Panel sizing starts with honest daily watt-hours and realistic sun data—not nameplate sticker watts alone. This guide walks through the solar panel size calculator logic so your array matches load, not guesswork.
Benefits
- Clear formula: minimum panel W ≈ daily Wh ÷ (peak sun hours × system efficiency).
- Uses location-based peak sun hours instead of assuming full noon all day.
- Shows intermediate values so you can cross-check against solar daily yield and battery bank planners.
How it works
- Enter total daily energy need in watt-hours (sum loads × hours or use a load audit).
- Set peak sun hours for your site and season—typical values range from 3–6 hours.
- Apply system efficiency (default ~80%) for wiring, controller, and inverter losses, then review minimum panel watts.
FAQ
How do I calculate solar panel size in watts?
Divide daily watt-hours by the product of peak sun hours and system efficiency (as a decimal). Example: 2,400 Wh ÷ (5 h × 0.80) ≈ 600 W minimum array rating before safety margin.
What are peak sun hours?
Peak sun hours are the equivalent full-sun hours per day for your location—one peak hour equals about 1,000 W/m² irradiance. Winter, tilt, and shading lower this number; use seasonal data when sizing off-grid systems.
Should I add extra panel capacity beyond the calculator result?
Yes. Real installs need headroom for cloudy days, battery round-trip loss, and inverter clipping. Many designers add 20–30% on top of the minimum watts unless a detailed yield model is used.
Technical specifications
- Formula: panel_W ≈ daily_Wh ÷ (peak_sun_h × efficiency_fraction).
- Inputs: positive Wh/day, sun hours, and efficiency (1–100%).
- Output: minimum panel wattage at STC nameplate—not guaranteed daily harvest.
- Planning margin: +20–30% recommended for weather and storage losses.