Tesla’s promises don’t compute with current physics and economics of batteries • Hacker News Board

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#51

Post by kumarvvr » Sat, Nov 25, 2017, 4:32 AM UTC

nimos wrote: post #30

The Tesla superchargers currently charge at around 2% a minute up until about 80% which is 40 minutes to hit 80%. Tesla is advertising 400 miles in 30 minutes which is 80% of the 500 mile capacity. What is so hard to believe about a 33% improvement over a couple year old tech that is a couple years from release? Here are current industrial/transportation/residential electric prices in US [0]. They think Tesla will pa…

Comparing on a percentage point basis, you have to ensure that the underlying physical system is equivalent, in this case, the capacity of the batteries.

Current superchargers charge at 2% / minute. I am assuming that's the maximum rate of charge, given the current supercharger infrastructure.

Lets assume that 2% / min is, say, at a 100 kW power level.

When charging a truck, assuming the supercharger technology isn't changed, the charging will still be at 100 kW power level.

So if the truck has 10 times the battery capacity, then the equivalent %age rate of charge will be 0.2%, not the same 2% as the capacity of the battery to be charged has changed.

Personally I think Elon is either going to add multiple charging inputs per truck and combine it with a special supercharger, or have some sort of port in the truck to which a special connector is connected to transfer huge amounts of power safely, not unlike a dock at the under side of the truck, or maybe the front.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#52

Post by maratd » Sat, Nov 25, 2017, 4:34 AM UTC

excalibur wrote: post #44

I think most people are in agreement that the lithium ion battery is less-than-ideal technology that's due for replacement. And we have a number of innovations in battery technology vying for the opportunity. It's starting to feel a bit like Tesla's massive investments are only serving to further entrench the existing battery model. He's basically working to replace Big Oil with Big Lithium. There's no denying the be…

> And we have a number of innovations in battery technology vying for the opportunity.

No, we don't. We have lots of news articles about amazing breakthroughs and absolutely nothing in actual production.

> It's starting to feel a bit like Tesla's massive investments are only serving to further entrench the existing battery model.

If you can come up with a battery chemistry that outperforms lithium ion, there will be nothing stopping the absolutely massive torrential downpour of money on top of you. Batteries are used everywhere, not just in cars. A new chemistry that works well would be huge. The problem is that there's lots of hype and marginal results when it comes to new battery tech.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#53

Post by kumarvvr » Sat, Nov 25, 2017, 4:34 AM UTC

cperciva wrote: post #39

jepler wrote: post #31

Earlier quoted context omitted.

Look at charging rates in watts (watt hours per hour) instead of in percentage; those semis have much larger capacity batteries, so they need a higher charging rate in W to charge 80% in 30 minutes than a vehicle with a smaller battery.

They don't have larger capacity batteries . They have batteries with more cells . Sure, the total charging rate is a higher Wattage, but you can charge cells in parallel. The scaling here is exactly the same as with the "larger battery" versions of the Model S having more horsepower; higher capacity = higher throughput when you're dealing with battery banks.

Wait, are you concluding that having batteries with more cells is not the same as increasing the capacity of the system?

For any battery system, the capacity is the product of the number of cells and capacity per cell.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#54

Post by chrishacken » Sat, Nov 25, 2017, 4:37 AM UTC

kumarvvr wrote: post #51

nimos wrote: post #30

The Tesla superchargers currently charge at around 2% a minute up until about 80% which is 40 minutes to hit 80%. Tesla is advertising 400 miles in 30 minutes which is 80% of the 500 mile capacity. What is so hard to believe about a 33% improvement over a couple year old tech that is a couple years from release? Here are current industrial/transportation/residential electric prices in US [0]. They think Tesla will pa…

Comparing on a percentage point basis, you have to ensure that the underlying physical system is equivalent, in this case, the capacity of the batteries. Current superchargers charge at 2% / minute. I am assuming that's the maximum rate of charge, given the current supercharger infrastructure. Lets assume that 2% / min is, say, at a 100 kW power level. When charging a truck, assuming the supercharger technology isn't…

I'm no battery expert, but is it possible that they have several battery compartments that can all be charged simultaneously? Thus reducing charge time?

Edit:

Just read the latter part of your post after I wrote this. I think this is the most likely scenario. "Personally I think Elon is either going to add multiple charging inputs per truck and combine it with a special supercharger,"

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#55

Post by cperciva » Sat, Nov 25, 2017, 4:38 AM UTC

kumarvvr wrote: post #53

cperciva wrote: post #39

Earlier quoted context omitted.

They don't have larger capacity batteries . They have batteries with more cells . Sure, the total charging rate is a higher Wattage, but you can charge cells in parallel. The scaling here is exactly the same as with the "larger battery" versions of the Model S having more horsepower; higher capacity = higher throughput when you're dealing with battery banks.

Wait, are you concluding that having batteries with more cells is not the same as increasing the capacity of the system? For any battery system, the capacity is the product of the number of cells and capacity per cell.

My point is that having a larger capacity battery automatically increases the wattage at which you can recharge. It's not like a gas tank where a 100L tank takes longer to refill than a 50L tank.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#56

Post by kumarvvr » Sat, Nov 25, 2017, 4:38 AM UTC

baddox wrote: post #48

nimos wrote: post #30

The Tesla superchargers currently charge at around 2% a minute up until about 80% which is 40 minutes to hit 80%. Tesla is advertising 400 miles in 30 minutes which is 80% of the 500 mile capacity. What is so hard to believe about a 33% improvement over a couple year old tech that is a couple years from release? Here are current industrial/transportation/residential electric prices in US [0]. They think Tesla will pa…

All these EVs use roughly the same small cells, right? Essentially thousands of the same cells used in hobbyist RC aircraft (with which I’m fairly familiar)? Unless I’m mistaken, each little cell should theoretically be chargeable in parallel, limited only by heat, massively parallel wiring, and the one massive input carrying ridiculous current. In theory, if one cell takes 30 minutes to charge, all cells could be ch…

If all of them are connected in parallel, then you are right. It's like filling an array of glasses in the rain.

However the superchargers connect to the vehicle through a power port, which is relatively small. So it may not have as many parallel connections. You could split the charging to individual cells inside the car, allowing for parallel charging of all the cells simultaneously, but that means that the supercharger has to handle the cumulative power requirement of all the cells in parallel. So if you have 500 50W cells, then the super charger has to have the capacity to handle 25 kW of power. And that much power requires some very bulky cabling, even with a 3-phase supply.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#57

Post by kumarvvr » Sat, Nov 25, 2017, 4:41 AM UTC

chrishacken wrote: post #54

kumarvvr wrote: post #51

Earlier quoted context omitted.

Comparing on a percentage point basis, you have to ensure that the underlying physical system is equivalent, in this case, the capacity of the batteries. Current superchargers charge at 2% / minute. I am assuming that's the maximum rate of charge, given the current supercharger infrastructure. Lets assume that 2% / min is, say, at a 100 kW power level. When charging a truck, assuming the supercharger technology isn't…

I'm no battery expert, but is it possible that they have several battery compartments that can all be charged simultaneously? Thus reducing charge time? Edit: Just read the latter part of your post after I wrote this. I think this is the most likely scenario. "Personally I think Elon is either going to add multiple charging inputs per truck and combine it with a special supercharger,"

Yes it's possible. We could have a power port like a VGA cable with say 10 or 20 independent supplies, simultaneously charging the different battery units.

However those connectors will be very bulky and heavy. Maybe Elon is thinking of a mechanized system, say a power robotic arm sort of thing, or maybe tech similar to the instant battery changing station he demoed a few years back.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#58

Post by MentallyRetired » Sat, Nov 25, 2017, 4:43 AM UTC

> based on Bloomberg's estimates

Oh, good. I thought they were going to bring in a battery expert to disprove the battery experts that work for the company who, according to Bloomberg, has the most advanced charging systems on the market. Whew! Dodged a bullet, there.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#59

Post by wlesieutre » Sat, Nov 25, 2017, 4:43 AM UTC

chrishacken wrote: post #54

kumarvvr wrote: post #51

Earlier quoted context omitted.

Comparing on a percentage point basis, you have to ensure that the underlying physical system is equivalent, in this case, the capacity of the batteries. Current superchargers charge at 2% / minute. I am assuming that's the maximum rate of charge, given the current supercharger infrastructure. Lets assume that 2% / min is, say, at a 100 kW power level. When charging a truck, assuming the supercharger technology isn't…

I'm no battery expert, but is it possible that they have several battery compartments that can all be charged simultaneously? Thus reducing charge time? Edit: Just read the latter part of your post after I wrote this. I think this is the most likely scenario. "Personally I think Elon is either going to add multiple charging inputs per truck and combine it with a special supercharger,"

They do call it a "megacharger," and the port appears to have multiple connections

https://www.teslarati.com/tesla-semi-megacharger-charging-po...

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#60

Post by DannyBee » Sat, Nov 25, 2017, 4:43 AM UTC

vvanders wrote: post #21

_ea1k wrote: post #15

Earlier quoted context omitted.

I can't take this author seriously. There is no way that Tesla is paying $1/kw. That is way past the retail rate, and I bet that they are paying much less than the retail rate in many of their markets.

Yeah, that's definitely bullshit, esp considering residential power in the PNW is $0.07/kWh.

Residential power is often cheaper than commercial (at least, small scale) in practice. One reason is that commercial folks pay surcharges for power factor.

For example, in San Jose, CA, the average residential is ~$0.156/kwh

Commercial is $0.1408/kwh [1].

If you operate at a 90% power factor, and are surcharged the other 10%, ...

[1] https://www.electricitylocal.com/states/california/san-jose/

But yeah, at Tesla's scale, it should not be $1/kw.

I could believe that to be the all-in cost for a supercharger or something weird like that.

Because they should be paying close to the industrial rate, if not lower.