Why solar panels produce more in cold than in heat

Perfect Andalusia day at 104 °F ambient: panel is at 140-150 °F operating and loses 12-15% of rated power. Cold January day at 41 °F with sun: panel at 60 °F and produces 105-108% of rated power. The paradox explained.

Pmax temperature coefficient

Each panel has a datasheet value: 'Pmax temperature coefficient' typically -0.30%/°C to -0.40%/°C. Means for each degree above 77 °F reference, you lose that percent of power.

Concrete calculation

410 W panel with -0.35%/°C coefficient. At 140 °F (60 °C): 410 × (1 - 0.0035 × (60-25)) = 410 × 0.8775 = 360 W. Loss: 50 W (12%). At 60 °F (15 °C): 410 × 1.035 = 424 W. Gain: 14 W.

Why it happens: semiconductor physics

More temperature = more atomic vibration = more random collisions between electrons = fewer reach the useful circuit. Conversion efficiency drops. In cold: less vibration, more useful electrons, better performance.

When it happens

Day with full sun (air heat doesn't matter if cloudy). Panel ventilated from behind (not glued to roof). Clean panel. Wind helps cool: coastal breeze zones produce more than inland still air.

Panel types and heat tolerance

PERC: -0.35%/°C. TOPCon: -0.30%/°C (better in heat). HJT: -0.26%/°C (best). If you live in Texas, Arizona or Dubai, TOPCon or HJT pays its premium with higher annual production.

Best month of year is NOT August

In Spain and USA, the month with best irradiance/temperature ratio is typically April or May. Lots of sun, long days, mild temps. Real production can exceed July in many installs.

Combine with snow albedo effect.