I remembered that I saw the same toy before in the office, brought by the father of the little birthday girl, but I didn't take much notice of it until I saw it on the shelves. There were two other Green Science toys on the shelf: a Dynamo Torch (a flashlight powered by hand) and a Soda Can Robobug (a moving robot made out of a soda can - can't remember if it's wind up or not). The instruction manual for the Windmill Generator also mentioned an Enviro Battery kit (which I so want) but it wasn't available in Toy Kingdom.
Here's the Windmill Generator, all set-up and working:
Isn't it fun?