To my knowledge, they don't need much maintaince - even less than wind (no moving parts), only the replacement of batteries if present. In Germany, they are usually expected to last 20 years - that is, price calculations run roughly like:

(construction & installation costs) / (20 x (expected yearly production) x (feed-in tariff))

(See some data on this in my upcoming reply to Jérôme.)

As far as I know, the only significant problem with time is chemical changes in the semiconductor, which bring down the efficiency over time.

_{*Lunatic*, n.
One whose delusions are out of fashion.}