Hmm, interesting idea. I tried something like this before, only not in a pond, but something you should take note of is, you'd better cast it in resin. A plain glass or plastic container isn't strong enough, you need walls about two or three centimeters thick, or an inch or so.
What are the capabilities of your solar cell? CUrrent/voltage? I think I can help.
Oh, and not too big. The bigger it is, the less it's like a fountain and the more it's like a bomb.