Imported solar modules and cells will carry a minimum import price from December 4, set by a presidential proclamation that also puts a 15 percent duty on polysilicon derivatives. Until then, a Commerce Department rule keeps newly registered importers from rushing in material ahead of the date, capping polysilicon at 12 kilograms a week for any importer that registered with Customs and Border Protection on or after August 6. Neither document sets a retail price for a rooftop installation, and the homeowner-facing effect depends on how installers pass along an import cost the documents do not quantify.
The two documents divide the work. The proclamation holds every dollar figure, and the Commerce rule holds the anti-stockpiling limits and contains no rate or price at all.
The floor is written per watt and per kilogram at the border
The August 6 proclamation on polysilicon and its derivatives finds that these products “are being imported into the United States in such quantities and under such circumstances as to threaten to impair the national security of the United States.” From December 4, 2026, it sets minimum import prices of $21 per kilogram for polysilicon, $100 per kilogram for polysilicon ingots and wafers, $0.22 per watt for solar cells and $0.38 per watt for solar modules. It also imposes an additional 15 percent ad valorem duty on ingots and the derivatives listed in its annexes.
The floor works through the customs entry. If the entered value on the entry summary is below the applicable minimum, the proclamation says the goods “shall be subject to a specific tariff equal to the difference” between the two. An importer avoids that by documenting that the first arm’s-length sale will occur at or above the minimum, or that the sale follows fixed terms in a contract entered into before the proclamation was signed on August 6. The Secretary of Commerce may adjust the minimums “from time to time to reflect market conditions.”
Where “rooftop” enters, and where it does not
The proclamation’s operative text does not use the words rooftop or residential. The minimums attach to modules and cells as products, whatever their end use, so a rooftop array built from imported modules is covered the same way as a utility-scale project. The floor is a price at which imports must enter the country. It is not a price an installer must charge, and no official document read for this report estimates what it adds to a household quote.
A Commerce rule that sets no price
The Bureau of Industry and Security published its temporary final rule on September 24, effective September 22 through December 3, 2026. It restates the December 4 start for the minimum import prices and tariffs but publishes neither a tariff percentage nor a dollar minimum. Its purpose is narrower: stopping companies from bringing in unusual volumes before the floor applies. Commerce says it watches for imports “substantially greater than their historic averages” since August 6.
The rule defines a new importer of record as one that registered with CBP on or after August 6, 2026. For those importers the weekly limits are 12 kilograms under tariff line 2804.61.00, which covers polysilicon, and 7 kilograms for each of five lines in heading 3818.00. Two lines for semiconductor devices, 8541.42.00 and 8541.43.00, carry limits of 2,000 and 55 units a week. Twelve kilograms is about 26 pounds, a small allowance for a company starting from nothing.
Waivers, penalties and the December 3 end date
A new importer can seek a waiver by emailing Polysilicon232@bis.doc.gov between September 22 and December 3. The application asks for ownership information, 2025 import volumes, intended use of the products and a certification from a senior official under penalty of perjury, with a commitment not to stockpile before December 4. Commerce says it “intends to respond to applications within fourteen (14) days.” Customs brokers that help a client break the limits face license revocation or suspension under 19 CFR 111.53 and penalties under 19 U.S.C. 1641. The rule lists Stephen Astle, Director of the Defense Industrial Base Division, as the agency contact.
Because the caps expire on December 3 and the minimums begin the next day, the sequence is deliberate: restrained entries now, a priced floor afterward. New importers face stricter limits than importers registered earlier, whose volumes the rule instead measures against their historic averages.
What a quote can and cannot reveal
For a homeowner weighing a rooftop installation, the practical unknown is timing. Modules already imported, or sold under contracts signed before August 6, may have entered at lower prices than modules entering after December 4, and the proclamation makes that distinction at the border without telling any buyer which inventory an installer holds. The proclamation’s own wording is the only fixed reference: $0.38 per watt for modules and $0.22 per watt for cells, adjustable by the Secretary, effective December 4, 2026.
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This article was drafted with AI assistance from the cited official sources and checked against them before publication.
Warren Cohen is a finance writer based in Phoenix, Arizona, covering personal finance topics including credit, banking, and beginner investing. He earned his degree in business administration from Arizona State University and began his career working in consumer finance, where he gained direct experience with lending and credit systems. He now writes for personal finance websites and fintech platforms, focusing on clear, practical content that helps readers make informed financial decisions.
