The Tax Code Just Split Clean Energy in Two

OBBBA eliminated the Five Percent Safe Harbor for solar and wind facilities. Six words in the statute’s scope definition, “applicable wind or solar facilities,” are ones that battery storage developers should read carefully, because their technology is not in them.

VDE Americas published a technical memorandum this month titled “Navigating Beginning of Construction Requirements for Solar Projects,” a step-by-step playbook for developers scrambling to meet the July 4, 2026, construction commencement deadline imposed by the One Big Beautiful Bill Act. The guidance is thorough, practical, and aimed squarely at an industry facing a regulatory cliff. It is also, by omission, a document that clarifies just how differently the tax code now treats storage.

The split. OBBBA eliminated the Five Percent Safe Harbor for solar and wind facilities. Developers of those projects can no longer write a check for 5% of total project costs to lock in tax credit eligibility. The only remaining path is the Physical Work Test: demonstrating that “physical work of a significant nature” has commenced before July 5, 2026. Miss that date, and the placed-in-service timeline compresses sharply, a window that most utility-scale projects would struggle to meet.

Battery energy storage is governed by none of this. The OBBBA construction commencement restrictions apply to wind and solar facilities; storage projects continue to follow the prior framework, which preserves both the Five Percent Safe Harbor and the Physical Work Test as valid methods for establishing beginning of construction. There is no July 2026 deadline for storage. There is no compressed placed-in-service cliff.

What the Physical Work Test requires. For solar and wind developers who no longer have a choice, VDE Americas lays out the evidentiary standard in detail. The test demands proof of work that is “integral to the energy generation facility,” not merely preliminary. Site grading, foundation pouring, and the manufacture of custom components such as transformers all qualify. Planning, permitting, and design work do not. VDE recommends date-stamped photographs with GPS coordinates, detailed inspector reports, and contract language with technical specifications that satisfy Treasury requirements. The memorandum walks through a 5 MW solar project example to illustrate which onsite and offsite activities count.

The shift from a dollar threshold to a facts-and-circumstances assessment is the core challenge. Under the Five Percent Safe Harbor, compliance was objective: spend 5% of total project costs, document the expenditure, and the credit was locked. The Physical Work Test is inherently subjective. Whether a particular activity constitutes “significant” physical work is a determination that depends on the specific project, and the IRS retains discretion to disagree with a developer’s characterization.

The storage position. A developer with a 50 MW solar project and a co-located 25 MW battery system faces two entirely different compliance regimes for what may be a single interconnection point. The solar component must demonstrate physical work before July 5, 2026, with GPS-tagged photo evidence and inspector reports. The storage component can establish beginning of construction by incurring 5% of costs under the familiar, objective, prior framework, on a timeline that is not subject to the same cliff.

For standalone storage projects eligible for the Section 48E investment tax credit, the advantage is straightforward. Developers can establish eligibility through either method without the compressed timeline that now applies to solar and wind. The foreign entity of concern rules and material assistance cost ratios (set at 55% for projects beginning construction in 2026, per Treasury Notice 2026-15) still apply, but the construction commencement mechanics remain unchanged from prior guidance.

Hybrid implications. The practical effect for solar-plus-storage developers is that the storage component can serve as a scheduling buffer. If a solar project’s Physical Work Test timeline slips, the battery portion is not dragged into the same compliance risk. Conversely, a developer who cannot get physical work started on a solar array before July 2026 might reasonably shift project economics toward a larger storage component that retains full ITC eligibility under the prior rules.

This is not a theoretical consideration. SEIA reported this week that 57.6 GWh of new battery capacity was installed in the United States in 2025, with cumulative commercial and industrial installations reaching 19 GWh. The behind-the-meter segment held at 13% of total deployments. The market is large enough that the regulatory distinction between storage and solar has material financial consequences across thousands of projects in active development.

The documentation gap. VDE Americas’ playbook exposes a secondary problem. The shift to the Physical Work Test for solar means developers need institutional competence in a compliance framework most have not previously relied on. The Five Percent Safe Harbor was dominant precisely because it was simpler. Engineering, procurement, and construction firms will need to build documentation workflows that many lack today: photo protocols, inspector report templates, contract language that maps to Treasury guidance. Storage developers face no such learning curve.

The VDE memorandum is available publicly and covers both investment tax credit and production tax credit eligibility across commercial solar market sectors. It does not address storage, because it does not need to. That absence is the point.

Congress drew a line through the middle of the clean energy tax code. Solar and wind are on one side, facing a ticking clock and a subjective compliance test. Storage is on the other, with both paths open and no deadline in sight. For a technology that installed a record 57.6 GWh in 2025, the divergence arrives at a moment of significant market consequence.

Sources