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PV String Voltage Calculator

Solar string Voc and Vmp at site temperatures, checked against AS/NZS 5033:2021

How to use
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Photovoltaic string voltages for inverter compatibility and the AS/NZS 5033:2021 voltage limits.

Module Specifications

V

Maximum power voltage at STC, from the datasheet

V

Open circuit voltage at STC, from the datasheet

%/°C

Default -0.3 %/°C

%/°C

Default -0.4 %/°C

Site Conditions

Maximum PV array voltage 1,000 V

°C

Coldest recorded at the site (default -10 °C)

°C

Hottest recorded at the site (default 60 °C)

modules

Number of modules connected in series

String Voltages

Enter the module voltages and string length to see the string voltages.

How it's calculated

Temperature-corrected string voltage

Module voltages are rated at STC (25 °C cell temperature). The string is checked at the site's coldest and hottest temperatures.

String voltage at STC

modules in series

Highest voltage, coldest morning

temperature coefficient of Voc, %/°C (negative)
lowest site temperature, °C

Lowest operating voltage, hottest day

temperature coefficient of Vmp (or Pmax), %/°C
highest design temperature, °C

Limit check

Also keep under the inverter's maximum DC input and above its MPPT minimum.

Standards referenced

  • AS/NZS 5033:2021 (installation and safety requirements for PV arrays), maximum PV array voltage
  • Module datasheet values at STC (1000 W/m², 25 °C cell temperature)

Worked example: 14 modules at -5 °C

A domestic string of 14 modules with Voc 49.5 V, Vmp 41.6 V, αVoc -0.27 %/°C and αVmp -0.35 %/°C, on a site from -5 °C to 70 °C.

  1. 1. Voc at STC
  2. 2. Voc at Tmin
  3. 3. Vmp at STC
  4. 4. Vmp at Tmax

The coldest-morning Voc of 749.1 V is under the 1000 V domestic limit. Check the inverter too: its maximum DC input must exceed 749.1 V and its MPPT window must reach down to 490.7 V.

Frequently Asked Questions

String Voltage Questions Answered

Why does PV string voltage go up in cold weather?

A module's open-circuit voltage (Voc) rises as the cells get colder. The temperature coefficient of Voc is negative (for example -0.3 %/°C), so below 25°C the voltage climbs: Voc(min temp) = Voc(STC) × (1 + coefficient/100 × (Tmin - 25)). The coldest morning sets the highest string voltage.

What voltage limit applies to a PV string in Australia?

The calculator checks the string against the AS/NZS 5033:2021 maximum PV array voltage: 1000 V for domestic installations and 1500 V for commercial ones. The inverter's own maximum DC input voltage may be lower, so check it too.

Which temperatures should I enter?

Use the lowest ambient temperature expected at the site for the highest Voc, and the highest temperature you design for to get the lowest Vmp, which must stay above the inverter's MPPT minimum.

Where do I find Voc, Vmp and the temperature coefficients?

On the module datasheet: Voc and Vmp at STC (1000 W/m², 25°C), and the temperature coefficients of Voc and Pmax or Vmp, usually in %/°C.

Is the string voltage calculator free?

Yes. Anyone can use it without an account. A free account lets you save the result to a project and download the PDF report.

Reviewed by Ahmed Tayeh, electrical engineer at CableHero. The calculator is a design aid: the designer remains responsible for checking the installation against the standards.

Guides

Learn the method

How to use this calculator

Work out the string's Voc on the coldest morning and Vmp on the hottest day, against the system limit.

Read the guide: How to use the PV string voltage calculator

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