Sizing your solar array isn’t guesswork—it’s a quick calculation based on your energy use, local sunlight, and panel wattage. Use the steps and examples below to estimate your panel count with confidence.

The Fast Formula

Estimate your system size (kWdc)

Find your daily energy use (kWh/day)

From your bills: Monthly kWh ÷ 30

Or yearly: Annual kWh ÷ 365

• Peak Sun Hours (PSH): typical range 3.5–6.0 (cloudy vs. sunny regions)
• Performance Ratio (PR): losses from heat, wiring, inverter, dust (use 0.80 as a good default)

Convert system size to panel count

Example 1 (Typical Home)

• Monthly usage: 900 kWh
• Daily use: 900 ÷ 30 = 30 kWh/day
• Assumptions: PSH 5, PR 0.80, panel 400W
• System size: 30 ÷ (5 × 0.80) = 30 ÷ 4 = 7.5 kW
• Panel count: 7.5 kW ÷ 0.40 kW = 18.75 → 19 panels
• Roof area (estimate): ~21 ft² per panel ⇒ 19 × 21 ≈ 400 ft² (+10–20% spacing)

Example 2 (Higher Use / Lower Sun)

• Monthly usage: 1,200 kWh
• Daily use: 40 kWh/day
• Assumptions: PSH 4, PR 0.80, panel 410W
• System size: 40 ÷ (4 × 0.80) = 40 ÷ 3.2 = 12.5 kW
• Panel count: 12.5 ÷ 0.41 = 30.5 → 31 panels
• Roof area (estimate): ~31 × 21 ≈ 650 ft² (+10–20% spacing)

Rule of thumb: Each 1 kW of panels produces roughly 3–6 kWh/day, depending on your local sun and site conditions.

Five Factors That Change Your Panel Count

1. Peak Sun Hours: Less sun ⇒ larger system needed.
2. Shading: Trees, chimneys, or neighboring buildings reduce output.
3. Orientation & Tilt: South-facing with a reasonable tilt is best; east/west needs slightly more capacity to hit the same annual kWh.
4. Temperature & Ventilation: Hot panels produce less—good airflow helps.
5. System Hardware: Micro-inverters/optimizers and higher-efficiency modules can reduce panel count for the same kWh target.

Want a Belusi Energy Right-Size Check?

Send us:

• Your average monthly kWh (or a recent bill photo),
• Your address or city (for local sun estimates),
• Your roof photos or layout (if available), and
• Preferred offset (e.g., 80%, 100% of your usage).

We’ll return a tailored panel count, roof layout suggestion, and an expected annual kWh—optimized for Belusi Energy standards.