beeeerock
Active Member
I do recognize that regeneration attempts to put back into the battery what it can every time you take your foot off the accelerator peddle. When the Highlander went into mondo-large size in 2008, we ordered the hybrid model and took delivery of the first one in the Interior. Obviously the ICE component of the drivetrain was the heart of the vehicle, with some minor electric capacity intended to help with fuel economy. I don't think it did much better than the non-hybrid version, but that's another story! However, regeneration was an important part of the system and it was also tied to the brake pedal, not just when you took your foot off the gas. I took an interest in how it worked and how efficient the vehicle was... my introduction to regenerative braking - LOL
The thing about regeneration is you will never put back into the battery on the way down the hill what you took out on the way up. I tried to comment on that in my last post, but upon re-reading it even I can't even get that out of my post properly, and I wrote it! :redface:
Without worrying about exact math, let's say the electric drive train is 85% efficient. So it would take 100 kWh from the batteries to put 85 kWh of energy to the tires. In this case of elevation, the energy goes to lifting the car up, adding potential energy to the car. We'll forget about the wind friction and other losses and concentrate only on the energy associated with elevation.
So you're at the top of the mountain and you've added 85 kWh of potential energy into the car by lifting it that far, by draining 100 kWh out of the batteries. Now you're headed back down and by the time you get back to where you started, you will have to bleed off all that potential energy in some way or another. In this case, through regenerative braking. But like the battery to tire energy conversion, there is an energy loss associated with converting the energy from the tires back into energy in the batteries. Let's say it's also 85% efficient. That means when you get to the bottom of the hill in this theoretical world where there are no other energy losses to confuse things, 85% of the 85 kWh end up back in the batteries. That's 72.25 kWh. So the trip up the mountain and back down again, in a perfect world in a perfect vacuum, cost 27.75 kWh. That energy went to heat in the batteries, power inverter, variable frequency drive (however they do it), etc. If you had not gone up and down that hill and had taken the flat road around the mountain instead, you'd still have the missing 27.75 kWh in the batteries.
Obviously this is MUCH improved from the ICE vehicle, which would have lost all that energy (all 85 kWh of it) through the brakes! But taking the mountainous road is going to come at an energy cost, even with regeneration, which is the point I was attempting to make.
