Since there are so many LEAF newcomers here I think it is best to explain why using lots of regen braking
isn't the most efficient way to drive. The oldtimers here take this stuff for granted, having discussed it at length long ago.
The idea of capturing energy of motion (kinetic energy) via regenerative braking is a neat idea. Why waste that energy as heat using friction brakes, right? It is true that if the choice is to use friction brakes or regen braking the choice is easy: go with regen.
However, regenerative braking is somewhat inefficient. Think about what happens: the motor magnetic fields are reversed and the motor, which is directly linked to the wheels via a reduction gear set, then becomes a generator and is used to charge the battery. The problem is that this process loses energy at several steps. Taking energy out of the battery, propelling the car, then using regen braking to put energy back in the battery has considerable losses.
How efficient regen braking is has been much debated here with most guesses falling in the 50% to 70% range. Even at the high end of that range, every time you use regen braking you are only converting 70% of the kinetic energy back to kilowatt-hours in the battery. And when you then use that battery energy to get going again you have additional efficiency losses as the chemical energy in the battery is converted to electricity, which is converted to kinetic energy. At each conversion step there are losses. This is basic physics and I will leave it there.
So, if regen braking is somewhat inefficient, what to do? As the "hypermilers" here well know, the solution is to avoid braking and drive at a constant speed as much as possible. Better to keep the kinetic energy of motion (momentum) going than to convert it back to chemical energy in the battery and then back to kinetic energy again. And one way to do that is to coast when conditions permit; no energy is being drawn from the battery and no energy is being lost to inefficient regen braking.
Of course it isn't possible to always drive at a constant velocity, especially in heavy traffic. But an efficient driver will look ahead and anticipate slowdowns so as to slow gradually. If conditions permit, that stoplight up ahead turns green for example, then one can gradually accelerate back up to speed with most of the kinetic energy retained from not slowing too much.
By contrast, inefficient drivers will brake sharply, losing energy, and then accelerate quickly, having to replace that lost energy from the battery. Since regen braking isn't a completely efficient process some energy is lost during that stop/go conversion. Regen braking is certainly much better than using friction brakes to slow but the most efficient way to drive is to brake as little as possible and try to maintain one's speed where possible.
Before somebody mentions it, there is one exception to the idea that coasting is better than regen and that is when descending hills at high speeds approaching terminal velocity. When moving at terminal velocity the energy from the acceleration of gravity is being lost to aerodynamic drag. In that case it would be better to slow down and recover some of the energy via regen rather than lose it to drag. But, in most cases, coasting to maintain kinetic energy is preferable to the inefficiencies of regen plus accelerating back up to speed again.
For more information about driving efficiently, check out
Stoaty's Guide to Energy Efficient Driving of the Leaf.
