DonC said:
Regen gets some of the energy back but it's better not to use in in the first place.
I'm sorry, this is the first I've read of this. I am not a volt owner, forgive me, but interested in purchasing one. So, to be clear: we should not use brake regen?
As a thought experiment, suppose you have a completely drained battery and accelerate (on flat ground) from 0 to 40 MPH using the gas engine, then immediately use regenerative braking to slow to a stop. The energy you recover goes into the battery, which now has charge you can use to accelerate the car -- but if you do so, using nothing but the battery, you won't get up to 40 MPH. I don't know offhand how fast you could end up going -- 10 MPH, 20 MPH, maybe 30 MPH, but not 40 MPH (on level ground). This is all a factor of the inefficiency of technology; it's impossible for modern regenerative brakes to recapture 100% of the energy used to bring the car up to speed. Some of the energy gets dispersed as heat or in other ways. The same is true over other speed ranges, too -- if you accelerate from 40 MPH to 60 MPH and then brake back to 40 MPH, you won't get back enough energy to go back up to 60 MPH.
(Of course, the above thought experiment simplifies a lot of details, like the fact that the Volt's batteries should never be
completely drained, and the fact that regenerative braking in a Volt won't bring it quite to a full stop. It's just an idealized thought experiment meant to illustrate a point.)
So, from a practical driving point of view, the order of preference for saving energy is:
- Accelerate only as much as you must. For instance, in city traffic, pay attention to the traffic a block or two ahead, to stop lights ahead, and so on, so that you can minimize your use of brakes. On the highway, let off the accelerator and coast prior to braking at an exit. (Of course, it's possible to take such techniques to an extreme that will annoy other drivers, and I'm not advocating that.) Higher speeds, especially beyond a certain point, are less energy-efficient than slower speeds, so don't drive too fast, either.
- Use regenerative braking. On a Volt, you can do this via the "L" setting on the shifter, via the regen paddle on the steering wheel, or via light to moderate use of the brake pedal. Using regenerative braking recaptures some of the energy carried in your momentum.
- Use conventional brakes. When applied hard, and when you get below some slow speed (5 or 10 MPH, IIRC), the brake pedal uses conventional brakes. This braking method converts your momentum into waste heat. Of course, you shouldn't hesitate to brake hard when it's required for safety!
FWIW, I'd been taught to do #1 in my driver's education class in high school; and although regenerative brakes were not yet available then, light braking was also recommended as being better for wear and tear on the brake systems. Thus, I've been well-trained to drive a modern hybrid or electric car. I'm sure the same is true of many others -- but we've all witnessed people who accelerate fast and leave braking to the last moment, which wastes fuel even in conventional cars.
