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Solar string size calculator

How many panels in series for your inverter: cold Voc and hot Vmp checked.

Try the circuit in the labBuild it on the simulator's bench and measure it.

How it is worked out

A panel's voltage rises in the cold: cold Voc = Voc × (1 + coefficient × (Tmin − 25)). With −0.27 %/°C at 15 °C a 49.9 V panel reaches 51.2 V. The string's cold Voc must stay under the inverter's maximum PV voltage, or the inverter can be damaged.

Voltage falls in the heat: on a hot roof the cells run near 70 °C, and Vmp drops about 12 %. The string's hot Vmp must stay above the bottom of the MPPT range, or the inverter stops harvesting in the middle of the day.

This uses the Voc coefficient for Vmp too (Vmp's coefficient is a little larger, so leave one panel of margin at the low end). Panel data is on the label on the back or in the datasheet.

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