REDARC solar panels will perform at their peak with the panel face angled directly towards the sun.
In practice this is not always achievable, so REDARC recommend having your panels face NORTH at an angle of between 20° and 40° from the ground.
This will ensure the best total output from your panel across the course of the day, no matter what season.
In Australia, the sun is almost always in the NORTH half of our sky (Darwin and other locations at the same or higher latitude sometimes experience the sun in the SOUTHERN half of the sky).
As such facing your panel NORTH ensures the best angle to the sun for a fixed panel across the course of the day.