Where the Energy Goes: Electric Cars
Electric vehicles (EVs) are more efficient than their gasoline-powered counterparts. An EV electric drive system is only responsible for a 15% to 20% energy loss compared to 64% to 75% for a gasoline engine. EVs also use regenerative braking to recapture and reuse energy that normally would be lost in braking and waste no energy idling. See All-Electric Vehicles for details.
EVs are 60% to 73% efficient, depending upon drive cycle. However, if the energy recaptured from regenerative braking is counted (i.e., recounted when it is re-used), EV energy efficiency can exceed 77%. (For more information on how vehicle efficiency is calculated, see Vehicle Fuel Efficiency.)
![Energy Requirements for City (Stop and Go) Driving: Energy Lost in Charging the Battery (16%), Accessory Losses (4%), Net Regenerative Braking Energy Returned to the Battery and Subsequently to the Road (32%), Energy to Wheels (54% to 62% + 32% [recovered] = 86% to 94%), Electric Drive System Losses (18%), Idle Losses: 0.](https://fueleconomy.gov/feg/images/energy_reqs_city_ev_121621.png)
Energy requirements in this diagram are estimated for stop-and-go city driving using the EPA FTP-75 Test procedure.
The electric drive systems of electric cars are much more efficient than the engine and transmissions of conventional vehicles. Still, some of the vehicle's energy is lost through drivetrain inefficiencies.
When charging the battery, energy is lost in converting alternating current (AC) from the electrical grid to direct current (DC) for use in the battery, as well as in overcoming the battery's resistance to charging, which increases as the battery reaches its capacity.
Charging losses can vary with the specific vehicle, type of charging system used, the state of the battery, and ambient conditions (weather).
Energy steering and the powertrain cooling and control systems use energy. This estimate does not include losses from cabin heating or cooling, which can be significant in extreme temperatures.
Braking Losses
When you apply the brakes in a conventional vehicle, energy initially used to overcome inertia and propel the vehicle is lost as heat through friction at the brakes.
Elecric cars use regenerative braking to recover some energy that would otherwise be lost in braking, making them more efficient than comparable conventional vehicles, especially in stop-and-go traffic.
Wind Resistance (Aerodynamic Drag)
A vehicle expends energy to move air out of the way as it goes down the road—less energy at lower speeds and more as speed increases.
This resistance is directly related to the vehicle's shape and frontal area. Smoother vehicle shapes have already reduced drag significantly, but further reductions of 20%–30% are possible.
Rolling Resistance
Rolling resistance is a resistive force caused by the deformation of a tire as it rolls on a flat surface.
New tire designs and materials can reduce rolling resistance. For cars, a 5%–7% reduction in rolling resistance increases fuel efficiency by 1%, but these improvements must be balanced against traction, durability, and noise.
An EV’s electric motor stops when the vehicle stops. The motor doesn't waste energy idling.
Electric cars use regenerative braking to recover energy typically wasted in braking. Since more braking takes place in stop-and-go traffic, they are most efficient in city driving.
When you apply the brakes, the vehicle's inertia turns an electric motor-generator, producing electricity that is then stored in a battery. The electricity can later be used to power the electric motor, which supplies power to the wheels.
Electrical accessories such as lights, windshield wipers, navigation systems, and entertainment systems require energy and lower fuel economy.
Losses from accessories such as electric door locks and signal lights are minuscule, while losses from seat and steering wheel warmers and climate control fans are more significant.
In very cold conditions, auxiliary electrical losses can account for more than 40% of energy use in city driving.
Unlike a conventional gasoline or diesel vehicle, which uses heat from the engine to help warm the cabin, all heat must be provided by electricity.
![Energy Lost in Charging Battery (10%), Accessory Losses (2%), Net Regenerative Braking Energy Returned to the Battery and Subsequently to the Road (6%), Energy to Wheels (71% to 73% + 6% [recovered] = 77% to 79%), Electric Drive System Losses (15%), Idle Losses (none). Highway driving does not include significant idling.](https://fueleconomy.gov/feg/images/energy_reqs_hwy_ev_121621.png)
Energy requirements in this diagram are estimated for the EPA Highway Fuel Economy Test procedure (highway driving with an average speed of about 48 mph and no intermediate stops).
When charging the battery, energy is lost in converting alternating current (AC) from the electrical grid to direct current (DC) for use in the battery, as well as in overcoming the battery's resistance to charging, which increases as the battery reaches its capacity.
Charging losses can vary with the specific vehicle, type of charging system used, the state of the battery, and ambient conditions (weather).
The electric drive systems of electric cars are much more efficient than the engine and transmissions of conventional vehicles. Still, some of the vehicle's energy is lost through drivetrain inefficiencies.
Energy steering and the powertrain cooling and control systems use energy. This estimate does not include losses from cabin heating or cooling, which can be significant in extreme temperatures.
Braking Losses
When you apply the brakes in a conventional vehicle, energy initially used to overcome inertia and propel the vehicle is lost as heat through friction at the brakes.
Electric cars use regenerative braking to recover some energy that would otherwise be lost in braking.
Since there is little braking in highway driving, regenerative braking offers little advantage over a conventional vehicle on the highway.
Wind Resistance (Aerodynamic Drag)
A vehicle expends energy to move air out of the way as it goes down the road—less energy at lower speeds and more as speed increases.
This resistance is directly related to the vehicle's shape and frontal area. Smoother vehicle shapes have already reduced drag significantly, but further reductions of 20%–30% are possible.
Rolling Resistance
Rolling resistance is a resistive force caused by the deformation of a tire as it rolls on a flat surface.
New tire designs and materials can reduce rolling resistance. For cars, a 5%–7% reduction in rolling resistance increases fuel efficiency by 1%, but these improvements must be balanced against traction, durability, and noise.
Highway driving includes little to no idling. The EPA highway driving cycle (HWFET) includes no idling.
An EV’s electric motor stops when the vehicle stops. The motor doesn't waste energy idling.
Electrical accessories such as lights, windshield wipers, navigation systems, and entertainment systems require energy and lower fuel economy.
Losses from accessories such as electric door locks and signal lights are minuscule, while losses from seat and steering wheel warmers and climate control fans are more significant.
In very cold conditions, auxiliary electrical losses can account for more than 25% of energy use in highway driving.
Unlike a conventional gasoline or diesel vehicle, which uses heat from the engine to help warm the cabin, all heat must be provided by electricity.
![Energy Requirements for Combined City/Highway Driving: Charging Losses (10%), Accessory Losses (3%), Net Regenerative Braking Energy Returned to the Battery and Subsequently to the Road (22%), Energy to Wheels (65% to 69%% + 22% [recovered] = 87% to 91%), Electric Drive Losses (22%), Idle Losses (near 0).](https://fueleconomy.gov/feg/images/energy_reqs_comb_ev_121621.png)
Energy requirements in this diagram are estimated for 55% city and 45% highway driving. See the estimates for city and highway driving for more information.
When charging the battery, energy is lost in converting alternating current (AC) from the electrical grid to direct current (DC) for use in the battery, as well as in overcoming the battery's resistance to charging, which increases as the battery reaches its capacity.
Charging losses can vary with the specific vehicle, type of charging system used, the state of the battery, and ambient conditions (weather).
The electric drive systems of electric cars are much more efficient than the engine and transmissions of conventional vehicles. Still, some of the vehicle's energy is lost through drivetrain inefficiencies.
Power steering and the powertrain cooling and control systems use energy. This estimate does not include losses from cabin heating or cooling, which can be significant in extreme temperatures.
Braking Losses
When you apply the brakes in a conventional vehicle, energy initially used to overcome inertia and propel the vehicle is lost as heat through friction at the brakes.
Electric cars use regenerative braking to recover some energy that would otherwise be lost in braking.
Wind Resistance (Aerodynamic Drag)
A vehicle expends energy to move air out of the way as it goes down the road—less energy at lower speeds and more as speed increases.
This resistance is directly related to the vehicle's shape and frontal area. Smoother vehicle shapes have already reduced drag significantly, but further reductions of 20%–30% are possible.
Rolling Resistance
Rolling resistance is a resistive force caused by the deformation of a tire as it rolls on a flat surface.
New tire designs and materials can reduce rolling resistance. For cars, a 5%–7% reduction in rolling resistance increases fuel efficiency by 1%, but these improvements must be balanced against traction, durability, and noise.
An EV’s electric motor stops when the vehicle stops. The motor doesn't waste energy idling.
Electric cars use regenerative braking to recover energy typically wasted in braking.
When you apply the brakes, the vehicle's inertia turns an electric motor-generator, producing electricity that is then stored in a battery. The electricity can later be used to power the electric motor, which supplies power to the wheels.
Electrical accessories such as lights, windshield wipers, navigation systems, and entertainment systems require energy and lower fuel economy.
Losses from accessories such as electric door locks and signal lights are minuscule, while losses from seat and steering wheel warmers and climate control fans are more significant.
In very cold conditions, auxiliary electrical losses can account for more than 33% of energy use in combined city/highway driving.
Unlike a conventional gasoline or diesel vehicle, which uses heat from the engine to help warm the cabin, all heat must be provided by electricity.
Note: Energy use and losses vary from vehicle to vehicle. These estimates are provided to illustrate the general differences in energy flow in different vehicle types during different drive cycles.
Estimates primarily based on analysis of a 2012 Nissan Leaf. Charging losses based on tests of several EVs by Argonne National Laboratory.
Lohse-Busch, H., et al. 2013. Ambient Temperature (20°F, 72°F and 95°F) Impact on Fuel and Energy Consumption for Several Conventional Vehicles, Hybrid and Plug-In Hybrid Electric Vehicles and Battery Electric Vehicle. SAE 2013-01-1462, https://doi.org/10.4271/2013-01-1462.
Lohse-Busch, H., et al. 2012. Advanced Powertrain Research Facility AVTA Nissan Leaf testing and analysis.
Thomas, J. 2014. Drive Cycle Powertrain Efficiencies and Trends Derived from EPA Vehicle Dynamometer Results. SAE 2014-01-2562, https://doi.org/10.4271/2014-01-2562.
Carlson, R., J. Wishart and K. Stutenberg, K. 2016. On-Road and Dynamometer Evaluation of Vehicle Auxiliary Loads. SAE Int. J. Fuels Lubr. 9(1):2016, https://doi.org/10.4271/2016-01-0901.
Rhodes, K., D. Kok, P. Sohoni, E. Perry, et al. 2017. Estimation of the Effects of Auxiliary Electrical Loads on Hybrid Electric Vehicle Fuel Economy. SAE Technical Paper 2017-01-1155, https://doi.org/10.4271/2017-01-1155.
Pannone, G., B. Betz, M. Reale, and J. Thomas. 2017. Decomposing Fuel Economy and Greenhouse Gas Regulatory Standards in the Energy Conversion Efficiency and Tractive Energy Domain. SAE Int. J. Fuels Lubr. 10(1):202-216, 2017, https://doi.org/10.4271/2017-01-0897.