The place i've been to used compressed air for most of the time. reducing the frequency of water washes
It would use far less water than crops.
You can clean them with electrostatic force. Also, you can jut flip the panel over. You definitely don't need to use water regularly and you certainly don't need it to be anything but within a reasonable PH.
Maybe blowing air would work.
Especially if you do it regularly so the dust blows off before it gets stuck.
I discovered that compressed air works great for cleaning my car interior. Have to be careful to hold your breath, though, don't want to breath in the gunk.