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| Piles of Tesla owners stranded at charge stations abandons their EV's. |
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| pickle9000:
--- Quote from: Andy Chee on January 20, 2024, 12:09:18 pm --- --- Quote from: Dan123456 on January 20, 2024, 11:58:27 am --- --- Quote from: Ice-Tea on January 20, 2024, 10:33:50 am ---I honestly don’t know man. I think focusing on the grid (and future of the grid) should be the priority as EV’s powered by coal aren’t really any better. ——————— Often stated, but wrong: (Poland runs mainly on coal) --- End quote --- So are you arguing we should just replace all fuel with coal powered EVs as one study suggests it might be better? I’m no environmental activist be that sounds like a pretty bad idea to me :P --- End quote --- I presume EVs are better, not because they run from coal, but because they are fuel agnostic (i.e. nuclear, solar, wind, hydro, waste veggie oil, timber, hydrogen, natural gas, mice running in wheels, whatever). --- End quote --- EV efficiency reduces component count not to mention regen. No transmission, There's a reason diesel electric locomotives and heavy equipment exist. |
| Siwastaja:
--- Quote from: jonpaul on January 20, 2024, 05:48:26 pm ---Batteries activity like all chemical reactions are goverened by the Arrhenius equation https://en.wikipedia.org/wiki/Arrhenius_equation Thus for every 10 dge C or K fall in temperature, the activity is reduced by 1/2. --- End quote --- Mostly OK, but you are missing two facts: 1) Arrhenius equation is a practical observation, a generalization of many reactions. It's not a law of physics. Different reactions behave differently. It's also an interesting question whether (dis)charging a li-ion cell counts as "chemical reaction" at all. 2) Relative numbers are meaningless when we need absolute numbers. For example, if initial efficiency is 90%, then quadrupling the losses is catastrophic for something like EV driving range. If initial efficiency is 99%, then quadrupling losses is nearly meaningless. In EV batteries specifically, larger capacity battery pack (made of same technology than a comparison pack) gets linear advantage in losses and power capability. E.g., if a 30kWh pack is able to produce 100kW of driving power and 30kW of charging power with 90% average efficiency, a 60kWh pack made of same cells produces 200kW of driving power, 60kW of charging power, at 95% average efficiency. Additionally, EVs can utilize thermal insulation and battery heating when being charged from mains. (Using battery power to heat battery would result in similar loss than just letting the battery heat up from its internal losses.) How well is stuff like this done depends on vehicle - also how much it's needed. It's worth understanding what would be the worst case efficiency, in case battery is charged, then left to cool without connection to mains power, for a few days so that the large thermal mass of battery cools down to equilibrium with ambient. Then battery efficiency loss might be large enough that it can't be ignored anymore - I'd say in range of 10-40% depending on vehicle and driving habits, at temperature like -30degC. |
| tom66:
--- Quote from: jonpaul on January 20, 2024, 05:48:26 pm ---Batteries activity like all chemical reactions are goverened by the Arrhenius equation --- End quote --- Lithium ion batteries are not chemical batteries (they work completely differently to the majority of other batteries which undergo chemical changes in their discharge/charge process), and consequentially their performance does not match the Arrhenius equation. And your 1/2 capacity lost per 10 deg C is absolute madness. My car is at worst down 15% capacity at -5C, compared to 30C ambient. The issue with lithium ion batteries in low temperature is their open circuit voltage falls and ESR increases and so less capacity is usable under low temperatures, the car must ensure that the cell voltage does not fall below the critical level. The capacity is not lost - just inaccessible. This is why EVs appear to reduce in available range and many EVs expend energy on heating the battery up as it makes this capacity accessible once the battery has warmed up. The loss of range in EVs in low temperatures is principally due to the reduced efficiency of cabin heating, battery, and tyres, and for vehicles without a battery heater the reduction can be greater. Usually winter weather carries other factors like heavier wind and rain which impact efficiency too, but having a heatpump makes a huge difference, which is why the majority of EV models have a heatpump as at least an option now. |
| Siwastaja:
Yeah, the claim about capacity loss to half per each 10degC is usual jonpaul, total and obvious bullshit which is obvious to anyone who has ever used batteries of any kind. What would even be the reference level? Your range is 400km at +25degC so it must be 200km at +15degC and 100km at +5degC? Just ridiculous. Even if you mentally modeled li-ion battery as chemical reaction, then capacity relates to amount of material that can react, and Arrhenius is not claiming disappearance of reagents into thin air, that would be rewriting pretty much everything we know about our universe. Instead, analogous to reaction rate going down is increase in voltage sag, in other words, increase in ESR or decrease of efficiency. When capacity is defined as charge (coulombs, Ah), you get full capacity out even at -30degC, if you can accept using low discharge currents near end of the curve to prevent voltage sagging below the under-voltage lockout levels of the loads like the drive inverter - this is exactly why EVs start limiting power at the end of discharge, finally entering a limb mode: they are making sure you get pretty much every Coulomb out. Then again, when capacity is defined as energy capacity (Wh), then you have capacity loss which is actually equal to the efficiency loss. Note that even if the loss doubled per each 10degC (which isn't true, but it's in the same ballpark, so let's play along), it's totally different from remaining efficienc (or energy capacity) halving. This is elementary school math: when loss doubles 1% -> 2%, efficiency (and thus energy capacity) doesn't halve, but goes from 99% to 98%, a 1.01% difference, not 50% as jonpaul is saying. The percentage of jonpaul being wrong is then 4950.49504950...%, which doesn't much differ from his usual contributions. |
| fourfathom:
--- Quote from: pickle9000 on January 20, 2024, 06:20:41 pm ---EV efficiency reduces component count not to mention regen. No transmission, There's a reason diesel electric locomotives and heavy equipment exist. --- End quote --- And that reason is torque at zero RPM. There are other reasons (on ships, for example) but torque and low-RPM capability are (I believe) the big reasons, not efficiency. |
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