And still they're rarely installed. I knew more people in the 90s who were ripping them out or leaving them dry (they were popular for pool heating in some areas) than installing them.
I've considered it several times, and it came down to it being too much work.
PV is much simpler, and if it stops working you can just ignore it.
I once designed a solar swimming pool heater that had no moving parts and required no maintenance. I never built it because I didn't have a pool.
