A while before the anticipated unveiling of the Tesla Semi, Elon Musk tweeted, “It can transform into a robot, fight aliens and make one hell of a latte.”
Those claims remain unconfirmed, but let’s take a moment to see if the Tesla Semi does indeed break the laws of physics.
Range, Battery Size, & Weight
Musk himself stated at the unveiling that the Tesla Semi highway range was due to extremely low aerodynamic drag.
One of the major surprises in the unveiling was the long range of the pair of vehicles, 300 miles and 500 miles. Experts were surprised and in fact predictions had been made that it would be impossible to achieve such range and the battery sizes and weights would be enormous. (I wrote a couple of articles later in response to the various false claims.)
The Tesla Semi consumes less than 2 kWh/mile. It can be shown by a number of different means that this energy consumption is certainly possible and valid. (Also see this for a deep dive on electric trucking.)
Electrical efficiency is high and regeneration reduces energy in short-haul use.
The evidence that aerodynamics reduces required energy is clear. For example, Daimlers aerodynamic Freightliner Super truck doubled mileage.
Unimproved electric truck efficiency combined with data on the effects of aero improvements underscore Tesla’s sub-2 kWh/mile efficiency. Battery pack size can be estimated at 500 kWh for 300 miles of range and 800 kWh for 500 miles of range. The difference between the diesel and electric semi can be compared to find the weight difference. The electric truck chiefly adds motors and battery, but has no transmission, just a simple reduction gear. The Tesla cab is carbon fiber, so there is some reduced weight there by comparison.
The Department of Energy gives a breakdown of Class 8 semi tractor component weights. The Diesel Powertrain components for a class 8 semi weighing 18,000 lbs weigh about 7,000 lbs.
What is removed when we go electric? Engine — 2500 lbs, transmission — 1000 lbs, 300 gallons of diesel — 2000 lbs, and 1000 lbs of driveshaft, empty fuel tanks, exhaust, particulate trap with urea tank, and injection. The electric truck also dispenses with the solid axles and tandem transfer shaft. The electric motors and reduction gear are countered by the weight savings in carbon fiber cab. For comparison, a Bolt motor is 76 kg. Tesla Semi has 4 motors.
Musk stated the battery pack uses the same cells as the Powerpack, which us NMC chemistry. Each Powerpack is 3,575 lbs and has 210 kWh of energy capacity.
The cabinet and cooling are not optimized for lowest weight. In the truck, the cooling systems would not be duplicated and would be more efficient due to moving air under operation. The physical cabinet would be built into the chassis, thus saving weight as well. We can estimate the battery weight per 210 kWh at about 3,300 lbs. 500 kWh would require about 2.4 times the weight of one Powerpack, or about 7,900 lbs, a penalty of only about 900 lbs for the 300 mile range vehicle. For the 800 kWh pack, the weight would be about 3.8 x 3,300, or about 12,500 lbs, but a long-range diesel sleeper cab should be compared and that is an extra 4,000 lbs, or a total drivetrain weight of 11,000 lbs, so the Tesla Semi comes out to about 1,000 lbs more for the 300 mile range Semi (~19,000 lbs), or 1,500 lbs more than a sleeper (at ~23,000 lbs). Those weights are competitive with existing diesel Semis. The area under the cab is sufficient to house the batteries.
Here are some DOE bullet points on what’s in a semi truck as well as the weights of these components:
- Powertrain includes engine and cooling system, transmission, and accessories.
- Truck body structure includes cab-in-white, sleeper unit, hood and fairings, interior and glass.
- Miscellaneous accessories/systems includes batteries, fuel system, and exhaust hardware.
- Drivetrain and suspension includes drive axles, steer axle, and suspension system.
- Chassis/frame includes frame rails and crossmembers, fifth wheel and brackets. Wheels and tires include a set of 10 aluminum wheels, plus tires.
A typical diesel day cab could cost $120,000, but that’s usually a 12 liter or smaller engine. Costs can go up from there. The Peterbilt 389 costs from $136,000 to $156,000.
Cheaper diesel day cabs may have smaller engines and also may not have tandem axles.
Given NMC chemistry, 1 million miles is possible. A 300 mile range truck would require about 3,500 cycles, including capacity drop, while the 500 mile range truck would require about 2,400 cycles. Those are easily within reach of NMC cells used in Tesla Powerpacks, warranted for daily cycling for 10 years and 70% capacity retention, a figure of 3,650 cycles minimum.
Up until recently, NMC cells have been NMC 111. NCA has been 0.8-0.15-0.05. So up until recently, NMC has had more cobalt.
Several battery makers will introduce NMC 811 soon, including LG Chem and SK, so that’s expected to change. (Article coming this weekend diving into this topic.)
As Tesla is offering of 7¢/kWh, there is still room for a 7¢/mile tax and still get $20,000 less in fuel costs compared to diesel.
Diesel at $2.80/gal x gal/6 mile = 46.7¢/mile
Tesla Semi at 2 kWh/mile x 7 c/kWh = 14¢/mile
Add 7¢/mile EV tax for the Tesla Semi and we get 24¢/mile
Diesel is still about 20¢/mile more than electricity in that latter scenario.
100,000 miles/year x 20¢/mile savings = $20,000/year fuel savings.
And that doesn’t count the maintenance and insurance savings.
Fleet managers and buyers are probably very eager to lower other operation and maintenance costs besides fuel. There is no way they would even order one Tesla Semi on a trial basis without seeing some pretty firm and convincing math to prove it was at least possible.