Hmmmm, I guess in survivalism, redundancy is key. So if the power goes, and the alternative solutions fail during cloudy days. Then in the case of zombies one could build a large closed "hamster" wheel put 3-4 zombies inside and some meet on a stick in front. Or, incase of no zombies, then you could fill the wheel with as many politicians as you can, and put a dollar bill on a string in front. In order to generate energy.
Just have to be willing to improvise.