I suspect a huge chunk of that is labor costs rather than materials.

Labor costs even more in Australia, yet total systems are installed for about 1/3rd - 1/4th the cost of the US. It’s not labor.

It is labor. It's code. The amount of labor required to do an installation to code in the US is easily 50% more, if not more than that. Australia also has standardized streamlined racking that works on much higher percentage of roofs, the US has a lot more custom construction.

>Labor costs even more in Australia

This is really surprising to hear. Are you sure about that?

Australia's minimum wage is significantly higher than in the US. An adult working as a burger flipper at McDonalds can expect a minimum of $27.81 / hour.

yup. not just the minimum - skilled labor costs are very high too.