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Engineering Tool

Solar String Sizing Calculator

Work out how many panels can go in series on a string, within the inverter's MPPT window and under the maximum system voltage, using temperature-corrected module voltages.

Sources listedReviewed July 2026Our methodology

Inputs

View result
Datasheet STC value.
Straight off the datasheet. The minus sign is optional; it is read either way.
Use the Vmp coefficient, or derive it only from documented module data. The minus sign is optional.
Use the documented minimum cell design temperature.
Use the documented maximum cell design temperature.

Live result

Edit inputs

Min per string

3modules

Max per string

11modules

Cold Voc / module

53.5V

Hot Vmp / module

35.9V

Max string Voc (cold), limit 600 V

589V

Save or file this result
Key takeaways
  • Cold mornings raise a module's open-circuit voltage, so the coldest expected temperature sets the maximum panels you can safely put in series.
  • Hot afternoons lower the operating (Vmp) voltage, so the hottest expected temperature sets the minimum string length to stay within the inverter's MPPT window.
  • The result is a calculated range of modules per string, an estimate to sanity-check a design, not a substitute for a licensed system designer.

How it works

A module's voltage moves with temperature. The colder it gets, the higher the open-circuit voltage (Voc) climbs, so the maximum string length is set by the coldest moment, when Voc peaks:

Voc(cold) = Voc × (1 + βVoc × (T_cold − 25)), where βVoc is the module's documented Voc temperature coefficient (negative, in %/°C).

  • Maximum modulesis the largest count whose cold-temperature string voltage stays under both the inverter's maximum system voltage and its MPPT ceiling: floor(V_max ÷ Voc(cold)).
  • Minimum moduleskeeps the hot-day operating voltage (Vmp) above the inverter's MPPT floor: ceil(MPPT_min ÷ Vmp(hot)).

Vmp uses its own documented temperature coefficient for the MPPT checks; the tool no longer substitutes the Voc coefficient. Enter the applicable equipment limits and design temperatures, then confirm the final design against AS/NZS 5033 and the exact product documentation with a licensed system designer.

Estimates only: for guidance, not a quote or a compliance certificate. Verify against the current AS/NZS standards and a licensed design. The maths runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately save the result.

Source ledger3 sources

Continue this work

AS/NZS 5033Standard

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Frequently asked

Is this calculator free to use?
Yes. The string sizing calculator is free and needs no sign-up. It runs entirely in your browser.
Is my data stored or sent anywhere?
The calculation runs in your browser. Nothing is sent to Wattbench unless you sign in and deliberately select Save result.
Which temperature coefficient does it use?
It uses the entered Voc coefficient for open-circuit voltage and a separate entered Vmp coefficient for MPPT operating voltage. Confirm both against documented module data. The result is an estimate, not a substitute for a licensed designer.
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