Solar Payback Period: How to Calculate Yours (2026)

Your solar payback period is how many years it takes for bill savings to equal what you paid for the system. Installers’ estimates often lean optimistic. With a spreadsheet, NREL’s PVWatts and your own bills, you can check them in under an hour. In 2026 there’s one big change: don’t subtract a 30% federal credit from a system you own. That credit (25D) ended for installs after Dec 31, 2025, per the IRS.

Solar Payback Period: The Simple Formula

Payback (years) = net system cost ÷ first-year savings

That’s a rough first pass. The spreadsheet method below adds the things that move the answer: export credits, panel degradation and rate increases.

Step 1: Gather Your Inputs

Input	Where to get it
Net cost	Quote price minus any state or utility rebate
Yearly production	NREL PVWatts for your address and system size
Self-use %	Share of solar you use when it’s produced (estimate, or ask your installer)
Retail rate	Your bill’s $/kWh, including delivery charges
Export rate	Your utility’s net metering or net billing credit
Degradation	Panel warranty (often about 0.5%/year; check yours)
Rate increase	Your assumption. Run a 0% case and a 3% case

Step 2: Build the Columns

For each year (rows 1–25):

Production = year-1 kWh × (1 − degradation)^(year − 1)
Self-used kWh = production × self-use %
Exported kWh = production − self-used
Savings = self-used × retail rate + exported × export rate (raise both rates by your escalation each year)
Cumulative savings = running total

Payback is the first year when cumulative savings pass net cost.

Example (Illustrative Assumptions)

Example only: $24,500 net cost (7kW at $3.5/W, the LBNL 2024 cash median), 9,800kWh year-1, 50% self-use at $0.30/kWh, exports at $0.10/kWh, 0.5%/year degradation, 0% rate increase.

Year-1 savings: 4,900 × $0.30 + 4,900 × $0.10 = $1,960
Simple payback: $24,500 ÷ $1,960 ≈ 12.5 years
In the spreadsheet with 0.5% degradation, cumulative savings pass the cost in year 13. With a 3%/year rate increase added, it happens in year 12.

What the Simple Formula Misses

Loan interest and dealer fees, which can add years.
Inverter replacement during the system’s life, unless it’s under warranty.
Fixed monthly charges that solar can’t offset.
Moving. If you sell early, payback depends on what buyers pay for the system.

The Full 25-Year Table for the Example

Here’s what the spreadsheet shows for the example above, using the same inputs. The first set of columns holds rates flat. The second raises both the retail and export rates 3% a year. All figures are rounded (illustrative).

Year	Production (kWh)	Savings, flat rates	Cumulative, flat	Savings, +3%/yr	Cumulative, +3%/yr
1	9,800	$1,960	$1,960	$1,960	$1,960
5	9,605	$1,921	$9,702	$2,162	$10,299
10	9,368	$1,874	$19,165	$2,445	$21,944
12	9,274	$1,855	$22,884	$2,568	$27,016
13	9,228	$1,846	$24,729	$2,631	$29,648
15	9,136	$1,827	$28,393	$2,764	$35,108
20	8,910	$1,782	$37,393	$3,125	$49,992
25	8,689	$1,738	$46,170	$3,533	$66,819

The flat case passes the $24,500 cost in year 13. The 3% case passes it in year 12. Over 25 years, the flat case saves about $46,000, and the escalating case about $67,000. Neither includes inverter replacement or financing.

Spreadsheet Formulas You Can Copy

Put inputs in a block at the top and reference them. One layout:

Cell	Input	Example
B1	Net cost	24500
B2	Year-1 production (kWh)	9800
B3	Self-use share	0.5
B4	Retail rate ($/kWh)	0.30
B5	Export rate ($/kWh)	0.10
B6	Degradation per year	0.005
B7	Rate increase per year	0

Then in rows 10 to 34 (years 1 to 25), with the year number in column A:

B (production): =$B$2*(1-$B$6)^(A10-1)
C (savings): =(B10*$B$3*$B$4+B10*(1-$B$3)$B$5)(1+$B$7)^(A10-1)
D (cumulative): =SUM($C$10:C10)
Payback year: =MATCH(TRUE,INDEX(D10:D34>=$B$1,0),0)

Change any input and the payback year updates.

Sensitivity: Which Input Matters Most

Using the same $24,500 system and 9,800 kWh, with exports at $0.10, here is simple payback in years for different retail rates and self-use shares:

Retail rate	30% self-use	50% self-use	70% self-use
$0.15/kWh	21.7	20.0	18.5
$0.20/kWh	19.2	16.7	14.7
$0.30/kWh	15.6	12.5	10.4
$0.40/kWh	13.2	10.0	8.1

Your retail rate moves payback the most, followed by self-use under net billing. EIA reports the U.S. average residential price at about 16.5 cents/kWh in 2024, but state averages vary widely. For how exports are credited, see net metering vs net billing.

Worked Example: Adding a Loan

A loan replaces the up-front cost with monthly payments. Using LBNL’s loan-financed median of $4.7/W, the same 7 kW system is priced at $32,900. On a 20-year loan at an example 7.99% APR, the payment is about $275 a month, or $3,300 a year. That’s more than the $1,960 year-one savings, so the household pays more each year than it saves until the loan ends. The total paid would be about $66,000.

7 kW system, 20-year loan	7.99% APR	3.99% APR
Price financed	$32,900	$32,900
Monthly payment	about $275	about $199
Total paid over 20 years	about $66,000	about $47,800

Low “headline” rates often come with a dealer fee built into the price. See solar loan rates and dealer fees and lease vs loan vs cash.

Payback vs Return on Investment

Payback only tells you when you break even. Two other numbers help compare solar with other uses of the money:

Lifetime savings ratio: 25-year cumulative savings ÷ net cost. In the flat-rate example, $46,170 ÷ $24,500 = about 1.9. Every dollar spent comes back about 1.9 times over 25 years.
Net lifetime savings: cumulative savings − net cost. That’s $46,170 − $24,500 = $21,670 in the flat case and $66,819 − $24,500 = $42,319 with 3% rate increases.
Internal rate of return (IRR): in a spreadsheet, put −24500 in year 0 and each year’s savings below it, then use =IRR(range). It gives a yearly return you can compare with a savings account or loan rate.

Adjusting for Time-of-Use Rates and Fixed Charges

If your utility uses time-of-use pricing, one retail rate isn’t accurate. A more careful version splits self-used kWh by period:

Use PVWatts’ hourly output (downloadable as a CSV) to see how much solar falls in each rate period.
Multiply each period’s self-used kWh by that period’s rate.
Use the export rate for each hour if your utility credits exports hourly, as California’s Net Billing Tariff does. See NEM 3.0 explained.

Fixed monthly customer charges stay the same with or without solar. Leave them out of the savings column entirely. Also check for non-bypassable charges that export credits can’t offset.

Inputs Checklist

Net cost after confirmed rebates only.
Production from PVWatts or the installer’s shade-adjusted estimate.
Your actual retail rate, including delivery charges.
Your utility’s current export rate and tariff name.
Degradation from your panel’s warranty sheet.
A conservative rate-increase assumption, plus a 0% case.

Adding a Battery to the Model

Add the battery’s price to net cost. Then raise self-use by the kWh the battery shifts each day, times its round-trip efficiency. For example, Tesla lists the Powerwall 3 at 13.5 kWh usable. A battery that shifts 8 kWh a day for 365 days moves about 2,900 kWh from export to self-use, minus losses. Under the example rates, each shifted kWh is worth $0.30 − $0.10 = $0.20, so about $580 a year before losses. Compare that to the battery’s installed price. For more, see is a solar battery worth it.

FAQ

What is a good solar payback period?

There’s no official benchmark. Compare it to the panel warranty (often 25 years) and how long you plan to stay.

Does a battery shorten payback?

Under net billing it can raise self-use, but it adds cost. Model it as its own line.

Should I include the 30% tax credit?

Not for a homeowner-owned system installed in 2026.

How do I calculate my solar payback period?

Divide net system cost by first-year savings for a rough number, then use the 25-year spreadsheet above to include degradation, rate changes and export credits.

Why is my installer’s payback shorter than mine?

Check whether they assumed rate increases, full retail credit for exports, or a federal credit that no longer applies to owned systems.

Does the solar payback period include maintenance?

Only if you add it. Put any expected inverter replacement in the year you expect it, as a negative savings entry.

Sources: NREL PVWatts; LBNL U.S. Distributed Solar and Storage 2025 Data Update (2024 prices); IRS Residential Clean Energy Credit; DOE Homeowner’s Guide to Going Solar; EIA average residential price 2024; Tesla Powerwall 3 datasheet. Accessed Oct 2026.