Energy consumption of cars
The energy consumption of cars is mainly due power lost to the following three processes:
- Friction with air
- Breaking
- Accelerating
Less important is the loss due to rolling resistance. The above three factors are independent of the propulsion system: electric cars, fuel cell cars, and cars with combustion engine lose about the same amount of energy to these three effects.
An important difference between electric- and combustion-engine cars is the thermodynamic efficiency of the generation of the energy. Electric energy is usually generated in big (500 to 1000 MW) power stations that operate at an efficiency of about 40%, which means that about 40% of the chemical energy content of the fuel (coal, natural gas, oil, etc.) is converted into electric energy. The relative small car engines, on the other hand, operate at an efficiency of around 25%.
Other losses—which are difficult to quantify—are in the production of gasoline (or other fuels such as diesel used in combustion engines), the transport of electricity from power station to electric outlet, and losses in charging batteries of the electric cars. If it is assumed that these losses are on the same order of magnitude, it follows that electric cars consume about 15% less energy than gasoline cars.
(To be continued), see David MacKay