Efficiency
Ratio of usable electrical energy to incident solar energy -- indicates the effectiveness of a solar cell or system.
Also known as: Module Efficiency, Conversion Efficiency
What Is Efficiency?
Efficiency describes how effectively a solar cell or solar module converts incident solar energy into electrical energy. It is expressed as a percentage and is one of the most important metrics for comparing PV products.
Efficiencies of Different Technologies
| Technology | Cell Efficiency | Module Efficiency |
|---|---|---|
| Monocrystalline (PERC) | 22—24% | 20—22% |
| TOPCon | 24—26% | 22—24% |
| HJT | 24—26% | 22—24% |
| Polycrystalline | 18—20% | 16—18% |
| Thin-film (CdTe) | 18—21% | 15—19% |
| Perovskite (lab) | up to 26% | In development |
| Tandem (lab) | up to 33% | In development |
Influencing Factors
Real-world efficiency is affected by:
- Temperature: Higher temperatures reduce efficiency (temperature coefficient)
- Irradiance: At low irradiance, efficiency decreases
- Shading: Partial shading can disproportionately reduce yield
- Ageing: Modules lose approximately 0.3—0.5% power per year through degradation
Practical Tip
A higher module efficiency means more power per area. When roof space is limited, high-efficiency modules are worthwhile, even if they are somewhat more expensive.
Related Terms
Solar Cell
Semiconductor device that converts sunlight directly into electrical current through the photoelectric effect.
Solar Module
Assembly of multiple solar cells in a weatherproof housing for generating electricity from sunlight.
STC (Standard Test Conditions)
Standardised test conditions (1,000 W/m², 25 °C, AM 1.5) under which the rated power of solar modules is measured.
Temperature Coefficient
Metric indicating how much a solar module's power decreases per degree Celsius of temperature rise (typical: -0.3%/°C).
PERC
Passivated Emitter and Rear Cell -- cell technology with an additional passivation layer on the rear side for higher efficiency.