Performance Ratio
Performance ratio (PR) is a metric that quantifies how efficiently a solar PV system converts available solar energy into useful electrical output, accounting for all real-world losses compared to the theoretical maximum. It is expressed as a percentage.
PR = Actual Annual Output (kWh) ÷ (System Rated Power (kW) × Annual Irradiance (kWh/m²/kWp))
A well-designed system with no shading, minimal soiling, and quality components typically achieves PR of 78–85%.
Losses that Reduce PR
The gap between 100% and actual PR represents the cumulative effect of all system losses:
- Temperature losses: ~5–10% (panels operate above 25°C STC)
- Inverter efficiency losses: ~2–3%
- Wiring and connection losses: ~1–2%
- Module quality/mismatch: ~1–2%
- Soiling losses: ~1–5% (depends on climate and maintenance)
- Shading: 0–20%+ (site-dependent)
- Monitoring and downtime: ~0.5–1%
Industry Performance Ratios by System Type
- High-quality residential (unshaded, premium components): 80–85%
- Standard residential: 75–80%
- Commercial rooftop: 78–83%
- Utility-scale fixed-tilt: 80–85%
- Utility-scale single-axis tracking: 82–87%
PR in SolarScope
SolarScope's production estimates use a default performance ratio of 0.80 (80%), which is appropriate for a standard, well-maintained system. Advanced users can adjust the performance ratio in project settings to reflect site-specific conditions such as higher soiling rates in dusty environments or known shading losses.