How a spinning wheel can move a bus
A flywheel stores energy as motion rather than chemistry. An electric motor spins a heavy rotor; when the bus needs power, the rotor turns a generator, which converts that rotation back into electricity for the drive motor. As energy is drawn off, the flywheel slows. Recharging means using electricity to spin it up again.
The key is speed: a compact rotor can hold useful energy when it spins very rapidly. That makes a flywheel well suited to bursts of power, such as accelerating a bus after a stop. Unlike a battery, it can also accept energy quickly, so a short charging opportunity may be valuable.
The tradeoff is energy versus engineering
A bus must carry enough stored energy to reach its next charging point, not merely pull away from the curb. Flywheels generally store less energy for their weight than batteries, so the vehicle’s route and charging arrangements matter. The rotor also has to be contained in a strong enclosure: a fast-spinning heavy part demands careful engineering if it is damaged. Bearings and other systems must limit energy lost as heat and friction while it spins.
That makes a flywheel bus less like a conventional bus with a different fuel tank and more like a vehicle built around a repeating rhythm: charge, travel, recharge. Its advantage is quick energy transfer; its constraint is how far that stored rotation can carry the bus before the next top-up.
