Earlier quoted context omitted.
> I tell them they will break even in a few years Then why don't more companies offer to become your electricity provider and install the solar panels for free? They could say "We promise that your energy bills will be cheaper this year than last year (as long as you don't use more energy), and within a few years you'll own the panels and can switch to a different electricity provider."
One reason is issues with property ownership. In the U.K. a company could do this but if the original customers were to see the house, they’d have no legal means of compelling the new owners to take up the arrangement. At least that’s what I understand.
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.