Real energy output is just one of many possible ways of measuring PV, but it’s even less predictable than number of panels. Fixed installations produce less power per year than 1 or 2 axis tracking etc. Different locations mean different amounts of transmission losses etc.

But even the best model is going to get blindsided by politics. Europe would have been well severed by massively investing over the summer in PV to reduce it’s dependence on Russian natural gas. They didn’t do so but I was very much expecting a push for the fastest to install alternative to natural gas turbines which is PV.