Wow, I admire people who do projects which I wouldn't even start once the little "feasibility study" in my head is finished.

Before starting with your supercolling with Peltier elements I would do some math and calculate how much energy you need to considerably cool the water and whether your charging system can supply this. You see, I like the theoretic approach, first check with little effort whether the big effort is justified.

But then again, you want the little boy in you fulfilled