The power useage figure assumes that the course is completely flat; is it? The power used to climb a hill is normally enourmous compared to the losses from drag & rolling resistance. Also trying to store energy from rolling down the other side isn't as good as you might think due to all the losses turning the energy into electricity, converting it to the right voltage, storing it and then doing all that in reverse again when you want to use it.
As for panels, the best ones right now are tripple-junction GaAs; they are like 3 cells on top of each other. Normally cells only get to use some of the red light, but putting cells efectively underneath you get to use more wavelengths and hence convert more of the sunlight to electricity. They cost a bit more, but if you are limited on area/weight or need maximum power for example in space, it pays off.