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PV String Designer

Panels per string, checked against MPPT limits.

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The PV string designer checks panels per string against the inverter's MPPT window, maximum PV voltage and current limits, including the rise in open-circuit voltage on a cold morning. It warns before a string configuration can damage the inverter.

How the PV String Designer works

  1. Enter the panel data

    Use the datasheet values for Voc, Vmp, Imp, Isc and wattage, plus the Voc temperature coefficient. Do not use the marketing wattage alone.

  2. Enter the inverter limits

    Record maximum PV voltage, MPPT minimum and maximum voltage, maximum operating current and, separately, maximum short-circuit current.

  3. Set the string layout

    Choose panels per string and number of strings. The tool reports cold-condition string voltage, operating voltage, per-MPPT current and any limit breach.

Worked example

Eight 580 W panels per string

Voc 51.5 V, Vmp 43.2 V, Imp 13.43 A and a −0.3%/°C coefficient at −10°C, on an inverter with a 500 V maximum and a 125–425 V MPPT window.

  • 412 V at standard test conditions
  • 455 V at −10°C, inside the 500 V limit
  • 345.6 V operating voltage, inside the MPPT window
  • 13.43 A per MPPT with two strings on two trackers

Assumptions and limits

  • Panel values are at standard test conditions (1,000 W/m², 25°C). Cold voltage rise is calculated from the temperature coefficient you enter.
  • Shading, soiling, mismatch and cable loss are not modelled here. Use the protection and cable tool for conductor sizing.
  • Confirm connector ratings and the inverter's separate Isc limit. Operating current and short-circuit current are different limits.

Frequently asked questions

How many panels should go in a string?

The maximum string size depends on panel Voc, temperature-adjusted voltage and the inverter's maximum PV voltage. The designer checks the configuration against those limits.

What happens if the string voltage is too high?

The tool shows a warning when the calculated string voltage exceeds the inverter's maximum PV input voltage, which can damage the inverter.

Does the tool check MPPT current?

Yes. It compares string and array current with the MPPT input limit and flags configurations that exceed it.

Related tools

Last updated 17 October 2026Maintained by Mishka Energy.

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