Solar Electrical Rules - Updated December 2025

Minimum number of solar panels per inverter 'string'.

Single phase 5-6kW inverters typically need three or four panels per string (MPPT) minimum.
Three phase inverters usually need 6 panels minimum per string (MPPT).
Insufficient voltage means that the inverter won't be able to start that string up.
This often means the entire inverter will see it as a fault and not start up.

Maximum number of solar panels per string.
All residential installations in Australia are allowed 1000V strings.
Single phase inverters almost never allow anything more than 600V, some as low as 550V
Most 3 phase inverter MPPTs will operate fine with strings around 950V-1000V

If you look at the datasheet of any panel it will show some important numbers...
VOC (open circuit voltage) at STC (Standard Test Conditions).
Coefficient of Voc expressed as a negative value per degree C temperature change (e.g. -0.25%)
In addition to this you need to know what the minimum temperature at first light is where you live.
VOC increases as temperature decreases so you need to factor in local record minimum temperatures.
In Perth it is -2 degree C.

The calculator below does all the mathematics for you...

Solar Panel Maximum Voltage Calculator

Open Circuit Voltage (Voc) at STC

Typically between 20-50V for residential panels

Temperature Coefficient of Voc

%/°C

Usually between -0.2% to -0.4% per °C

Minimum Expected Temperature

°C

Lowest temperature panels will experience

Perth (-2°C)

Sydney (-3°C)

Adelaide (-3°C)

Melbourne (-5°C)

Canberra (-10°C)

Hobart (-2°C)

Brisbane (5°C)

Darwin (10°C)

Number of Panels in String

Total panels connected in series

Maximum String Voltage

474.3 V

This is the maximum expected voltage for your string

Calculation Details

Panel Voc at STC: 39.8 V

Temperature adjustment: +19.1%

Adjusted panel voltage: 47.4 V

Panels in string: 10 panels

Formula: V_max = Voc × [1 + (TempCoeff/100) × (T_min - 25)] × N

Where:

Voc = Open circuit voltage at STC
TempCoeff = Temperature coefficient (%/°C)
T_min = Minimum expected temperature (°C)
N = Number of panels in string
STC temperature = 25°C

Important: Ensure your inverter's maximum DC input voltage is higher than this calculated value with a safety margin. Cold temperatures significantly increase panel voltage, which could damage inverters if not properly accounted for.

Solar4Ever have been selling and installing solar in Perth, WA since 2011. If you want a quote please get in touch.

(08) 9467 9655

or email

This review was written by Andrew MacKeith, Solar4Ever service manager since 2011.