Solar Panel Output Calculator

How to Calculate Solar Panel Energy Output

Solar panels don't produce their rated wattage around the clock. Actual energy output depends on panel wattage, number of panels, peak sun hours at your location, and system efficiency losses (wiring, inverter, temperature, shading).

The Formula

Daily Energy (kWh) = Panel Watts × Number of Panels × Peak Sun Hours × System Efficiency / 1000

System efficiency accounts for: inverter losses (~4%), cable losses (~2%), temperature derating (~5%), soiling (~2%), and panel mismatch (~2%). Combined: ~80–85% typical.

Peak Sun Hours by Region (examples)

| Location | Peak Sun Hours | |----------|---------------| | Arizona, USA | 6–7 | | Germany | 3–4 | | Australia | 4.5–6 | | UK | 2.5–3.5 | | Pakistan | 5–6 | | India | 4.5–6.5 |

Practical Examples

Example 1: 20 × 400W panels in Karachi (5.5 peak sun hours), 82% efficiency. Daily = 20 × 400 × 5.5 × 0.82 / 1000 = 36.1 kWh/day = ~1,083 kWh/month.

Example 2: 10 × 300W panels in UK (3 hours), 80% efficiency. Daily = 10 × 300 × 3 × 0.80 / 1000 = 7.2 kWh/day = 216 kWh/month.

Factors That Reduce Output

Panel temperature above 25°C reduces output ~0.4%/°C above STC. East/west facing panels produce 15–20% less than south-facing. Partial shading can cut output dramatically if panels are in series.