Solar Panel Size Calculator
Estimate solar system size and panel count from electricity usage.
This page is an editable estimator with realistic defaults so you can model your own situation in minutes.
Solar size kW = target daily kWh / (sun hours x performance ratio).
Treat the result as a planning estimate and verify important numbers with the relevant official source before acting.
| Monthly usage | 900 kWh | |
|---|---|---|
| Target offset | 90% | |
| Panel wattage | 400 W |
Assumptions
- Solar production depends on roof orientation, shade, weather, panel degradation, inverter losses, and local interconnection rules.
- Savings depend on net metering, export credits, time-of-use rates, fixed charges, incentives, and financing.
- Confirm solar system design and payback with qualified installers and utility program rules.
How this calculator works
Formula used
Solar size kW = target daily kWh / (sun hours x performance ratio).
Example calculation
Plug in your own numbers and the result updates instantly. Solar size kW = target daily kWh / (sun hours x performance ratio).
Solar Panel Size Calculator FAQ
Is this solar panel size calculator exact?
No. It is an estimate for planning only. Actual bills, savings, and sizing depend on utility tariffs, weather, usage behavior, equipment efficiency, installation quality, local code, and product specifications.
What electricity rate should I enter?
Use your all-in average rate if possible: supply, delivery, taxes, and riders divided by total kWh. Time-of-use plans, demand charges, fixed fees, and tiered rates can change the result.
Should I verify before buying equipment?
Yes. Confirm solar, battery, generator, HVAC, water heater, insulation, window, and electrical decisions with qualified installers, electricians, utility programs, and local permitting requirements.