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Solar Panel Calculator
Estimate the system size and number of panels from your usage and sun hours.
System size
—
Solar array needed.
| Panels needed | — |
|---|---|
| Daily production | — |
| Roof area (approx) | — |
| Losses | — |
Show our math
Enter your figures above to see the step-by-step working.
An estimate — get a site assessmentEverything computed client-side — nothing leaves this page
How the Solar Panel Calculator Works
Sizing a solar array starts with how much electricity you use. Divide your monthly kWh by 30 for a daily figure, then divide by your location’s peak sun hours (the equivalent hours of full-strength sun per day, often 4–6) and by a system efficiency that accounts for losses of around 20% from wiring, heat and inverter. That gives the system size in kilowatts; divide by your panel wattage for the number of panels.
It’s a planning estimate. Real output depends on roof orientation, shading, local weather and panel quality, so a professional site assessment refines the number.
system kW = (monthly kWh ÷ 30) ÷ (sun hours × efficiency)
Frequently Asked Questions
How many solar panels do I need?
Work out your daily kWh, divide by peak sun hours and efficiency for the system size, then divide by panel wattage. A typical home needs around 15–25 panels.
What are peak sun hours?
The number of hours per day equivalent to full-strength sunlight. It varies by location and season — often 4 to 6 hours in the US.
Why include system losses?
Real systems lose around 15–25% to wiring, heat, inverter conversion and dirt, so the array must be sized a bit larger than the raw math suggests.
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