From what I know about sharks, they may be curious, but if you're not chumming and it doesn't look like a seal, you'll be ok. Fiberglass would be the choice. But any kind of sealed plastic would work.
See, I would just say don't worry about mounting the solar panel. Deign your hull, then just bolt it to the top. If you want to get really fancy, you could control it base on time of day and GPS location, so that you're always aimed at the sun. This could be computed by the computer.
Also look into getting a lens that can focus more light on the panel. You can cheat like that.
If you have a lens that can concentrate light, your solar panels can be smaller.
See, with solar, you only need the force of a gentle continuous push to get there. Everything else just gets you there faster.