Just a side thought..
why not just leave the shaft as up and down and then custom form some tube coils around the shaft fitting the shaft with some rare earth magnets making a linear dynamo? a bridge rectifier per coil so it outputs on both up and down strokes, wire them in parallel and feed them into say a 30a solar regulator.....
The only downside to using the dynamo that I can think of would be regulating the voltage but that should be sortable with a good solar regulator

