3.8kW of bog-standard polycrystalline cells, installed by a local company in less than a day. £5500, five years ago; I receive over £500 in feed-in-tarriffs every year. And this is at 56 degrees north.

(I never considered doing it myself - a dangerous hassle, and in any case the FIT scheme required an approved installer and a <4kW scheme. Storage or offgrid would be completely infeasible, it's too seasonal.)