Solar Panel Efficiency Explained – What Really Affects Performance?

Introduction

When investing in solar power, most people focus on the wattage rating of the panels. However, that number alone doesn’t tell the full story. In practice, solar panel efficiency – how effectively the panel converts sunlight into usable electricity – depends on a variety of real-world conditions.

Orientation and Angle

The position of your panels is one of the most important factors. In the UK, south-facing panels at an angle of around 30–40 degrees usually capture the most sunlight. Even a small deviation from the ideal orientation can reduce efficiency.

Shading and Obstructions

Shadows from trees, chimneys, or nearby buildings can have a surprisingly large impact on output. Modern panels with half-cut cells or micro-inverters can limit the damage, but shading remains a common cause of lower-than-expected performance.

Temperature Effects

Solar panels work best in cooler conditions. High heat reduces voltage output, meaning performance can drop during hot summer days. This “temperature coefficient” is one of the key technical specifications worth checking before you buy.

Dirt, Dust, and Maintenance

A thin layer of dust or bird droppings can cut efficiency by several percent. While solar panels are generally low maintenance, occasional cleaning is recommended to keep them performing at their best.

Age and Degradation

Solar panels naturally lose efficiency over time, typically around 0.5% per year. Most manufacturers guarantee at least 80% of their original performance after 25 years.

Conclusion

By understanding what really affects solar panel efficiency, you can make smarter decisions when designing and maintaining your system. Proper orientation, avoiding shading, and choosing panels with strong temperature performance will ensure you get the most from your investment.