I agree, the idea is great! But I also feel that it might not be too practical. As part of my research, I often measure coastal current speeds, tides and wave forcings. At times I do think about ways to harness these energies in useful ways. Truth is, it's very difficult. Big waves may be able to supply energy to an oceanic wave buoy...but that's about it. Tidal currents may provide energy if they're strong enough, but not really for individual users that are on-the-go. So...yes...a cool idea, but really it's probably not much more than an expensive gadget...