How much energy can regen get back in your Tesla

Using my Tesla Model S, I did few tests to find out how much energy can be captured back into the battery when using regenerative braking.

Get free Suercharging (and other cool stuff) on a Tesla if you use this link:

Tesla's blog post from 2007 about regen braking in the Roadster

Here is a quote from their blog post:
"How much energy does it recover?

Unfortunately, the adage “your mileage may vary” applies to regen as well. The amount of energy you can recover depends on how and where you drive. From the powertrain point of view it looks pretty good. The energy conversion efficiencies from chemical to electrical (battery), DC current to AC current (inverter), electrical to mechanical (motor), and torque to force (transmission and wheels) are all quite high and work just as efficiently returning energy into the battery. The bigger problem is aerodynamic losses and higher speeds and rolling friction of the tires. These both act to slow the car, but the energy dissipated cannot be recovered. We must also remember that, even though the battery-to-wheel conversion efficiency is pretty good (up to 80% or so), the energy makes a full circle back into the battery and it gets converted twice for a net efficiency of at most 80% * 80% = 64%."

In other words, the drive train round trip efficiency is 64% at best. After adding the other losses (aerodynamic and tires) it becomes clear that there is only a small amount available we can get back.

[JuergThomann]

Great video about regen. I had the opportunity to drive a Tesla in the Swiss Alps and I was amazed about the amount of energy I "gained" back simply by driving down a mountain.
Keep up the good work!

[peterthorsen]

Unless I misunderstood something, I think the regen efficiency is miscalculated in the video. I would use the follow formula, assuming a speed af 35 mph and a consumption at 35 mph (tires/motor/aero) of 200 Wh/m:
Energy spent (tires/motor/aero) driving 7 miles (up or down) = 7 miles * 200 Wh/mile = 1.4 kWh
Potential energy gained going up: 5.2 kWh - 1.4 kWh = 3.8 kWh
Energy retrieved going down: 1.7 kWh + 1.4 kWh = 3.1 kWh
Potential energy retrieved = 3.1/3.8 * 100 % = 81.5 %
Of course this is just a ballpark figure, but I believe the principle of calculation is more correct than the one used in the video

[DELHIBOMBAYDARBAR]

Immaculate explanation. In final analysis it's 32% because we still be driving car. The real gain comes from not expending any input energy, either battery or hybrid. Thx.

[damaliamarsi]

If I won the lottery I would buy a Tesla and just drive it around the country (USA) until the thing died. Seems very relaxing and you can enjoy the scenery.

[andysaputra]

Thank you for your 'forensic analysis' over regenerative braking. Just a little addition from me, battery also tends to charge slower compared when we utilise the battery. I think that's also why not all energy are captured when we slows down with regenerative braking. Cheers!

[scdi]

Got 10 miles back driving down Mount Hood in OR.

[therandomtester]

You can NOT say I used 5.2 kWh going up, gained 1.7kWh going down and than say it's about 30% effective!
If you spend 5, 2 kWh going up, and gain 5, 2 kWh going down, either you end up at another place (lower) or you have more than 100% effective regen (not possible).
Also, your kWh numbers (or %) will vary with how steep of a hill, how fast your going etc. etc. So, if you drive the same hill at say 20mph faster, the numbers will look totally different, maby 6, 5kwh up and gain 0, 5kwh going down.

These sort of numbers has to be compared to driving the same distance on flat surface in same conditions.
I tried to do that with my Leaf (CC set to same speed up and down a hill and then on a relatively flat surface).
It's very hard to come to an accurate conclusion as these testes should be conducted in controlled enviroment with more accurate readings than the car will provide. But looking at my numbers, the regen on the Leaf is at least 70% effective, but looks more like 90%.

Testing in different speeds, we found that increasing the speed by 10km/h (i.e. 50 to 60 or 70 to 80 km/h), consumption (on Leaf) increases by around 13%.
Tests on a road going a bit up and down showed that going at steady speed has far lower consumption than following the terrain as would be most economic in a fossil car. So regen is much better than building up speed, telling me that the regen must be close to 90% effective. In this test CC was at around 50-60 km/h while "following terrain"-speed was around 35-70 km/h.

[nsshing]

I'm impressed by the KE recycled.

[PaleHearse]

Great job on your videos. Very comprehensive.

[aliabouelazz]

hey a calculated the efficiency of the drive train of this tesla based on the numbers given in this video i found 83.5%
taking into account drag, tyre roll, variation in altitude and monitoring system consumption using theorem of mecanical energy derived from 2nd newtons law

[BrenttheGreat]

It will be interesting to see how much power is regained when they introduce trucks pulling 30, 000 pound loads. I imagine the extra weight would help capture a lot of energy. Of course getting up the hill will drain the battery in the hurry as well.

[ryanzhang]

U have to subtract the energies the car use to travel at the level elevation with the same distance and speed.

[JRo]

For me, the real issue with regen is that it should be applied to the brake pedal only. It is more efficient to coast forward than to regen, try to recover that energy and then use it to propel forward. It is not much and it doesn't make much of a difference in the larger battery sizes but coasting is definitely more efficient.

Try disabling regen altogether or even switching to neutral when coasting (as a test) and you'll see how the car just glides effortlessly. If regen can be applied only on braking action, it would not only be more efficient but the driving experience would improve as well. Of course, one-foot driving with 100% regen applied on deceleration can't be beat for bumper-to-bumper traffic so ideally, regen should be adjustable.

I had brake-only regen when I was a kid. I installed a dynamo on my bike that charged a battery and powered a light. It would kill me, especially uphill, to have the dynamo engaged at all times. I installed a switch on the hand brake so charging would only happen when I pressed it. Way better.

[nielsdaemen]

10:30 I think it is a hardware limit rather than a programmed feature, because If the motor/generator isn't spinning fast enougn you simply can't get 60KW out of it.

[marting.]

Maybe another way of looking at this problem:
The potential energy can be calculated with (mass*gravity*height) = 3.6 kWh
On the way down some energy is lost due to tires, aerodynamics and drivetrain (assume 200 Wh/mile). These are the losses that occur on a flat road (1.4 kWh for 7 miles). The battery gained 1.7 kWh. The the remaining energy of 0.5 kWh (14%) is lost due to regenerative braking.

[Cloxxki]

You could calculate the potential energy of the car on the top of that mountain and see how much of that was list due to mentioned losses.
Kinetic energy is just what you need to get the mass up to speed, or what's released when hitting the face of a mountain.
Coasting down that hill would have gone too quick in places, and not return a single joule to the battery. In a car race, coasting may be we worth it. You lose some energy but gain the equivalent or more in track time. Plus you cool the drivetrain systems. Brakes might like some help though.

[Soniti]

I would be curious to see what the total amount of power lost as heat is, because I suspect that’s what’s eating a big chunk of the power available to be recaptured. I wonder if cooling down the conductors would increase their efficiency, and allow more free energy to be reharvested.

[racecrashrepeat]

Hold on. I dont think this test shows much at all. Your going down a hill so your using the motors less and there is less weight to carry back down the mountain. I was so sure you were going to do the test in a more accurate way. 1 - Drive up the mountain and then down back again with regen disabled. Then do the same trip up and then down with regen on. Then compare the 2 trips and show what regen really gives us vs not using regen. I hope you understand we want to know regen vs enegry lost. This shows uphill vs downhill with regen. But there is no regen uphill so not an accurate test.

[dondakin]

I think going up and down a mountain is not a good wy to quantify regen.It would be better to accelerate to 60 mph then regen back down to zero. Film your dash and then play back the video and graph the results ie plot the power every second by looking at the video. The area under the curve is the total amount of power used in and out. You can then take a ratio of the power you put in to accelerate vs what you got back when you decel. You will get a higher number then 20% this way you remove most of the wind and rolling resistance energy that you use up over time.When you go up a mountain you are mixing up a lot of other ideas and complicating the issue. The amount of regen you get back will always be a function of the driving conditions and will vary a lot.

[MpowerSkill]

I heard once that regen burns your tires up. More than normal braking because it's doing regen whenever you're not on the gas unlike when I drive my ICE car and coast sometimes.