UK its partly roof size/shape limiting the amount of panels you can get in the optimum location, partly the weather, and partly install costs.
If its going to take me 8 years at least to pay back vs. not having it I am not going to bother. Some people got lucky with lifetime buy back rates for the panels to the grid so they made bank of theirs with 50p a kwh ( and electric was around 24p a kwh to buy from the grid) but those rates got cut to like 4p a kwh, when even a cheap EV tarrif is like 9p a kwh
There are some finance deals available from the likes of Eon but its hardly high end gear, which I think is needed to make the most of the UK roofs and UK sun. Time you start paying interest on it, it becomes an even worse deal.
I would save more money by just having a battery installed and charging it on my EV tarrif overnight.