Solar Panel Calculator
Estimate solar panel system size, installation cost, annual savings, payback period, and 25-year ROI based on your electricity bill and location.
Your usage & roof
Updates as you typeSizing approach
How should we size the system? ?
Electricity use
Monthly bill ?
—
$/mo
Electricity rate ?
Typical: $0.10 – $0.35
$/kWh
Location
Quick location preset ?
Peak sun hours / day ?
Roof
Available roof area ?
sqft
—
Cost & financing
System cost per watt ?
Typical: $2.50 – $4.00
$/W
Incentives ?
Custom incentive %
%
How are you paying? ?
Loan APR ?
%
Loan term
years
Lease payment ?
% of cost / mo
Advanced assumptions (panel wattage, degradation, rate escalation)
Panel wattage ?
W / panel
Panel degradation ?
% / year
Utility rate escalation ?
% / year
Display (optional)
Currency
Cumulative cash flow
Upfront cost, then years of savings — with degradation & rate escalationYear —
Energy —
Savings —
Outflow —
Net —
Positive cash flow
Negative cash flow
Breakeven marker
Year-by-year schedule
| Year | Energy produced | Savings | Loan / lease outflow | Cumulative net | Progress |
|---|
Formula
System kW
=
Monthly bill × 12 / 365 / rate
Peak sun hours
- Monthly bill
- Average monthly electricity cost
- Rate
- Utility electricity cost per kWh
- Peak sun hours
- Average hours/day of full-rated sunlight in your area
- Panels
- Ceiling of (System W / panel wattage)
- Net cost
- Gross install cost minus incentives
- Payback
- First year where cumulative savings exceed net out-of-pocket
Worked example — your numbers
- Monthly usage = —
- Daily usage = —
- System size = —
- Panels needed = —
- Gross install cost = —
- Incentives applied = —
- Net cost after incentives = —
- Effective payback = —
The schedule below applies your chosen panel degradation (annual output loss) and utility rate escalation year-by-year, so the yearly savings shift gradually rather than stay flat. Annual savings are capped at your actual bill — solar doesn't earn you credit beyond what you were paying.