A post on Facebook claims to show an electric car self-charging as it is driven, using a generator attached to the wheel to harness the energy generated as it spins. The post claims that this is “something that no [electric vehicle] manufacturer has done so far”, and adds that the design eliminates the need to stop at charging points during a journey or charge a vehicle overnight.
The reason that no electric manufacturer has already done this is because doing so would break the laws of physics.
In their fact check of a different version of the same claim, Climate Feedback explained a battery cannot be used to charge itself based on the law of conservation of energy and the second law of thermodynamics.
The law of the conservation of energy states that energy can not be created or destroyed, only converted from one form to another. In the example of an electric car, energy can’t be perfectly transmitted from a battery through to the axle which turns the wheel and then back to the battery, as the energy generated from the wheel turning is transferred to the ground in the process of accelerating the car.
Energy is therefore lost, which means the same amount can’t be channelled back into the battery. Eventually this would deplete the battery, to the point where it would have to be charged at a conventional charging point.
Climate Feedback also points out that the claim in the Facebook post also breaks the second law of thermodynamics, which states that as energy is transferred or transformed, more and more of it is wasted.
In the example of an electric car some of the energy would quickly be lost through heat and friction.
If the method of self-charging the car were to work, this would effectively mean that a machine had been invented that could remain in perpetual motion. Machines that hypothetically work in this manner are widely deemed to be scientifically impossible, due to the reasons set out above.