What are peak sun hours?

Peak sun hours (PSH) is the equivalent number of hours per day when solar irradiance averages 1,000 W/m². A location with 5 PSH receives the same total daily solar energy as 5 hours of direct midday sun. PSH values range from about 2.5 (northern Europe, cloudy climates) to 7+ (desert regions like Arizona or the Middle East).

Why is system efficiency less than 100%?

Real-world PV systems lose energy through inverter conversion (typically 5–10%), wiring resistance, soiling and shading, module temperature rise above STC, and panel degradation over time. A combined efficiency of 75–85% is a realistic range for most grid-tied systems.

Should I round up or down the panel count?

Always round up to the nearest whole panel. A fractional panel does not exist, and rounding down would leave your system under-sized for your target. The calculator automatically rounds up for you.

Does this account for battery storage?

This tool calculates the number of panels needed to generate a target daily energy amount. For off-grid or battery-backed systems, add additional panels to cover charging losses and autonomy days — a separate battery sizing calculation is recommended.

What panel wattage should I use?

Use the STC (Standard Test Conditions) rated wattage printed on the panel's datasheet, typically between 250 W and 600 W for residential and commercial panels. Monocrystalline PERC and TOPCon panels commonly fall in the 380–430 W range as of 2024.

How accurate is this calculation?

The calculation is accurate for preliminary sizing. Final engineering designs should use detailed simulation software (PVsyst, SAM) with site-specific irradiance data, exact shading analysis, and measured system losses.

PV Array Sizing Calculator

Enter your daily energy need, panel wattage, and peak sun hours to find out exactly how many solar panels you need.

System Parameters

Daily Energy Target (kWh)

Total kWh you need the array to produce per day.

Peak Sun Hours (h/day)

Hours of equivalent full-sun irradiance per day at your site. Typical range: 3 – 6 h.

Panel Rated Power (W)

STC-rated wattage per panel from the datasheet.

Overall System Efficiency (%) 80%

50% (poor) 75% (typical) 99% (ideal)

Panels Required

—

solar panels (rounded up to whole panels)

Parameter	Value
Enter values and click Calculate

Panel Count vs. Peak Sun Hours

PSH (h/day)	3 h	4 h	5 h	6 h	7 h
Results appear after first calculation

Summary

This PV array sizing calculator helps homeowners, engineers, and solar installers determine how many photovoltaic panels are needed to meet a daily energy target. It factors in system losses such as inverter efficiency, wiring losses, and panel degradation so the result reflects real-world performance rather than ideal lab conditions. Enter your location's peak sun hours (PSH), your target daily energy output in kWh, the panel rated wattage, and system efficiency to get an accurate panel count.

How it works

Enter your target daily energy consumption in kilowatt-hours (kWh).
Input the peak sun hours (PSH) for your location — typically 3 to 6 hours per day.
Enter the rated wattage of your chosen solar panel (e.g. 400 W).
Set the overall system efficiency to account for inverter, wiring, and temperature losses (default 80%).
The calculator divides effective energy need by the daily output per panel to give you a panel count.
Review the summary table showing array capacity, daily yield, and monthly/annual estimates.

Use cases

Sizing a rooftop solar system for a residential home.
Pre-engineering commercial or industrial PV installations.
Comparing different panel wattages to minimize roof space.
Validating a solar installer's panel count quote.
Estimating off-grid system requirements for a cabin or RV.
Academic and engineering coursework on renewable energy.
Quickly checking if a battery-backup system can be self-sufficient.
Sensitivity analysis on system efficiency and peak sun hours.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu