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A string against the controller: the cold-morning Voc

Solar PV physics · Advanced · about 15 minutes · part of Solar PV Systems

In series the voltages add, so five 100 W modules make a 112 V string at 25 °C, and 119 V at a 10 °C dawn. A controller rated for 100 V input sees that once, at sunrise, and dies before breakfast. The string-sizing rule: the array’s Voc at the site’s record low must stay under the controller’s maximum input, with margin.

A string against the controller: the cold-morning Voc: the circuit on the simulator's bench

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How it works

String of 5: Voc 0 V now, 0 V at the record low of 10 °C, against the controller's 100 V input. Within the limit.

The inspector of any module shows its string's roll-up and this warning; the Pillar 3 design-rule check will fail a design on it.

Try it on the bench

  1. Select Panel 5: the string roll-up shows Voc at 10 °C over the controller’s 100 V, in red.
  2. Delete Panel 5 and wire Panel 4 to the controller: four in series stay under 100 V with margin.
  3. Set the record low to 0 °C in ⚙ settings: even four is marginal. Sizing uses the site, not the day.

Parts on the bench

In the course

Solar PV Systems, module “4 · Array configuration and the string window”.

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