Estimate your payback period, 25-year savings & ROI vs your power bill.
Your electricity use
From 12 months of bills. No kWh? (monthly $ ÷ rate) × 12.
$
All-in rate: total bill ÷ total kWh.
~17.5 sq ft per 400 W panel.
kWh per kW per yr. US median ~1.3; sunny SW 1.6–1.8.
System cost & incentives
$
2026 US installed ~$2.35–$3.50/W.
$
Enter the quoted price before incentives.
Federal 25D credit is $0 in 2026 for cash/loan — see notes.
Financing
The % off your offset bill the provider passes on. You don't own the system.
Inverters usually need one swap around year 12–15.
Net 25-year savings
—
enter inputs
Solar Panel Savings Estimator — guide & how to use
Estimate only — not a quote or financial advice. Real production depends on
roof orientation, tilt, shading, soiling, and local weather. Figures are nominal (not discounted to
present value) and assume 1:1 net metering up to your usage. Get an installer site assessment or run
NREL PVWatts for your exact
ZIP before deciding. All math runs in your browser — nothing is sent anywhere.
What it does
This estimator sizes a solar system to your annual electricity use, then walks the next
25 years to show your payback period, net 25-year savings, and
ROI. It applies panel degradation and utility-rate
escalation each year, checks whether the system fits your roof, and
adapts the math for cash, loan, or lease/PPA financing.
How to use it
Enter your annual kWh (from your bills) and your all-in $/kWh rate.
Set the production ratio for your area and your system cost
($/W or a quoted total).
Pick cash, loan, or lease and read your payback, 25-year savings, and ROI.
Worked example
A home uses 10,500 kWh/yr at $0.1765/kWh with a production ratio of
1.3 and a price of $2.75/W, paying cash:
System size = 10,500 ÷ 1.3 = 8.1 kW (about 21 panels at 400 W).
Gross cost = 8,077 W × $2.75 = ~$22,212; with $0 federal credit in
2026, net cost ≈ $22,212.
With 3%/yr rate escalation and 0.5%/yr degradation, cumulative savings cross the net cost at roughly
year 10–11, and net 25-year savings land around
$40,000–$45,000 — an ROI near 180–200%.
Your numbers will differ — this is the math the tool runs, shown step by step.
How the math works
System size (kW) = annual kWh ÷ production ratio.
Roof fit: ~17.5 sq ft per 400 W panel. If the panels won't fit, the system is capped
to your roof and we show the % of usage offset.
Year-n production = year-1 production × (1 − degradation)n−1.
Year-n rate = current rate × (1 + escalation)n−1.
Year-n savings = min(production, usage) × rate (credited production is capped at your
usage — surplus is not paid at retail).
Payback = the year cumulative savings first cover net cost (cash) or cumulative loan
payments (loan), interpolated to one decimal.
Loan payment = P·r ÷ (1 − (1+r)−N), with r = APR/12 and N = term × 12
(straight-line P/N if APR = 0).
Accuracy notes & 2026 changes
This is an estimate, not a quote. Orientation, tilt, shading, soiling, and weather all
move the real number; a site assessment or NREL PVWatts run is more precise.
2026 federal tax credit: the 30% residential credit (IRC §25D) expired 12/31/2025 and
is $0 for cash/loan systems installed in 2026. We default federal to $0; the incentive
field is for state/local rebates. The 30% commercial credit (48E) can still flow through on
leases/PPAs to ~2027 — a reason lease savings may look better now.
Net metering: savings assume each offset kWh saves the full retail rate (1:1). Many
utilities have moved to net billing / lower export rates (e.g. California NEM 3.0), so we conservatively
cap credited production at your annual usage and don't pay for surplus.
Degradation default 0.5%/yr reflects modern Tier-1 panels (warranties guarantee ~85–90%
output at year 25). Cheaper panels degrade faster.
Escalation default 3%/yr is a long-run US average (~2.5–3.5%). Don't extrapolate a
recent short-term spike across 25 years.
Not included: cleaning, roof reinforcement, insurance/property-tax effects, and
financing-related home-value changes. The optional inverter-replacement toggle adds one swap (~$2,250)
around year 13. All figures are nominal — a true comparison would discount to present value (NPV).
How to embed this tool on your website
No account, no coding. Copy the embed code and paste it where you want it to appear:
It's the year your cumulative bill savings equal your net upfront cost. This tool walks year by year with degradation and rate escalation, then interpolates to one decimal — more accurate than dividing net cost by year-one savings.
Does the 30% federal tax credit still apply in 2026?
Not for cash/loan purchases — the residential §25D credit expired 12/31/2025 and is $0 in 2026. We default federal to $0; the incentive field is for state/local rebates. Leases/PPAs may still pass through the 30% commercial credit to ~2027.
What is the production ratio?
The kWh each 1 kW of panels makes per year in your climate. US median ~1.3; sunny Southwest 1.6–1.8; cloudy Northwest/Northeast ~1.0–1.1. Run NREL PVWatts for a ZIP-accurate value.
Which electricity rate should I enter?
Your all-in rate: total bill ÷ total kWh. Solar offsets delivery fees and taxes too, so using only the supply charge undercounts savings.
Why is a lease ROI not shown as a percentage?
A lease/PPA has $0 upfront and you don't own the system, so a cash-basis ROI is misleading. We show lifetime bill savings with $0 down instead.
Is it really free?
Yes. 100% free, everything runs in your browser — none of your inputs leave your device.