On June 6, 2026, Judge Colleen Kollar-Kotelly of the U.S. District Court for the District of Columbia struck down IRS Notice 2025-42. The Notice, issued following enactment of the One Big Beautiful Bill Act (“OBBB”), eliminated the Five Percent Safe Harbor as a pathway for large-scale solar projects to establish “beginning of construction” under the Section 45Y and 48E clean energy tax credits. The Court found the the Notice was arbitrary and capricious under the APA, vacated the Notice in full, and remanded to the IRS.
What Happened
Since 2013, solar developers have relied on two methods to “begin construction” and lock in clean energy tax credits: the Physical Work Test (commencing significant physical work) and the Five Percent Safe Harbor (paying or incurring at least five percent of total project costs). The IRS reaffirmed both methods repeatedly over a decade, and Congress made no change for projects to safe harbor.
Following the OBBB and Executive Order 14,315, the IRS issued Notice 2025-42, which eliminated the Five Percent Safe Harbor for most solar projects (retaining it only for systems of 1.5 MW or less). The Notice offered just one paragraph of reasoning, citing the need to prevent “circumvention” and “artificial manipulation” of eligibility and to “ensure that a substantial portion” of a project is built by the deadline established under the OBBB.
The Court’s Reasoning
Ultimately the court held that the Notice was arbitrary and capricious on the following three grounds:
- No reasoned explanation. The IRS’s single-paragraph justification failed to explain how projects using a well-established method were “circumventing” Safe Harbor eligibility requirements. The Court refused to credit the government’s litigation-stage “stockpiling” rationale, holding that outsiders’ speculation about agency motives cannot substitute for the agency’s own reasoning.
- Unjustified technology-specific targeting. The Section 45Y and 48E credits are technology-neutral, yet the Notice stripped the Safe Harbor only from wind and large-scale solar while leaving it intact for other clean energy technologies, and the record contained no reasoned basis for that distinction.
- Failure to address reliance interests or alternatives. The IRS ignored a decade of industry reliance on the Safe Harbor standards and disregarded multiple commenters’ proposals for targeted solutions, such as restricting the Safe Harbor only for purchases from prohibited foreign entities or implementing new audit and reporting procedures. The IRS argued that the industry could not “seriously” rely on this method of safe harboring since the applicable tax credits were of “recent vintage”, the Court rejected these arguments and pointed to the lineage of the tax credits and the Safe Harbor’s historical relevance as “an established, defined concept in tax law.” Due to consistent availability of this Safe Harbor, the IRS “could not escape the duty to explain its change in policy by arguing that the reliance interests at issue were not ‘serious.’”
What This Means Now
The Five Percent Safe Harbor is back in play for solar projects (1.5MW and greater) approaching the July 4, 2026, beginning-of-construction deadline. Developers who had been scrambling to satisfy the Physical Work Test may once again rely on expenditure-based qualifications.
But proceed with caution. The court itself acknowledged that an appeal is virtually certain and that the IRS may issue revised guidance on remand. Until the appellate process concludes, uncertainty remains. The prudent course for developers is to structure transactions to preserve eligibility under both the Physical Work Test and the Five Percent Safe Harbor wherever possible.
