PV string voltage and current fundamentals, how temperature coefficient drives cold-weather Voc overvoltage risk, maximum and minimum string length calculations, string-to-inverter matching, and combiner box and fusing basics.
String sizing is the calculation that keeps a PV string's voltage inside an inverter's rated DC input window across the full range of temperatures a site will ever see — too long a string risks overvoltage damage on the coldest morning of the year, too short a string falls out of the inverter's MPPT tracking window on the hottest afternoon. This module works through the temperature-coefficient math behind both limits, a fully worked maximum-string-length example, and the combiner box and fusing rules — NEC 690.9's three-or-more-parallel-strings fusing threshold in particular — that follow directly from it.
By the end of this module you should be able to calculate a maximum allowable string length from a module's Voc temperature coefficient and a site's record low temperature, explain why the minimum-string check is governed by an entirely different variable (hot-temperature Vmp, not cold-temperature Voc), and state exactly when NEC 690.9 requires per-string fusing — content Module 11's inverter selection and Module 15's installation practice both build directly on.