I have a half round window (8 ' w x 4'h) which, like all double paned windows in my experience, has failed after about ten years. It is now completely clouded. I can not see replacing it with the same thing. What other options are there, and their relative merits? I.e., single pane glass? Plexiglass? Should i be going to commercial glass companies vs window companies? The building is a converted barn, and I'm in the northeast where energy efficiency is important... within reason! Thanks for any thoughts.