Well-to-Wheel Efficiency
Well-to-wheel efficiency is the share of primary energy that ultimately becomes mechanical energy at a vehicle’s wheels across the complete energy-supply and vehicle-conversion chain.
Two linked stages
The well-to-tank stage covers extracting or producing primary energy, processing or generating the energy carrier, transporting it, and delivering it to the vehicle. For an EV, this can include electricity generation plus transmission, distribution, and charging losses.
The tank-to-wheel stage covers converting stored onboard energy into motion at the wheels. For an EV, that includes losses in the battery, inverter, motor, drivetrain, and supporting systems. Well-to-wheel efficiency combines the two stages, so the result depends on both the upstream energy pathway and the vehicle.
A figure is meaningful only when its system boundary, electricity or fuel pathway, geography, time period, and assumptions are stated. The same EV can have different well-to-wheel results with different electricity mixes or charging-loss assumptions.
Well-to-wheel efficiency is an energy metric, not automatically a greenhouse-gas result or a complete life-cycle assessment. Emissions depend on the energy sources and processes, while a life-cycle assessment can also include vehicle and battery production, maintenance, and end of life.
For vehicle-level energy use and range, see Understanding EV Range.