Tool 01 · Calculator
Solar calculator — cost, size and payback
Separate fixed charges, solar used at home and exported electricity. Estimate system size, remaining bill and simple payback with explicit annual assumptions.
Prefilled numbers are examples, not verified local rates or a quote. Replace them with your bill and installer data. Complete the billing assumptions below to calculate.
Billing and production assumptions — required
Use your average bill and the same-period fixed charges. Enter 0 only if a charge or export payment truly does not apply. Self-use is the share of solar production used at home, not the share of your bill covered.
The 1,200 yield and zero minimum bill are examples; verify your roof estimate and tariff. The minimum bill is an annualized floor (12 × monthly minimum), not a month-by-month simulation. Annual credit offsets energy charges only; the cash-export scenario reports revenue separately, and no-credit ignores the entered export price. Confirm settlement eligibility. Monthly rollover, expiry, time-of-use and demand charges are not modeled.
Estimate solar size, panel count, remaining electricity bill and simple payback with explicit fixed-charge, self-use and export-credit assumptions. Prefilled values are examples; this is a flat-rate annual planning scenario, not a utility bill forecast.
No email required. Instant browser-based planning math with clear assumptions.
How this calculator stays honest
- Usage: (bill − fixed charges) × 12 ÷ variable import rate. Fixed charges must be below the total bill. If your tariff cannot be reduced to this flat-rate model, do not treat the result as a bill forecast.
- Production: annual use divided by your yield assumption, rounded up to whole panels. The rounded array sets production and cost. Self-use is a user assumption capped at annual load, not an hourly load simulation. Use the sun look-up for resource context, not a roof-specific guarantee.
- Savings: avoided imports plus export credit applied to remaining annual energy charges. Fixed charges stay; unused export credit is shown separately. Confirm actual credit eligibility, settlement and expiry with your utility.
- Payback: net cost divided by first-year bill savings, excluding maintenance, degradation, financing and future rate changes. No positive savings means no payback in this model.
- Federal credit: not assumed by default. The site uses the IRS in-service-by-2025 rule already documented in the federal credit guide.
What this tool estimates
Estimate solar size, panel count, remaining electricity bill and simple payback with explicit fixed-charge, self-use and export-credit assumptions. Prefilled values are examples; this is a flat-rate annual planning scenario, not a utility bill forecast.
No email required. Results are calculated in your browser; use them as a planning estimate, not a guaranteed quote or savings forecast.
How the math works
Annual use subtracts fixed charges before dividing the bill by the import rate. Whole-panel size sets production and cost. Choose annual energy-credit offset, separately paid cash export, or no compensation. The remaining annual bill cannot fall below fixed charges or twelve times your monthly minimum total bill. Cash export revenue is reported separately from bill savings. Simple payback uses total first-year benefit before ownership expenses.
Key variables that change your result
Fixed charges and import rate
Subtract fixed monthly charges before converting the remaining bill into estimated kWh. Only avoided energy purchases count as import savings.
Solar production and self-use
Use a roof-specific annual production estimate and an explicit self-use scenario. The tool does not infer hourly use or roof shading.
Export settlement and minimum bill
Choose the scenario matching your verified tariff. Annual credits offset energy charges only; separate cash export is revenue, not a bill reduction. The minimum is an annualized floor, not monthly settlement.
Quote price per watt
Compare cash-price quotes on dollars per watt before considering loans, rebates or sales projections.
Questions homeowners ask
How is this solar calculator calculated?
What do I need to use this calculator?
Does this calculator account for my state?
State context matters
Find your state solar guide
Costs, incentives, export rules and payback inputs vary by state. Open your state guide before treating any calculator result as a buying decision.