Solar Panel Calculator

Estimate solar panel system size based on monthly usage, sun hours, and system efficiency.

Panels Needed
— panels
Rounded up.

Usage Tip

Peak sun hours vary by region and season; size for the lower winter figure if you want year-round coverage.

THE MATH
daily kWh = monthly ÷ 30
system size (kW) = daily kWh ÷ sun hours × (100 ÷ efficiency)
panels = round up( system size × 1000 ÷ panel wattage )
A solar array must produce your daily energy use during the available peak sun hours, scaled up for system losses. Panel count is the system size divided by each panel rating.
Enter your monthly kWh usage from a power bill, local peak sun hours, a system efficiency (about 80 percent), and the panel wattage.
The result rounds up to whole panels.
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.