A lot of people assume a tax credit works like a coupon: claim it, get a check for the difference. Solar tax credits don’t work that way, and the gap between those two ideas is worth understanding before you assume a small tax bill means losing out on a credit you were counting on.
What “Nonrefundable” Actually Means
A refundable credit can reduce your tax bill below zero, and the IRS sends you the difference. A nonrefundable credit can only reduce your bill down to zero; it can’t generate a payment beyond that. Both the residential solar credit (for anyone who installed before it ended) and the commercial credit businesses still use fall into the nonrefundable category, classified under the tax code’s subpart for nonrefundable personal credits.
That distinction sounds abstract until you run real numbers. Say your solar credit works out to $9,000, but your federal tax liability for the year is only $4,000. A refundable credit would send you a $5,000 check. A nonrefundable credit uses the $4,000 to zero out what you owe, and the remaining $5,000 doesn’t just disappear.
Carryforward, Worked Example
That’s where carryforward comes in. The federal residential solar credit statute explicitly allows any unused amount to carry to the succeeding taxable year, where it’s added to whatever credit you’d otherwise claim that year. Using the example above: the unused $5,000 rolls into next year’s return. If your tax liability next year is $6,000, you’d apply the full $5,000 carryforward plus any credit generated that year, potentially zeroing out your bill again, with no cap on how many years it can carry forward until it’s fully used.
This is genuinely useful to know before you install, not just after: a large credit against a modest tax bill isn’t wasted. It just takes longer to fully use.
Who This Applies to in 2026
Worth being precise about scope here, since this changes depending on when you installed. If you purchased a residential system with cash or a loan and it was installed before December 31, 2025, the federal credit and its carryforward provision still apply to your return. If you’re purchasing a residential system in 2026, this entire mechanism is moot for you: the federal residential credit ended, so there’s no credit to carry forward in the first place. If you leased your system or signed a PPA, the credit was never yours to claim; the provider claims it and may pass savings through your rate.
For businesses, the credit is very much still active, and this is where the mechanism matters most going forward.
Commercial Carryback and Carryforward Work Differently
A business claiming the 30% Investment Tax Credit under Section 48E falls under the general business credit rules rather than the residential statute above, and those rules are less generous on the back end but more flexible going forward. Unused general business credit can generally be carried back one year and forward for 20 years, a meaningfully longer forward window than most people expect, though the one-year carryback is often overstated in casual explanations that confuse it with narrower provisions for tax-exempt entities.
We’ve covered the broader cost and timing picture for commercial systems, including the 2026 safe-harbor deadline, in a separate post on commercial solar panel cost, worth reading alongside this one if you’re weighing a business installation.
If your tax situation is anything other than straightforward (multiple income sources, other credits already reducing your liability, a business with variable income year to year), this is exactly the kind of question worth running past a CPA before you finalize a system size or a financing structure, not after.
Want to know what your specific numbers actually look like? Contact Pacific Solar and we’ll walk through how this applies to your situation before you sign anything.
Frequently Asked Questions
Does unused solar tax credit ever expire?
For the residential credit (on systems installed before it ended), no fixed expiration is built into the carryforward provision; it continues until fully used. For the commercial credit, the standard 20-year carryforward window applies.
Does this carryforward mechanism apply to California’s SGIP battery rebate too?
No. SGIP is a separate state rebate program with its own rules, administered through your installer rather than your tax return, and it isn’t a tax credit and doesn’t carry forward the same way.
If I refinance my home, does that affect the carryforward?
No. The carryforward is tied to your tax return, not your mortgage or the property itself.