sparkyps wrote:Coasting is 0% efficient
Try this test, speed up to 30mph, coast to a stop. Measure energy recovered by coasting. Answer is 0
Now speed up to 30mph and regen brake to a stop. Measure energy recovered by Regen braking. Answer > 0
SeanNelson wrote:The big, big thing you're missing here is: how far did you go? It's pretty useless to recover 80% of your energy (which I suspect is pretty optimistic) if you've only gone, say, 200 feet when just coasting may have taken you 1500 feet.
Sean's example is correct. Let's say the car that coasted to a stop went 1500 feet. The car that braked with regen goes 200 feet. It's all fine & good that some energy was recovered, but you'd then be spending all of it + more to go the extra 1300 feet to reach the car that coasted.
This is a debate that comes up once in a while, probably because there's so much misinformation on the Internet suggesting that it's possible to bend the laws of physics. I watched a guy on YouTube who was illustrating / teaching the "best" way to hypermile a Volt. He maintains that driving in "L" (maximum regen) at all times is the key to efficient driving. He uses the same logic that coasting recovers 0 energy / Regen braking recovers > 0 energy - but blissfully ignores how much farther he could have traveled slowing down / coasting in N.
The end goal in hypermiling is about driving the farthest distance on the least amount of energy. Regardless of the cars we drive, efficient driving always comes back to Newton's Law that a body will remain at rest or in motion unless it is acted upon by an external force. For that reason, the amount of energy your brakes recover is irrelevant because it is NEVER as much energy that was spent in getting the vehicle in motion.