Solar panel efficiency is one of the key performance factors potential buyers consider. But focusing too narrowly on efficiency ratings can miss the bigger picture. This article provides an in-depth look at what solar panel efficiency really means and how it impacts system performance.
Defining Solar Panel Efficiency
Efficiency indicates what percentage of sunlight striking a solar panel is converted into usable electricity. It represents the ratio of electrical output to input irradiance.
For example, a panel rated at 18% efficiency and receiving 1,000 W/m2 of solar irradiance would produce 180 Watts of power (18% of 1,000 W) under standard test conditions.
Efficiency ratings are measured under controlled lab test conditions and indicate peak performance. Real-world output is typically 80-90% of rated efficiency due to factors like temperature effects.
Commercial Solar Panel Efficiency Levels
- Monocrystalline silicon – Typically 18-22% efficient, can exceed 24% for high-end products. Represents majority of panels on the market currently.
- Polycrystalline silicon – Average efficiency around 15-18% for most economical models on the market today.
- Cadmium telluride thin film – Modules achieve 16-22% in lab tests and 10-16% in field deployments.
- CIGS thin film – Range is wide from 12-19% for commercial products. New prototypes exceed 20% efficiency.
- Amorphous silicon thin film – Considerably lower than crystalline silicon, ranging from 6-9% typically.
Key Factors Affecting Efficiency
Solar Cell Material – Monocrystalline silicon produces the highest efficiencies, followed by polycrystalline and thin-film technologies. Material purity and crystalline structure affect performance.
Temperature – All solar panels suffer reduced efficiency as operating temperature rises. Proper solar design factors in this impact.
Solar Spectrum and Light Intensity – Converting diffuse or low-intensity light is less efficient than direct beam irradiance. Low-light conditions impair output.
Angle of Incidence – As sunlight strikes panels at sharper angles, more reflection occurs, decreasing power production. Optimal panel tilting is key.
Soiling and Shading – Buildup of dirt or snow on panels lowers output substantially. Even minor shading also significantly curtails efficiency. Proper maintenance and solar access are essential.
Equipment Age and Degradation – Gradual degradation occurs over decades of operation, with output declining 0.5-1% annually. Newer high-quality panels age better than early generations.
Evaluating Solar Efficiency in Context
Focusing narrowly on peak efficiency percentages can miss the bigger picture. Lower-efficiency panels often out-produce high-efficiency models in real-world conditions based on:
- Cost Per Watt – Panels with lower rated efficiency can offer better value by costing substantially less per watt of generation capacity.
- Temperature Resistance – Technologies like thin-film often lose less efficiency than silicon at high operating temperatures.
- Shading Tolerance – Monocrystalline is vulnerable to shading, while polycrystalline and thin-film are more robust.
- Low-Light Performance – Thin-film panels can out-produce silicon under diffuse or overcast conditions due to material properties.
- Degradation Rates – Some technologies like thin-film experience faster initial output declines that level off, while silicon degrades linearly. Long-term performance differs.
Improving Real-World Efficiency
While panel selection is important, solar system design, siting, maintenance and operations play pivotal roles in extracting maximum efficiency:
- Optimal siting and tilt to maximize irradiance received and minimize shading, soiling risks.
- Using lower temperature-coefficient panels in hot climates.
- Proper spacing between rows to prevent inter-row shading as the sun moves.
- Tracking systems that follow the sun during the day for peak incidence angle.
- Robust cleaning and maintenance to minimize soiling losses from dirt buildup.
- Monitoring array performance and diagnosing any issues causing underperformance.
- Employing microinverters or power optimizers for panel-level maximum power point tracking.
- Considering higher-efficiency panel options when space constraints exist.
In most cases, moderate efficiency panels installed properly will out-produce high-efficiency panels sited poorly over the long term. Holistic solar design trumps exclusively chasing higher efficiency ratings.
