Choosing solar panels: look past the label at these 5 specs

The biggest number on a panel datasheet is the wattage — yet two 550 W panels can perform very differently in the field. The specs that should drive your decision are printed smaller.

1. Efficiency

Efficiency decides how much power you get from a limited roof. On tight roofs, one percentage point of efficiency compounds into a real capacity difference.

2. Temperature coefficient

Panels lose power as they heat up. A lower coefficient (e.g. −0.29 %/°C) means measurably more production through a Turkish summer.

3. Warranty structure

Product and performance warranties are different things. 12–15 years product and 25–30 years performance is a good baseline today — and a local warranty counterpart matters as much as the number.

4. Annual degradation

First-year and subsequent annual power loss rates shape total output over 25 years. Low degradation quietly earns money in the long run.

5. Bankability

The manufacturer's financial strength is what a 25-year warranty is actually worth. Tier-1 lists aren't sufficient on their own, but they are a sensible first filter.