bicycles generating electricity?

I was thinking someone could apply the Hybrid techniques used in cars to bicycles. So, whenever you are going downhill your brakes could be electrical generators to help you move the bike uphill when you needed a little more boost from an electric motor. also, when parked solar panels could be in between the spokes of a wheel to charge up the battery while the bike was parked for when you needed the charge to go uphill. Though it is true the theft of the solar panels (or electric engine or batteries might be a problem in some locations) in most locations this would be a very efficient way to travel when you needed that extra boost of power for going uphill after a long days work or in the heat of summer.