I just saw this data online about installed solar around the world and plotted it out.
China is well ahead with total installed Solar, followed by Japan, Germany and USA, which are all about the same!
The numbers change a lot when population is taken into account as shown in the graph below. Australia and Germany are well in the lead, then Japan and Italy at the same level.
The US is surprisingly low, at only 25% of the top 2 numbers and came in 6th on the list, behind the United Kingdom!
With much lower solar energy per square foot in high latitude countries like the UK and Germany, it must be a lot more expensive to install Solar Power in these northern countries than in the US.
Also they have much more cloud coverage through the year and snow cover in winter!
So they must have much better incentives for installing solar! Or maybe their fossil fuel energy costs are a lot higher?