200 kWh Roadster Pack: How is Tesla Pulling This Off?

[mongo]

I was surprised also during the preview that the 2020 Roadster will have a 200 kWh, mostly because of the additional weight,
and also considering the constant improvement of the cells. So there must be some specific reasons to justify it.

Or is it for justifying the price, otherwise a 120 kWh Roadster could have been sold around the price of a 100 Model S or X.

Note: I assume that the next generation of Model S and X will get a 120 kWh. So I think that a Roadster with a single 120 kWh
would be also more optimum to keep cool than a dual 100 kWh batteries packs placed on top of each other.

Regarding cooling, the cells are coupled to coolant tubes on their sides, so having the heat generation spread across more cells would increase the cooling ability of the pack (more cell -> more tubes, more cells-> less heat per cell).

Pack size is likely due to the desired discharge rate for longevity, 250 MPH is a lot of power, even if you are aerodynamic (made up numbers) At a drag coefficient of 0.23 and a frontal area of 2m^2 that is 770kW output. So with a 120kWh pack, it would be running at a greater than 6C discharge rate.

Better write up:
Tesla’s Next-Gen Roadster: A (speculative) technical look at the car that will “smack down” gasoline powered cars

 

[Cloxxki]

I was surprised also during the preview that the 2020 Roadster will have a 200 kWh, mostly because of the additional weight,
and also considering the constant improvement of the cells. So there must be some specific reasons to justify it.

Or is it for justifying the price, otherwise a 120 kWh Roadster could have been sold around the price of a 100 Model S or X.

Note: I assume that the next generation of Model S and X will get a 120 kWh. So I think that a Roadster with a single 120 kWh
would be also more optimum to keep cool than two 100 kWh batteries packs placed on top of each other.

Anyway, I can't wait to see some Nurburgring numbers!

I don't see a point for a needlessly large and heavy 200kWh pack.
And I object that we have actually see a true cell improvement from them either in power or energy density since Tesla launched the 90kWh pack, which in inself was only in some ways better as DC fast charging had to be limited over swift degradation. 2170's seem to offer less power density than 18650's and similar energy density. Charging seems marginally faster though, but that could be down to better cooling design also.

 

[Peteski]

Better write up:
Tesla’s Next-Gen Roadster: A (speculative) technical look at the car that will “smack down” gasoline powered cars

Just skim read that article and I think it's a good summary of the pros and cons. I don't necessarily think the Roadster 2020 needs to be the ultimate track car, as it's strengths are going to be its everyday usability combined with colossal power and long range. It's not like a Bugatti Chiron is a great track weapon either, but still highly desirable as a hypercar. But the Roadster is a much better proposition for cruising around in on a daily basis and isn't going to require your own oil refinery to run! In that sense alone it brings a whole new dimension to the practicality of a hypercar and for me that's what would really interest me as a potential owner. But I still want to see a smaller battery option!

 

[ICUDoc]

Just skim read that article and I think it's a good summary of the pros and cons. I don't necessarily think the Roadster 2020 needs to be the ultimate track car, as it's strengths are going to be its everyday usability combined with colossal power and long range. It's not like a Bugatti Chiron is a great track weapon either, but still highly desirable as a hypercar. But the Roadster is a much better proposition for cruising around in on a daily basis and isn't going to require your own oil refinery to run! In that sense alone it brings a whole new dimension to the practicality of a hypercar and for me that's what would really interest me as a potential owner. But I still want to see a smaller battery option!

Yes. I want a great GT with long range.
All this track-talk applies to a very small fraction of consumers.
No car can be all things to all people, and a track-focussed version wouldn't trouble me- but just hurry up and deliver the Roadster 2020 as described, please!

 

[ShaunRF]

It's true, but you're still fighting against basic physics with excessive mass. As a trained physicist you should be able to relate to that surely? There's a good reason why the Porsche 919 can lap the ring 87 sec faster than the Nio EP9. The Nio is 1735 kg vs 849 kg for the Porsche. Non of the inherent EV advantages can remotely overcome that kind of weight difference. Remember all those dynamic loads generated by that mass are going through 4 little rubber contact patches, however cleverly you apply it.

Perhaps a better comparison would be the Porsche GT2 RS at 1470 kg. Even with just 690 hp, it's still over 5 sec quicker than the Nio with 1300 hp. So that's trading only 265 kg for around 600 hp. I say again from experience, mass is critically important when it comes to achieving lap times!

Handling/weight arguments aside, I'm not sure its apropos to directly compare horsepower figures between an ICE car with a multi-speed gearbox and an electric car with a single reduction gear. Even with the torque advantages of an electric motor, 1,300hp through a single gear does not behave the same as 1,300hp though a quick shifting six speed box. Especially for a track like The Ring, where you can't just gear it for a relatively narrow speed range.

No disrespect intended of course. I'm not an engineer or a physicist, just some dude on the internet.

 

[Peteski]

Handling/weight arguments aside, I'm not sure its apropos to directly compare horsepower figures between an ICE car with a multi-speed gearbox and an electric car with a single reduction gear. Even with the torque advantages of an electric motor, 1,300hp through a single gear does not behave the same as 1,300hp though a quick shifting six speed box. Especially for a track like The Ring, where you can't just gear it for a relatively narrow speed range.

No disrespect intended of course. I'm not an engineer or a physicist, just some dude on the internet.

I agree it's not fair to compare peak power figures directly, but I would still expect the Nio EP9 or Tesla Roadster to comfortably out drag a Porsche GT2 RS at any speed appropriate to a track environment. The Porsche would certainly be at a power disadvantage overall, but it's considerably lighter!

In very simple terms an EV has a constant power output (therefore gradually reducing torque with speed) while an ICE has roughly constant torque across its relatively narrow rpm operating range (therefore torque dropping in step increments with each gear). So with ICE you get much more of a stepped torque delivery vs a slowly declining torque curve with EV. Actually a CVT transmission in an ICE car (something we used to simulate in F1 as an ideal benchmark against seamless shift gearboxes) would be much closer to an EV in its torque delivery at the road wheels.

 

[Peteski]

Yes. I want a great GT with long range.
All this track-talk applies to a very small fraction of consumers.
No car can be all things to all people, and a track-focussed version wouldn't trouble me- but just hurry up and deliver the Roadster 2020 as described, please!

Agreed. It's just that some people are presuming the Roadster will be better at absolutely everything, including handling and track lap times, so I thought I'd post up a reality check!

 

[scaesare]

They could have gotten well over 150kWh in a bespoke Roadster back then, even with pre-Mode S 18650's. Oh, and 1,000hp.

And a 100 cycle life.

Having to buy a new $175,000 pack every 5 years might not exactly be the statement they wanted to make about EV's...

 

[CarlK]

Agreed. It's just that some people are presuming the Roadster will be better at absolutely everything, including handling and track lap times, so I thought I'd post up a reality check!

Just to make it clear no one has said it will be better at absolutely everything. On the other hand I'm pretty sure it will be better than anything you can buy this side of half a million or even a million dollars in everything that maters. I also agree with the other poster that track performance is not as important as some want to make it to be. It gives common buyers the bragging right and brand identification but you will never get the ultimate bragging right by buying a "mere" $200K car anyway. That said I still think Roadster will surprise us on the track. No one would have believed the 250+ mph top speed before the unveiling event. Computer control and electric drive together can do wonders. There's a lot to be explored and Tesla will.

 

[Peteski]

Just to make it clear no one has said it will be better at absolutely everything. On the other hand I'm pretty sure it will be better than anything you can buy this side of half a million or even a million dollars in everything that maters. I also agree with the other poster that track performance is not as important as some want to make it to be. It gives common buyers the bragging right and brand identification but you will never get the ultimate bragging right by buying a "mere" $200K car anyway. That said I still think Roadster will surprise us on the track. No one would have believed the 250+ mph top speed before the unveiling event. Computer control and electric drive together can do wonders. There's a lot to be explored and Tesla will.

I thought you were one of those saying it would be better in every metric you could possibly imagine? In my book "handling performance" is hardly a trivial metric for a sportscar, but I'm not particularly fussed about track lap times either. Neither do I care about a 250 mph top speed, which is totally irrelevant to pretty much everyone. Acceleration will be phenomenal and I'm attracted to the everyday practicality, but the rest is all highly debatable given the forecast weight of a 200 kWh battery.

 

[CarlK]

I thought you were one of those saying it would be better in every metric you could possibly imagine? In my book "handling performance" is hardly a trivial metric for a sportscar, but I'm not particularly fussed about track lap times either. Neither do I care about a 250 mph top speed, which is totally irrelevant to pretty much everyone. Acceleration will be phenomenal and I'm attracted to the everyday practicality, but the rest is all highly debatable given the forecast weight of a 200 kWh battery.

That's where we have the differences. Definitely reflects different thinking between an engineer and a physicist. You are too hung up on the "weight" part but not willing to look at rest of the equation. For example we don't want to add weight to a light aerobatic airplane but then those 20 ton jet fighters with fly by wire and thrust vectoring could out-maneuver it. We'll soon find out how this future machine can do but I'd refrain from making judgement from past experiences. If you have not noticed it yet this is exactly what Elon said he does engineering design by the first principle and not by analogy. Or else most of things we see would never have happened.

 

[ecarfan]

I was surprised also during the preview that the 2020 Roadster will have a 200 kWh, mostly because of the additional weight, and also considering the constant improvement of the cells.

You are correct that cells are improving. And now Jerome Guillen of Tesla has made some specific statements to that effect. See Tesla is working on new and improved battery cells

It is entirely possible that by the time the Roadster goes into volume production, Tesla cell energy density may be significantly better than it is today.

When Elon announced the new Roadster and stated the pack would be 200kWh, my reaction was “I would prefer a 100kWh pack to save weight and money”. I don’t need 600+ miles of range. 300 miles is plenty.

 

[CarlK]

You are correct that cells are improving. And now Jerome Guillen of Tesla has made some specific statements to that effect. See Tesla is working on new and improved battery cells

It is entirely possible that by the time the Roadster goes into volume production, Tesla cell energy density may be significantly better than it is today.

When Elon announced the new Roadster and stated the pack would be 200kWh, my reaction was “I would prefer a 100kWh pack to save weight and money”. I don’t need 600+ miles of range. 300 miles is plenty.

Sounds like there will be some improvements when the Roadster comes out although my take is 200 kWh battery is not for the range but for the ability to put out enough power to achieve the maximum acceleration and top speed.

 

[Peteski]

That's where we have the differences. Definitely reflects different thinking between an engineer and a physicist. You are too hung up on the "weight" part but not willing to look at rest of the equation. For example we don't want to add weight to a light aerobatic airplane but then those 20 ton jet fighters with fly by wire and thrust vectoring could out-maneuver it. We'll soon find out how this future machine can do but I'd refrain from making judgement from past experiences. If you have not noticed it yet this is exactly what Elon said he does engineering design by the first principle and not by analogy. Or else most of things we see would never have happened.

Perhaps I'm too hung up on the weight because I know how important and fundamental it is to vehicle handling, tyre wear and stress. I'm not only a general engineer, I'm a vehicle dynamicist who has worked at the cutting edge of motorsport for a couple of decades before I decided I preferred being a ski bum, lol. I'm not making this up or making any sort of controversial statements here. This is about as basic as physics gets and if you refuse to see the elephant in the room (close on 1000 kg of battery to haul around at 1-2G) then fair enough!

Your analogy to jet fighters is not very relevant to a car reacting all its forces through 4 little rubber contact patches. Once we move away from that fundamental limitation then weight might play less of a leading role, but we are far from that situation with the Roadster.

Design by first principles is exactly what we do in F1. There is a minimum weight regulation and not one competitive car in the history of the sport has ever started on the grid above that minimum weight. There have certainly been a few setting off below it though, lol.

 

[strider]

Glad we continued the discussion. I agree w/ @CarlKI think the 200kWh pack was due to discharge rates at high speed/high acceleration and that the range was an afterthought. After weight, heat is the next bogey for EV engineers to wrangle. I still want to see that liquid cooled rotor Telsa filed a patent on in real life...

 

[MP3Mike]

I still want to see that liquid cooled rotor Telsa filed a patent on in real life...

You mean what they are already doing in the S&X now? Or do they have a newer patent? (But if they are going with the Model 3 motors I don't know that it is even necessary.)

 

[Peteski]

Glad we continued the discussion. I agree w/ @CarlKI think the 200kWh pack was due to discharge rates at high speed/high acceleration and that the range was an afterthought. After weight, heat is the next bogey for EV engineers to wrangle. I still want to see that liquid cooled rotor Telsa filed a patent on in real life...

I think it's just one big marketing statement. 1.9 sec 0-60, 250+ mph max speed and a 600 mile range. Even the 200 kWh pack just sounds bigger and better if you don't think too much about the consequences. It's a clever strategy as it has certainly grabbed all the headlines and not many people have picked up on the weight issue or blown it off as being something that can be compensated for with the tech.

Personally I'm not buying into the Roadster in this spec. I think Tesla still have a huge learning curve ahead when it comes to building all out sports cars. In many ways the original Roadster was a more focused effort as a sportscar and certainly was in its weight! But for cruising around or tearing up drag strips I'm sure the new Roadster will be just fine, like a Model S is fine for those purposes at 2200 kg.

I suppose some of the other over-bloated hypercars are not that much better, with the Chiron posing piece weighing in close to 2000 kg (although that's still light compared to even a 100 kWh Model S). The real top performance cars like the McLaren P1 are in the order of 500 kg lighter and much faster around anything with a few corners. Even the relatively modest powered Porsche GT3 at 1400 kg is faster than pretty much all the heavyweight hypercars around a track and even the front engined Viper ACR and Merc AMG-GT are seriously quick at around 1500-1600 kg. The Lambo Aventador (current production record holder at the Nurburgring) is also not much over 1500 kg. I notice Bugatti have been pounding the Chiron around the Nurburgring recently but no lap times reported.

 

[CarlK]

I think it's just one big marketing statement. 1.9 sec 0-60, 250+ mph max speed and a 600 mile range. Even the 200 kWh pack just sounds bigger and better if you don't think too much about the consequences. It's a clever strategy as it has certainly grabbed all the headlines and not many people have picked up on the weight issue or blown it off as being something that can be compensated for with the tech.

Personally I'm not buying into the Roadster in this spec. I think Tesla still have a huge learning curve ahead when it comes to building all out sports cars. In many ways the original Roadster was a more focused effort as a sportscar and certainly was in its weight! But for cruising around or tearing up drag strips I'm sure the new Roadster will be just fine, like a Model S is fine for those purposes at 2200 kg.

I suppose some of the other over-bloated hypercars are not that much better, with the Chiron posing piece weighing in close to 2000 kg (although that's still light compared to even a 100 kWh Model S). The real top performance cars like the McLaren P1 are in the order of 500 kg lighter and much faster around anything with a few corners. Even the relatively modest powered Porsche GT3 at 1400 kg is faster than pretty much all the heavyweight hypercars around a track and even the front engined Viper ACR and Merc AMG-GT are seriously quick at around 1500-1600 kg. The Lambo Aventador (current production record holder at the Nurburgring) is also not much over 1500 kg. I notice Bugatti have been pounding the Chiron around the Nurburgring recently but no lap times reported.

We just have agree to disagree. Form what we know now I will be more than satisfied with the handling of even the Model 3 performance (yes according to Motor Trend it matches track performance of 1000 lb lighter track spec'd Cayman GT4 and actually betters than that of the also lighter Ferrari 458 Italia). I have no doubt the Roadster will do even better. I'll take just that any day of the week. Whether it will match a pure bred race car on the ring is not of my concern. Like I said it's nothing more than the bragging right and brand identification for most. Not to mention I DO NOT want to drive a stiff car everyday even it can set a ring record. I want to drive the car not just to collect one. On the other hand good acceleration can be used everyday. The fastest one I have now is the 3.2 sec X P90D. I know I can enjoy more in everyday drive. It's not just how fast it goes but it's also how it feels when you touch the pedal. Besides you can comfortably drive any Tesla as slow as you want to too. There is no sacrifice there. Couldn't wait to drive the new Roadster.

You could always buy any of those cars you mentioned if not interested in the Roadster. Why wouldn't you?

 

[Peteski]

We just have agree to disagree. Form what we know now I will be more than satisfied with the handling of even the Model 3 performance (yes according to Motor Trend it matches track performance of 1000 lb lighter track spec'd Cayman GT4 and actually betters than that of the also lighter Ferrari 458 Italia). I have no doubt the Roadster will do even better. I'll take just that any day of the week. Whether it will match a pure bred race car on the ring is not of my concern. Like I said it's nothing more than the bragging right and brand identification for most. Not to mention I DO NOT want to drive a stiff car everyday even it can set a ring record. I want to drive the car not just to collect one. On the other hand good acceleration can be used everyday. The fastest one I have now is the 3.2 sec X P90D. I know I can enjoy more in everyday drive. It's not just how fast it goes but it's also how it feels when you touch the pedal. Besides you can comfortably drive any Tesla as slow as you want to too. There is no sacrifice there. Couldn't wait to drive the new Roadster.

You could always buy any of those cars you mentioned if not interested in the Roadster. Why wouldn't you?

I'm a lot more likely to buy a Model 3P actually. It's not quite so heavy and as you say it appears to handle very well with a nice EV power delivery. Although at 1800 kg I don't think it's going to be as nimble as something like a Cayman GT4. I bet that lap around Willow Springs was a lot harder to achieve and must have hurt the tyres more than the GT4. Again it's just basic physics and 400 kg is a lot of extra tyre load. The Cayman is one of those cars that really deserves more power as the chassis is easily capable of pushing harder. A stock GT3 is more on a par with the Model 3P for power and I don't think the 3 would live with that on a track. A GT4 with similar power could be even quicker, but Porsche won't go there for obvious reasons.

I'm not actually disagreeing with you either about the strengths of the Roadster. Just merely pointing out the cons of a huge 200 kWh battery. You just have more faith than I do that Tesla can magically overcome those cons.

 

[Peteski]

Not to mention I DO NOT want to drive a stiff car everyday even it can set a ring record.

Unfortunately that will be a problem too with all that weight to support. A Model X is already a fairly harsh ride on 22" rims and this won't have the same amount of suspension travel to play with. So we can expect a pretty firm ride by default.