control on the ground.
First, sort every component into one of two buckets
The single thing installers get wrong is treating "domestic content" as one rule. It's two, and a component lands in exactly one bucket.
Bucket one, steel and iron: 100% US-made. This applies to the structural steel and iron in the project, which the IRS guidance (Notice 2023-38) points at directly: PV module racking, piles and ground screws, and the rebar in your foundations. There's no percentage here. It's all or nothing, and it has to be made in the United States.
Bucket two, manufactured products: a percentage. Everything that isn't structural steel or iron is a "manufactured product," and these count toward an adjusted-percentage calculation rather than a 100% test. For a project that began construction in 2026, that threshold is 50% (it was 45% for 2025 starts and steps up to 55% after 2026).
The detail that matters for hardware also trips people up: the same IRS guidance says nuts, bolts, screws, washers, clamps, and fittings are not subject to the 100% steel and iron rule, even though they're made of steel. They're treated as manufactured-product components. So your fasteners don't have to clear the 100% bar, but their cost does feed the percentage calculation, which means domestic fasteners help your number and the documentation on them still has to exist.
What the bonus is, briefly
You don't need to be able to file this, but you should know what you're documenting toward. The domestic content bonus is a 10-percentage-point adder to the investment tax credit if the project also meets the prevailing-wage and apprenticeship requirements. Without those, the adder is 2 points (projects under 1 megawatt get the full 10 without them). Whether your project clears the manufactured-products percentage, and how the credit ultimately lands, is your tax advisor's call. Your job is to hand them documentation that survives scrutiny.
The three things you need from every manufacturer
For each component you're counting, the IRS recordkeeping expectation comes down to three documents from the manufacturer:
A signed domestic content certification. A statement, signed under penalties of perjury by someone who can bind the manufacturer, that the component meets the requirement. This is the manufacturer's to sign, not yours and not your distributor's.
Manufacturing-location information. Where the component was actually manufactured, meaning real manufacturing, not final assembly of foreign parts.
Direct-cost data. The manufacturer's direct cost of the US versus non-US content, which is what the adjusted-percentage math runs on. Without it, the component can't be scored.
A component with no paper trail doesn't count, no matter where it was actually made. The rule that matters at audit is what you can prove, not what's true.
What to demand from a hardware supplier
This is where a distributor earns its place. For the fasteners and hardware in your bill of materials, ask your supplier for three things, and don't accept the order without them:
Country-of-origin, made-in-USA certification for the specific parts you bought.
Mill and lot traceability, tying the material back to its source so the certification isn't just a sticker.
The direct-cost breakdown you'll need to fold those line items into the manufactured-products percentage.
We stock domestic-made fasteners and can provide the country-of-origin and mill documentation to back them, which is exactly the paper your filing needs for the hardware line items. The same goes for the rest of your solar hardware.
When you're building the domestic side of your bill of materials, pulling the hardware line items from a distributor who can document them is a good deal less painful than chasing certs after the fact.
What we don't do is sign the manufacturer's certification statement or run your credit math. That certification is the manufacturer's, under penalties of perjury, and the filing is your advisor's. We supply the domestic hardware and the documentation that supports it.
The installer's checklist
Sort your bill of materials into the two buckets first: structural steel and iron on the 100% side, everything else on the percentage side. For every component you're counting, get the manufacturer's signed certification, the manufacturing-location statement, and the direct-cost data, and store them where an auditor could find them in three years. For the hardware specifically, require country-of-origin certs, mill and lot traceability, and the direct-cost breakdown at the time of purchase, not after. Then hand the whole package to your tax advisor to run the percentage and file.
The projects that captured this bonus cleanly are the ones that treated documentation as part of procurement, collected at the purchase order, not as a scramble at filing. If you locked in before July 4, you still have time to do it the clean way. Start with the suppliers who can hand you the paper without a fight.
There's a reason to get this right beyond the filing, too. As more projects go after the bonus, clean domestic-content documentation is becoming something developers look for before they award the work, not just something the team assembles at tax time. A supplier who can hand over the certs, the traceability, and the cost data without a scramble makes the whole project easier for their customer to close, and makes their own hardware the easy line to keep on the bill of materials. That's the position worth being in on both sides of the purchase order.
For domestic-made fasteners and hardware with the country-of-origin and mill documentation your domestic content filing needs, contact us at [email protected].
