A new set of solar panel tariffs is about seven weeks away, and federal regulators have already started policing the rush to beat it. On September 24, 2026, the Commerce Department's Bureau of Industry and Security published a temporary rule to restrict stockpiling of polysilicon and its derivatives, a key material in solar products. The rule runs through December 3, 2026. The next day, December 4, a 15 percent tariff on polysilicon products and minimum import prices on solar cells and modules take effect. For Southern California property owners and developers pricing commercial solar this fall, that date now belongs on the project calendar.
What the new solar panel tariffs change on December 4
The tariffs come from Proclamation 11052. It was signed August 6, 2026 under Section 232 of trade law and published in the Federal Register on August 11, 2026. It takes effect at 12:01 a.m. Eastern on December 4, 2026. A Morgan Lewis analysis published October 5, 2026 reports the same effective date and terms and does not mention any amendment, delay or court challenge.
The proclamation does two things. First, it adds a 15 percent duty on covered polysilicon products and derivatives. Some trading partners get different treatment: UK products get a 10 percent rate, and for products of Japan, Korea, Taiwan, Switzerland, Liechtenstein and EU member states, the Section 232 tariff plus the regular duty rate totals 15 percent. Second, it sets minimum import prices, which are price floors for each step of the supply chain:
- Polysilicon: $21 per kilogram
- Ingots and wafers: $100 per kilogram
- Solar cells: $0.22 per watt
- Solar modules: $0.38 per watt
When an import's entered value falls below the floor, the proclamation charges the difference as an added tariff. The Commerce Secretary may also adjust these prices.
The law firm Morgan Lewis reports that the proclamation also includes an onshoring program. Under the proclamation, companies with approved plans to build or expand U.S. production may import covered products without Section 232 duties, within limits Commerce sets. Plans must commit that construction will start by January 20, 2029.
Why the anti-stockpiling rule matters now
A tariff date announced months ahead gives importers time to bring in product before it applies. The September rule is designed to limit that kind of stockpiling.
According to the Federal Register document, the rule took effect September 22, 2026. Commerce can notify Customs and Border Protection of importers whose volumes are substantially greater than their historical averages, and those importers are barred from further entries before December 4. New importers that registered with Customs and Border Protection on or after August 6, 2026 face fixed weekly caps. For solar cells assembled into modules or panels (tariff code 8541.43.00), the cap is 55 units per week. Companies can apply for waivers, and Commerce says it intends to respond within 14 days of receiving an application.
In plain terms, the rule narrows the window to bring in large volumes of imported panels before the floor applies. That could affect what distributors have on hand and how long suppliers hold quotes this fall.
Where commercial solar pricing stands
The tariff news lands on a market where system-level costs were already rising. The Solar Energy Industries Association (SEIA) released its Q3 2026 Solar Market Insight report on September 10, 2026. It found that commercial system pricing rose 5.6 percent year over year, to $1.77 per watt in Q2 2026.
Module prices moved the other way. The same report found that distributed-segment module prices fell an average of 16 percent year over year, to $0.37 per watt. For comparison, the new $0.38 per watt floor for imported modules is above that Q2 figure. SEIA also reported that logistics costs rose more than 15 percent, averaged across segments. It said Section 232 tariffs on copper, steel and aluminum continue to raise balance-of-plant costs, which cover the racking, wiring and electrical equipment around the panels.
The same SEIA report lists two other trade actions that touch commercial projects directly:
- On July 28, 2026, foreign-produced power inverters were added to the FCC's Covered List.
- On August 26, 2026, an executive order restricted imports of power generation equipment from covered foreign entities. SEIA says the final impact will depend on guidance released within 120 days.
The California picture
California is still a large commercial solar market, but it is changing. SEIA's report says California installed 256 MWdc of commercial solar in Q2 2026, driven by the continued buildout of NEM 2.0 projects. It also notes that commercial projects in the state are now smaller and fewer under California's Net Billing Tariff, because of heavily reduced compensation for power sent back to the grid.
Nationally, SEIA reported 638 MWdc of commercial installations in Q2 2026, up 11 percent from Q2 2025. Its forecast calls for the commercial segment to contract by an average of 7 percent over the next two years, followed by accelerated growth from 2028 through 2030. The report also names interconnection delays, permitting hurdles and confusion over federal rules as key challenges for commercial developers this year.
Lower export value, higher system costs and new trade rules together put more weight on project design. Under net billing, conversations about a project more often turn to sizing solar to on-site use and pairing it with battery storage to shift output into peak hours. You can read more about how Burge approaches commercial solar, battery storage and EV charging.
What this means for your project
None of this answers whether to build now or later. That depends on each site, its load, its utility rate and its timeline. The December 4 date is a natural checkpoint for questions that often come up on commercial proposals this fall:
- Equipment status. On a signed proposal, have modules, inverters and racking already been purchased, or do they still need to be ordered? Is the price fixed, or can it change if equipment arrives after December 4?
- Quote validity. How long does a proposal's price hold, and what would trigger a revision?
- Equipment sourcing. Where are the modules and inverters made, and how does the FCC inverter action described in SEIA's report apply to the models specified?
- Schedule risk. Interconnection and permitting often set the real timeline. When will the utility interconnection application be filed, and how long is review expected to take?
- Design fit. Under net billing, how is the system sized to the property's actual load profile, and does adding storage change the picture?
A full year of utility bills, a site plan, and notes on planned load changes, such as new EV chargers or electrified equipment, let a contractor design and price a system around the actual site rather than a rule of thumb.
Nothing here is legal, tax or financial advice. Trade rules can change, and guidance on some actions is still pending.
How Burge Energy can help
Burge has been building in Southern California since Dan Burge founded Burge Construction in 1977. Burge Energy brings that same family-owned approach to commercial solar, battery storage and EV charging, on new builds or existing buildings. We design and build systems sized to how your property actually uses power, and we coordinate equipment and utility interconnection. We also help you plan around changes like these so your schedule and budget reflect current conditions. Request an Energy Assessment.
Sources
- Measures to Restrict Stockpiling of Polysilicon and Polysilicon Derivatives Under Proclamation 11052 (FR Doc. 2026-19537), U.S. Department of Commerce, Bureau of Industry and Security / Federal Register, September 24, 2026
- Adjusting Imports of Polysilicon and Its Derivatives Into the United States (Proclamation 11052), Federal Register, August 11, 2026
- Solar Market Insight Report Q3 2026, Solar Energy Industries Association (SEIA) / Wood Mackenzie, September 10, 2026
- US Department of Commerce Imposes Temporary Anti-Stockpiling Restrictions on Polysilicon, Derivative Imports, Morgan Lewis (law firm analysis), October 5, 2026
This article is general information, not legal, tax or financial advice. Facts are current as of October 15, 2026; rules and programs can change.