Can World’s Tallest Mountain Recharge A Tesla Model S Via Regenerative Braking – Video

8 months ago by Steven Loveday 35

Regenerative braking is a feature found on electric vehicles, which can recover some of the vehicle’s energy when the accelerator pedal is released, regenerated power back through the powertrain rather than causing waste energy from braking.

Tesla and The Hill: A Love Story

Tesla and The Hill: A Love Story

Some cars, like the Chevrolet Bolt, function well with “one pedal driving.” The regeneration does enough that you can avoid the brakes, except in obvious circumstances.

We have seen different “experiments” regarding the technology. One of which is towing an electric car with all wheels on the ground.

Another is letting the vehicle coast down a hill. Engineering Explained on YouTube attempts to see how this will work with a Tesla Model S. With everything considered, unless the mountain was about twice the height of Mt. Everest, you could never really fully recharge the car.

Video Description via Engineering Explained on YouTube: 

How big of a hill is needed to recharge a Tesla? How about A Nissan Leaf? Ultimately, it’s a matter of potential energy, and how much energy the Tesla could recover, based on its regen efficiency. There are gearboxes, motors, inverters, controllers, and finally the battery which the energy must transfer through, which all have efficiency losses. This is to mention nothing of rolling resistance or air resistance. Energy = force times distance, so this will allow us to determine what height is needed to recharge a Tesla. And finally, it’s imperative to put things in terms of Mt. Everest units. It’s a tall hill.

For more on regenerative braking, check out the video below.

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35 responses to "Can World’s Tallest Mountain Recharge A Tesla Model S Via Regenerative Braking – Video"

  1. ClarksonCote says:

    I recaptured over 70% of the Volt’s battery coming down Mount Washington. Of course, that battery is smaller than a Model S. 🙂

    1. Brian says:

      Very cool. So Mt. Washington would be too much for my CMax to handle, unlike the various mountain passes in Vermont.

  2. Pushmi-Pullyu says:

    “How big of a hill is needed to recharge a Tesla? How about A Nissan Leaf? Ultimately, it’s a matter of potential energy, and how much energy the Tesla could recover, based on its regen efficiency.”

    I submit that the steepness of the hill, or lack thereof, is one of the two deciding factors; the total altitude change is the other. The hill must be steep enough to overcome the rolling resistance. Practically, it must also be sufficiently steep to keep the car moving at a good speed. You might, in theory, be able to regenerate the battery when moving at 10 MPH, but nobody except the extremely stubborn dedicated would creep along for miles and miles at 10 MPH!

    Mt. Everest? That seems like a pointless comparison. No road going up a steep mountain goes straight up; it winds around, or if necessary uses switchbacks. So the question is how steep the road is, not how steep the mountain is!

    * * * * *

    In real-world terms, all I can say is that a friend of mine who drives a first generation, circa 2000 Honda Insight, said that when he drove down the other side of the Colorado Rocky Mountains, it regenerated his battery to 100%. That Insight is a non-plug-in HEV with a NiMH battery pack, similar to an early Prius.

    1. Brian says:

      I had a 2nd generation Insight, with the same battery (0.5kWh for those interested). It would charge completely in about 500′ of descent. After that point, the car would essential go into neutral and coast. It picked up a lot of speed on a long downhill. I don’t miss that.

      Today, my CMax Energi holds a lot more in its 7.6kWh battery (obviously). I haven’t yet met a hill that could charge it to full, even the various mountain passes in Vermont. Based on Mr. Cote’s statement, it sounds like Mt. Washington would do the trick. In fact, it may be the only road in the northeast that could recharge the CMax.

      1. guyinacar says:

        I did it in a Prius almost a decade ago, and it absolutely charged to 100% on the way down. In fact, I had to open the windows and run the cabin heat (which was recommended for hybrids at the time) on the way down. Of course, the ascent is mostly gas, and the ratio of fuel/battery couldn’t be controlled manually by the driver. In my current PHEV BMW, I’d be able to hit the summit at 0% battery, and then fill on the way down, because nowadays the ratio can be manually controlled by the driver.

        Agree with the comment above. It’s not impressive that regen will fill a battery while “dragging the brakes” (light regen, really) down the ~40 minute descent of Mt. Washington. That’s normal. What’s impressive is the engineering allowing a pure EV to make it up there in the first place.

        Hmm… I wonder if the new P100D could break the overall uphill speed record?

    2. MikeG says:

      Another data point–my Tesla 85 (RWD) gained about 10 miles from the I-70 Eisenhower tunnel exit to Denver. The Tesla display shows the capacity gains in jumps, not as a steady increase.

      This is roughly 3kWh gained plus the drag and rolling resistance to cover that same distance.

    3. Bill Howland says:

      Regeneration happens on plenty of hills – If the rise over run of the terrain is low enough the road traversing top and bottom can be direct. If high, The road engineers design a cirular path to the top.

      The regeneration rate, being variable on EV’s, is not that dependent on the speed. You can have quite a bit of regeneration at 15 mph, or just a little at 80 mph, or vice versa or anything in between. So there is no problem keeping up with traffic.

  3. Trollnonymous says:

    Didn’t someone tow a MS and recharged it that way?
    Thought I read it here.

    1. Pushmi-Pullyu says:

      Yes. There were reports of one or more Model S owners in Russia towing their car at a low speed, using regen to charge the battery… which is not recommended, or at least not on a regular basis.

      Russia at that time had no Superchargers, and I’m not sure if it has any even now.

      An article on the subject from March 2015:

      http://insideevs.com/watch-tesla-model-s-get-charged-towed-video/

  4. Priusmaniac says:

    What I find stunning is actually the reverse, a Model S would be able to drive to the top of the Mt. Everest.

  5. Codyozz says:

    Guys, I am happy to report that with my ’13 Volt I was able to go from ~%5 SOC to about ~95% SOC driving down Mauna Kea from an elevation of 9,500′ to sea level. Making the trip even more fun, I was out of gas and nearly out of electricity as I made the Mauna Kea Visitor Center (mid mountain).

    I’m also happy to report that if I had continued on (the road goes to 13,600′) I would for sure have done a full 100% recharge on my smallish battery.

    Conclusion: Even from Mt. Everest I don’t think you could gain back more than 30 or 40 kWh on the descent.

    1. Ken Sherman says:

      The recoverable energy is larger in a heavier car. It also takes more energy to get it up the hill.

      1. Codyozz says:

        Ken, I can also report that me and 10 of my EV buddies did a Regen Contest on Mauna Kea a few months ago to see if we could determine which cars were bettter or worse. We had a good field of contenders and the metric was kWh recovered. We had two Model S (60&p85) two 13 Volts, one 17 Volt, one Kia Soul, and four LEAF’s. We all drove identical speeds up to about 5000′ el, and turned around and drove to the ocean. The guy in the Kia couldn’t figure out his kw, but the Nissans fared much better (and worse) than all the others. I recovered about 3.5 (average) and the winner (13 LEAF) recovered about 4.4 kWh. We had one old 11 LEAF that only recovered about 2 kw. The Teslas both recovered about 4 which were good for 3rd and 4th places. But they sure as heck didn’t outperform the field even though they are much heavier. I was surprised too.

    2. Codyozz says:

      I would suspect that the rear wheel drive has something to do with the results (as rear wheels only can do about 30-40% of the braking on a car) and that another friends 90D might have won, had he participated. I wished we’d had one of our VW eGolfs and a BMW i3 as well but they couldn’t make it. Maybe we should do one again this summer.

  6. Bill Howland says:

    You would think that with the number of years gone by, and the hundreds of thousands of electric cars made, that the ‘Great Brains’ would get this stuff right.

    First of Mr. Loveday : “…Friction is created, and the car will slow, without even engaging the brake pedal, sending the captured power back to the battery….”

    Friction is actually a complicated physical process, but the simple end result that everyone knows is ADDED HEAT. While this added heat may at some times and places may be useful, at present there are no EV’s nor none planned to utilize the frictional heat from the brakes for other purposes. Other frictional losses are bearing, windage, and tire heating losses, and shock/strutt losses – and only one of those has even been theoretically considered as recoverable electric energy.

    Since all frictional losses result in heat, there is little electricity to be recovered from this process, and therefore it is not used in any EV. EV’s recover/regenerate/recooperate electrical energy using a Generator or Dynamo (if you prefer) to produce electrical energy directly, since you need a drive motor in the first place.

    As far as the ‘Budding College Professor’ goes – it would help if he had more realistic diagrams.

    For instance, in the 4 ev’s I’ve owned there has never been any hint of maintenance of the Generator SLip-Ring Brushes – primarily because no EV (or at least, no commercially available EV) HAS THEM, because they have no slip-rings period.

    In most EV’s the magnets, or induced magnetic field is rotating, and it is the STATOR which is recovering the recooperated energy which is Stationary, hence the name.

    DC machines used 100 years ago had rotating armatures and commutating brushes – which optionally had regeneration – but MOST PEOPLE are interested in somewhat more modern Electric Cars, and how they work.

    1. dgate says:

      Well said, I too was curious if anyone would point out the misuse of the word friction in this instance. Just shows most are into bragging rights rather than details of how the modern EV works.

      1. Bill Howland says:

        Thanks dgate. The future ‘college professor’ didn’t say very much at all – I wonder how he’d field a question as to:

        “What controls the RATE of regeneration?”

        He said it was ‘force on the wire’, which is true enough, but his answer to the above question – NOT giving him the benefit of the doubt this time – may have been a knee slapper.

        Tried to watch his “All about AC” treatise but couldn’t find it.

      2. Bill Howalnd says:

        I see Loveday silently removed the reference to FRICTION causing regeneration. Uh, you’re welcome, guys.

  7. Jim On Oahu says:

    We have a LEAF. There’s a rather steep 3-1/2-mile hill that we need to climb on our way to town. The way up uses 25 miles of battery. The same way down (one-peddle driving) recharges 15 miles of battery. Thus the 7-mile round trip uses 10 miles of battery. All data according to dash display.

    1. codyozz says:

      Jim, you should try (if you can) to determine how many KILOWATT kWh you regen on that descent. The guessometer will never produce accurate results for you as temp, time and prior driving all factor into that number. You can estimate kWh using the bars on your dash, but it would be more accurate to have a starting State of Charge (SOC) and ending SOC to extrapolate kwh reclaimed on your descent. It’s not too hard on the LEAF since 1 kw represents about 5%. And with 12 bars on the dash, you can estimate that each bar represents about 1.6 kWh. Except bars aren’t exact, unless you JUST TURNED OVER a bar at the start and just turned over another bar at the end.

      1. MikeM says:

        I’d use the %charge indication.

        The bars roughly track %charge but lack the (≈1%) granularity/resolution of %charge. That’s in addition to the other vagaries.

        On reflection, this is probably what you meant by
        SOC(end) – SOC(start).
        Oh well, never mind!

    2. SparkEV says:

      Are you moving at the same speed up and down the hill? What energy use do you see if you drive on flat road for same distance at same speed?

      Speed is the crucial part in determining how much energy you get back. If you’re traveling too fast, there may not be regen to put back in the battery. How much regen you get is a function of slope and speed.

      For example, if the hill only provide 10 kW while your speed at 55 MPH uses 10 kW on flat road, you wouldn’t see any regen going down that hill. But if the hill is steep enough to provide, 20 kW, driving down the hill at 55 MPH (10 kW used) would still net 10 kW going to the battery.

  8. Nfuzzy says:

    I gained roughly 7kwh or 34% SOC coming down pikes peak in my 15 leaf. Have done this twice with similar results.

    1. Scott says:

      Wow. And I really mean WOW. I’ve been talking about running up to Woodland Park from Ft Collins and working in Pike’s. I could see doing that and still camping at Lake George- on the same charge from CO Springs.

      That’s awesome. (2013 Leaf with 48k miles.)

      1. Nfuzzy says:

        Possible but probably cutting it real close to go to lake George. I came all the way back to i-25 to measure that gain because really that is all downhill.

  9. Nix says:

    Meanwhile, Republicans begin their war against wind and solar:

    http://www.environews.tv/012417-wyoming-gop-introduces-bill-penalizes-outlaws-wind-solar-energy/

    And the new administration begins silencing the EPA and other fed. gov’t agencies, freezing their spending. Effectively neutering them.

    http://thehill.com/homenews/administration/315989-trump-clamps-down-on-federal-agencies

    1. Ziv says:

      That bill can’t even get out of the GOP led committee. I don’t think it will ever see the light of day. It lost a vote again on Monday.

      http://www.wyomingnews.com/news/revenue-committee-kills-wind-tax-bill-again/article_4bd00d82-e202-11e6-86f3-5bdb1350050a.html

  10. McKemie says:

    I have twice moved new imievs home from the points of purchase, 150-200 miles, using regen to charge. I towed (with a Tesla) about 30 miles per segment, then drove 30-50 miles. The projects worked exactly as expected. I effectively drove the imievs on SuperCharger energy.

  11. Steven says:

    I think he neglected to calculate that atmospheric density will vary with altitude.

    1. Gravity increases as you get lower down, though – and air density is a tiny factor in this scenario.

  12. jim stack says:

    The Tesla is able to REGEN more than other plugins. In real life you would not be at Zero Energy when you go down hill. If a car with a smaller battery got full the REGEN would not work and you would waste all the extra energy. So the Tesla is the best for REGEN and the model 3 will be even better.

  13. Anderlan says:

    The funny part is that the program guessing your miles remaining will start telling you you have infinite range based on the guess that you’ll keep up the same regen regime indefinitely.

  14. The best way to design regen – is to integrate it on the brake pedal. Coasting makes the best use of the energy “stored” in the moving car – because it uses it to move the car forward.

    The only losses during coasting – are going to happen anyway. Regen will always lose more energy, by definition.

    Yes, let’s have regen – for when you need to slow down. Regen is much better than friction brakes; but coasting is much better use of the energy.

    By coasting, you accelerate less, and you lose less energy, too. VW has the best example of how to design regen.

    1. Doggydogworld says:

      “One-pedal” driving is convenient in traffic, though. Also, it’s hard to get the right “feel” with brake-pedal regen.

      You are correct about coasting, of course. It drives me nuts when I read people who want to maximize regen to increase range. Hypermilers see regen as their enemy!