Robert Murray Smith, best known for his homemade graphene and supercapacitors is at it again. This time, in his experiments he's using the natural metabolism cycle of plants to generate electricity.
(Not a lot, mind you, but enough to run a small motor or charge a phone.)
https://www.youtube.com/watch?v=wV6Y_JZQTso
From what I gather it's more about the bacteria (rhizobium?) than the plant, so I'm assuming this could fit into nearly any growing system. Kind of neat to be able to harvest one more useable product from the garden.