In both cases, the vehicle has an electric engine. The energy required by the engine of an electric vehicle is provided by a battery, which is previously charged through the power grid. In a hydrogen vehicle, instead, the hydrogen in its tank is used by a fuel cell to produce electricity to power the engine. In an electric vehicle, the system’s efficiency depends on the battery’s efficiency, while in a hydrogen vehicle, you have to consider both the efficiency of the electrolyzer that produces hydrogen as well as the efficiency of the fuel cell that converts it into electricity. Today, an electric vehicle is still 2.5 times more efficient than a hydrogen car.