I don’t do windows but my robot does. At least that’s what the WinBot W730 can do. Its made by ECOVACS and its pretty cool. It crawls up the window, like your robot vacuum and maps out its work then, using suction to keep it on the window, it cleans the glass and works its way around vertically. To see the pictures its incredible.
Seriously, its a real gadget! The one issue I overheard the booth representative talking about related to power loss and the unit falling off the glass. I shot some video and took some pictures. I also found an excellent NY Times article from this past fall. Amazon currently lists this at $399.00 and its Prime eligible.