PV String Sizing Calculator
Project:
Date:
By:
Module
Model:
-- Select a module --
Inverter
Model:
-- Select an inverter --
Site Conditions
Min Ambient T (°C):
Max Ambient T (°C):
Mount Type:
Rooftop (flush)
Rooftop (rack)
Ground (open rack)
Carport / awning
Cell Adder (°C):
Max Cell T (°C):
Vmp Margin (× startup):
String Configuration
Str
MPPT Channel
Mods/Str
Par
Voc max (V)
Vmp min (V)
Isc tot (A)
Imp tot (A)
W/str
V
Vmp
Isc
Imp
Result
Design Alerts:
Select an inverter and configure strings.
System Summary
Total Modules
0
kW DC
0.000
kW AC
0.000
DC/AC Ratio
-
% of Max DC
-
Status
-
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Calculation Basis
Voc_max = Voc_STC × [1 + (B_Voc / 100) × (T_min - 25)] × modules per string. Per NEC 690.7 correction for minimum ambient.
Vmp_min = Vmp_STC × [1 + (B_Vmp / 100) × (T_cell_max - 25)] × modules per string. T_cell_max = max ambient + mount adder.
Isc_tot = Isc_STC × [1 + (a_Isc / 100) × (T_max - 25)] × strings in parallel. For NEC 690.8(A)(1) wire and OCPD sizing, multiply by 1.25 separately.
Imp_tot = Imp_STC × strings in parallel. Conservative for MPPT current check.
Per-string checks: OK (green) = comfortable, WARN (amber) = within 5% of limit, FAIL (red) = over limit, "?" = channel not in library.
Result priority: FAIL > DUP (duplicate channel) > "?" (missing channel) > WARN (margin tight) > PASS.
Paralleled MPPTs (Tesla PW3 MPPT1+2, MPPT5+6) appear as separate channel entries with doubled current limits when added to the inverter library.
B_Voc and B_Vmp should be NEGATIVE. a_Isc should be POSITIVE. Sign errors in the module library silently invert the correction.