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.

Evidence-first · every figure sourcedReviewed July 2026Our methodology

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 recommended range of modules per string — an estimate to sanity-check a design, not a substitute for a licensed system designer.

Module Voc (open-circuit)VDatasheet STC value.Module Vmp (at max power)VVoc temperature coefficient%/°CDatasheets show this negative — enter the number, e.g. 0.27.Coldest cell temperature°CLocal record low is a good guide.Hottest cell temperature°CCells run hotter than air — often 30–40°C above ambient in sun.Inverter max system voltageVMPPT minimum voltageVMPPT maximum voltageV

Min per string

3modules

Max per string

11modules

Cold Voc / module

53.5V

Hot Vmp / module

36.5V

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 + β × (T_cold − 25)), where β is the temperature coefficient of Voc (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)).

This tool applies the Voc coefficient to both Voc and Vmp as a conservative approximation; for exact MPPT tracking, consult the datasheet's Vmp or Pmax coefficient. Maximum-voltage limits follow AS/NZS 5033 in Australia. Always confirm a final design with a licensed system designer.

Estimates only — for guidance, not a quote or engineering specification. Nothing you enter is stored or sent anywhere; the maths runs entirely in your browser.

Good to know

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?: No. The calculator runs in your browser and stores nothing. The figures you enter are not saved or sent anywhere.
Which temperature coefficient does it use?: It applies the module's temperature coefficient of Voc to both the open-circuit and operating voltages — a conservative, common approximation. For precise MPPT tracking, also check the datasheet's Vmp or Pmax coefficient. The result is an estimate, not a substitute for a licensed designer.

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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 + β × (T_cold − 25)), where β is the temperature coefficient of Voc (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)).

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?

No. The calculator runs in your browser and stores nothing. The figures you enter are not saved or sent anywhere.

Which temperature coefficient does it use?

It applies the module's temperature coefficient of Voc to both the open-circuit and operating voltages — a conservative, common approximation. For precise MPPT tracking, also check the datasheet's Vmp or Pmax coefficient. The result is an estimate, not a substitute for a licensed designer.