Also worth pointing out that much of the US is below 49 degrees latitude. Which is south of most of Europe. Washington DC and San Francisco are at a similar latitude (38) as Melbourne (-37). Most of the US is perfectly situated for getting pretty decent solar power around the year. Yes it gets cloudy sometimes. It's usually not continent wide. You can compensate with cables and batteries. The US is far behind because of policy and their local energy monopolists blocking progress. Not because of anything to do with the weather or geography.
Prices have a lot to do with scarcity. Which with monopolists has more to do with the lack of a free market than with a scarcity of resources. Installing solar is about 3-5x more as expensive in the US as in Australia. The permitting process in the US is more expensive than the total cost of buying and installing in Australia. That's a policy problem in the US. All the hand wringing around that topic isn't helping a lot. A bit of pragmatism could improve things a lot and probably very quickly. Australia is showing how to do that. And yes, they have rain there too and you can go skiing pretty close to Melbourne. That isn't stopping them.