Nice setup. I would be a bit concerned about water which was contaminated with petroleum products or other organic molecules. Some of them have boiling points very close to water and so would come over and be condensed with the steam.

If you know you don't have stuff like that in your water then this would be a good unit. Paint the pressure cooker black and stick it in a solar oven, running the copper tube out the side if you want to tap the sun.
-Blast