Model S Efficiency and Range

As we near first customer deliveries of Model S it is an exciting time here inside of Tesla Motors! One of the most important and impressive performance aspects of Model S is its remarkable efficiency and range. It has a range that far exceeds any other production EV ever built, including our own Tesla Roadster! We are, needless to say, very proud of this and are excited to share more details here of how the Model S has come together through the final phases of efficiency tuning and optimization. We have exceeded our initial engineering targets and are confident that as a customer you will be delighted with the result.

Back in 2008, JB wrote a similar blog about the efficiency and range of our Tesla Roadster. At that time, we had recently completed tests demonstrating 244 miles of range on the Roadster. This was based on the 2-cycle EPA test procedure that incorporated a blend of highway and city driving cycles (55% city cycle driving and 45% highway cycle driving specifically). That blog is recommended background reading even for a Model S customer since most of the details and physics that affect range are the same in both vehicles and all electric vehicles for that matter. It also gives a description of what you as a driver can do to affect range positively and negatively relative to the EPA test procedure results. Actual results will vary for many reasons, including driving conditions and how you drive and maintain your vehicle. At Tesla we pride ourselves on transparency with customers and feel that range is a topic where this is particularly important. There is not a single fixed range for any given vehicle or battery. The simple reality is that driving range can and will vary by a large amount depending on how you operate the vehicle and external factors such as wind and elevation change. The goal of providing this information is so that the driver/customer has a more complete picture of what can affect his/her range and are in a better position to predict and control the outcome.

With the 85 kWh Model S battery we set a goal of delivering a range greater than 300 miles using the 2-cycle EPA test procedure that we used with the Roadster. This is a goal that no EV in history had ever achieved. We are thrilled to say that we exceeded this goal.

As we have done in the past, we also want to share more data and a complete picture with you. As many drivers of our Roadster (and other EVs) have experienced, it is possible to get range that is different than the 2-cycle EPA procedure (both higher or lower). We have some customers that have even driven Roadsters more than 300 miles on a single charge under ideal conditions. Other drivers might get less than 200 miles by driving at higher speeds or with heavy use of cabin air conditioning or heat.

Vehicle speed is by far the largest variable in the range you can achieve. In order to help customers plan and predict this we will share a computer model used to simulate how far a Model S is predicted to travel under the following conditions:

  • Constant speed (such as using cruise control)
  • Flat ground, no wind
  • Climate control OFF or using vent only (no heat or air conditioning)
  • 300 lbs of vehicle load (driver plus passenger or cargo)
  • Windows up, sunroof closed
  • Tires inflated to recommended pressures
  • New battery pack (<1 year, <25,000 miles)


One quick takeaway from this graph is that the 85 kWh Model S is expected to achieve 335-240 miles of range during constant-speed highway driving at 50-70 mph with the conditions listed above. This is a most impressive result and represents many extensive improvements in powertrain and vehicle technology over the Tesla Roadster. We have applied years of engineering effort and lessons learned from thousands of Roadsters in dozens of countries to make these improvements. These results are more compelling than those achieved by any other EV.

You can also see that at slower speeds it could even be possible to exceed 400 miles in a Model S under the conditions above. We haven’t internally demonstrated that yet and we are planning a prize for the first customer that actually drives over 400 miles on a single charge. :)

One of the points that we feel represents a useful summary of this data is the range at a constant 55 mph under the conditions above. For the 85 kWh Model S this is slightly greater than 300 miles.

The improvements over Roadster range are clear from the comparison of curves. This is due in part to the larger battery capacity in the 85kWh Model S (versus about 55kWh in Roadster) but also due to substantial vehicle platform efficiency improvements in the Model S.

Even though the Model S is a much larger and heavier car than Roadster with ridiculously more cargo capacity the total battery energy consumption on the highway is only about 10% more than for the Roadster! This is quite amazing and results largely from the Model S having the best aerodynamics of any sedan in its class with a Cd of approximately 0.24. Model S aerodynamics are so optimized that the total aerodynamic drag force experienced by the car – which is significantly larger in frontal area – is almost the same as a Roadster for a given speed.

Many variables affect the actual range experienced by our drivers. Here is a summary of how a small selection of these factors affects vehicle range and their relative impacts.

Vehicle Speed

Sustained high speeds have the most dramatic effect on driving range, as the first graph above clearly shows. This is because aerodynamic resistance increases with the square of speed, requiring higher forces to push the air out of the way. In contrast slower city driving speeds are more efficient and electric vehicles have a unique benefit in stop and go, low-speed driving due to regenerative braking. If you are ever in doubt about reaching your destination, driving more slowly is the best way to stretch your range. Relative to range at a steady 55mph you can see a 50% increase or 50% decrease in range due to vehicle speed decrease or increase.

Climate Control and Outside Temperature

Climate Control energy usage is related to keeping the cabin at a comfortable temperature. Maintaining a desired temperature in the cabin requires energy draw from the battery, which affects range. It is challenging to generalize how much the use of climate control will affect your range. It depends predominantly on how different the cabin temperature is from the outside temperature, if there is a large heat load from the sun, and how long you operate the climate control system. If you are driving slowly for a very long time and operating climate control continually it will have the largest percentage impact on your range. In very hot or cold operating conditions with typical usage of climate control and driving at speeds around 55 mph you may see a 10-15% reduction in range.

New EPA Rating Procedures: 5-cycle vs. 2-cycle

When the Tesla Roadster was certified, the EPA only used a 2-cycle test that was carried out under conditions of 75 degrees Fahrenheit ambient temperature and with varying acceleration rates and driving speeds for both city and highway tests topping out at 60 mph. Recently, the EPA incorporated three additional cycles into their tests that push vehicles to greater limits. The additional cycles added as part of the new “5-cycle test” include a cold driving cycle that requires heater use, a hot weather cycle with air conditioning operation, and a high-speed cycle (reaching 80mph) with rapid accelerations.

We are very pleased to report that Model S has exceeded our initial range expectations by about 20 miles and has achieved a Roadster equivalent 2-cycle range of 320 miles and a 5-cycle range of 265 miles. This sets a new record for electric vehicle range!

Conclusion

To explain energy usage vs. driving style even more clearly, we’ve been rolling out the Go Electric Digital Experience in our Tesla Retail Stores to help customers visualize the EV energy needed to accommodate their individual driving and life style. The Go Electric Experience will be hitting teslamotors.com later this summer. We highly recommend you check it out.

The Model S sets a new benchmark as a high-performance premium sedan that is fun to drive and goes further than ever thought possible with an electric car. We are looking forward to rolling out Model S to our customers this quarter and are always interested to hear back from you about your EV experience.

Best regards,

-- Elon and JB

Updated June 7, 2012.

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Kommentarer

offworld@ymail.com

There are several relationships in motor/generator design that are hard fixed by physics:

PowerOut=Torque*RPM*UnitsConstant, where the constant depends on the choice of units.
Torque=Current*WireLength*FieldStrength*UnitsConstant, again depending on choice of units.
Efficiency=PowerOut/(PowerOut+MechanicalLosses+ElectricalLosses)

The primary Electrical Losses are eddy currents, copper windings heating, and switching losses due to stray and intrinsic feature capacitance which shunt power away from the windings ... both in the motor and the drive electronics.

For iron core PM and induction motors the eddy current losses are unavoidable, as are capacitance losses between the windings and the core. In addition high inductance from the coil being wrapped around the iron core, requires increasing currents to provide the energy stored in the inductance. These all cause additional (I^2)*R losses for the higher currents needed to overcome the eddy current and capacitive losses, as well as the increased currents caused by the winding inductance. The relatively small loss currents, become large increases in losses due to the current squared factor.

Both iron core induction motors and iron core PM motors, have fixed pole geometries, which as the poles come into alignment, vary the torque due gap field strength changes as the poles shift in and out of alignment. Torque thus becomes a function of angular position, and losses are constant, so efficiency is function of angular position.

Air core PM designs like CSIRO, avoid these losses for higher efficiency.

The Tesla designers discussing motor design in other Tesla blogs and forums, lump ALL PM designs together, dismissing them as only a few percent better in efficiency, without noticing that air core PM designs like CSIRO are SIGNIFICANTLY more efficient.

Both in the basic electrical losses ... and in highly improved torque functions less/not dependent on angular position. Lower losses, less torque ripple, less heating.

offworld@ymail.com

Your blog makes the point above "One of the most important and impressive performance aspects of Model S is its remarkable efficiency and range."

86% efficiency compared to advanced CSIRO style designs at 99% isn't that remarkable, especially when you consider that for regen braking the energy captured and made back available is roughly 0.86*0.86=.73 where for the higher CSIRO efficiency that is 0.99*0.99=.98 .... a 34% increase in regen performance.

For stop and go driving cycles, and driving in rolling areas, that .98/.73=34% increase in regen performance that really is a significant increase in range over the existing S85 design. Add to that the reduced eddy and copper losses of a CSIRO style design, and pick up another .99/.86=15% in the traction motor/drive side.

Sure PM's are not as cheap up front in manufacturing as copper windings and iron cores ... but over a 300,000 mile life of the Tesla S85 .... that additional 15% and 34% add up in reduced coal/gas required to power a Tesla that sum well above the initial PM costs. And someday ... they can be recycled .... the coal/gas is locked into our environment, probably where it shouldn't be.

So ... care to provide a motor shell, so we can give you and apples to apples demonstration, that bolts directly to your test equipment and cars?

offworld@ymail.com

Hi Elon,

For the last 6 years I've been researching/designing tractor motors inspired by the CSIRO solar racing wheel motor that are cost reduced for production, performance enhanced, with slightly better efficiency (it's really hard to do much better than CSIRO motor/drive 98% efficiency numbers, but possible, even at the Tesla required performance envelope).

http://www.csiro.au/Outcomes/Energy/Powering-Transport/In-wheel-motor-fo...

When I started this project, it was to turn one of my Corvairs into a very fast EV as an everyday driver. S85's are very cool .... so is a very fast old school Corvair :)

I've spent the last several weeks modeling several cost reduced, significantly improved air core PM BLDC designs which should easily fit inside the existing Tesla motor housing, with better performance and similar costs.

Would it be possible for Tesla to supply an empty S85 motor housing so we can provide a demonstration? .... would need shaft, bearings, end bells, and outer housing for a blot up demo. Do not need/want stator/rotor stacks or windings ... just an empty motor housing and shaft that will plug into your dyno and S85 as a drop-in.

I'm certain you will be surprised ... if you can get me the housing in April, we can probably set up a demo mid-summer. Will probably take us a few months to machine/cast the required parts, and assemble for test in your form factor.

If interested, result can either be for your licensing, or cooperatively offered as an after market upgrade. High performance operation is a lot easier with very low losses, and a bit better range for free.

John