Solar String Calculator

Panel voltage and temperature move in opposite directions for standard crystalline silicon panels — datasheets specify a negative temperature coefficient for Voc, meaning voltage rises as the panel cools below its 25°C rated test condition and falls as it heats up in direct sun. This is why solar installers in cold climates have to size strings more conservatively than installers in consistently warm climates, even when using the exact same panel and inverter.

A panel's datasheet Voc is measured at a 25°C standard test condition, and real Voc climbs meaningfully higher than that rating on a cold morning — often by 10% or more in genuinely cold climates. A string sized using the uncorrected rated Voc can appear safely under an inverter's maximum DC voltage limit on paper while actually exceeding that limit in real cold-weather conditions, which risks equipment damage and is exactly the failure mode proper temperature-corrected string sizing is meant to prevent.

The inverter's maximum power point tracker (MPPT) only operates correctly within a specific voltage window, so a string with too few panels produces a voltage below that window's floor and won't track properly, while too many panels risks exceeding either the MPPT's ceiling or the inverter's absolute maximum voltage rating. The minimum and maximum figures together define the safe and functional range your actual string design needs to fall within.

Panels wired in series (within one string) add their voltages together while current stays the same, but strings wired in parallel to each other add their currents together while voltage stays the same — so the two configurations are limited by entirely different inverter specifications. Max parallel strings is governed by the inverter's maximum DC input current divided by each individual string's current output, independent of the voltage constraints that determine panels per string.