Solar Panel Sizing Calculator
Estimate a solar array's nameplate size and approximate panel count from daily energy demand, peak-sun-hours, system efficiency and module power.
How to use this calculator
- Enter the target daily energy, local peak-sun-hours assumption, an overall efficiency percentage and individual panel rating.
- Review the worked example for solar panel sizing calculator and compare the inputs with your own units.
- Change one assumption at a time and recalculate if you need a second scenario.
Array size estimate
Required array kW ≈ daily kWh ÷ (peak-sun-hours × system efficiency fraction); panel count rounds up to a whole panel.
- The calculation compresses shading, inverter and wiring losses into one entered efficiency and assumes the entered sun-hours apply to the chosen design period.
- The result is calculated from the values entered; the page does not independently verify assumptions, data quality or real-world suitability.
Worked examples
Eight kWh per day
At 8 kWh/day, 4 peak-sun-hours and 75% overall efficiency, the estimate is 2.67 kW. With 400 W panels it rounds up to seven modules.
8 ÷ (4 × 0.75) ≈ 2.67 kW; ceiling(2,667 ÷ 400) = 7 panels.
The simple estimate is about 2.67 kW, or seven 400 W panels.
Understanding the result
Seasonal solar resource and real system losses matter more than panel nameplate rating alone.
Roof orientation, shading, weather, storage, export rules, inverter limits and site safety require a proper design.
Important notes
Use local solar resource information and a qualified installer for an actual system.
Displayed figures are rounded for readability. Preserve more precision during intermediate calculations and verify the labels and units before using the estimate.
Frequently asked questions
What does the Solar Panel Sizing Calculator show?
Seasonal solar resource and real system losses matter more than panel nameplate rating alone.
What assumptions should I check?
Use local solar resource information and a qualified installer for an actual system.
Does this replace expert or authoritative guidance?
Roof orientation, shading, weather, storage, export rules, inverter limits and site safety require a proper design.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.