What Makes the Tesla Roadster Stand Out?

[Topher925]

Slides 7 and 8 here imply that the voltage stays constant while the amp-hour capacity drops substantially (15% from 25C to 0C) with temperature for a lithium battery.
http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/evs17poster.pdf

Yes, but that's not telling the whole story. Slide 7, top center graph, shows that as discharge current increases and temperature decreases the affective capacity decreases just as Peukert's Law states. However, the experimental data in this graph shows that at low current densities the affective capacity begins to converge to some value greater than 7Ah.

So of course temperature will always decrease the affective capacity, but my point was that its both temperature and operating conditions that affect the observed capacity, not just temperature alone. For example in an electric car which has high discharge rates the affect of temperature on capacity can be substantial, even if you account for relaxation. But for an application like the Kindle, where the battery is discharge over a period of a month or so, the affects of temperature on capacity can be insignificant.

 

[mheslep]

Well the math (from Russ's NREL slides) says all. The internal resistance of any battery, created mainly by the chemistry kinetics, is R = ΔV/I = f(SOC,T,charge/discharge,cycle*). The energy wasted is approximately I² R, meaning useful capacity decreases with increasing load. For high power Li Ion batteries R is typically very, very low, perhaps 1 milliohm for even a laptop sized battery, when T is greater than ~0 deg C.

*Cycle, or battery age, is my addition.

 

[baywax]

I'm unaware of any place in the US that could do without year round.

Wait, I've seen some of those American bowling alleys... they're huge!

 

[Physics-Learner]

well i guess we need to define what temperature extremes are, then.

i think of california as having lots of areas without extremes.

 

[mheslep]

well i guess we need to define what temperature extremes are, then.

i think of california as having lots of areas without extremes.

"[URL LA Hits All-Time High of 113 Degrees
[/URL]
"At Sacramento International Airport, extremes have ranged from 18 °F (−8 °C) on December 22, 1990 to 115 °F (46 °C) on June 15, 1961"

Redding, Ca July average high: 98.3F

and so on. Not much humidity, which is nice for people and other evaporative cooling systems, useless for batteries.

 

[Physics-Learner]

you picked one day in la. la also had one of the coolest summers on record.

lots of northern california, like san francisco, has cloudy weather all the time.

california has a long coast line, where the majority tend to live.

 

[mheslep]

you picked one day in la.

So? As I said:

I'm unaware of any place in the US that could do without year round.

Cook a discharging EV battery in that kind of heat for a few days without some kind of thermal management and you will likely measurably shorten its (currently expensive) life. Drive up into the Sierras in the Winter without a battery heater and you may find the vehicle range cut in half while there.

 

[Topher925]

you picked one day in la. la also had one of the coolest summers on record.

lots of northern california, like san francisco, has cloudy weather all the time.

california has a long coast line, where the majority tend to live.

Most people won't buy a car if they can't drive it one or two days out of the year. This is a big reason why you see so many SUVs and trucks in the northern part of the states that get a lot of snow.

 

[Physics-Learner]

most of these first purchases are not single-car families. but i don't think a few days in a year is going to deter sales of an ev without a superior tms.