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How to Read a Solar Panel Spec Sheet
Power, efficiency, temperature coefficient, warranty — how to compare solar panels like a pro by reading the spec sheet correctly.
WaterFuelAndSolarEnergy.com Editorial Team Updated January 2025 8 min read
A panel spec sheet looks dense, but a few numbers tell you almost everything: maximum power (W), module efficiency, temperature coefficient, degradation rate, and the product/performance warranty terms.
The numbers that matter
Key spec-sheet terms
| Term | What it tells you | Better if |
|---|---|---|
| Max power (Wp) | Rated output under test conditions | Higher per panel is usually better |
| Module efficiency (%) | Area needed for a given power | Higher uses less roof space |
| Temperature coefficient | Output loss per °C above 25°C | Lower (closer to 0) loses less in heat |
| Degradation (%/yr) | Annual output decline | Lower keeps more output over time |
| Warranty (product/perf) | Coverage on faults vs guaranteed output | Longer product + strong performance |
What is the temperature coefficient?
It’s how much power a panel loses for each degree above 25°C. A coefficient of -0.34%/°C means it loses 0.34% output per extra degree — hot-roof panels run hot, so a low coefficient matters in warm climates.