A Free Ride?

Some more exploration of a dual-mode electric motor/generator. Shown is an updated sketch of an enclosed motorcycle- I quite like the styling possibilities presented by the format.

Further to the motorcycle itself, is where the dual use part comes in. An idea is to run drums on axles, covered with rubber, in small trenches in carparks. The axles would be fitted with a differential, which would in turn receive drive from a small wind-turbine, via a gearbox.

The whole point is that the vehicles are sitting for most of the day, all their components unused- commuters all travel within fairly specific windows of time.

In this situation, vehicles would position their drive wheels in such a way as to take torque from the rotating drums, the motors would be reversed and engaged as generators- this would save manufacturing and installing extra generators to charge the vehicles anyway. The electricity produced over the 8 hours or so that the vehicles are parked could either go towards re-charging their cells, the logical outcome, or fed back into the grid.

Because the installation of the car-park components is fairly simple, with no integral generator, the wind turbines themselves could be fairly simple. My initial idea was to have a conventional propellor blade, at a safe height, but this would require two differentials- and a lot of mechanical loss. Instead, a vertical axis turbine would be better suited- less complexity, and could be more efficiently constructed, inexpensively with very lightweight materials, ie. like a sail. Of course, each section of ground drums would have drive from only one turbine- they would always be turning at a different rate. Gearing would ensure that the resistance from the vehicles was not so great as to stall the aerodynamics- the full weight would not be supported by the drums either, just enough to maintain enough turning friction. A lot of detail must be worked through- safety, capacity for larger vehicles etc. but I think there could be some promise here.

Edit: A waterwheel would of course be the most efficient way to apply drive, as it would not require a differential. Could this be set up in downtown areas to take advantage of harbour currents? tide changes?