Tesla Electric Semi-Truck?

[ERD50]

This link (page 7) says a full aerodynamic diesel requires 230 HP @ 65 mph, fully loaded.

So 230 HP is 172 KW; so if Tesla aerodynamics are so much better, maybe 120 KW is in the ballpark? Aero is the largest consumption on the chart. I think Tesla gave a Cd figure for their truck, not sure if they listed a typical semi. But much of this could change between now and the release, but I don't think solar panels on the roof will be done, except as for "green window dressing" PR.

-ERD50

 

[NW-Bound]

Good thing you also question the benefits of the solar panels. If the number in the Wiki article is truthful, then there's a lot of details to ask to qualify it. Maybe that Swiss truck sits around a lot during the day to get charged, or it makes long stops.

A large trailer measures 8' x 40'. That's about 30 sq.m. Over much of the US, the solar radiation is 4.5 kWh/day/sq.m., averaged over a year. The best commercial PV panel has an efficiency of 22%. A trailer covered with horizontal PV cells will generate 30 kWh/day on the average. That's good for 15 miles, using Tesla's number, and less than 10 miles using Nikola's.

 

[NW-Bound]

This link (page 7) says a full aerodynamic diesel requires 230 HP @ 65 mph, fully loaded.

So 230 HP is 172 KW; so if Tesla aerodynamics are so much better, maybe 120 KW is in the ballpark? Aero is the largest consumption on the chart. I think Tesla gave a Cd figure for their truck, not sure if they listed a typical semi. But much of this could change between now and the release, but I don't think solar panels on the roof will be done, except as for "green window dressing" PR.

-ERD50

Very good document. That same chart says that out of 230 HP, aerodrag consumes 113 HP, while other factors eat up the rest. All the new electric semi-trucks look very similar in profile (Tesla, Nikola, and Cummins), and highly aerodynamic compared to current diesel trucks. If Tesla comes out much better, perhaps it has some secret sauce the other guys do not know about.

 

[NW-Bound]

Never knew much about semi-trailer trucks, but this thread got me interested. I went to Tesla site and saw that they list the Cd (drag coefficient) as 0.36. How's that compared to others?

A quick look on the Web found a number of 0.608 for an old-style truck engine with the flat front like the Swiss truck above. It was of course awfully un-aerodynamic. When a trailer was attached to it, the Cd went up to 0.704.

Drag force is directly proportional to Cd, if two designs have the same frontal area. For semi-trucks, I would think their frontal areas are the same in order to match the standard trailers that they pull.

However, to compare with other designs, we need a few details. Was the 0.36 value quoted by Tesla obtained with a special trailer? And what is the Cd of the Nikola and Cummins designs?

 

[ERD50]

Musk did not mention a special trailer, but he did point out that the sides of the back of the truck automatically extend out to meet the sides of the trailer, so that it forms a smooth edge even with a variety of trailers (though I would think this dimension would be part of the standard (or maybe there are several 'standard' sizes, or a range?). And though I'm skeptical of much of what Musk says, I am impressed that he/his team brings little innovations and new thoughts to an old product.

Comparing Cd to the sports car, Bugatti Chiron, is a little misleading, though makes great bullet points in a presentation. In the "Engineering Explained" youtube videos, it is explained that that car has a top speed ~ 250 mph, and at that speed, drag requires enormous amounts of power to overcome, and ICE give off lots of heat for each HP, so therefore this car requires a LOT of cooling (air through radiators). And providing that air surface increases drag, which increases power requirements, which increases cooling requirements, and it just gets ridiculous.

So I expect a more modest sports car would have a much better Cd, but haven't found numbers on that.

-ERD50

 

[NW-Bound]

Tesla does pay good attention to aerodynamics, and its vehicles sport low Cd's. For example, the Tesla 3 is 0.24. How's that compared to other cars? I did a quick look and here are some typical numbers for common cars.

Audi A4: 0.29
BMW 5 series: 0.27
Chevy Volt: 0.28
Toyota Prius: 0.25

So, modern cars are a lot better in this aspect than the monsters of the 1950-1960 era. The advantage of Tesla cars is not as great as it is made to be.

See: http://ecomodder.com/wiki/index.php/Vehicle_Coefficient_of_Drag_List.