The solar cooker looks to be the most promising. Simple but elegant, but as the inventor indicated, most useful in places with few fuel options (which could be an increasing...)

The windmills are neat looking, but expensive. At about $5/watt (10 m/s), the payoff time (compared to grid electricity) would probably be greater than their useful life of the turbines. They also look to me like they'd be noisy. Still, in some situations, they'd be handy to have.


The Hydro thing is interesting. As I understand it, it utilizes waste power from the engine (of which there is plenty) to perform electrolysis on water. The hydrogen can be burned, so this is essentially an efficiency improvement applied to a hugely wasteful engine. It's also clever in that it leverages the existing systems (electrical and combustion) with little modification.

I'm naturally skeptical of the claims, but it looks like it could still work. The net energy from the device itself is negative, but since it's using waste energy, the overall efficiency of the larger system could still be greater than without it. Having said that, I'd guess that it's WAY overpriced. Electrolysis is simple to do, and I'm sure that one could cook up their own for a fraction of the cost.
http://en.wikipedia.org/wiki/Electrolysis_of_water

The Prius, btw, also uses waste power (via the alternator), but utilizes electrical rather than chemical means. But, it also uses regenerative braking, so there is more synergy of having the hybrid components in the drive train.