Electric Vehicle Efficiency

Electric Vehicle Efficiency

How much more energy efficient? Very Much.

Chatting about EVs at Earth Day

For some drivers, it is satisfying to drive a vehicle that wastes so little energy. The in-vehicle conversion efficiency of an EV is nearly 100%, as the stored electrical energy is converted to motion with almost no waste heat. In contrast, 70% to 80% of the energy in an internal combustion engine is ultimately lost as waste heat, through exhaust, braking, and radiation from the radiator. When a regular gas engine is cold, it has very poor fuel economy. At low speeds, an internal combustion engine needs to keep its explosions going, just so that the engine is ready to rev up to the higher rotational speeds needed for maximum torque when accelerating from a standstill. Thus petroleum fueled cars are especially wasteful in short distance city driving. They are comparatively efficient when warmed up and racing at highway speeds.

This provides an opportunity for drivers of plug-in hybrids (PHEVs) to maximize their overall fuel economy by choosing to drive electrically at low speeds, with lots of regenerative braking, or on long downhills with much regenerative braking (e.g., mountain or canyon-lands driving) and saving the gas engine for uphill or level highway driving. By sensible switching of drive mode, I have sometimes been able to extend the all-electric range of my PHEV threefold or more.

Most EV drivers take great satisfaction in the amount of power that is returned to the battery through regenerative braking. Using brakes in a conventional car to turn motion into waste heat seems like stone-age technology. Some EVs, such as the Chevy Bolt and Teslas, are equipped with such strong regenerative braking that one can often drive entirely using just the accelerator pedal (push down to speed up; let up on the “gas” to slow down to a full stop). One-foot driving is not everyone’s cup of tea, but it highlights the efficiencies possible with electrical propulsion.

Are there cons to driving such an efficient vehicle? Yes. See The Driving Experience for the glories of waste heat when driving in winter.