How to Calculate Solar Panel

What is Solar Panel?

A solar panel number calculator estimates how many panels are needed based on annual electricity usage, local peak sun hours, and individual panel wattage.

Formula

Annual output (kWh) = Panel wattage × Peak sun hours × 365 × System efficiency | Solar insolation varies by location

P: Panel rated power (W)
H: Peak sun hours per day (hours)
η: System efficiency (0.75–0.85)
E_annual: Annual energy output (kWh)

Step-by-Step Guide

1Annual generation per panel (kWh) = Wattage × Sun hours/day × 365 / 1,000
2Panels needed = Annual usage / Annual generation per panel
3UK average: 2.5–3.5 peak sun hours/day
4Add 15–20% for inverter losses and shading

Worked Examples

Input

3,500 kWh/yr, 3 sun hours/day, 400W panels

Result

Per panel: 438 kWh/yr; Panels needed = 3500/438 ≈ 8 panels

Frequently Asked Questions

What is Solar Panel Number?

A solar panel number calculator estimates how many panels are needed based on annual electricity usage, local peak sun hours, and individual panel wattage. Use this calculator for accurate, instant results.

How accurate is the Solar Panel Number calculator?

The calculator uses the standard published formula for solar panel number. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

What units does the Solar Panel Number calculator use?

This calculator works with inches, percentages, kilowatts, watts. You can enter values in the units shown — the calculator handles all conversions internally.

What formula does the Solar Panel Number calculator use?

The core formula is: Annual generation per panel (kWh) = Wattage × Sun hours/day × 365 / 1,000. Each step in the calculation is shown so you can verify the result manually.

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