Panel Technology

Temperature Coefficient

Temperature coefficient measures how much a solar panel's power output decreases for every degree Celsius the cell temperature rises above the Standard Test Conditions baseline of 25°C. It is expressed as a percentage per degree, written as %/°C, and is always a negative number because output drops as temperature increases.

A typical PERC panel has a temperature coefficient of around -0.35% to -0.40%/°C. This means that for every degree above 25°C, the panel loses 0.35% to 0.40% of its rated output. On a hot summer day when cell temperatures reach 65°C (40 degrees above STC), a panel with -0.38%/°C would lose roughly 15% of its rated power.

Advanced cell technologies offer better temperature coefficients: HJT panels typically achieve -0.24% to -0.26%/°C, while TOPCon panels range from -0.29% to -0.34%/°C. Over a system's 25-year life in a warm climate, this difference can translate to thousands of kilowatt-hours of additional production.

Temperature coefficient is most impactful in hot climates like the US Southwest, Middle East, and tropical regions. In cooler northern climates, the effect is less pronounced because cell temperatures stay closer to STC more of the time.

When comparing panels for a hot-climate installation, prioritize lower (closer to zero) temperature coefficients. This specification is listed on every panel's technical datasheet.

Frequently Asked Questions

Do solar panels work worse in hot weather?

Yes. All silicon solar panels produce less power as they get hotter. The temperature coefficient tells you exactly how much output drops per degree above 25°C. Panels in hot climates can lose 10-20% of their rated output on the hottest days compared to their STC rating.

What is a good temperature coefficient?

Lower (closer to zero) is better. Standard PERC panels at -0.35%/°C are acceptable. HJT panels at -0.25%/°C are excellent. If you live in a hot climate, the improvement from -0.38% to -0.26% can generate 5-8% more energy annually over the system's lifetime.