In my 2017 Prius, is it more energy efficient to coast to a stoplight ahead, or use the brakes, assuming it’s a safe thing to do? Thanks!
Use your brakes because they actually help with the battery life . Coasting will not save you anything that you can really measure… I also don’t think of it as being safe .
Google ( Prius brake regeneration ) for a better explanation then I can give.
Edit : I understood this question as wanting to put the vehicle in neutral , not just coasting up to stop signs .
Coasting is OK, as long as you are in Drive. Some re-gen occurs every time you let off the throttle. I think it is adjustable on some hybrids, not sure about a Prius.
Every time you touch the brake pedal, there is the possibility of the brakes themselves being used to slow the car and that is energy that you lose as heat.
Just consciously trying to judge time and distance so you CAN coast will improve your mileage because it forces you to look far ahead. Looking far ahead while still remaining aware of what surrounds you is both safer and more efficient for driving.
This is a good topic for the Facebook Prius Owners Club. I am an admin there and I have seen the topic discussed and debated there. Another good resource if you are into this topic in general (Maximizing a Prius vehicle’s performance) is Peter Neilson. He writes about this type of topic frequently. As a person who enjoys learning about green cars, I think with the Prius you are splitting hairs. It regenerates electricity when coasting and also when braking. I think the Prius folks will tell you that avoiding hard braking is always better. Gentle braking is another story. The regen works very efficiently in that mode. Many new green vehicles allow you to vary the regenerative braking force using the paddles on the steering wheel. I enjoy doing it. I think you would too.
I suggest you’ll find more information, along with much opinion, on a Prius site. As an owner of a Gen 4 Prius, which yours is, if you watch the real time performance window you’ll see that letting up completely on the accelerator pedal results in a modest rate of regeneration (one must maintain a very slight amount of throttle pressure to purely coast without regen). Pressing the brake pedal a bit more increases regeneration, though initially regeneration only. When sufficiently heavy braking is demanded the mechanical brakes are recruited to the mix, so smoothly it can be difficult to detect exactly when this occurs but I believe it’s after the indicator reaches the bottom, max. regen level. I believe coasting in neutral does not create regeneration, and Toyota advises against it (check the manual).
Low current charging may be more efficient than rapid charging (it depends variables like battery chemistry and charge level), so it’s conceivable that when approaching a stop regenerating at a lower rate over a longer time by relaxing the accelerator early may put more total energy back into the traction battery and heat it less than does delaying deceleration and creating higher current regeneration with the brake pedal later. Letting off early also will consume less fuel.
I hope you’re not coasting to the extent that it will annoy the people behind you.