UK homes use far less electric than the US, and air conditioning is almost unheard of.

Commonest UK size for solar is currently 3-4kWp, which is plenty for household independence, and above 5 or 6 rare. Earlier systems were smaller as panels were costly. I think somewhere around 5 is the point an installation is considered commercial rather than domestic making larger even less attractive.

Exorbitant or not it pays based on UK electric prices and feed in tariffs.