Has anyone returned their Tesla?

[mswlogo]

No problem, it came as a surprise to me when I first noted the strong correlation between fuel consumption and summer and winter temperature, when I bought my first Prius in 2005. I started logging the consumption data, and as I was commuting ~40 miles each way each day, the the data seemed reasonably reliable. This was the pattern of consumption, which happens to match very well with the change in temperature through the seasons. It convinced me that increased drag from cooler air seems to play a significant part. As a pilot, I'd already experienced the significantly increased lift in cooler air (and the converse, too), so this seems pretty logical:

And how can you conclude it's all air density. Unless you NEVER turn the heater on. 90% of cool weather reduction in efficiency is the heater, as most everyone here has eluded to. I frequently run with HVAC off, seats off and wheel off in the winter and get pretty close to summer efficiency (but not quite).

 

[d.c.palmer]

As I've said before: use heated seats, turn down the AC - and preheat your car on cold mornings.

 

[Glan gluaisne]

And how can you conclude it's all air density. Unless you NEVER turn the heater on. 90% of cool weather reduction in efficiency is the heater, as most everyone here has eluded to. I frequently run with HVAC off, seats off and wheel off in the winter and get pretty close to summer efficiency (but not quite).

I didn't conclude it was ALL air density change at all, however, the laws of physics apply to cars, just like anything else, so there will be an aerodynamic drag change with any change in air density, and air density is proportional to temperature (amongst other things). The plotted pattern has a very strong correlation to seasonal temperature change here, and although correlation does not prove causation, it is pretty convincing, all the same.

By the same token, aerodynamic drag should be reduced when the humidity is high, given that water vapour is less dense than air, although I suspect the impact of this is way below the detection threshold for such a simplistic data acquisition method as I used back then.

As I stated, the car that data set came from was a Prius hybrid, so all of the cabin heating will have come from waste heat from the engine (the Prius didn't have a reversible heat pump for the AC). This also means that fuel efficiency in warm weather will have been impacted by the AC, though, as would the efficiency in humid weather, when the electrically driven AC heat pump may have been providing dry air for demisting.

All told, that pattern of energy use versus season is such a good match for the seasonal air temperature variation that it's pretty hard to argue against the major part of it being due to increased aerodynamic drag in coller air, IMHO.

 

[mswlogo]

I didn't conclude it was ALL air density change at all, however, the laws of physics apply to cars, just like anything else, so there will be an aerodynamic drag change with any change in air density, and air density is proportional to temperature (amongst other things). The plotted pattern has a very strong correlation to seasonal temperature change here, and although correlation does not prove causation, it is pretty convincing, all the same.

By the same token, aerodynamic drag should be reduced when the humidity is high, given that water vapour is less dense than air, although I suspect the impact of this is way below the detection threshold for such a simplistic data acquisition method as I used back then.

As I stated, the car that data set came from was a Prius hybrid, so all of the cabin heating will have come from waste heat from the engine (the Prius didn't have a reversible heat pump for the AC). This also means that fuel efficiency in warm weather will have been impacted by the AC, though, as would the efficiency in humid weather, when the electrically driven AC heat pump may have been providing dry air for demisting.

All told, that pattern of energy use versus season is such a good match for the seasonal air temperature variation that it's pretty hard to argue against the major part of it being due to increased aerodynamic drag in coller air, IMHO.

Well, Your chart also correlates exactly when folks turn on their heater. You have no idea how much is air density vs the heater. I think most agree air density has impact and sure, the pattern would be the same for the heater and air density. unless you isolate one from the other you have no idea which is contributing to most of the amplitude change. But you keep assuming it’s all air density. Because it correlates with seasonal temperatures.

All you have shown is EV is less efficient in winter and nothing more. I think we all know that.

On a Model S/X temperature also triggers the battery heater.

 

[Glan gluaisne]

Well, Your chart also correlates exactly when folks turn on their heater. You have no idea how much is air density vs the heater. I think most agree air density has impact and sure, the pattern would be the same for the heater and air density. unless you isolate one from the other you have no idea which is contributing to most of the amplitude change. But you keep assuming it’s all air density. Because it correlates with seasonal temperatures.

All you have shown is EV is less efficient in winter and nothing more. I think we all know that.

On a Model S/X temperature also triggers the battery heater.

Perhaps worth re-reading my post again?

How. exactly, does turning on a heater that is run from waste engine heat change the fuel consumption?

The heat going to the heater in that car would, in summer, be dissipated by the radiator and cooling system. In winter, part of that waste heat is just diverted to heating the cabin.

It seems that several who are commenting on this data set haven't taken the time to read and understand the text that goes with it. Might be useful to do so, as it does help to explain both the rationale and the laws of physics that support the correlation that I observed back then (2005 to 2007, BTW, so before any Tesla was on the road here in the UK).

 

[mswlogo]

Perhaps worth re-reading my post again?

How. exactly, does turning on a heater that is run from waste engine heat change the fuel consumption?

The heat going to the heater in that car would, in summer, be dissipated by the radiator and cooling system. In winter, part of that waste heat is just diverted to heating the cabin.

It seems that several who are commenting on this data set haven't taken the time to read and understand the text that goes with it. Might be useful to do so, as it does help to explain both the rationale and the laws of physics that support the correlation that I observed back then (2005 to 2007, BTW, so before any Tesla was on the road here in the UK).

Your correct that I missed that it was a Prius. But the Prius also has an Electric heater. So it depends on how long the trips were to know what contributions were the electric heater vs air density. Also the Winter impact didn’t look anything like the the amount of impact we are talking about on a pure EV. Also ICE engines (like the one in Prius) are known to be less efficient regardless of air density drag coefficient effects. So the chart is even less meaningful as a conclusion that air density is a huge effect on EV.

My guess is the largest impact on the Prius in winter is the cost of keeping the engine warm in winter to meet emissions. And not air density.

So many variables and huge leap to assume it’s mostly air density drag causing it.

So you have:

Running ICE engine more to maintain temp.
Electric assist heater.
ICE engine running less efficient (less efficient fuel too)
Air Density Drag

And probably more. And you conclude it’s air density.

 

[Glan gluaisne]

Your correct that I missed that it was a Prius. But the Prius also has an Electric heater. So it depends on how long the trips were to know what contributions were the electric heater vs air density. Also the Winter impact didn’t look anything like the the amount of impact we are talking about on a pure EV. Also ICE engines (like the one in Prius) are known to be less efficient regardless of air density drag coefficient effects. So the chart is even less meaningful as a conclusion that air density is a huge effect on EV.

My guess is the largest impact on the Prius in winter is the cost of keeping the engine warm in winter to meet emissions. And not air density.

So many variables and huge leap to assume it’s mostly air density drag causing it.

No, the Prius doesn't have an electric heater, it runs from waste engine heat. Whenever I used the precondition button on the remote in winter the engine would start to run the cabin heat. Not sure why Toyota didn't just make the electric heat pump that runs the AC reversible, like the one in the Nissan Leaf, but for whatever reason they stuck with using engine waste heat for the heater.

As someone who has built and designed aeroplanes, and worked as a flight test scientist for over 20 years, I'm reasonably familiar with the way air density changes with temperature, and can state categorically that it accounts for a significant proportion of the increased energy used in cold weather, just to overcome drag. Engine efficiency doesn't change much with temperature/density, but power output does. The increased power output from a higher charge density on cold weather doesn't have much impact on efficiency, though, as modern IC engines use mass flow air sensing, which compensates for air density changes.

The change in aerodynamic drag with air density is well understood and just working through a few examples for a given set of conditions will show the magnitude of the impact it has. I have given both the drag equation and some worked examples earlier to illustrate the magnitude of the effect.

 

[mswlogo]

No, the Prius doesn't have an electric heater, it runs from waste engine heat. Whenever I used the precondition button on the remote in winter the engine would start to run the cabin heat. Not sure why Toyota didn't just make the electric heat pump that runs the AC reversible, like the one in the Nissan Leaf, but for whatever reason they stuck with using engine waste heat for the heater.

As someone who has built and designed aeroplanes, and worked as a flight test scientist for over 20 years, I'm reasonably familiar with the way air density changes with temperature, and can state categorically that it accounts for a significant proportion of the increased energy used in cold weather, just to overcome drag. Engine efficiency doesn't change much with temperature/density, but power output does. The increased power output from a higher charge density on cold weather doesn't have much impact on efficiency, though, as modern IC engines use mass flow air sensing, which compensates for air density changes.

The change in aerodynamic drag with air density is well understood and just working through a few examples for a given set of conditions will show the magnitude of the impact it has. I have given both the drag equation and some worked examples earlier to illustrate the magnitude of the effect.

I’m sure preheating your Prius had zero impact on your fuel consumption in winter as well. Add that to the list of variables. It would have avoided the electric assist though. But Preheating is a HUGE waste of energy. And it shows in your chart. I’m going to conclude that it was all preheating. I’m joking, but that would be as lame as saying it’s all air density.

I’ve not owned a Prius but what I do know and have read it does have electric assist heater (maybe not every year). Also the plug in Prius does have a heat pump now.

Your chart is meaningless here.

This topic is discussed heavily elsewhere and the consensus is the Winter Blend of fuel which has less energy is the primary reason for the drop. Lots of comments that their mpg was still low on warm winter days because of the fuel in their tank. The 2nd is engine “warm up” before it runs most efficient. Your preheating will put a pretty heavy weight on waste due to “warm up”.

Winter blend is gradually changed through out the year. Practically matches your chart.

 

[Glan gluaisne]

I’m sure preheating your Prius had zero impact on your fuel consumption in winter as well. Add that to the list of variables. It would have avoided the electric assist though. But Preheating is a HUGE waste of energy. And it shows in your chart. I’m going to conclude that it was all preheating. I’m joking, but that would be as lame as saying it’s all air density.

I’ve not owned a Prius but what I do know and have read it does have electric assist heater (maybe not every year). Also the plug in Prius does have a heat pump now.

Your chart is meaningless here.

This topic is discussed heavily elsewhere and the consensus is the Winter Blend of fuel which has less energy is the primary reason for the drop. Lots of comments that their mpg was still low on warm winter days because of the fuel in their tank. The 2nd is engine “warm up” before it runs most efficient. Your preheating will put a pretty heavy weight on waste due to “warm up”.

Winter blend is gradually changed through out the year. Practically matches your chart.

I'm not at all sure how you can say "your chart is meaningless here" as that is just direct contradiction of the very well known laws of physics. The drag equation is both simple, and proven beyond any doubt to be true (it's the same as the lift equation, with the critical area and coefficient swapped).

There's no such thing here as "winter blend fuel" either, our fuel is the same all year around, so that's another red herring.

Just to try and make this clearer, here is some hard data, along with two representative calculations to prove the point that drag is significantly greater in cooler air:

The Prius projected frontal area, A = 2.14m² (data provided by Toyota)

The Prius drag coefficient, Cd = 0.26 (data provided by Toyota)

The drag equation is 0.5*ρ*Cd*A*V²

ρ for air at 20°C is 1.2041kg/m³ (source: Density of air - Wikipedia )

ρ for air at 0°C is 1.2922kg/m³

Assuming an average speed of 18m/s (just over 40mph, reasonable for the single lane A and B road commute I was doing at the time), then we get the following figures for aerodynamic drag:

For the 20°C condition:

0.5*ρ*Cd*A*V²= 0.5*1.2041kg/m³*0.26*2.14m²*18² = 108.534 N aerodynamic drag

For the 0°C condition:

0.5*ρ*Cd*A*V²= 0.5*1.2922kg/m³*0.26*2.14m²*18² = 116.475 N aerodynamic drag, an increase of 7.3126%, just from the air being cooler.

The conclusion is clear and inescapable; cooler air is denser and causes more aerodynamic drag, and more drag needs more engine power to overcome it.

Sure there are other factors, like the reduced energy recovery from cold tyre deflection, from the slower flexure response of cold rubber, the effects of preheating in extremely cold weather (bear in mind that winters are relatively mild here, though, and really cold nights that need morning preheating are sporadic). There are also other effects like increased viscous drag from cooler oil in the transmission and engine for a time after start up, and probably a slightly increased drag coefficient from the very tiny impact of the higher cabin air flow rate, but none of these change the fact that the seasonal change in aerodynamic drag is both real and significant.

 

[MaDProFF]

I do not agree on some peoples thought the car will be obsolete in 10 yrs as it is a computer on wheels, Computers are cheap to upgrade, (Tesla I beleive have been upgrading some computers and HW for on earlier models FOC) in 10 yrs Battery replacements will be far cheaper than now, (not that you will need a battery replacement in 10 Years at current rates) I personally think it will be far cheaper than an ICE car to run it for longer, with the added bonus of still have a far cheaper running cost.

Also there will be 3rd party companies to rebuild and rewind motors as well.

 

[pgkevet]

I do not agree on some peoples thought the car will be obsolete in 10 yrs as it is a computer on wheels, Computers are cheap to upgrade, (Tesla I beleive have been upgrading some computers and HW for on earlier models FOC) in 10 yrs Battery replacements will be far cheaper than now, (not that you will need a battery replacement in 10 Years at current rates) I personally think it will be far cheaper than an ICE car to run it for longer, with the added bonus of still have a far cheaper running cost.

Also there will be 3rd party companies to rebuild and rewind motors as well.

I hope you're right but my own belief is that there will be additional sensors by then and even if batteries can be replaced the market will have moved on to better tech so the cost of doing so in small numbers will be prohibitive. It;s not so much rewinding motors as the rest of the drive unit - complex beasts they've already had to imporve bearings for. As to the build quality and spares cost for the rest of the car it'll be a case of can be done but uneconomic. Of course computers can be upgraded but by the time you stick in a new motherboard for a new processor and faster, bigger memory and new graphics processors etc the only thing left is the box and you need a new power supply for that and USB4 - so you buy a new prebuilt unit for less preloaded with current OS that will no longer run on the old one.

I don't think there is any enforceable obligation on manufacturers to supply parts for out of production vehicles for a set period. It's mostly myth although they will have some stocks and hopefully 3rd parties if demand is high - but will it be with all the new competition by then?

 

[MrBadger]

I don't think there is any enforceable obligation on manufacturers to supply parts for out of production vehicles for a set period.

Absolutely correct, but if Tesla (or any other manufacturer) are seen to be selling a car with an unreasonable limited lifetime, then that will be commercial suicide.

 

[Dejavus]

Plus, i personally think this is like an airplane, they do last lot longer than 5 - years, am sure there are commercial airplanes that have been in service for more than 15 year and are still ticking along nicely.

"According to airfleets.net – a website which monitors most major airlines – of the world's 30 largest carriers (based on passenger numbers), Delta Airlines has the most mature planes with an average age of 17 years."

 

[Dejavus]

I have the SR+ and absolutely love it.

My only problem is the range as i’m doing about 70 miles commute every day and its costing me 140 miles in range, believe this is mainly because of the weather, i have the heating on auto set to 25 and heated seats on low. my concern with this is that at the moment its manageable but in the future with degradation this could be an issue and i’m looking to keep the car for 10+ years.

I’m now considering getting a refund within the next couple of days and saving up for the long range model.

I’m just wondering of the returns process is simple enough as i read the conditions online but it talked about if you have an incentive then you cant have a refund, is that correct? Surely most tesla have the ev incentive.

Any help would be much appreciated

Hi Mike,

How was your return experience, what was the process?

Did you had to call or you just drove to West Drayton/ Dartford to drop off the car?

Thanks

 

[Glan gluaisne]

Plus, i personally think this is like an airplane, they do last lot longer than 5 - years, am sure there are commercial airplanes that have been in service for more than 15 year and are still ticking along nicely.

"According to airfleets.net – a website which monitors most major airlines – of the world's 30 largest carriers (based on passenger numbers), Delta Airlines has the most mature planes with an average age of 17 years."

Around 20 years or so ago, I regularly flew an aeroplane that was built two years before I was born. At that time it was over 45 years old and still going strong. There are some airlines in out of the way places still flying aircraft built in the 1940's. Some of them, like the DC-3, are pretty much indestructible, the only limit on how long they can carry on working is really spares availability. I think they stopped making DC-3s in 1943.

 

[Xopher78]

Get the Long Range. I have a 200 mile round trip commute, have done 9.6k miles since Aug 21st and have never once s*** the bed. Simples.

 

[navt]

@Mikeoneuk85 Sorry to see you returned your SR+. I know this thread when a bit off topic but what was your experience (not that I plan to return my car)? Is a LR on order?

 

[Rooster6655]

I don't think there is any enforceable obligation on manufacturers to supply parts for out of production vehicles for a set period

Well I believe EV1 owners may disagree " the cost of maintaining a parts supply and service infrastructure for the 15-year minimum required by the state of California meant that existing leases would not be renewed, and all the cars would have to be returned to GM's possession."