A few years ago, I saw a dog-powered butter churn that was actually used years back in northern PA. It was basically a treadmill, but for a dog to generate the mechanical motion and churn the butter. I kid you not!
I'd have to imagine that a solar powered reader would make the most sense. I haven't kept up with current calculators, but have the solar powered ones caught on, or have they gone the way of the dinosaurs? If they don't work for calculators, I don't see them popular for e-readers.