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HeizerDesk Solar Panel Calculator
Enter what you use and your local sun hours. This returns the system size in kilowatts, a panel count at your chosen wattage, and the roof area that array actually needs.
Your numbers
Result
Panels needed
21
panels
- System size
- 8.4kW
- Roof area required
- 441sq ft
- Calculated requirement
- 8.33kW
- Estimated annual output
- 11,038kWh
- Daily need at target offset
- 30kWh
How this is calculated
- Daily need = (monthly kWh ÷ 30) × target offset.
- System size in kW = daily need ÷ (peak sun hours × system efficiency).
- Panels = system kW × 1000 ÷ panel wattage, rounded up.
- Roof area = panels × area per panel.
Before you order
- Peak sun hours is not daylight hours. It is the equivalent hours of full-strength sun per day, and it varies enormously by location and season.
- The roof area figure is panels only. Real installations need fire setbacks and walkways, so plan on noticeably more roof than this.
- Orientation and shade matter more than most people expect: a north-facing or partly shaded array can lose a third of its output.
- Net metering rules decide whether over-producing is worth anything, and they vary by utility.