The petroleum fuel cycle is much less efficient than the 25% or so of the gasoline or diesel burning engine figure implies. Oil is lost and consumed at every step of the way from exploring and drilling the wells to the tailpipe of the vehicle that uses it. I have seen the figure 6% as a peak efficiency of the petroleum fuel cycle.
The battery charge-discharge cycle has become enormously more efficient in recent years, up to 99% efficiency in lithium-ion batteries. Computer-controlled modern coreless (no heavy iron core for the motor coils to be wound on) permanent-magnet motors are very efficient, too. and, if they are integrated into the wheels and hubs of vehicles, transmission losses are eliminated (the wheels have to have bearings anyway) by not having gears, CV joints, etc. - no drivetrain. Regenerative braking uses the motors as generators when braking is needed. The power produced by the motor/generators is used to recharge the batteries. Only when the batteries are fully charged is the braking power dissipated (wasted) in resistance grids (dynamic braking). The friction brakes are needed only to bring the vehicle to a complete stop from about 10 mph, as wheel motor/generators can be designed and controlled to slip the tires on dry pavement at speed (above about 10 mph or so), still without stopping the wheels. Wheel propulsion motors that are designed for maximum braking (slipping the tires on a dry pavement) have to be designed to dissipate a lot of power for a short period of time, and a lesser amount for longer periods, such as "engine" braking (retarding) on long downgrades. Having the motors out in the wheels makes for excellent ventilation especially with wheels designed to pump air through the wheels and over the motors. Even high-efficiency motors still waste some power as heat.
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The petroleum fuel cycle is much less efficient than the 25% or so of the gasoline or diesel burning engine figure implies. Oil is lost and consumed at every step of the way from exploring and drilling the wells to the tailpipe of the vehicle that uses it.
I have seen the figure 6% as a peak efficiency of the petroleum fuel cycle.
The battery charge-discharge cycle has become enormously more efficient in recent years, up to 99% efficiency in lithium-ion batteries.
Computer-controlled modern coreless (no heavy iron core for the motor coils to be wound on) permanent-magnet motors are very efficient, too. and, if they are integrated into the wheels and hubs of vehicles, transmission losses are eliminated (the wheels have to have bearings anyway) by not having gears, CV joints, etc. - no drivetrain.
Regenerative braking uses the motors as generators when braking is needed. The power produced by the motor/generators is used to recharge the batteries. Only when the batteries are fully charged is the braking power dissipated (wasted) in resistance grids (dynamic braking). The friction brakes are needed only to bring the vehicle to a complete stop from about 10 mph, as wheel motor/generators can be designed and controlled to slip the tires on dry pavement at speed (above about 10 mph or so), still without stopping the wheels.
Wheel propulsion motors that are designed for maximum braking (slipping the tires on a dry pavement) have to be designed to dissipate a lot of power for a short period of time, and a lesser amount for longer periods, such as "engine" braking (retarding) on long downgrades.
Having the motors out in the wheels makes for excellent ventilation especially with wheels designed to pump air through the wheels and over the motors. Even high-efficiency motors still waste some power as heat.