Transparent factors
Every coefficient is published in the methodology table, sourced from EPA, EIA, NREL and peer-reviewed research, with the measurement year attached.
Policy update: the 30% federal residential solar tax credit (IRC §25D) was terminated by the One Big Beautiful Bill Act and does not apply to installations completed after 31 December 2025. Our solar calculator defaults to 0% for a 2026 purchase — here’s what changed.
See your carbon impact. Calculate your payback.
Two calculators, one honest answer. Estimate your household’s annual CO2e in tonnes, then model what rooftop solar would actually return — net cost, the year you break even, and 25 years of savings under the rules that apply today.
Why GreenPayback
Numbers you can check, not a sales pitch.
Most solar calculators are lead-capture forms wearing a calculator’s clothes: enter your details, get three sales calls. Ours shows every emission factor, runs entirely in your browser, and never asks who you are.
No email, no lead form
No accounts, nothing gating the result, no analytics on your inputs. The maths runs client-side — your electricity bill never reaches a server, ours or anyone’s.
Current tax rules
Many competing calculators still subtract a 30% federal credit that expired at the end of 2025. Ours is gated on your installation date, so the answer matches the law as it stands.
Calculator 01
Household carbon footprint calculator
Fill in what you know and leave the rest at the US average. Results update as you type, in metric tonnes of CO2 equivalent per person, per year.
Your estimated footprint
Per year
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tonnes CO2e · per person
Your household burns — of home energy shared across —. Overall you sit —
Loading chart…
Read this comparison carefully. The national averages count everything — including the goods, services and public infrastructure behind you. This calculator covers home energy, travel, diet and waste, which is roughly 70–80% of a typical footprint, so a result below the US average is expected rather than an achievement.
Where your next tonne is hiding
Calculator 02
Solar payback & ROI calculator
Model the real return on a rooftop system: gross cost, any federal credit you qualify for, net out-of-pocket, and the year cumulative savings overtake what you paid.
Your solar return
25-year modelPayback period
—
Year cumulative savings exceed net cost
Gross system cost
—
Federal tax credit
—
Net cost
—
After credit & incentives
Simple ROI
—
Over 25 years
25-year net savings
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Lifetime bill savings minus net cost
Adjust the inputs to see your break-even year.
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The amber curve is cumulative bill savings; the dashed line is your net cost. Where they cross is your payback.
Based on displacing grid electricity at the US average emission factor. On a coal-heavy grid this is considerably higher; on a hydro- or nuclear-heavy grid, lower.
These are educational estimates, not financial, tax or engineering advice. Real quotes, roof orientation and shading, local net-metering rules and your personal tax liability all change the outcome materially. The federal credit, where it applies at all, is non-refundable — you must owe federal income tax to use it. Confirm eligibility with a qualified tax professional and get at least three itemised installer quotes before committing.
Policy
What happened to the federal solar tax credit
If you have read anywhere that home solar comes with 30% off from the federal government, that guidance is out of date. Here is the current position, with the primary sources.
The credit was terminated early
The Residential Clean Energy Credit under IRC §25D gave homeowners a 30% non-refundable credit on the cost of a purchased solar system. The Inflation Reduction Act had extended it through 2032.
The One Big Beautiful Bill Act (P.L. 119-21, signed 4 July 2025) repealed it roughly nine years early. There is no §25D credit for expenditures made after 31 December 2025.
“Installed” beats “paid” — and it catches people out
§25D(e)(8)(A) treats an expenditure as made when the original installation is completed, not when the money left your account.
Paying in full in December 2025 for a system that was commissioned in January 2026 earns you nothing. This is the single most common misunderstanding right now, and it is worth several thousand dollars.
Credits already earned are not lost
The Act did not touch the carryforward rules. If your installation completed on or before 31 December 2025 and your tax liability was too small to absorb the whole credit, the unused portion carries forward indefinitely until it is used up.
Track it on IRS Form 5695. Select “on or before 31 Dec 2025” in the calculator above to model that case.
What is left: leases, PPAs and the states
Third-party ownership still reaches federal money. Under a lease or power-purchase agreement the installer owns the system and can claim the commercial §48E credit, which may be reflected in the rate you are offered. You claim nothing yourself, and you do not own the asset or capture the home-value benefit.
State and utility programs are untouched by federal law. Rebates, state credits, SRECs and property-tax exemptions vary enormously — enter yours in the incentives field above.
More detail: what happened to the federal solar tax credit, and what is still available in 2026 — including the installation-date trap and the 2027 deadline on leases.
The honest answer
Is solar still worth it without the credit?
When it still makes sense
- Your rate is high. Above roughly 18¢/kWh the maths still works in most of the country. Every cent of retail rate is a cent solar earns back.
- You have full retail net metering. Being credited at retail for exports is worth more than most incentives.
- You are staying put. Payback is now commonly 9–14 years without a credit. Panels last 25–30, so the free-electricity phase is real — but only if you are still living there.
- Your rate keeps climbing. Solar is a hedge against escalation. Set the escalation input to what your utility has actually done over the last decade, not to a hopeful number.
- You can pay cash. Financing interest is not in this model and it can push payback out by years.
When it probably does not
- Cheap power. Below about 12¢/kWh, payback commonly runs past 15 years on our default scenario, and near 10¢ it stretches to 18 — most of the equipment’s warranted life.
- Net billing instead of net metering. Moving from retail credit to avoided-cost export rates commonly adds 3–5 years. Model it with the retail-share field.
- Heavy shade or a poor roof aspect. Production is the numerator of the whole calculation. Get a real site-specific estimate rather than trusting a national average.
- A roof due for replacement. Re-roofing under an installed array costs thousands. Do the roof first, or fold that cost into the comparison.
- You are moving within five years. Solar generally increases home value, but not reliably by the full net cost.
Cheapest first. Before spending $24,000 on generation, spend a few hundred on reduction: LED retrofits, air-sealing, attic insulation and a setback thermostat typically cut home energy 10–20%. That shrinks the system you need to buy, which improves the payback on whatever you do install.
Methodology
Every number we multiply by
Emission factors are US national averages. Your grid, your car and your utility will differ — treat the output as a well-grounded estimate, not a measurement.
| Input | Factor | Source |
|---|
How payback is calculated
Year 1 savings = production × retail-credited share × your electricity rate, minus annual maintenance.
Each subsequent year, production falls by the degradation rate and the rate rises by the escalation rate:
saving (n) = P₀ × (1−d)n−1 × share × R₀ × (1+e)n−1 − O&M
We accumulate that series and find the year the running total crosses net cost, interpolating within the year for a decimal answer.
What we deliberately exclude
No financing interest, no inverter replacement around year 12–15, no property-value uplift, no SREC income, and no state credits unless you enter them.
Each of these can swing payback by years, which is exactly why they belong in a real quote rather than a national default. A calculator that quietly assumes them in your favour is selling something.
Why per-person matters
Home energy and household waste are shared costs; diet and travel are personal. We divide the first two across the people you enter, keep the rest personal, and compare the result to per-capita national averages.
Calculators that report a household total against a per-person benchmark systematically make large households look worse than they are.
Known limitations, stated plainly. Public-transit intensity depends heavily on how full the vehicle is and our factor uses pre-2020 load factors, so it likely understates current emissions. Diet tiers come from a UK cohort study normalised to 2,000 kcal/day and cover production only — not retail, cooking or household food waste; a US-basis average diet is around 1.7 t CO2e/year (Heller & Keoleian 2018), so use these tiers for comparing choices rather than as an absolute. Grid electricity is a national average; your eGRID subregion may be 2× higher or lower.
Questions
Straight answers
Is the federal solar tax credit still available in 2026?
No. The 30% Residential Clean Energy Credit under IRC §25D expired for expenditures made after 31 December 2025, under the One Big Beautiful Bill Act (P.L. 119-21). If you buy solar with cash or a loan in 2026, there is no federal tax credit for you to claim.
I paid in 2025 but installation finished in 2026. Can I still claim it?
No. §25D(e)(8)(A) treats the expenditure as made when the original installation is completed — not when you paid. If installation finished after 31 December 2025 the credit is unavailable regardless of when money changed hands.
I installed in 2025 but could not use the whole credit. Is the rest lost?
No. The carryforward rules were not changed. Unused §25D credit from a qualifying pre-2026 installation carries forward indefinitely until fully used. Track it on IRS Form 5695.
Is there any way to still get federal value from solar in 2026?
Only indirectly, through third-party ownership. With a lease or PPA the provider owns the system and can claim the commercial §48E credit, potentially passing value to you as a lower rate. You claim nothing yourself, you do not own the system, and you do not get the home-value benefit. Compare the lifetime cost of a PPA against cash purchase carefully — the escalator clause matters more than the headline rate.
How long do solar panels take to pay for themselves in 2026?
Nationally, commonly 9–14 years without the federal credit, up from roughly 7 years when it existed. The spread is wide: high-rate states with strong net metering can still land near 8 years, while cheap-electricity states can run past 18. The calculator above is more useful than any national figure — put in your own rate and quote.
Are solar panels still worth it without the tax credit?
For many homeowners yes, but the margin is thinner. The deciding variable is now your utility rate. Above roughly 18¢/kWh with decent sun and full net metering, a 25–30 year panel life still leaves many years of essentially free electricity after break-even. Below about 12¢/kWh with net billing rather than net metering, it often no longer pencils out.
How much does an 8 kW solar system cost in 2026?
Roughly $21,000–$29,000 installed, at about $2.60–$3.60 per watt depending on state, installer and equipment. NREL’s modelled benchmark runs near the top of that range; marketplace-quoted prices tend to sit lower. Since §25D expired, that is the full out-of-pocket cost with nothing federal subtracted.
What is net metering, and why does it change payback so much?
Net metering credits the power you export at the full retail rate. Net billing credits it at a much lower wholesale or avoided-cost rate. California’s NEM 3.0 cut export credit from roughly 30¢ to about 5–8¢/kWh. Moving from one regime to the other can add three to five years to payback on an identical system, which is why we expose it as an input rather than assuming 100%.
What is the average carbon footprint per person in the US?
About 17.6 tonnes CO2e per person per year on an all-sources basis, against a global average near 6.6 tonnes. Figures around 14 tonnes that you will also see quoted are usually energy-related CO2 only, excluding other greenhouse gases — make sure you are comparing like with like.
How accurate are carbon footprint calculators?
Directionally useful, not precise. Independent comparisons find differences of a couple of tonnes CO2e per person between calculators given identical inputs, because they use different emission factors and draw system boundaries in different places. Use them to compare your own choices and track change over time, not as an audited number.
How much CO2 does home solar actually offset?
A typical 8 kW system producing around 11,000 kWh a year displaces roughly 4 tonnes of CO2 annually at the US average grid factor — near 100 tonnes over its life. The real figure depends entirely on your regional grid mix: a coal-heavy grid offsets far more per kWh than a hydro- or nuclear-heavy one.
What is the difference between energy payback and financial payback?
Energy payback is how long panels take to generate the energy used to manufacture them — typically one to two years for modern silicon PV. Financial payback is how long to recoup your money, now usually a decade or more. Panels become carbon-positive long before they become cash-positive.
Do I have to give you my email to see the results?
No. Both calculators run entirely in your browser and nothing you enter is transmitted anywhere. Any site that demands a name and phone number before showing an estimate is running a lead-capture form, and that data is typically sold on to multiple installers.
Reference
Glossary
- kW vs kWh
- A kilowatt is a rate of power — how big your system is. A kilowatt-hour is an amount of energy — what your meter bills. An 8 kW system might produce 11,200 kWh a year.
- Payback period
- How many years of accumulated bill savings it takes to equal your net out-of-pocket cost.
- Simple ROI
- Total net savings over the modelled life divided by net cost, as a percentage. It ignores the time value of money, so it flatters long-dated returns.
- LCOE
- Levelised cost of energy: total lifetime cost divided by total lifetime generation, giving a cents-per-kWh figure you can compare directly against your utility rate.
- Net metering
- Exported solar power is credited at the full retail electricity rate.
- Net billing
- Exported power is credited at a lower wholesale or avoided-cost rate. Materially worse for payback.
- SREC
- Solar Renewable Energy Certificate — a tradable credit for each MWh generated, available in some state markets and a real income stream where it exists.
- Degradation rate
- The annual percentage decline in panel output. Around 0.5%/year is the modern median at module level; system-level decline is usually a little steeper.
- CO2e
- Carbon dioxide equivalent — all greenhouse gases converted to the amount of CO2 with the same warming effect over 100 years.
- eGRID
- EPA’s database of US power-plant emission rates, split into subregions. It is the reason a kWh in West Virginia carries far more carbon than one in Washington State.
- §25D
- The Internal Revenue Code section that created the residential clean energy credit for homeowner-purchased systems. Terminated for expenditures after 31 December 2025.
- §48E
- The clean electricity investment credit claimed by businesses — including companies that lease solar systems to homeowners or sell power under a PPA.
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Provenance
Sources & last updated
Last reviewed
Primary sources for the factors and defaults on this page: EPA eGRID2023, EPA GHG Emission Factors Hub (2025), EPA passenger-vehicle emissions, EPA WARM, CBO transportation emissions, Scarborough et al. 2014, U. Michigan CSS Carbon Footprint Factsheet, EIA Electric Power Monthly, NREL PVWatts, LBNL Tracking the Sun, CRS IN12611, and the IRS OBBB FAQ.
Where sources disagree we have said so on the page rather than picking the flattering number. Found an error or a stale factor? We would genuinely like to know.
How we make money. GreenPayback is free. We may earn from clearly labelled links to services we would recommend anyway, and from licensing this calculator to installers and utilities. We are never paid to produce a particular answer, we run no ad networks, we sell no data, and nothing you type into either calculator is transmitted to us or anyone else. If a link pays us, it says so next to the link.