If all goes according to plan (hahaha, this is 2021!), we should be moving shortly to a small, 7-year-old house that has solar panels on the roof. It's only about a 3mx3m area (I'm guessing), so not huge. They're on a more or less South-facing roof in Gloucestershire, so (very roughly) what kind of generation will that produce?
Also, what should I be looking for in terms of maintenance or potential costs?

I just read an article on "The Net Zero House" in my monthly "The Chemical Engineer" magazine and for solar power (if that's what you have and they are not solar heating panels) it assumes an average panel area of 1.6 m² which can generate 300 W, so assuming that you have 6 panels and you receive the UK average of 4.5 hours per day, that's 6 x 300 x 4.5 x 365 / 1000 = around 3000 kWh per year. So you might export power during the day, and import at night, unless you have batteries to store the power?

We've got solar panels and we get on average 3200kw a year. That's a 3.5kw array of 14 panels (250watt each).

South facing roof too.

It was an 8 year payback based on feed in tarrif at the time, so was well worth doing.

Our surplus power during the day is fed into the hot water via immersion. So it all helps.

That works out to be 2.5 hours per day of sunlight in not-so-sunny sunny South Wales

Well I assume you mean at full capacity. They rarely get up to 3.5kw.

In summer we can get 25kwh a day. But obviously much lower in winter. So 2.5kwh a day on average could be right.

Thanks Gents, that's good info.

Ah - this thread has got me thinking about the utterly disastrous Green Homes Grant!

I applied in October as I already had a valid quote for an air source heat pump from a registered supplier - happy days.

As of today - what, 5 months later, I’ve had only a couple of nonsense emails from the scheme. When I’ve phoned, they’ve said all is OK (very comprehensive quote) and I should hear shortly. Nothing.

A month or so ago my supplier contacted me to say they’d give me a discount if I didn’t go with the scheme. Of 30 customers, only 3 had received their voucher. The result was that the supplier’s work had completely dried up and they were about to put their people on furlough!

The scheme has achieved precisely the opposite of what it set out to do: stopped people who would have been investing in green energy sources from doing so and killed the flow of work for previously busy companies. In the meantime, I’ve spent £1000 on heating oil and £250 on boiler repairs. The winter is nearly over. What a total mess!

That's a very depressing story, MRS. But entirely believable.