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Energy-efficient driving

Energy-efficient driving

I am currently experimenting with ways how to drive my Tesla as energy-efficiently as possible, and I have found a way where preliminary results show a 10% reduction in consumption.

Story: I currently have a loaner, provided by the fantastic Denmark Tesla team, when my 12-V Battery malfunctioned for the 3rd time in 3 weeks - they actually transported a loaner 400 miles to Stockholm and brought down my car for repair - WOW!!

This loaner, though, consumes about 10% more energy than my proper car with identical trips, identical settings and, as far as I can see, identical driving. Because of an imminent long haul this concerned me very much, so I started to think of ways of bringing down the consumption. I got the advice from a Tesla man: drive it as you would drive an ICE.

OK, fine. I have developed a style of driving with ICE:s that invariably beats their own consumption figures (and we all know that they are the "optimal" ones anyway). It is quite easy - roll the car in Neutral as much as circumstances allow.

I tried this with the loaner, and it immediately yielded really good results - minus 10%, from 310 Wh/mile to 278 Wh/mile in 40 degrees F.

The Tesla is built with such a small wind and rolling resistance so that these 2 factors coupled with the huge mass makes the Tesla roll "for ever", especially in a down-slope. If there's just a small decline it doesn't even lose speed.

The gearbox is so well-made that I learned in less than 2 minutes how to change back and forth between Drive and Neutral without anyone noticing anything.

So, if you free-roll and want to lose speed, put it in Drive and engage re-gen. If you want to keep the speed or increase it, just put it in Drive and - well, drive.

The Cruise Control doesn't do this well - it constantly gives small "puffs" of energy and then brakes, for instance when you reach a small hill, and the re-gen cannot be 100% efficient, so you lose more than you gain, whereas, if the hill is small enough, you just roll over it in Neutral or you see it coming and accellerate slightly BEFORE the hill and roll down after it (never accellerate uphill, if it can be avoided).

This car has such eminent rolling features that this can be done without at all disrupting the traffic flow, if applied intelligently (mostly meaning rolling downhill, but also anticipating a traffic jam or light).

I called Tesla and asked them if this could in any way, shape or form damage the car (I am driving a loaner, and I am much more careful with other people's properties than with my own), and the answer from the Danish SC was an unequivocal NO.

My lifetime average consumption (incl. the multiple showing-off accellerations in the beginning - I am only human...) with my proper car is 289 Wh/mile, with the temp has varied between 29 F and 50 F. Applying the free-roll system, I think I will get it down to 260 or thereabouts. Will keep you posted.

Would be interesting to hear, if anyone else has tried this and their experiences.

Robert

NKYTA | 25 October 2013

@robert
"experimenting with ways how to drive my Tesla as energy-efficiently"

Well, I can guess you'll hear some of the following comments on this post, ad infinetum - and then there will be some outliers. ;-)

1) Great service experience!
2) 12 V issues three times in three weeks? You've got a lemon!
3) Wow, that much, really? Might be worth a try to see if I get that in my P85 too.
4) What percentage are you really going to save in a flat area, no hills?
5) Are you crazy? I bought this car to drive it and I still pay much less in electricity than gas in an ICE!

I'm partial to #3, but locked into the #5 zone right now. Grin!
:-)

robert | 25 October 2013

And my answers would be:

1) Yes, unique, fantastic.
2) That possibility is occupying a lot of my thoughts.
3) Please do.
4) None. However, Sweden isn't Utah, nor even Holland or Denmark.
5) I bought the car "to save the planet". Having bought it, an additional feature is the almost indecent happiness that driving a Tesla brings with it. But primarily it is all about energy consumption and CO2, and to waste energy is tantamount to killing this planet, regardless of the price. Think where most energy is derived from!!!!! Then stop the wasting of it.

Robert

robert | 25 October 2013

I just got an answer from Jerome Guillen to my direct question if the free-roll system can harm the car:

"You are free to drive safely as you please."

I take that as a NO, it won't harm the car. Excellent.

Robert

Tâm | 25 October 2013

@robert:

I am not sure Neutral can re-generate electricity back to the battery or not. The less re-generative brake you can feel (such as switch from Standard to Low) the less re-generating electricity to your battery.

So, may be the question is: Is it better to 1) put it in Neutral so the car can roll freely without using electricity from the battery or 2) keep it in Drive so it can re-generate electricity back to the battery?

I would set the car to cruise as much as possible and release it (by pushing the stalk away from you) when I want to slow down to a stop then let the regenerative brake system does its magic.

Benz | 26 October 2013

Can you put the car in neutral while driving at high speeds as well (100 miles/hour) in an ICE car?

Tâm | 26 October 2013

@Benz:

There's no technical restriction to put an ICE to Neutral while rolling downhill at 100mph.

I experimented that on a Prius at about 65 mph and that would shut the gasoline engine off while the car coasted downhill but that would not regenerate any electricity to the battery so I always set it on Drive from then on.

Notre | 26 October 2013

Very interesting. I too use to coast the ICE car. Two comments:

1: Coasting also means less influx and efflux of current to and fro, and less battery wear which is good.

2: I fear accidentally engaging the Parking brake which could be fatal driving at high speed, or is there a mechanism preventing that?

robert | 26 October 2013

@Tam
Neutral doesn't re-generate anything, but doesn't waste anything, either. The whole point is that it is more energy-saving to let the car roll freely, when topography so allows, than either driving with the foot or Cruise Control. Drive doesn't generate anything at all, as long as you don't brake (=regen). Same as in an ICE car, but Tesla has advantages that normal ICE cars don't have, i.e. extremely low rolling (no regular transmission)/air resistance coupled with a heavy mass.

@Benz
Oh yes, no problems at all, if it is a manual gear, i.e. stick shift car. Automatic cars should NOT roll in Neutral, hence my question to Tesla. Tesla can, according to the 2 answers I have got.

Robert

Benz | 26 October 2013

Robert, actually by driving the Model S in neutral you can get a higher range out of a single charge. That is great.

robert | 26 October 2013

@Notre

Manual 4.7 If you try to shift into a gear that the current speed pr4ohibits, you hear a chime and the gear does not change.

It doesn't say so specifically, but I am very convinced that it applies to the parking brake as well. You don't have to use the coasting technique to accidentally press the Parking Brake, and I feel sure that this has been foreseen.

BUT I AM NOT GOING TO TRY!

Robert

Tâm | 26 October 2013

@Notre:

If I recall correctly, at high speed for a Prius, shifting to Park would become Neutral. and the car would continue to coast.

For Model S, at low speed (such as 10's mph, pushing the shiny chrome Park button would abruptly stop your car (Make sure you wear your seat belt or you might suffer teeth/head injuries from this.)

I have not experimented with high speed on Model S but I assume it would abruptly brake the car to a stop.

robert | 26 October 2013

@Benz

That was the whole object of the exercise. I need to go about 240 miles with no chance (or time) for recharging, in almost freezing weather. So I started thinking.

Robert

Notre | 26 October 2013

I just checked the Parking brake. Driving faster than 8 km/h (5 or 6 mph) it does not engage, so no problem. Will definitely try free rolling to extend max range.

Brian H | 26 October 2013

Regenned energy returned to the battery is a % (60 - 80) of the amount used to get to that speed in the first place, less rolling resistance. Then when you use it (from the battery) there are losses (around 10-20%) involved.

A perfectly timed rolling stop with no regen suffers no losses other than rolling resistance (which eventually stops you). But the limitations on your control and time spent are rather extreme! Nothing for nothing.

Sofie S. | 26 October 2013

@Robert

If you have the accelerator pedal between acceleration and regeneration, Does it consume a lot of energy ?

robert | 26 October 2013

@Brian H

I honestly - after some 30 years driving this way - can't see where I lose control at all. It all depends on how intelligently one applies the system. Unless you're alone on the road, it has to do with mental forecasts on what is going to happen, the topography, speed limitations, traffic lights etc, and that applies to all driving, whether a Tesla or not. One has to look a bit further afield than just the car in front of you. The only consequence that this system MIGHT have is more wear of the normal brakes, but, it is a matter of a split second to engage Drive and lift the right foot, and then you're back to where you normally would be.

The time spent is precisely the time the journey takes, and "my" system does not slow the ride, nor does it interrupt the normal flow of the traffic. So no time loss.

So I don't understand either of your drawbacks. Had you said: you have to concentrate on your driving more than otherwise, I would agree, even if it becomes second nature after a while. At the same time I don't think that would be a bad thing, generally speaking.

And, isn't it regenerated rather that regenned? :-)

Robert

robert | 26 October 2013

@Sofie S

I have just had the Tesla for 3 weeks. I think probably not, but I am not an authority. I personally find it very difficult indeed to keep the meter precisely there, and I don't honestly want to direct my concentration towards that aspect of my driving, since it would entail my staring at the Energy app all the time. Coasting/free rolling saves you from that - then the energy for propelling the vehicle forward definitely is off.

Robert

robert | 26 October 2013

Oh, stupid me, Sofie S.

I should have answered:

Yes. Mental. :-)

Robert

bp | 26 October 2013

Like with the climate system, should Tesla add a "Range Mode" setting for cruise control - which would optimize more towards energy efficiency than maintaining close to a constant speed?

July10Models | 26 October 2013

It only takes minimal practice to press the accelerator just enough for neutral. Keeping my foot in contact with the side wall gives you more precise control. The car does roll for what seems an extended distance but keep in mind it weighs two and a half tons. This way when your speed overshoots you can just lift your foot slightly to add regen or wait to bleed of speed if there are no cops around. You should only use regen to come to a complete stop or when slowing down is a must for the given distance to obstacle. I have gotten the energy consumption savings you are seeing and my car is set for max regen. Amazingly engineered vehicle.

bcimae.co.us | 26 October 2013

+1 bp

shs | 26 October 2013

Robert,

There is one source of loss with coasting that you should thing about: drag. If you are going down hill in vacuum (hold your breath) then it is fine to let the car accelerate from gravity as potential energy is converted to kinetic energy and then let the process reverse as you go back up the hill on the other side - nothing lost and nothing gained. In the real world, I calculate and Tesla’s range vs. speed graphs would seem to confirm, that if your downhill speed is allowed to increase more than about 15% then the losses from increased drag will exceed the losses from regenerations and you would have been better off using regen to keep the speed down. In fact going slower will always win when it comes to efficiency.

hillcountryfun | 26 October 2013

bp +++1!

I would really like for Tesla to add an economy mode for folks who are less interested in the performance aspects of the car and more interested in conserving energy. They don't have to market this new feature (if they feel that would detract from the car) and continue to make the normal (high performing) mode the default.

AmpedRealtor | 26 October 2013

@ shs ,

I hear this opinion quite a bit, but have yet to find someone who can actually prove the assertion using equations or citing someone who has made the calculations. I don't believe that regen is more efficient than coasting, assuming that you do not need to limit your coasting speed. Intuitively, kinetic energy goes through fewer conversions, hence fewer losses, than converting that kinetic energy to electricity, storing that electricity, and then withdrawing that power at a later time when it's needed.

Efficiency is described as the greatest distance traveled using the least amount of energy. By coasting, especially on a downhill, you are maximizing distance traveled while using almost zero energy. Using regen limits your speed, converting any kinetic energy that would have otherwise gone into moving your car forward into electrical energy and incurring approximately 40% loss of energy during the conversion (minimum 30% loss during regen plus efficiency loss when later removing that energy from the battery). The negative effect of wind resistance would have to be greater than the 40% energy loss incurred through the regenerative braking system in order for regen to be the more efficient process.

At least that's how I look at it.

shs | 26 October 2013

Drag goes with the square of the speed, and so a 15 to 20 percent increase in speed should increase drag losses to be equal to the regen losses you mention. Or perhaps another way of looking at it is that drag will keep you from completely converting you potential energy into kinetic energy as you will not gain as much speed in air as you would in a vacuum. If you look at the Tesla range vs speed graphs, loss of range with higher speed is very evident - increased drag is the main reason.

mikefa | 26 October 2013

i was told shifting back and forth between Drive and Neutral while going down a hill is not advisable in an ICE because it shortens the life of the transmission. Although the Model S does not have a transmission, turning the regen On and Off abruptly with a load can't be good either.

shs | 26 October 2013

In the US at least, I believe that it is not legal to drive in Neutral.

tezzla.SoCal | 26 October 2013

you can't drive in neutral; only coast. :)

shs | 26 October 2013

@tezzla,

You are right of course, but at least in CA it is coasting in neutral that is not legal!

AmpedRealtor | 26 October 2013

While drag may increase with the square of the speed, what is the actual amount of energy reduction due to drag? If you have a really tiny number, you can square it many times and never come close to the loss number experienced during regen. How large is the overall number, that's my question. Just having one variable in an equation squared doesn't mean the resulting number is going to be meaningfully high.

shs | 26 October 2013

At low speeds drag is not the real issue, so if we are talking about the speed increasing from 20 to 30 MPH - not an issue. I first contemplated this issue after talking to other MS owners at the Folsom SC where someone mentioned that he had hit 110 MPH coasting down from Tahoe. Drag is clearly an issue at this speed. In fact I think that if you look at the MS' range vs. speed data you will see that drag is the dominate factor in determining range at speeds, say above 50 or 60 MPH, as the range goes down with the square of the speed.

SCCRENDO.Ca.US | 26 October 2013

Interesting academic discussion but seriously guys. I am all for saving energy. That's why I got the Tesla and trying to get solar for my roof. Frankly I usually have more than enough charge on my battery for my daily needs and on the occasion that I am running tight I am not sure how many real world miles you are gonna save. Rather than traumatize myself worrying about when to switch from neutral to park I would rather stop off at a Blink station and grab a cup of coffee to get me back those 10 extra miles.

shs | 26 October 2013

Sccrendo,

Actually I agree with you. My wife and I used to carpool in our 2006 Honda Insight and I used every trick in the book to keep our trip mileage above 70 MPG. Believe me there is no one more smug or self-righteous than two vegetarian Sunday School teachers carpooling in a car that gets more than 70 MPG. Unless of course, you are driving a Tesla powered (largely) be solar panels. Problem the Tesla is just too much fun to drive to poke along at 45 in the right hand lane or take it easy coming out of a corner. You won’t catch me doing that unless I am very low on range. Go for it.

But I do like academic discussions, especially about the MS.

Prasad B | 26 October 2013

@robert@bis.se - thanks for sharing this. i tried this first thing in the morning for my local non-highway driving and I can see a big difference. i will keep trying this as and when it can be safely done without distracting my driving.

nickjhowe | 26 October 2013

Re. the parking brake - remember that at speed (not sure what the cut off is) the 'P' control switches from a parking brake (toggle on) to an Emergency Brake (push/hold on, release off)

tes-s | 26 October 2013

Just drive 25mph. You'll see a dramatic increase both in range and "saving the planet" - well beyond shifting to neutral.

Thomas N. | 26 October 2013

Wow, I just drive my car and drive it like a moron. I don't ever think it has been over 75mph but it has so many 0-60 runs that it's not even funny. After 6 weeks we're still under 1000 miles because we don't drive on freeways or long distances.

Our average energy is 375 Wh/mile! I guess if we really want to sell it four years from now I'll have to work on driving it at 30mph for about a year to average it down.

On the plus side it's stored in a garage at all times, is plugged in every minute that it is not driving, lives in the nice climate of Southern California and will never see snow or salt.

I seriously don't put any thought into how I drive it. I just have a lot of fun with it.

J.T. | 26 October 2013

@Thomas N

How dare you simply enjoy your car. This forum clearly dictates that one must (kind of afraid of using the word "obsess") sweat the details in order to get the true Tesla experience.

Keep it up and someone's going to put a crease in your frunk. :-)

mjs | 26 October 2013

+1 jtodtman

SCCRENDO.Ca.US | 26 October 2013

I'm totally with Tom however have over 14000 miles in 6 months. Average wH/mile = 346 since I got the car and I do mostly freeway driving in the HOV Lane. Not sure I am gonna put it into R, N or P anytime soon.

RZippel | 27 October 2013

Just a word of warning. Power is control is what you learn driving ships. Never ever risk not to have no power available. In "normal" driving situations that might not be any issue. But you should not plan for those only. If, to avoid an accident, trying to get the gear back in is the difference between a little throttle to make a turn wider to get past an obstacle or whatever and hitting something, you might (if you still can) regret this.

People tend to be overconfident of what they can do in normal situations, not applicable to the rare but not to be excluded non-normal events. I would rather try to keep the car with a sensitive foot in coasting or ask TM to make the bandwidth wider in which the car will by itself not accelerate or regen, as an option (low/high coast range) than to risk not having power available if needed. That's on of the reasons why it is forbidden to have cars in neutral on public roads, not if the transmission can take it or if the power steering or braking works (in most cases today it does in neutral bbut not all!).

I would not want that by the way with the higher coast bandwidth, I want immediate engine response in both ways. Control is life...

Brian H | 27 October 2013

RZ;
+1
Yes, that's what I meant and robert didn't get.

hillcountryfun | 27 October 2013

Instead of shifting to Neutral, can't you get almost the same improvement by changing the regen to low? I believe this is what BMW has on the i3, they automagically change the regen to low/off? when the vehicle is moving at highway speeds...

AmpedRealtor | 27 October 2013

I've just hit 303 Wh/m lifetime average and yesterday I averaged 280 Wh/m going to the store. On Wednesday I averaged 250 Wh/m driving home from Scottsdale - about 40 miles. I typically drive about 5 MPH over the limit and rarely exceed 70 MPH on the freeway unless I'm passing. I've had to change my display to Ideal Range because that more closely matches the actual range I get during daily driving.

Thomas N. | 27 October 2013

I set my display to Ideal Range as well and then mentally divide it in half because that's what I'm going to get. They should have a new setting: "Jacka$$ Range" and I would be happy.

shs | 27 October 2013

As hillcountryfull pointed out, one can decrease regen and coast more easily with the Low Regen setting, but the labels clearly imply this will decrease the range.

Notre | 27 October 2013

Tried low regen today. Soft and pleasant, but had to use the brakes frequently. Also tried coasting, but did not save measurably.

hillcountryfun | 27 October 2013

Notre: Could you tell a difference in the Wh/mile between coasting and low regen? Thanks -

Notre | 27 October 2013

No, I can't say, but braking wastes energy, so I guess low regen is less efficient. I enjoyed the smoothness though.

Robert Hodgen | 27 October 2013

Let off the accelerator gently until you zero the power consumption meter. I assume that this is almost the same thing as coasting.

Being able to judge the distance remaining until a stop and how much regen to use is an essential skill. Developing a sensitive right foot also makes for smoother driving. Just enough of a challenge to keep driving interesting.

The zen of one foot driving. . . . . . .

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