Driving Range for the Tesla Model S Family
teslamotors.com
teslamotors.com
Under normal conditions, I use 350 Wh/mi (watt-hours per mile). This is 17% more than "rated range" because -- and this is a technical term -- I drive like a madman.
However, when driving to Tahoe (7000 feet higher), I end up using 850 Wh/mi: over 2x higher electricity consumption, because mountains.
All this talk of tires and wind resistance is a red herring for topography, which does more to limit/extend range than any other factor.
What's more, this could be so easily addressed with software: when I input my destination into GPS, the car should tell me my expected range. It knows the topography. Use the force, car!
Taken one step further, since Tesla is constantly transmitting telemetry to home base, Tesla HQ likely knows the average battery consumption of all other drivers who have ever driven that route. This would allow non-topographical variables (traffic lights, potholes, road conditions) to be factored into the range calculation as well.
Edit: Mistakenly used kWh/mi instead of Wh/mi units. Hat tip to Tarrosion for the correction.
Of course, this will impact all cars, though I find only a few MPG difference in our vehicles driving up to the ski resorts around Tahoe.
One curious thing I've noticed is that my relatively-high-Torque-and-HP car with a manual transmission gets almost the same mileage on flat ground versus going up and down mountain ranges, assuming there's no net elevation gain.
My girlfriend's fairly underpowered Subaru with a 4 speed automatic does significantly worse in the hills than it does on flat ground.
Also interestingly, the Tesla should get significantly better mileage in thinner air (on flat ground) where a gas-engined car has to deal with less air to burn which balances out the lower wind resistance.
Would also be interesting to see how the elevation change would affect a tesla at net 0. Say, drive from Sacramento to Truckee and back; I think the range should be plenty.
Thats only true if you have an old carbureted car that requires turning a screw under the hood to adjust the air-fuel mixture. Modern cars measure the amount of O2 in the exhaust and adjust the mixture to keep the moles-of-O2 to moles-of-gasoline ratio roughly fixed.
The thinner air means you have to open the throttle wider to achieve the same manifold pressure, which in turn means that with the throttle wide-open, the engine will produce less power. But the thinner air should have no effect on the amount of gas you need to burn to achieve a particular amount of power.
[Edit: you can think about it this way: A 89 MPGe Tesla Model S going up a steep hill at only 44 MPGe is still twice as efficient as a 20 MPG SUV driving on the flat.]
Say you get a good rate and pay $0.10 per kilowatt hour for electricity. That means if you charge your car at home, you're paying $35 per mile to drive. That doesn't seem right.
Possibly it's watt-hours? That'd be a per mile price of 3.5 cents, which seems about the right order of magnitude.
Another interesting way of looking at this then, is that the amount of power required to power s single 100 Watt Light bulb for 3 1/2 hours could move an entire Tesla + person inside 1 mile. Wowsa.
If you've ever had to push a car manually in that situation, you'll notice that it's very easy to keep it moving once you get started, as you only have to overcome the rolling resistance. I've never pushed a Tesla before but I'd bet that it's far easier than a regular car, and a regular car isn't that hard to push already.
According to this page:
http://physics.ucsd.edu/do-the-math/2011/11/mpg-of-a-human/
A human walking takes between 100-200Wh/mi, so the Tesla isn't that far off.
Based on what exactly? A Tesla Model S weighs at least 1000 lbs more than similarly sized cars.
That said, there is evtripplanner.com, which I found to be EXCELLENT at estimating range when I drove from Portland to Yosemite this summer. I summarized the estimate vs actuals in the Tesla forums:
http://www.teslamotors.com/forum/forums/made-it-portland-yos...
This is super powerful. This in combination with a service like Waze in cars would produce some of the most accurate traffic and estimation data for travelling. I'd be interested to see Tesla incoroporating all these factors into their in-car estimation for ETA.
<anecdote>
Every morning I drive in the HOV lane of the 101. Waze and Google Maps give me traffic-based ETAs that are about 20 minutes longer than Tesla's. And every morning, Tesla wins. (And since I am a dork I continue to pit the 3 apps in this lopsided battle.)
The 20 minute delta is precisely the difference between the HOV and non-HOV lanes. My guess is that the Tesla traffic estimator is using telemetry from other cars on the road, which are also using the HOV lanes like me.
</anecdote>
This is purely speculative, but the technology certainly exists that would allow Telsa to do this.
The 500Wh/mi difference is essentially the energy needed to lift the car. Consider another hypothetical car, much less efficient, that took 2000Wh/mi on level ground; then it might take 2500Wh/mi going uphill, which is only 25% more.
Note that the Tesla will also recharge its batteries going downhill with regenerative braking, so it mostly balances out - as long as you don't completely flatten the battery going up.
I would have guessed that most of the loss of efficiency (as in the fuel's heat of combustion divided by the displacement of the car's weight) of a gas car was heat loss from the internal combustion engine. But I know very little about cars.
For example: Teslas improve general efficiency considerably by (for example) using regenerative braking, which will be utilised in normal driving but not if you're travelling up a big hill on a freeway.
Furthermore, they're particularly heavy cars - a Ford Fusion (similar sized saloon) is about 1500kg, whilst the Tesla is 2100kg, presumably because of the batteries - the extra effort to lift up a hill is linear in the weight, so it'll be at least a 25% drop in the surplus cost over normal driving.
Overall, it's not really an efficiency thing because the costs of fuels vary so much. For pure heat-to-wheel efficiency, the most important one is that since Teslas are about 80% efficient at turning power into motion, and charge efficiency is about 97%, and a combined cycle power station is about 55% efficient at converting heat energy into power, then the total efficiency from heat to wheel is about 43%, whilst a modern petrol car might be expected to see more like 30%.
"To help you better anticipate your charging needs, Model S will now calculate the projected energy remaning at your destination using your predicted speed, the elevation, and other factors along your route. Trip Energy Prediction is only active while using Navigation."
By default it charges to 80%. This can be overridden by the user (in preparation for long trips), though after a few days it reverts back to the 80%. This is the improve the overall durability of the battery -- that is, the maximum capacity remains higher for longer if the battery is not fully charged every cycle.
Not to mention the 85 mph most people actually sit on.
For the 85 KWh battery pack going at 55 mph you'll get about 350 miles of range. Going at 85 mph you'll just over 200 miles of range. That's slightly more than a 40% reduction.
I can't understand this, is first torque meant to be toggle?
Cars based on permanent magnet motors do not need to use power to maintain the rotor's magnetic field. On the downside, the field cannot be shut off, so they always have hysteresis loss and cannot freewheel as nicely as induction motors can.