Solar String Sizing Calculator

Inputs

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PV module STC nameplate power.
W
Open-circuit voltage at STC from the module datasheet.
V
Voltage at maximum power at STC from the module datasheet.
V
Module short-circuit current used for input-current screening.
A
Module operating current at maximum power.
A
Signed percent per C from the datasheet. Negative values make Voc rise in cold weather.
%/C
Signed percent per C used for MPPT operating-voltage checks.
%/C
Lowest expected ambient/module temperature for open-circuit voltage checking.
C
High operating cell temperature used for low Vmp and MPPT start checks.
C
Absolute maximum DC voltage from the inverter or charge-controller datasheet.
V
Minimum MPPT operating voltage.
V
Maximum MPPT operating voltage.
V
Startup voltage requirement, if higher than the MPPT minimum.
V
Maximum input current for the checked MPPT channel.
A
Modules wired in series per string.
modules
Number of parallel strings on the checked MPPT input.
strings
Nominal inverter AC output power used for DC:AC ratio.
W
Planning ratio used to estimate target module count.
x

Results

Default result
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Minimum modules in series (N_min)
6 modules
Pass

higher of hot MPPT minimum and startup voltage checks

Also computed

Maximum modules in series (N_max) Pass 13 modules

lower of cold Voc and cold MPPT-high checks

Planned series margin (M_s) Pass 3 modules

closest module-count margin to a voltage limit

Cold string Voc (Voc_cold) Pass 451.6 V

must stay below absolute maximum DC voltage

Hot string Vmp (Vmp_hot) 286.5 V

used for MPPT low/start checks

Cold string Vmp (Vmp_cold) 381.7 V

used for MPPT high operating check

Array DC power on MPPT (P_dc) 8,000 W

Method notes 3 notes
  • Cold Voc uses the signed module Voc temperature coefficient at the entered cold design temperature.
  • Hot Vmp uses the signed Vmp coefficient at the entered hot cell temperature for MPPT minimum and startup checks.
  • This is a string voltage/current screen only. Final PV design must verify product datasheets, conductor ampacity, voltage drop, overcurrent protection, rapid shutdown, grounding, disconnects, listings, adopted code and permits.

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