I've actually done a 35-mile, level-ground trip in my P85 that was 241wh/mile... it was at night on a freeway, at 55mph w/ cruise control, headlights on, HVAC off. I was not very popular with the passing trucks. :frown: I routinely do a specific 50-mile trip around here for about 275wh/mile that is mostly freeway travel w/ some gentle hills involved... as long as I stay in the right-hand lane and don't really hold people up, there is plenty of opportunity to drive "slow enough". What's nice about the Model S is that I can hit the pedal and zoom off if I choose, but I
can do 275wh/mile in this big car when I want to. I totally think 250wh/mile should be do-able in the Model 3. The question is, can it do
200wh/mile via the "economical" driving that allows the Model S to go 305 miles (as shown in Ideal Range mode)?
Battery
People talk about minimum battery capacities a lot on here, but I personally believe there is no “floor” below which Tesla won’t go… that enables the EPA staff to drive the car 200 miles during their test (probably 205 so that there is no doubt). I'll refer to that as the "EPA200." There will be larger battery options that allow the car to go further, but Tesla will charge extra for those.
It’s been said in many presentations that improvements to battery density average about 7.5% per single year. (There is no guarantee of a year-on-year improvement, but the breakthroughs have averaged out to that amount since Li-Ion batteries were first rolled out by Sony in 1991.) By the time 2017 rolls around, energy density will have improved by 5 years’ worth over 2012, or 1.075*1.075*1.075*1.075*1.075 = 1.436. Batteries of equal capacity will also fall in physical volume by similar multiples. In 2017, an 85KWh battery will fit into a space that is 1/1.436th of the current Model S battery volume, which is approximately 2.13m x 1.22m x 0.15m or 0.38 cubic meters. Model 3 battery pack will take advantage of the latest improvements to density and anything else they can conjure up at the Gigafactory, to fit 85kWh into 0.27 cubic meters, and I believe this will actually be the volume of Tesla's Model 3 pack, since easier comparisons can be made about how far Model 3 can go on 85KWh vs. the Model S, which will have been on the road for 5 years.
Just to show some math, here is that progression of capacity that fits into the Model S pack volume, with a 7.5% improvement each year:
| 2012 | 85.0 |
| 2013 | 91.4 |
| 2014 | 98.2 |
| 2015 | 105.6 |
| 2016 | 113.5 |
| 2017 | 122.0 |
| 2018 | 131.2 |
| 2019 | 141.0 |
| 2020 | 151.6 |
| 2021 | 163.0 |
| 2022 | 175.2 |
(If Tesla ends up accelerating this increase due to whatever chemistry research goes on inside the Gigafactory, things will be even better, but I won't assume that.)
Power Electronics
The 2017 Model 3 will use an all-new generation of power electronics, and basically convert energy back and forth more efficiently than the 2012-vintage Model S does now. Consider what JB Straubel had to say here
JB Straubel | Energy@Stanford SLAC 2013 - YouTube
* Let’s assume the Model 3 invertor and motor provide a given torque using only 95% of the energy my car requires.
* Let’s assume the Model 3 recharges the battery 5% better during regenerative braking.
* Let’s assume that Vampire Drain will be smaller than it is today, and also that the touchscreen is smaller than 17" (and dashboard is also smaller), and the computer systems in the car use less juice.
Car Size & Aerodynamics
A major factor affecting the Model 3 car is its physically smaller size.
Let’s assume it has the same mass as BMW’s 320i – about 3275lbs. (Putting it very unscientifically, the lightness of aluminium is offset by the weight of an EV battery.) This is vs. 4633lbs for the Model S-85, so the Modl 3 is only pushing 71% of the mass up to cruising speed.
Also, being physically smaller means it will have a lower coefficient of drag. The Model S is the most aerodynamic production car on the road today, with Cd of 0.24 per manufacturer’s claim
and independent measurement. Can they get the Model 3 down to 0.23? Aerodynamics will continue to play a crucial role for Model 3,
especially for cruising speeds and range. Driving around town, you rarely move over 45mph and don’t benefit from aerodynamics too much; you’re also more likely to be able to charge here and there, and won't think about flat batteries. However, on longer trips, it's more likely to be over 50mph (on expressways, freeways etc.), and aerodynamics have a major impact on range. Assuming cameras are allowed in place of side mirrors by 2017, they'll be guaranteed on the Model 3 because they will allow for a lower-capacity battery to achieve EPA200. If for some reason you want to drive around with old style mirrors on your car, they will be sold along with the note that they shorten the range of your car.
The cabin heater and AC compressor will require less power, since the interior volume of the car is smaller.
Wheels & Tires
The Model S is a big heavy performance car and starts out with 275/25ZR22 tires. The basic Model 3 will have perhaps the same as the base BMW 320i, which I believe is 225/50VR17 tires – so, a lot less rolling resistance, and somewhat improved aerodynamics, than Model S. Tesla will likely be lobbying Dunlop, Pirelli etc. to come up with a special tire for their needs – ultra-low rolling resistance – for the OEM parts.
I totally agree with you that Tesla will create aerodynamic wheels and that these shall be the standard equipment on the base car. Great way to increase range by a few percent, and will pay for themselves (as far as Tesla's costs are concerned) by shrinking the size of battery required to achieve EPA200 by that same few percent. Other wheels will be available for extra money.
Efficiency & Range
So with all those differences to take into account (none of which we really know the hard data on), let’s consider what they could mean for the range of the Model 3. Elon repeatedly says 200 miles, but they won’t be saying “a 200 mile range no matter what you do” or even “200 mile range if you drive economically” - it'll be "the EPA tested it and they got 205 miles." They will follow up with a specification for getting some other number which they believe is repeatable - for example, 55mph, level ground at sea level, zero wind, no HVAC and so on, will get you 220 miles. If the Model 3's efficiency increases allow it to achieve EPA200 at only 200wh/mile, at that efficiency, it'd use 40kWh. Allow 5KWh for buffers and you have a
45KWh battery in the base model.
Its upper power limit will be lower than what I currently have (320KW) but I can impose my own upper limit if I want to, which allows me to achieve 275wh/mile whenever I want. Restricting the upper power limit is a pretty non-fun way to guarantee longer distances - since you can't get up steep hills very easily, or accelerate with super-speed. Tesla Motors could fake that in the base Model 3, to give the notion that it is a cut-down car, and allow buyers of higher-spec cars to feel better. I do not believe Elon would want to do that, however. I believe restraint with the accelerator pedal, and looking ahead to anticipate slow-downs (in order to exploit regen) will be two great ways drivers can achieve extra miles.
