Question of the week: Why can't hybrids use dynamos to generate energy?
Fri, 01 May 2026
Dear Honest John,
"Many years ago, lights on push bikes could be charged by dynamos from the rotation of the wheels.
Why can't charging of the batteries on hybrids use this system in addition to braking etc.?"
- CM
Dear CM,
While it would technically be possible to add a dynamo to a hybrid vehicle in order to generate additional electricity, the result would actually be a net loss of energy.
The dynamo itself would create additional rolling resistance, which would then requie extra energy from the engine or electric motor to power the vehicle to the same speed.
It would also require a dynamo of significant size in order to generate any meaningful energy, so the drag created would be substantial. There is also the fact that no energy transfer can be made without a degree of loss, so a proportion of any energy generated would be lost to heat and electrical resistance.
The result would be a vehicle that uses more fuel and electrical energy than an identical one not fitted with a dynamo. The current system of harvesting energy when braking makes sense because it utilises the vehicle's kinetic energy which would otherwise be lost to heat through the brake pads and discs.
Modern hybrids and EVs use regenerative braking. This system essentially turns the car's electric motor into a giant dynamo when you lift your foot off the accelerator or hit the brakes.
The key difference is timing. Regen braking only captures energy that would otherwise be wasted as heat in your brake pads. It uses the car's momentum to charge the battery while simultaneously slowing the vehicle down.
If you ran a dynamo while trying to maintain speed, you’d be braking while trying to go, which is incredibly inefficient.
