About the String Sizing
String sizing sets how many solar modules connect in series per string so that the string voltage always stays within the inverter's MPPT operating window and never exceeds its maximum input voltage — across the full temperature range at your site.
Formula
Max modules/string = V_dc,max ÷ V_oc(at T_min)
- V_dc,max
- Inverter maximum DC input voltage (V)
- V_oc(T_min)
- Module open-circuit voltage at the coldest expected cell temperature (V) — Voc rises as temperature falls
How to calculate it
- 1Get the module Voc, Vmp and the temperature coefficient of voltage (β, %/°C) from the datasheet.
- 2Correct Voc up to the minimum site temperature (cold raises voltage — this sets the maximum series count).
- 3Correct Vmp down to the maximum cell temperature (hot lowers voltage — this sets the minimum series count to stay in the MPPT window).
- 4Choose a series count between the min and max that also respects the inverter's maximum string current.
Worked example
With a 1000 V inverter and modules at 49.5 V Voc corrected to ~54 V at cold-morning temperatures, the maximum is 1000 ÷ 54 ≈ 18 modules per string; the minimum is set by the MPPT lower bound at peak summer temperature.
What you can calculate
- Temp-corrected Voc
- MPPT window
- Series/parallel
- Safety margin
Standards & references
Frequently asked questions
Why does temperature matter for string sizing?
Solar module voltage rises as temperature falls. A string sized only for warm conditions can exceed the inverter's maximum input voltage on a cold, sunny morning — damaging the inverter or tripping it. Sizing must use the coldest expected temperature for the maximum count.
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