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Over Sizing a solar inverter.

Oversizing is putting more panel power on an inverter than its rated maximum.

For example 6.6kW of panels on a 5kVA inverter.

The reason why this works is because solar panels never make their rated output. Not even close. When the panels are flash tested in the factory it's at a frosty 5°C and with a really bright 1000W per square meter of irradiance. In the real world, its much warmer and less bright and the light is less directly aimed at the cells inside the panel.

Real life conditions result in 25-30% less output than the maximum...even when the sun is perfectly overhead.

So that's why it works. Oversizing pushes the output closer to the inverter upper limit for longer througout the day so you get more power without having to buy a larger and more expensive inverter.

The Clean Energy Regulator allows oversizing by 33.33%. Go beyond that and you lose the $170 or so rebate per panel. Recent changes have allowed oversizing by more than 33.33% as long as a battery is connected to the inverter, but the manufacturer of the inverter doesn't always allow that.

Undersizing an inverter is also possible, but again is limited to no more than 33.55 % of the inverter capcity. So for example a 5kVA inverter can have no less than 3.75kW of panels.