[lyschoening]

The key here is that this method does not require a battery. In practice though I am skeptical that this contraption would live much longer than a rechargeable battery combined with something more versatile such as a hand crank.

[makomk]

For comparison, that's in roughly the same ballpark as the amount of energy one of the tiny, cheap rechargable batteries in a dollar-store solar light can store. Potential energy just isn't all that viable.