Our house is not exactly small, and optimistically you could fit 10 PV panels on the roof. At least according to the quote I received, but having scouted installations in the nearby places, 8 might be more realistic. (Shape of the roof is a factor.)
Assuming energy prices overall grow as they have over the past decade, it would take 12-15 years to break even on the installation cost. That's with 10 panels. With 8, add a couple of years. And assume there will be no additional maintenance or replacement costs to consider.
So, at least in the UK: unless you are wealthy enough to have a large house with a sufficiently large roof, PV installations are not yet financially viable. It should be better in the rural regions where houses tend to be larger. With more installation surface area available, the marginal cost of each PV panel goes down and the marginal benefit of its energy production goes up.
Hence, in the UK, for a single-family dwelling, a roof with space for 14 panels should be enough to make the installation viable. A house with that much roof surface, at least near us, starts from approximately £700k.
The UK has a lot of cloud cover so I do wonder if we should stick with wind power which is doing really well with the off shore installations.
Plus nuclear... For the rare times the wind doesn't blow.
We just don't get that much sunlight throughout the year to start with.
The unaffordability of UK property is a separate question.
I’m facing almost directly south without any shade from trees.
A special historical example: https://en.wikipedia.org/wiki/Chancel_repair_liability