Understanding Your Solar Panel Output

Rated vs Actual Output

A "400W" panel produces 400W only under perfect lab conditions (STC: 1,000 W/m², 25°C, AM 1.5). In real life, expect 75-85% of rated output on average.

Factors That Affect Output

1. Sun Hours (Biggest Factor)

Peak sun hours vary dramatically by location. Arizona gets 6.5 hours/day while Michigan gets 3.8. This alone creates a 70% difference in annual production.

2. Panel Tilt & Orientation

South-facing panels at an angle equal to your latitude produce the most energy annually. Panels facing east or west produce about 15-20% less.

3. Temperature

Solar panels lose about 0.3-0.5% efficiency per degree Celsius above 25°C. Ironically, hot sunny places lose some output to heat, while cool sunny places (like Colorado) are ideal.

4. Shading

Even partial shading can dramatically reduce output. A single shaded cell can reduce a panel's output by 30-80% due to how cells are wired in series.

5. System Losses

Inverter conversion, wiring, soiling, and mismatch typically account for 15-20% system losses. This is why we use a 0.8 derate factor in calculations.

Maximizing Output

• Keep panels clean (2-5% loss from dirt)
• Minimize shading (trim trees if possible)
• Use microinverters or optimizers to reduce shading impact
• Optimal tilt angle (latitude × 0.9 for annual production)
• Monitor system performance to catch issues early

Use our kWh output calculator to estimate your system's production.