Solar Panel Calculator
Estimate solar panel count from monthly kWh and peak sun hours.
This solar panel calculator estimates how many solar panels are needed to meet a household's energy usage, based on monthly electricity consumption, local peak sun hours, and individual panel wattage.
Enter your monthly kWh usage and local peak sun hours, and the calculator returns an estimated number of panels needed.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 30 daily kWh, 5 peak sun hours, 0.4 kW panels, 80% efficiency | ≈19 panels | Panels = 30 ÷ (5 × 0.4 × 0.8) = 30 ÷ 1.6 ≈ 18.75, rounded up to 19 panels. |
| 20 daily kWh, 4.5 peak sun hours, 0.35 kW panels, 75% efficiency | ≈17 panels | Panels = 20 ÷ (4.5 × 0.35 × 0.75) = 20 ÷ 1.181 ≈ 16.93, rounded up to 17 panels. |
The Solar Panel Sizing Formula
Panels needed = daily kWh usage / (peak sun hours x panel wattage in kW x system efficiency factor). Peak sun hours (not total daylight hours) represents the equivalent hours of maximum sunlight intensity a location receives daily, which varies significantly by geographic location and season.
Why System Efficiency Matters
Real-world solar systems lose some energy to factors like inverter conversion losses, panel temperature effects, and wiring resistance - a system efficiency factor (commonly around 75-85%) is applied to account for this gap between a panel's rated output and its actual real-world energy production.
How to Use the Solar Panel Calculator
- Open the Solar Panel Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the solar panel calculator works.
Frequently Asked Questions
How many solar panels do I need for my home?
Divide your daily energy usage in kWh by the product of your area's peak sun hours, individual panel wattage (in kW), and a system efficiency factor (commonly 75-85%) to estimate the number of panels needed.
What are peak sun hours?
Peak sun hours represent the equivalent number of hours per day a location receives sunlight at maximum intensity (1,000 watts/m²) - this differs from total daylight hours and varies by geographic location and season.
Why don't solar panels produce their full rated wattage in real conditions?
Real-world factors like inverter losses, panel heating, dust, and less-than-ideal sun angles reduce actual output below a panel's rated capacity, which is why a system efficiency factor is applied when sizing a solar system.
How do I use this solar panel calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Solar Panel Calculator calculate?
Estimate solar panel count from monthly kWh and peak sun hours. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this solar panel use?
The formula is: panels = daily kWh / sun hours / panel kW / efficiency. Peak sun hours as a solar sizing concept became standardized alongside NREL (the US National Renewable Energy Laboratory, established 1977) solar irradiance mapping research, which measured how much usable sunlight different US regions receive - this data remains the basis for residential and commercial solar sizing calculations across the industry today.
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Last updated: September 27, 2026.