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Cold mornings raise Voc; hot noons cut power

Solar PV physics · Intermediate · about 12 minutes · part of Solar PV Systems

Voltage comes from the cells’ temperature, not the sun: Voc falls about 0.3 % for every degree the cells warm, and in full sun they run 20–30 °C over the air. A 10 °C dawn gives the highest Voc a string will ever show, and that is the number a controller must survive. A 35 °C noon gives cells near 60 °C and a tenth less power than the datasheet.

Cold mornings raise Voc; hot noons cut power: the circuit on the simulator's bench

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How it works

Ambient 10 °C, full sun: cells at 25 °C (NOCT 45 °C puts them (45 − 20)/800 × G over the air). Voc = 49.5 V × (1 + -0.3/100 × (25 − 25)) = 0.0 V; Pmax = 400 W × (1 + -0.4/100 × ΔT) ≈ 0 W.

Change the ambient in ⚙ settings (site conditions) and watch Voc move the other way from the temperature. The record-low field is what the string sizing uses.

Try it on the bench

  1. ⚙ settings → ambient 35 °C: cells near 60 °C, Voc drops about 5 V, power about 50 W.
  2. Ambient 0 °C (a Baguio dawn): Voc climbs past 52 V. Five of these in series would exceed 260 V.
  3. Turn the weather off: everything returns to the datasheet’s 25 °C.

Parts on the bench

In the course

Solar PV Systems, module “3 · Irradiance and temperature”.

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