Australia is also 4,000km wide. A time difference of 2 - 3 hours. This adds a few more hours of Solar with long distance transmission.

As you say, Australia is very big. Big sections of it are also, as a result, empty. The coast-to-coast "long distance transmission" is not in fact a thing in Australia.

China has long distance HV transmission, but it's crazy expensive and they built it because most of China's people live near its coast but most of its solar power is in the interior so the power needs to be moved.

Australia is exceptional for having a lot of humans who live somewhere that's incredibly sunny. The whole place is sunny. It'll vary from place to place whether that's only "Southern Spain" sunny or full-on "Middle of the Sahara Desert" sunny, but it's all very sunny indeed, if you were inventing a country to buy solar panels Australia would be that country.