I noticed that some company as Freeplay Energy Ltd make wind-up electricity generators for humanitarian purposes. One suggestion here is that besides making generators recharged by human power, one can also adapt them (increase the size) to allow animals to do the recharging (ie donkeys, ...) Animals can be set to work a lot longer and will probably also generate much more power.
On the other hand, the feed used for the animal could be used to produce electricity directly, which is likely to be more efficient.