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Solar panels in series calculator.
Cold weather raises panel voltage. Correct Voc for your coldest night and find how many panels can share one string.
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How many solar panels can you put in series?
Panel voltage rises as temperature falls. The corrected open-circuit voltage is Voc x {1 + [(lowest temperature - 25 °C) x coefficient %/°C / 100]}, and the string voltage is that figure times the panels in series (EC&M, Mike Holt's NEC 690.7 explainer). The string at its coldest must stay at or below the controller's maximum PV voltage, so the maximum series count is the controller limit divided by the cold Voc, rounded down. The same article gives the maximum source circuit current as panel Isc x 125%, shown here for the whole array.
Worked example. A 49.5 V Voc panel with a -0.27 %/°C coefficient at -25 °C: 49.5 x (1 + (-50 x -0.27 / 100)) = 49.5 x 1.135 = 56.2 V. A 150 V controller allows 150 / 56.2 = 2 panels in series.
Frequently asked questions
How many solar panels can I connect in series to an MPPT controller?
Divide the controller's maximum PV voltage by one panel's cold-corrected Voc and round down. Using the default 49.5 V panel at -25 C and a 150 V controller, that is 2.
Why use the coldest temperature?
Panel voltage rises as it gets colder, and it is highest on a cold, sunny morning with a full battery. Exceeding the controller's maximum can destroy it.
Where do I find the Voc temperature coefficient?
On the panel datasheet, often listed as "Temperature coefficient of Voc" in %/C. It is negative.
Series or parallel?
Series adds voltage and keeps current low; parallel adds current. Higher string voltage means thinner cable, within the controller's limit.
Sources
Checked
The voltage and current formulas come from the EC&M article citing NEC 690.7 and 690.8 (2016). Code editions and local rules differ, so check the current NEC and your authority having jurisdiction. The panel values are placeholders. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Planning estimate only. Exceeding a controller's maximum voltage can destroy it and create a fire hazard. Confirm every limit on the datasheets and have the installation inspected to code.