Solar Panel Efficiency
Solar panel efficiency is the percentage of solar energy (irradiance) that a panel converts into usable electrical energy under Standard Test Conditions (STC: 1,000 W/m² irradiance, 25°C cell temperature, AM1.5 spectrum). It is one of the most commonly cited PV panel specifications and directly affects how much area is needed to achieve a given system capacity.
A panel rated at 20% efficiency converts 20% of incident solar radiation into electricity. Under STC, a 1 m² panel with 20% efficiency produces 200 W (1,000 W/m² × 0.20).
Typical Efficiency Ranges (2024)
- Standard monocrystalline (PERC): 19–22%
- Premium monocrystalline (TOPCon, HJT): 21–24%
- Bifacial monocrystalline: 20–23% (front) + 5–15% additional from rear
- Polycrystalline: 15–17% (largely phased out)
- CdTe thin-film (First Solar): 18–19%
- Multi-junction concentrating PV (CPV): 40%+ (niche applications)
Real-World vs. STC Efficiency
Panel efficiency under real operating conditions is lower than the STC rating due to:
- Temperature: Panels typically operate at 40–70°C, well above the 25°C STC reference. Most silicon panels lose 0.35–0.45% efficiency per °C above 25°C.
- Irradiance variation: Panels perform less efficiently at low irradiance (cloudy days)
- Soiling: Dust and pollen on panel surfaces reduce light transmission
- Spectrum mismatch: Real-world solar spectrum differs from AM1.5
A panel rated at 20% STC efficiency might achieve 16–18% in typical real-world conditions.
In SolarScope
SolarScope uses the panel efficiency you enter in project settings (default: 20%) combined with a performance ratio (default: 80%) to calculate production estimates. Adjust these values to match your specific panel and system configuration.