Solar panels - what do I need to know?

[janewilliams20]

We've had a few leaflets, and now a phone call, suggesting that solar power might be a Very Good Idea, and while it's quite a big investment, it does look like an ecologically good idea, quite apart from the financial side. We will have a surveyor visiting us on Thursday to see what's what and what could be done.
The firm in question are these people, and they tell me their panels are made in the UK, and designed for UK weather.

I'm sure my eco-minded friends have already done the necessary research and can tell me all the traps, pitfalls, and questions to ask - right?