I put 40 panels and two Tesla inverters on my own roof, and I can tell you the tax paperwork got nearly as much household discussion as the hardware. If your property includes a rental unit attached to your primary home — an in-law suite, a garage apartment, a duplex where you live in one half — the tax question was always more complicated than the headline “30% federal credit” suggested. And as of 2025, the ground shifted under the entire topic.
So here’s the honest version, which is more useful than the confident version: the federal residential solar credit as most people knew it was terminated by 2025 legislation for installations after 2025. What follows is how the rules worked, what changed, why rental units were always a special case — and why, more than for any other article on this site, you need to verify everything here with a tax professional and current IRS guidance before making a single decision. This area of law changed recently and could change again.
The Quick Answer
Historically there were two different federal credits that could touch a home-plus-rental property, and they worked very differently:
- Section 25D, the residential clean energy credit, was the famous one — a percentage of system cost (30% in its final years) for solar on a dwelling you used as a residence. It was a personal credit, claimed on your own return, with no depreciation involved.
- The commercial investment tax credit (Section 48, later 48E) covered energy property used in a business — which is what a rental activity is in the IRS’s eyes. Different rules, different forms, interaction with depreciation, and typically claimed by landlords and third-party system owners.
A rental unit attached to your primary residence sat exactly on the seam between those two regimes. Then 2025 federal legislation ended 25D for installations after 2025 and reworked the commercial pathway’s timelines. Both halves of that seam moved.
How the Rules Worked Before 2026 (Historical Context)
For systems installed while 25D was alive, the core requirement was that the solar served a dwelling unit you used as a residence. Owner-occupied homes qualified. A property you rented out entirely and never lived in did not qualify for 25D — that was a business asset, pointed at the commercial credit instead.
The attached-rental situation was the nuanced middle. IRS guidance around 25D addressed mixed-use property: where a home was partly used as your residence and partly for other purposes, the credit generally had to reflect the residential share. The commonly applied framework was allocation — if a meaningful portion of the property’s use was the rental activity, the corresponding portion of the system cost wasn’t eligible for the personal residential credit. (There was a de minimis concept in the guidance where minor non-residential use didn’t force an allocation, but where those lines fell for any specific duplex or in-law suite was exactly the kind of thing tax professionals were paid to determine.)
Meanwhile, the rental portion wasn’t necessarily left out in the cold: because a rental is a business activity, owners sometimes pursued the commercial-side credit and depreciation (solar equipment serving a rental could be a depreciable business asset) for that share. But that path came with its own machinery — basis reductions, recapture rules if you sold early, and real recordkeeping. Anyone who claimed depreciation also signed up for depreciation recapture questions at sale time. None of this was ever a do-it-yourself-from-a-blog-post exercise, and I’m deliberately not putting percentages and dollar figures on it here, because the historical details matter less than the fact that they’re history.
What the 2025 Law Changed
Federal tax legislation enacted in 2025 substantially rewrote clean-energy incentives. The parts that matter for this article:
- The residential credit (25D) was terminated for installations after 2025. Homeowners who placed systems in service by the end of 2025 were the last to claim it. If you’re reading this in mid-2026 and planning a new purchase of a system for your home — attached rental or not — the 30% personal federal credit is not part of your math.
- The commercial/business-side credit (48E) survived on a different footing, with revised deadlines and qualification rules around construction timing and placed-in-service dates, plus new restrictions. This is the pathway that matters for rental activity and for third-party-owned systems — which is why leases and power-purchase agreements are suddenly a much bigger part of solar sales pitches.
- Timelines and details in this area are genuinely in flux. Rules were still being interpreted through IRS guidance after enactment, and Congress has demonstrated it will change this area abruptly. I am not going to state current percentages or cutoff dates as settled fact, because the confident-sounding version of this article would be the wrong one.
That last point is the whole spirit of this piece: anything you read about solar tax credits — including this — is a starting point for a conversation with a tax professional, not a basis for action.
Eligibility at a Glance
This table summarizes the landscape as of mid-2026 — verify current law before relying on any row. Legislation and IRS guidance after this article’s update date control, not this table.
| Scenario | Historical treatment (installs through 2025) | Status as of mid-2026 | What to verify with a professional |
|---|---|---|---|
| Solar on owner-occupied primary home, no rental use | 25D personal credit (30% in final years) | 25D terminated for post-2025 installs; no federal personal credit for new purchases | Whether any new federal or state incentive applies to your install date |
| Attached rental unit (in-law suite, owner-occupied duplex) | Mixed-use: 25D generally limited to the residential-use share; rental share pointed toward business treatment | Personal-credit path gone for new installs; business-side questions remain for the rental share | Allocation method, whether the rental share qualifies for any business credit/depreciation |
| Fully detached rental you don’t live in | Never 25D-eligible; commercial credit + depreciation territory | Business pathway (48E) exists with revised deadlines and rules | Current 48E qualification windows, basis and recapture consequences |
| Leased system / PPA (third party owns the hardware) | Owner (the solar company) claimed commercial credit, not you | Still the commercial pathway; terms and phase-downs revised by the 2025 law | What portion of the third party’s credit is actually reflected in your contract pricing |
| Any install completed during 2025 or earlier | Rules in effect at placed-in-service date | Credits claimed on past returns generally stand; documentation still matters | Amended-return questions, carryforward treatment, audit documentation |
If You Already Installed: Paperwork Is Your Friend
If your system went in while the old rules applied — mine did — the job now is defense, not offense. Keep the contract, itemized invoices, proof of the placed-in-service date, and, for a mixed-use property, whatever documentation supported your residential-vs-rental allocation (square footage, days rented, however your preparer built it). If you claimed depreciation on a rental share, keep the schedules; they determine recapture math whenever you sell. Past credits properly claimed under prior law don’t evaporate because the law changed, but you want the paper trail that proves “properly claimed.”
What I’d Do Before Spending a Dollar
If I were adding solar to a home with an attached rental in mid-2026, my sequence would be:
- Talk to a tax professional first, not last — specifically one who has dealt with mixed-use property and the post-2025 rules. The federal picture changed too recently for confident generalizations, including the ones in this article.
- Check current IRS guidance directly (IRS.gov instructions for the relevant credit forms) rather than trusting any article’s snapshot, and check your state and local incentives, which didn’t disappear with the federal residential credit and now carry more of the load.
- Get quotes for both purchase and third-party ownership. With the personal credit gone, lease/PPA structures that route through the commercial credit may pencil differently than they used to — read the escalator clauses carefully either way.
- Run the economics with zero federal credit assumed. If the project still works on electricity savings alone, every incentive that does materialize is upside instead of a load-bearing assumption.
Solar on a home with a rental unit can still make excellent sense — electrons don’t care about the tax code, and neither does your roof. But the incentive landscape rewrote itself in 2025, and the honest summary is that the rules are newer than the conventional wisdom about them. Verify with a professional and current IRS guidance before you sign anything. It’s cheaper than being confidently wrong.