sparky said:
GRA said:
...
Still, 750 miles/day would be easy now with the current speed limits (still had the universal 65 last time I did a road warrior trip), and 1,000 would be almost routine (instead of a marathon) if I needed to get somewhere, where the main limit on my driving time is my bladder capacity. :lol:
So, is your point that unless you can do 1000 mi in 14 hours you feel penalized?
That would allow you a total of 40 mins stopping or four 10-min stops over the whole trip (75 mph). Personally, if I'm in a hurry to go over 400 mi, I fly.
For business I agree that flying's the way to go, and it's one reason why I've thought that Tesla was wrong to be emphasizing long interstate routes instead of access to regional destinations early in the SC deployment, as anyone with the money to afford a Model S/X will fly for business once beyond a few hundred miles.
sparky said:
How fast and how far would an electric car need to charge and travel per charge in order to not feel penalized? For me, Tesla has almost perfected the trade with the S90. Perhaps adding 20% range and 50% charge rate would leave me without a perceptible need for improvement. Both of those seem very feasible in the near future.
I've been saying for a few years now that a guaranteed 4 hours at the interstate speed limit (or 5 above, the way most people drive) at 32-110 deg. F, with allowances for HVAC use, headwinds, elevation gain plus a reserve is the point at which BEVs would be acceptable to most people to replace ICEs on trips, assuming no more than a 45 minute charge before repeating the process (15 minutes or less would be preferred). Everything beyond four hours range is gravy, but shortening the charge time is more important. Since 6 western states (soon to be joined by a 7th, SD), have 80 mph rural interstate speed limits, and all of the rest but two have 75 mph limits, that requires at least 350 miles of range (320 miles plus 30 mile reserve), with allowances as above. Oh, and that's for the life of the car or at least 15 years, so you'd have to divide by at least 0.7 to get the required range when new. That implies that the highest priority battery R&D other than reducing cost, should be devoted to decreasing charging time and increasing usable SoC (both without increasing degradation) as well as slowing or eliminating degradation, instead of improvements to specific energy and energy density. Improvements in heating/cooling efficiency and insulation should also have a very high priority.
Taking the S85 as the base, according to Tesla at 32 deg. and 70 mph with the heat on the car has a max. range (with a range charge, something you don't want to do on a regular basis) of 219 miles, versus 252 miles at 70 mph with no HVAC. Since the difference in its range for every 5 mph appears to be about 20 miles when using heat at 32 deg. (65 mph @ 32 deg. w/heat = 239 miles; 60 mph @ 32 deg. w/heat = 260 miles), let's apply the same factor to 75 and 80 mph, which gives us a max. range under the same conditions of 199 miles @ 75 mph, and 179 miles @ 80 mph, call it 180. While the drag rise is steeper at higher speeds, the car is also heating the cabin for a shorter period of time, so lacking Tesla-provided data for speeds over 70 mph (they should provide it, but apparently they're afraid that would drive customers away) it's better than nothing.
Okay, taking 180 miles as our baseline (and that's with no allowances for headwinds or elevation gain), what would we need to get to 350? Well first of all, 180 is with a 100% charge, and that's not something that's good for the battery, so let's use a normal charge to 90%: 180 x .9 = 162 miles. Then, since batteries degrade, and we want to know the end of life range, we need to multiply by 0.7: 162 x .7 = 113 miles. Then we'd need 350/113 miles = 3.1 times the 85's battery pack capacity (assuming no changes in weight or volume), or 85 x 3.1 = 263.5 kWh. Of course, the charge taper starts at 80% not 90%, so if we want 30 minute charging we'd need even more capacity.
Just for comparison, the 15.9 gallons of gas that my Forester's tank holds is equivalent to almost 536 kWh (1 U.S.G. = 33.7 kWh per EPA).
The S85 apparently has a usable capacity of 75 or 76 kWhs, so boosting the usable SoC can buy us some improvement, but the real killer is the 0.7 to allow for degradation, along with the 0.9 for battery longevity or the 0.8 for charging time, and the 30+ miles for heating - reducing or eliminating those will have the largest effect of all on required pack size, and thus cost. Alternatively, the cost of batteries needs to be brought down enough to allow for a reasonably-priced mid-life pack replacement, which will also shrink the required size of the pack.
