This is something that I just thought off and although off topic it may be worth thinking about. Have you considered maybe using a small wind turbine generator mounted to the front (or rear) of the bike to generate power? I have a small ten watt one made by Pacific Sky Power and it does not require much wind to start generating power and the plastic prop is rather small. There are even replacement props for it that are constructed of carbon fiber that are extremely durable.

Just an idea I thought worth mentioning. I really like your project!