Solar Calculator
Turn a year of household electricity use into a practical array size, panel count, production estimate, and transparent payback scenario.
Enter your numbers
Changes calculate instantly and are written to this page’s URL.
Off by default. The federal residential credit ended for new homeowner installations after December 31, 2025 under 2025 law. Use this only for a hypothetical or independently verified exception.
Residential energy statement
Instant planning estimate · not a utility invoice
- System size
- 7.2 kW
- 400 W-class panels
- 18
- Annual production
- 10,800 kWh
- First-year savings
- $1,620.00
- Modeled net cost
- $22,320.00
How the solar calculator works
This solar calculator translates the electricity a home buys into an array that can produce a similar annual amount. Choose a state to load its EIA rate and a PVWatts-style production factor, then use either the monthly bill or monthly kWh from a utility statement. The result is an annual energy balance, not a promise that every monthly bill reaches zero.
Annual consumption is monthly consumption multiplied by 12. When bill mode is used, monthly kWh is estimated by dividing the energy charge by the selected cents-per-kWh rate. Fixed customer charges should be removed first because solar does not avoid them.
Array size divides annual use by a state production factor. Panel count rounds up because modules are discrete. Production factors already represent a planning-level AC yield, so the tool does not add a second hidden sunshine multiplier.
Simple payback divides net installed cost by first-year bill savings. Retail export credit, shade, roof direction, snow, time-of-use prices, degradation, financing, and maintenance can all change cash flow; use the dedicated payback page when those details matter.
Worked example
A home using 900 kWh each month uses 10,800 kWh per year. At 1,500 kWh per installed kW annually, it needs about 7.2 kW, or 18 panels rated at 400 W. At 15¢/kWh, the modeled first-year value is $1,620.
How to read the result
Treat the panel count as a starting layout. A contractor should model the actual roof planes and utility interconnection rules. The homeowner federal credit ended for new installations after December 31, 2025 under 2025 law, so the optional 30% scenario is off by default and only models a hypothetical or independently verified exception.
Planning inputs are deliberately editable because two homes in the same state can have different tariffs, roof conditions, equipment, and operating schedules. Save a scenario with “Copy link,” then change one assumption at a time. This makes the result useful for comparing decisions without implying false precision.
Common questions
Can I size solar from my electric bill?
Why does solar not erase every bill?
Does the calculator assume a federal solar credit in 2026?
How many 400 W panels fit in one kW?
Sources
Formulas and defaults are documented in our data method. The principal references for this page are:
- NREL — PVWatts Calculator documentation (2025) — Production modeling, array orientation, and system-loss context.
- EIA — Electric Power Monthly, Table 5.6.A (2024 annual) — Residential electricity price benchmarks by state.
- U.S. Department of Energy — Homeowner’s Guide to the Federal Tax Credit for Solar Photovoltaics (accessed methodology, 2025) — Background only; 2026 eligibility is never assumed.