Dave Paine
I have had a domestic hot water system in use since mid 80's.

2 @ 4ft x 8ft panels and an 80 gal tank which pre-heats the water going into the normal 80 gal electrically heated tank.

So far the only maintenance has been to replace the pump (I think the capacitor went bad) and the propylene glycol fluid (during a really cold winter without sun for many days).

I live in eastern PA and even in mid January with a sunny day we can get the 80 gal pre-heater tank up to 135 deg F.

I have no idea how long the photo-voltaic panels last. I hope the efficiency improves and the price becomes reasonable.