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Comment by bryanlarsen | Hacker News Reader

Assuming Tesla prices and full cycling of battery (aka from 100->0), draining a kWh puts about 2cents wear on your battery, so compensation would need to be above that price.

In practice you'd never allow your operator to drain you to 0, so 2 cents is very much on the high side.

In the California Tesla VPP trial, they pay 50 cents per kWh.

(correction: 20cents wear, not 2cents)

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I calculate about $12 per Model Y full battery cycle, how did you get 2 cents?

$12,000 (Model Y bat replace cost) * 300(miles for full drain)/300,000(total miles per pack)

= $12 per cycle

Edit: or 18 cents per kWh

The 2 cent figure is per kWh, not per cycle. Multiplying by the 75kWh pack size gives $1.50.

What about the remaining 10X? The calculation you’re doing isn’t the right one, because the battery wear isn’t directly related to miles driven; Tesla’s battery warranty is pricing in a “full stack” picture of battery degradation while actually driving.

Your computation implies that the battery has 0 value after ~1000 cycles, but battery manufacturers commonly warranty 3,000-5,000. In addition, cycle count is only one variable affecting degradation, others include the depth of discharge, the charging and discharging profiles, the thermal management, etc.

(This is one reason why a 10-year-old Tesla has noticeably different battery degradation than, say, a 10-year old Nissan Leaf, which has no thermal management and a very poor BMS)

Finally, even when battery degradation occurs, it doesn’t remove the battery’s entire capacity, so degraded batteries can still be used for stationary storage applications. While an extreme degradation like 50% is very bad for an automotive application, it doesn’t matter so much for small-scale grid storage, since space is usually not the limiting factor.

The nature paper seems to assume the car is doing a fast discharge to supply enough energy to the grid, so something like supercharging-- probably not the best on the battery. Tesla only warranties 375 cycles, so not sure what you mean? The 18 cents/kWh already assumes a more generous 1,000 cycles.

The $12,000 battery pack replacement cost is current market price, including any recycling or potential reuse of old pack.

Edit: actual battery replace including labor is $16,550 from a receipt https://www.currentautomotive.com/how-much-does-a-tesla-mode...

I don’t know about the nature paper’s assumptions, but supercharging provides far more power than could possibly be supplied to the grid via V2G — for instance, a 100A home service can draw at most 24kW (AC), while supercharging draws up to 250kW (DC). V2G would use the car’s onboard AC/DC converter, which usually tops out at 10-12kW, so it would be relatively slow discharge from the car’s perspective.

Edit: from the paper:

> We assume the home charging power as 1.92, 6.6, 22, and 1.92 kW for small, mid-size, large BEV, and PHEV, respectively

I don’t think the 22kW assumption is reasonable, but the others are comfortably within current L2 AC charging rates.

If you have a high mileage car and the engine blew up would you buy a brand new engine or get a used one?

On US ebay I see model 3 batteries for $5k

A BMW engine (the b58) is about $5k used, about $10k rebuilt, and somewhere above $20k new.

1,000 cycles is only 3 years (assuming a daytime commute plus discharging to the grid plus re-charging back up counts as a cycle). Most cars are definitely still under warranty after 3 years of driving (assuming a 5 year / 50k mile warranty).

Regardless, if you do have a high mileage ICE car that you want to save, the used engine is probably the way to go, and won't suffer a crippled range of a used battery.

In general, I like the idea of electric cars, but battery packs are not on the same level as an ICE engine in terms of replacement. If you're in the unfortunate position of owning something like a Volt, odds are you literally will not even be able to get replacement battery- and if you could, it would cost more to buy and install than the car would be worth when you were done. That exact scenario hit the news at least twice in the last year.

Cycle count is counted for every 0-100 charge/use. 1000 cycles in 3 years is unlikely for normal home use.

So, assuming commute + feed into the grid + recharge, it's closer to 5 or 6 years, and only the first two or three are under warranty?

Using your numbers: 300000 miles / 320 miles/cycle = 938 cycles. 938 cycles * 72kWh = 67500 kWh. $12000 / 67500 = 18 cents.

Dunno where I got my 2 cents from, that calculation was done 2 months ago.

I agree with your 18 cents/kWh. That's slightly more than the average cost of electricity in the US?..

That is interesting, that means for home-charging your electric cost (per mile) is about equal to the battery degradation cost.

Thats 2x cost than most think.

They'll only want to buy back electricity at times when demand exceeds supply. In Texas the price of electricity is $9/kWh during those times.

Presumably as we use more renewable energy, we'll need more temporary storage. Buffering out day/night cycles from solar generation, for instance, would be a daily occurrence not a rare event. $9/kwh might be reasonable in an emergency, but even 18 cents/kwh seems pretty high for daily use.

Your whole car depreciates, not just the battery. Depreciation cost for driving a mile is a lot more than the electricity cost.

For you though that cost is just part of the normal depreciation of using the vehicle. Allowing the utility to discharge your battery isn't part of the normal utilization for yourself so the cost should get included. We also don't usually think or talk about how much depreciation using a particular gallon of gas costs you so it muddies comparisons.

the "real" time-based prices have much more variability, if you have time-based prices you can buy for a lot less and sell for a lot more during peak. That difference can easily be double that 18 cents/kWh.

Petrol engines get worn too.

18 cents per kWh is something like 5-6 times the wholesale price of kWh. This means that using EV for large scale storage is highly uneconomical.

That excludes the cost of transmission and distribution, which is more than half the cost of electricity prices to rate payers.

And using batteries to smooth out the leaks will allow greatly reducing the peak size of equipment for T&D.

Additionally, look at wholesale markets for electricity, such as Texas', and you will see price swings during a day far far in excess of 18 cents/kWh. This indicates that storage is extremely economical today.

It's only used for those periods when demand exceeds supply. In Texas, the wholesale price of electricity is $9/kWh during those periods.

During a brownout energy is worth a lot more, dollars to tens of dollars.

But this article is not talking about brownouts this is talking about routine use.

It's not per cycle, but per kWh.

In any case I'm getting 10-20 cents depending on battery pack size and chemistry.

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