Hot vs cold: What's the ideal temperature for solar panel efficiency?

Sunlight is a solar panel's best friend. But heat, not so much.

The most common number you will see is 77 degrees Fahrenheit. That is 25 degrees Celsius, which is the temperature of the cell when manufacturers rate panels under standard test conditions, alongside irradiance of 1,000 watts per square meter. It's a good indicator, but it's not a magic outdoor temperature at which your roof achieves peak output.

So yeah, cold wins, technically. The efficiency of solar cells is typically higher at lower temperatures because the voltage decreases more than the current increases with temperature. The problem is that efficiency and total electricity production are not the same. A cold panel might generate more power from the same amount of sunlight, but a hot summer day might generate more power because there might be more sunlight.