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40 kWh dilemma

Discussion in 'Model S: Battery & Charging' started by Rifleman, Jun 28, 2012.

  1. Rifleman

    Rifleman Now owns 2 Model S's!!!

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    I have always planned on getting the 40 kWh. My daily drive is 65 miles round trip, with one day a week being about 90 miles. A car with 160 miles range seemed perfect for me (especially as I will still have a second car)

    Now that some new estimates of range and battery degradation are starting to become available, I am starting to have doubts about the long term viability of the 40 kWh pack. This is how I figure it :

    the 85 KW Model S gets 265 EPA range. 85/40 = 2.125 and 265/2.125 = 124.7 miles. So lets guesstimate that the EPA range will be 125 miles for the 40 kWh battery. I am assuming that the EPA estimate is in range mode, so lets take 125 *.8 to estimate the normal mode range. This give us a solid 100 miles of normal mode, real world range (not bad compared to the competition)

    This would be just fine for me, leaving 10 miles extra on the longest drive of the week (plus an extra 12 miles in reserve if I change the car to range mode). The problem begins when the pack starts to degrade. I drive about 15,000 miles a year, so after 3-4 years, my battery pack will not have the capacity that it did when it was new. Let's say it looses 25% capacity. Now I only have 75 miles real world range, and I am being forced to drive my trail blazer one day a week, and have to think about how far away lunch is if I choose to go out for lunch one any of the other days.

    The way I look at it, I have 2 real options :

    1. Pay the 10K extra and get the 60 kWh battery. This may mean adding an extra year to the loan, or deferring when my number comes up so that I have more time to save up to pay the difference as part of the deposit.
    2. Buy the 40 kWh battery, and just start saving, knowing that in 3-4 I have going to need to buy a new battery. Doing this is betting on a replacement 1, being available, and 2, costing $10,000 or less.

    What does the hive mind think, is my drive to long for the 40, or should I stay the course, and hope for the best down the road?
     
  2. bonnie

    bonnie Oil is for sissies.

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    I'd put some effort into ensuring a charge point at your destination, effectively cutting your need for range in half.
     
  3. Teslawisher

    Teslawisher Member

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    Something else to consider... charge points at the workplace.

    If there is one - would that factor into your decision or alleviate some anxiety here?

    If there isn't one - maybe you have time to discuss with your employer and get one installed before your car is delivered. Anyone else at your company have have plug-in EV or hybrid vehicles? Group with them to form a larger negotiating group.

    I'm in the same boat. 100 miles real world driving would be fine for me too, but I would have less anxiety about range degradation as you as my typical round trip is about 40 miles.
     
  4. Teslawisher

    Teslawisher Member

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    lol Great minds?? :tongue:
     
  5. vfx

    vfx Well-Known Member

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    a 2% a year range loss. What about buying a new longer range battery with that $10,000 in 10 years?
     
  6. epley

    epley P85 VIN 693

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    Also depends upon the driving conditions. If it's mostly freeway vs. in-town, as this will affect the range as well. Since the Tesla can charge anywhere, you can recharge a bit while at work so you don't have to worry about driving somewhere for lunch, etc. Having a 240/40 level charger would be even better. If the finances are doable, you won't regret the longer range of a bigger battery, but I don't think you have anything to worry about!
     
  7. ElSupreme

    ElSupreme Model S 03182

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    My driving (right now) is pretty much the same as yours. Four days I travel about 60 miles, the final day I travel ~75-80 miles.

    I am not using the 85kWh / 40kWh ratio when calculating my numbers. Rather I am using the 300miles / 160miles published numbers Tesla provided. I am not sure this is good or not. Anyway the ratios are different and you get slightly better numbers if you consider the ranges Tesla has published.This would give you about 142 miles per range charge and 114 miles for a standard charge. I am using 96 miles as my alert range in my spreadsheet. This accounts for some 80mph highway speeds.

    I am dealing with degradation with two assumptions. The first is I can always drive a bit slower on the days where I need to travel further. Second as I become more familiar with the car, I will become more comfortable running it to the very end of the battery. Third in the future I will gain charging opportunities. And finally I am also accepting that I will need to purchase another battery; hopefully this is after 150,000 miles / 8 years, but I am planning on 100,000 miles and 5 years (conveniently after my loan is paid off). I am also alerting in my spreadsheet if I come within 16 miles of my standard mode charge range.

    Also are you sure your driving habits will be the same in 5 years. Will you have the same job? Will you live at the same house? Will your current office move? A lot can change in 5 years.

    EDIT: And as much as Tesla won't like it I have no problem charging in range mode once or twice a week. It helps that I am already planning on buying a new battery.
     
  8. Teslawisher

    Teslawisher Member

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    You're definitely right here. If you get the bigger battery, you WILL use it, so it won't be for naught. :)
     
  9. Rifleman

    Rifleman Now owns 2 Model S's!!!

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    I actually already have the ok to install a 14-50 outlet at the fire station where I volunteer (and spend one night a week). Getting my actual job to install a charger is proving to be a much more difficult proposition, and I am not optimistic about getting a charger installed in the next decade or so.
     
  10. AndyM

    AndyM Member

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    Rifelman -
    You're right to do the math up front. Yet, you will have plenty of time to wait to hear from Model S actual owners with in-field experience before you have to make the decision.
    I view the EPA 5-cycle numbers as closer to worst-case... they are a calculation of driving behaviors anywhere between "hypermiler" and "leadfoot". Tesla's own range estimates have been exceeded on the Roadster, and I expect that trend to continue. So I would use Tesla's range estimates as conservative.
    2% decrease in range per year to accommodate battery degradation seems right to me.
    As for charging at the workplace: I am designing my charge habits so that the car charges when and where I sleep. Road trips can be an exception to that rule. But not my office.

    See if you can afford the bigger battery, to be flexible if you get laid off, or if other plans change in your life. Be prepared. Replacing it when you need it later will be more expensive than selecting one you might need today. I might be too risk-averse; I am not going to bet on prices that might go down in battery tech - yet.
     
  11. bint2k

    bint2k Member

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  12. ddruz

    ddruz Member

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    Rifleman, I am in a similar position as you with respect to deciding on batter size. If the battery did not degrade the 40 kwh would more than suffice. Currently I drive a Leaf and actually make it work fine, but with little room for unforeseen detours or emergencies, which is why I am looking forward to the Model S. I agree with you that the big unknown is the degradation. The 2% per year figure seems pretty conservative given what the Roadster owners have been saying particularly because you won't need to use the upper or lower 10% of the battery very often where most of the battery strain seems to reside.

    For what it's worth, I am able to get well above the EPA 73 miles per charge on the Leaf just by driving sensibly. I'd have to do jack rabbit starts, keep my AC on full blast all the time and drive under power right up to the stop light and apply my brakes at the last minute to get only 73 miles per charge. Similarly I expect sensible driving in Model S will give us much more than whatever the EPA number it has. We need to wait to see that before a truly informed decision can be made. It is entirely possible the 40 kwh car will weigh less than the 85 kwh car and the EPA number may be a nice surprise too.

    You need also to consider in addition to your miles driven between charges the topography of your route and the amount of climate control you use. Both can be big drains. If your route is mostly flat and your climate control usage is minimal my guess is the 40 kwh pack will work fine for you. However, if you have a lot of tall hills and/or use the climate control extensively, if you keep the car long enough at some point the degradation could be enough to push you over what the battery can deliver.

    My personal plan is to wait till the actual range numbers come out on the 40 kwh car before deciding. But if I had to make a decision at this point I would buy the 40 kwh car and take my chances on battery degradation. I have found there are lots more public charging stations going up all the time and even with a J1772 public charge point, a half hour plug in can buy a few extra miles to make it home in a pinch.
     
  13. petero

    petero Member

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    My two cents. I would go with the 60 kWh battery. I agree the 40 will fulfill 90% of your daily commuting needs today. Originally, I was going to get the 40 but keep in mind the 160 charged to 80%=128, if you are driving at 75mph the 128 becomes 102, and after 8-10 years allow another 20% and you may looking at 82 mile range.

    First, the 40 may not give you enough of a cushion on the longer trips. Second, you never know what the future will bring, new job with longer commute, new home, or something unexpected. Third, the 0-60 performance on the 60 is 5.9 which is very close to the 85.

    It may be a bit rude of me, but it is only money! Why risk compromising? This is a rare extravagance , I have never purchased such an expensive car.
     
  14. ddruz

    ddruz Member

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    IMO petero's viewpoint makes sense a lot of sense too. If you can afford the extra 10K then by all means the 60 kwh buys you insurance. But if that 10K is significant to you, and it is to many people, the decision between the two battery packs becomes quite important.
     
  15. drees

    drees Active Member

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    Don't forget to take into account weather when figuring range.

    If you need to run the heater or defroster that will reduce your range. Cold weather will also make the car less efficient due to higher friction and thicker air.

    If it is raining, water on the road will reduce your range. You can count on 10-15% reduction in range if the roads are anything more than damp.
     
  16. dsm363

    dsm363 Roadster + Sig Model S

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    While you can do your driving on the 40 kWh pack (especially if you can get work to install an outlet), I think you'd be much happier with the 60 kWh pack. It would free up your driving in standard mode almost regardless of driving style or weather. If you can get your work to install an outlet then you're set.

    I think it is wise to use worst case numbers as your guide until there are adequate charging places at work or Superchargers where you would need them. You just want to get in your car and drive. I never even look at my range in the Roadster because my driving is well under a standard mode charge. If I was driving at 80% of my standard mode range, I'd have to pay much closer attention.
     
  17. MikeK

    MikeK R#129, TSLA shareholder

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    I've driven electric vehicles for 12 years. First an EV-1, now a RAV4-EV. My RAV's real range is 80 miles if you drive 65-70 on the freeway, and I can hit 100 miles with very careful driving.

    I had originally planned to get the 40kWh pack in my Model S, but I decided on the 60 for the following reasons:
    • The Model S will be my only car
    • I occasionally want to drive farther than I can comfortably drive the RAV on a given day
    • Starting with the original 160 mile range for the Model S 40kWh pack and factoring in real world driving, HVAC usage, pack wear and calendar life, it seemed like the Model S range would drop to pretty close to my RAV's max range after some years of driving, and today, there are days that I have to take the Prius because I can't quite get there with the RAV (and I plan to sell that Prius!)
    • Perhaps most crucially, the 60kWh car will be able to Supercharge, while the 40kWh will not

    I think it's that last point that's one of the biggest deciding factors. For a longer trip, the extra range of the 60kWh combined with a Supercharger will make certain trips feasible that I just couldn't do with a 40kWh car.
     
  18. VolkerP

    VolkerP EU Model S P-37

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    Yes, but there is a - yet unknown - cost for adding this option to the 60kWh Model S. I made a poll on that, with result that it should be around $400. Still some money.
     
  19. Rifleman

    Rifleman Now owns 2 Model S's!!!

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    I am starting to lean to the 60 kWh battery. When you are already taking a loan for 50% of the vehicle, whats another $10,000? I am going to wait until we get some real world data on the 40 and 60 to make my final decision.
     
  20. ElSupreme

    ElSupreme Model S 03182

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    I think you should save the $10k now. And save up for a replacement battery. You can keep your payments lower for the first five years. Save up for another year, then buy/finance another (larger, perhaps better) battery pack. I wouldn't count on having the same battery pack for more than 8 years. The same that I wouldn't expect an ICE to go over 200,000 miles without major repairs.
     

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