A new federal tariff puts a $0.38-per-watt floor under solar modules. That's the new number in every commercial solar bid due before December 4.

President Trump signed a proclamation on August 6 putting a 15% tariff and a hard price floor under solar panels and the polysilicon that makes them — $0.38 per watt for modules, $0.22 per watt for cells, effective December 4. If you're pricing rooftop, carport, or ground-mount solar scope on any commercial job — including the data centers this policy is partly written for — that floor is now a line item, not a variable.

What exactly did the White House impose?

Using Section 232 of the Trade Expansion Act — the same national-security authority used on steel and aluminum — the administration set a 15% tariff and minimum import prices across the polysilicon supply chain: $21/kg for raw polysilicon, $100/kg for ingots and wafers, $0.22/watt for solar cells, and $0.38/watt for finished modules. Importers who can't certify that their first US sale clears those floors owe a tariff equal to the gap. The Commerce Department can also approve "onshoring plans" — companies committed to building or expanding US polysilicon, ingot, wafer, or cell capacity get to import qualifying equipment and materials duty-free while that facility is under construction. It takes effect December 4, 2026.

Why is a solar tariff a Construction AI Brief story?

Because the administration didn't frame this as a solar policy — it framed it as an AI supply-chain policy that happens to cover solar. Polysilicon is the base material for both semiconductor wafers and solar cells, and reporting on the proclamation ties it directly to reducing US exposure to Chinese-controlled polysilicon as AI's chip and electricity demand climbs. It's the same instinct behind the FCC's draft transceiver ban and Caterpillar's record data center backlog: AI's physical buildout keeps turning ordinary construction inputs into geopolitical chokepoints with a lead time attached.

Who actually pays the new floor?

Not everyone equally. The proclamation splits the market:

First Solar and Hanwha Qcells both run US-based module lines and publicly welcomed the action — a good signal that domestic-content product was already priced above the new floor, and stands to gain share as imports get more expensive. That's the opening for anyone specifying solar on a commercial job: domestic content isn't just a Buy America compliance checkbox anymore, it may also be the cheaper path after December 4.

What should a GC or solar EPC actually do with this?

Three moves, in order of urgency:

• Lock anything you can execute before December 4. Purchase orders and delivered product ahead of the effective date aren't subject to the new floor — that's a real, dated window, not a vague warning.
• Ask every module supplier where their product sits relative to the floor. A supplier already selling above $0.38/watt for modules or $0.22/watt for cells — likely anyone with US-based or onshoring-plan capacity — has little reason to move price. One still pricing off cheap Chinese-linked polysilicon does.
• Build the floor into bids due after the effective date. Treat $0.38/watt as a pricing floor input the same way you'd treat a published steel index — not the final number, but the number below which your supplier's price can't legally go without triggering the tariff.

The honest read: this doesn't blow up solar economics on its own — $0.38/watt is a floor, not necessarily far above where a lot of legitimate product already sits. But it removes the cheapest imported modules from the bid pool starting December 4, and it rewards contractors who lined up domestic or already-compliant suppliers before their competitors noticed. That's a precon conversation worth having this month, not in November.

Construction AI Brief tracks the AI buildout's supply chain the way it's actually hitting jobsites — three times a week. Subscribe at constructionaibrief.com.