Calculate the safe number of PV modules in series using panel voltage, temperature coefficients, inverter maximum DC voltage and MPPT voltage range.
☀️ Field Rule: Check both ends: cold weather Voc must stay below inverter max DC voltage, and hot weather Vmp must stay inside the MPPT range.
🔆 PV String → MPPT / Inverter
Panel Voc at STC
Panel Vmp at STC
Panel Imp / String Current
Panel Power
Voc Temp Coefficient
Vmp Temp Coefficient
Lowest Cell Temperature
Highest Cell Temperature
Inverter Max DC Voltage
MPPT Min Voltage
MPPT Max Voltage
Strings in Parallel Optional
Use the panel datasheet values at STC. Temperature coefficients are usually negative. If only one voltage coefficient is shown, use it for both Voc and Vmp as an estimate.
Vmp hot = Vmp × [1 + coef × (Tmax - 25) / 100] String Vmp = Vmp hot × panels in series
Series Range
Max series = floor(inverter max DC / cold Voc) Min series = ceil(MPPT min / hot Vmp)
Array Power
String power = panel watts × series count Array power = string power × parallel strings
📋 Quick Reference
Critical Limits
Cold conditionVoc rises
Hot conditionVmp drops
Never exceedMax DC V
Typical Inputs
Voc coefficientnegative
STC temp25°C
MPPT rangeinverter data
String Current
Series currentsame as panel
Parallel currentadds
Fuse checkrequired
📚 Engineering Notes
Cold Voc is the safety limitAt low temperature, module Voc increases. The cold-corrected string open-circuit voltage must not exceed inverter maximum DC input voltage.
Hot Vmp affects MPPT operationAt high cell temperature, Vmp drops. If the string Vmp falls below MPPT minimum voltage, the inverter may not track efficiently.
Cell temperature is not always ambientPanel cell temperature can be much hotter than ambient in full sun. Use conservative temperature assumptions for field design.
Check cable and protection tooAfter string sizing, check DC cable voltage drop, string fuse, isolator rating, inverter input current and local code requirements.
What is a Solar String Sizing Calculator?
A solar string sizing calculator helps determine how many PV modules can be connected in series for an inverter or MPPT charge controller. It checks cold-weather open-circuit voltage, hot-weather operating voltage, MPPT voltage range and inverter maximum DC voltage.
Why cold Voc matters in PV string design
Solar panel open-circuit voltage increases when module temperature drops. If too many panels are connected in series, the cold string Voc can exceed the inverter maximum DC voltage. This is one of the most important checks in PV string sizing.
Why hot Vmp matters for MPPT range
PV module Vmp decreases at high cell temperature. A string that looks fine at STC may fall below the inverter MPPT minimum voltage on hot days. This calculator estimates the minimum and maximum safe panel count based on those temperature effects.
Related solar design workflow
Use this page with a solar panel series and parallel calculator, MPPT charge controller calculator, solar battery bank calculator, PV wire size calculator, voltage drop calculator and solar fuse or breaker size calculator to complete a practical solar design workflow.
❓ Frequently Asked Questions
The maximum number is limited by cold-corrected panel Voc and the inverter maximum DC voltage. This calculator gives the maximum safe series count.
Solar cell voltage has a negative temperature coefficient, so voltage rises when temperature falls below STC temperature.
For Vmp hot checks, cell temperature is more relevant and can be much higher than ambient. For cold Voc checks, use the lowest expected module/cell temperature or a conservative local design value.