Todd Burch
Voltage makes me tingle.
Whuh oh. All of this is making that 300 mi pack look better and better. Might have to do some convincing of my other half...
Good analysis Todd. I find myself in a similar position. The 300-mile pack is a stretch from a $ position.
In addition to the long-term fuel savings we should also factor in parts & maintenance not required for an EV. Conversely, have to add in the cost of a charger, if planning to use level II at home.
To make a fair comparison though on fuel costs, the costs for electricity to charge should be included as well as similar analysis of rising electricity rates over the years. Granted, it's going to favor EV's by a big margin, but it's still relevant if we're talking total cost of transportation.
Doug_G
Lead Moderator
On the other hand, gas prices are likely to be even more volatile and on an upward swing. Peak oil production will guarantee that, even if unrest in the middle east doesn't.
For me, as much a stretch as the 300 mi pack might be, I think it makes the most sense. As the article dpeilow noted, the cheapest range/$ is with the 300 and even if I don't need 300 now, the 300 gives me the longest level of use before degradation would force me to buy a new battery. At the 230 level, getting near 70% capacity starts being a real issue for day trips to the coast or to my parents place 2 hours south. With the 300, I could avoid fully charging in range mode and have only 70% after degradation and still likely have the range I'd require most of the time. It might very well last me until fast charging infrastructure is in place, in which case my need for serious range drops even further. There's the very distinct possibility an initial 300 mile could last me until it's ability to hold a charge just completely falls off a cliff.
Todd Burch
Voltage makes me tingle.
Personally, I'm just planning on using my 240V outlet that's already in my garage, which I think is 15A(?). That gives 240V * 15A * 85% charging efficiency = 3.06 kW. If I drive 80 miles a day, that's 345Wh/mi * 80 mi = 27.600 kWh per day...which would require 9-ish hours of charging...something I can easily do overnight almost every night. If I can't, then I have that big battery as a buffer.
If I find a need I can always get a charger later, but I'm having a hard time envisioning scenarios where I'd need it.
Todd Burch
Voltage makes me tingle.
In my numbers, I bumped my personal electricity cost by 25% from its current value as an estimate...not sure how accurate that is, but I did at least consider it. I think it won't make a huge difference in the end...the majority of the cost is from the battery itself, not the electricity.
Your 240V outlet is likely a 30A circuit for a dryer. So you can chop the charge time in half.
bolosky
Member
- May 5, 2009
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I think that we're all missing an important point with regard to the battery pack degradation. Degradation is due to two things: calendar life and use (and environmental conditions, but I'll just assume those are constant and ignore them). The calendar life effect depends just on the battery chemistry while use depends on the number of cycles of a given cell.
It's the last point that's important here: if you've got a 300 mile battery and you drive it 100,000 miles, then you've used 333 cycles of the battery. Do the same thing with a 160 mile pack and you've used 625 cycles. Therefore, you'd expect the use part of the degradation to be nearly twice as large on the 160 mile battery than on the 300.
Put another way, I think that it's wrong to say that at 100,000 miles you'll be at the same percentage of the battery capacity regardless of the pack size. You'd expect the percentage loss to be smaller (by less than a factor of 300/160) for the 300 mile pack than for the 160. How much less depends on the relative contribution of calendar age to the capacity loss.
Taking a complete wild guess at it, if we say that half of the loss is calendar loss and half is due to use, and say that the 70% after 100K miles for the Roadster battery also hold for the model S if it had a 244 mile battery, then we see that 410 cycles (= 100,000 /244) is 15% loss (half of the 30% overall loss), so the use loss rate is about 0.0366% per cycle. The 300 mile battery after 333 cycles then would be at ~73% (219 mi), while the 160 mile would be at 62% (99 mi).
This makes the argument for the 300 mile battery a little stronger. Of course, how much stronger depends on the relative contribution of age and use which I just completely made up in the previous paragraph. It also may vary based on the different cells used in the 160 and 300 packs, though IIRC the 160 and 230 packs use the same cells, just more of them in the 230 so it should really be linear there.
It's the last point that's important here: if you've got a 300 mile battery and you drive it 100,000 miles, then you've used 333 cycles of the battery. Do the same thing with a 160 mile pack and you've used 625 cycles. Therefore, you'd expect the use part of the degradation to be nearly twice as large on the 160 mile battery than on the 300.
Put another way, I think that it's wrong to say that at 100,000 miles you'll be at the same percentage of the battery capacity regardless of the pack size. You'd expect the percentage loss to be smaller (by less than a factor of 300/160) for the 300 mile pack than for the 160. How much less depends on the relative contribution of calendar age to the capacity loss.
Taking a complete wild guess at it, if we say that half of the loss is calendar loss and half is due to use, and say that the 70% after 100K miles for the Roadster battery also hold for the model S if it had a 244 mile battery, then we see that 410 cycles (= 100,000 /244) is 15% loss (half of the 30% overall loss), so the use loss rate is about 0.0366% per cycle. The 300 mile battery after 333 cycles then would be at ~73% (219 mi), while the 160 mile would be at 62% (99 mi).
This makes the argument for the 300 mile battery a little stronger. Of course, how much stronger depends on the relative contribution of age and use which I just completely made up in the previous paragraph. It also may vary based on the different cells used in the 160 and 300 packs, though IIRC the 160 and 230 packs use the same cells, just more of them in the 230 so it should really be linear there.
Todd Burch
Voltage makes me tingle.
Bolosky: True, degredation is largely an effect of cycles used...For a constant daily drive distance, the 160mi pack will degrade faster. But now we're starting to get into the gray area where we don't have enough use data--so I just stuck with Tesla's estimate of 70% at 100K miles. But you're absolutely right--cycle use does tend to push toward the argument of the larger battery.
Although I'm not sure if it's a big difference...230 mi vs. 300 mi differs by 3% in your estimate.
Hopefully Tesla will put a lot of this kind of info out there in the coming year to help us all make our battery size vs. wallet size decision easier. Uncertainty (and that $20k upgrade) is the price we pay for adopting new technology I guess...
Although I'm not sure if it's a big difference...230 mi vs. 300 mi differs by 3% in your estimate.
Hopefully Tesla will put a lot of this kind of info out there in the coming year to help us all make our battery size vs. wallet size decision easier. Uncertainty (and that $20k upgrade) is the price we pay for adopting new technology I guess...
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I've no idea how battery use works internally, but this relies on an assumption. If I drive 100,000 miles and plug in every night, the number of times I charge is the same as is the length of charging time regardless of battery size. The 160 battery is closer to empty than the 300 each night, but it's not clear to me whether degradation is a function of how many times you charge vs. how empty the batteries are when you charge.
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bolosky
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Yes, it does assume that. My source for the assumption is comments that Tesla made about battery life, which I didn't manage to find in the two minutes I put into searching for it.
Of course, it's only roughly true. Draining your battery all the way down to zero is harder on it than taking it to 20%.
Doug_G
Lead Moderator
"Charge cycles" is a bit misleading, in that it implies you fully drain then fully charge the battery. That's not how they are used most of the time. A more appropriate measure might be how much total charge you put into the cell over its lifetime.
Also it's not just charging. Just sitting idle the battery slowly loses capacity; the higher the temperature the worse it is. It also shortens the lifetime if the battery is fully charged, which is why Standard mode only charges to 90%.
This all makes me feel better when I have to put my Roadster in storage mode during the worst of the winter. It's sitting in the cold with half a charge. Hopefully my battery will last longer than average. Of course my Model S will be used year 'round.
So when considering a 300 mile battery are you thinking you will do a Range Charge (all the way full) every time? AND drive the full range distance each of those times? Doubtful. Doing so will degrade the battery. We all have our occasional long 250m trip but the majority of us charge in standard mode the majority of the time.
Why keep an EV car battery topped in range mode "just in case" at the expense of battery life? Anyone here do that? These real world charging profiles should be figured into battery life calculation cycles.
Why keep an EV car battery topped in range mode "just in case" at the expense of battery life? Anyone here do that? These real world charging profiles should be figured into battery life calculation cycles.
bolosky
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No, of course not. That would be foolish. What I'm saying is that one component of the degradation of the battery is the amount of energy that's come out of it. As long as you don't push it too close to completely full or completely empty or run it outside of its temperature range, it doesn't matter if you go from 90%-10% 10 times or from 90%-80% 90 times, it's about the same effect on the battery. Given that, then the larger batteries will last longer than the smaller ones because the same distance travelled is less of a load on the cells, since they're bigger (and in the case of the larger batteries vs. the 160 more numerous).
benji4
Roadster 2.5 #0476
Probably nobody does that, but taking that same argument, the 160 mile battery doesn't seem like enough for any serious driving. Charge it in normal mode and perhaps you get 130 miles ideal range, and a bit of spirited driving maybe gets you down to 100. So you are almost starting to get down into LEAF territory there. The 230 mile pack is right in line with what you get with the Roadster and it seems like it might be hard to be happy with less than that especially if you already drive a Roadster.
You could always upgrade that to a 50A outlet as well. Shouldn't be too hard or expensive to do since most of the wiring is probably already there.
My typical standard mode range with snow tires and cold weather this winter has consistently been between 110 and 120 miles. I couldn't imagine life with a 160 mile pack.
I wonder if the government will eventually require better EV range disclosure. Like the city/highway stuff for MPG, EV would have to display something like 100/160 for typical/ideal.
