This site https://findenergy.com/solar/ has a lot of interesting information (albeit specifically for the US). Interesting to see that in Arizona, you're almost generating 2x more electricity from solar. Guess it makes sense with England being famous for its rainy weather. A thing to consider, especially when talking at these timescales, is that as more people adopt solar, the less you'll get from selling energy back to the grid. You could probably model it by looking at the rate of adoption over the past decade.