Does The Tesla Semi Make Any Sense?

hello everyone and welcome in 2017 Tesla said you could order and take delivery of your Tesla semi in 2019. well here it is 2022 and that has not happened yet but apparently it's going to happen this year which leads me to this interesting internal conflict I have with Tesla and that I think cool engineering is really cool but I also think deceptive marketing is one of the most infuriating things out there and Tesla happens to be very good at both of these things however with math you can turn deceptive marketing uh into reality and so that's what we're going to be doing in this video we're going to look at six aspects of the Tesla semi and see whether or not the math checks out who's excited looks like Bill Gates is let's do this so we're going to start out with battery size and weight because Tesla doesn't tell us what the weight of the battery is nor what the capacity of it is and so the big challenge with an electric semi is that there is a maximum limit on how much your semi with trailer can weigh and that is 80 000 pounds you cannot exceed this so if your truck weighs a lot and your trailer weighs a lot and your batteries weigh a lot well that means that's less cargo that you can take around because this is the ceiling you cannot exceed 80 000 pounds well from Tesla's impact report they say the semi has over 500 miles of range and can get better than 0.5 miles per kilowatt hour do some Simple Math 500 divided by half and that gives you an estimated battery capacity of about a thousand kilowatt hours assuming those two numbers are true and fairly close to reality now Tesla's battery chemistry they're capable of achieving around 0.275 kilowatt hours per kilogram of battery so we simply take a thousand divide it by 0.275 and that gives us 3 600 kilograms just for battery cells alone or about 8 000 pounds now again this is just the battery cells so you of course need a structure for all of that if you look at a large EV example that isn't necessarily all that weight efficient but a large EV example that can kind of give us the upper boundary of what this might weigh the Hummer EV has a 200 plus kilowatt hour pack that weighs about three thousand pounds so some rough math there if you multiply it three thousand pounds by five to get a one megawatt hour battery pack well then you get a 15 000 pound battery pack now Tesla is definitely going to be under that and they're definitely going to be over that unless they have some magic chemistry that they've created in the meantime so I believe it'll be somewhere between these two probably around 10 to 12 000 pounds for the battery now that's a lot right but it's not crazy and there's a couple reasons why it's not all that crazy so the average Class 8 meaning semi truck that's how they're classified in the U.S the average weight of one of these things uh the diesel ones is about 17 000 pounds and about four thousand pounds can be attributed to the engine and related components to that engine so that is a big chunk of weight certainly electric motors aren't going to weigh anywhere near this but you have that really heavy battery the other advantage that you have with electric semis is they're given a plus two thousand pound weight limit so an electric semi as well as a natural gas semi because these also have additional equipment that weigh more they're allowed a ceiling of 82 000 pounds which means you get a buffer of about 2 000 pounds extra for the EV uh and plus you know you don't have that giant heavy engine so while it's probably going to be slightly heavier than the semi uh part of it is allowed and you still won't have too much of a reduction in cargo capacity so as far as battery size and weight the map actually does check out okay so next let's talk about range because Tesla says this is going to be capable of 500 miles at maximum load and so we're going to go over two examples here one of which is the best case scenario make it as easy as possible for it to be able to do this and then the other is a bit more complicated so we need to go through a few of the variables Tesla says the drag coefficient of this Tesla semi is just 0.36 that is incredibly good it's also kind of hard to believe because you don't have complete control over the trailer if the trailer has some irregular shape to it that has a huge impact on the drag coefficient and that's not something you completely control so it's hard to to get this number but we're going to give it to them in this case also we have to look at the frontal area now if you look at the standard dimensions of one of these trailers in the U.S it's eight and a half feet wide and it's 13 and a half feet tall including the tires that's pretty much a box and it's pretty much unavoidable you pretty much have to use this area this box of an area as your frontal area now for this example I'm going to give them a foot off the bottom and say that some of that air passes underneath the truck and it's not obstructed as far as frontal area so we're going to give them a little bit of a benefit there with front area which we're not going to do for our second example we're going to assume that entire rectangle the velocity is going to be 60 miles per hour that's what Tesla said and they're reveal that they could do this at so the semi is traveling at 60 miles per hour coefficient of rolling resistance of the tires at just 0.005 that's extremely good efficiency of 95 from the battery to the wheels that's extremely good but it is theoretically possible in any uh we're going to see there's no wind and there's no time spent accelerating or decelerating we're just at a constant 60 miles per hour going down a perfectly Flat Road with no wind and all of the variables happen to work out in our favor well how much energy would you need in order to do that scenario for 500 miles you would need roughly 800 kilowatt hours and so that is less than a thousand so theoretically possible here if Tesla does come out and say that the battery capacity of the semi is 800 kilowatt hours or less I would then be skeptical of it actually achieving that 500 mile range because in the best case scenario that's basically the absolute minimum it would need in order to do it now if we look at a harder scenario so now we have this Tesla semi again fully loaded and four of those 500 miles for 20 of that it's going to be going up a one percent grade so for 100 miles one percent grade uh then you have a drag coefficient of 0.5 I think this is still really good so don't think that this is some crazy eye number it's still very good but just consider that you don't have this perfect trailer that matches and so your drag coefficient's a bit higher frontal area as we've gotten there we're traveling at 70 miles per hour that seems more realistic for a semi truck we're going to say the rolling resistance coefficient is slightly higher we're going to say our efficiency is 90 still really good again you have to consider auxiliary things that you're running so you know uh running the heat in the cabin or things like that uh if you have wind so we're going to say we have a 10 mile per hour headwind for this drive and uh we're spending some time accelerating and decelerating so we have to account for inertia in this equation well if you do this this scenario which isn't unfeasible right I mean this certainly Could Happen these are not numbers that are just like oh that's crazy I never would a semi truck ever encounter these scenarios if you do the math there well that gives you about 2 000 kilowatt hours of required energy meaning the actual range of this truck in these conditions is just 250 miles rather than 500. so Tesla's 500 mile per hour claim I think is possible assuming it is a 1 000 kilowatt hour uh battery but I wouldn't say in all scenarios uh that you're going to see that certainly you can see how easily that number can be less now the benefit that Tesla has going for them in these calculations is that they do it at full load it is rare that trucks out there on the road are actually all you know driving with full load the average is underneath that so if we're to look at a scenario like this ideal scenario here and we take out 30 000 pounds so the total weight is just 52 000 pounds of between cargo and the truck and batteries Etc then we're down to 640 kilowatt hours needed in order to achieve that so you can see that if your load goes down it does make a huge impact on how much energy you use because so much of the energy does go to Rolling resistance in these tires so next we get to weight and power both of these variables Tesla does not provide to us however super cool we can calculate both of them wait pretty easy and power a bit more challenging but we will figure it out so Tesla provides some information that allows us to calculate these two variables why because they told us an 80 000 pound Mass this was before legislation had allowed for 82 000. so an eighty thousand pound truck is able to accelerate to 60 miles per hour in 20 seconds now a truck of unknown weight without the trailer is able to accelerate to 60 miles per hour in five seconds well this is super easy to figure out Force equals mass times acceleration we've done something in a fourth of the time meaning our acceleration is multiplied by four which means we have one fourth of the mass so our Tesla semi according you know to their Reveal video is going to weigh about 20 000 pounds so there you have it now we want to discover how much horsepower does this truck have well we know the amount of work done work is force times distance so this truck applies a certain Force to drive a certain distance right and if you take that work and you divide it by time because we know how much time we spent well that gives you power power is work over time so we have force times distance divided by time we can substitute Force for mass times acceleration we can substitute distance for one-half acceleration times time squared because we know our acceleration that's 60 miles per hour in 20 seconds and so you can simplify that all down into this equation here once you plug those in one half mass times time times acceleration squared so we have all those variables we know our Mass we know our time we know 60 miles per hour in 20 seconds is the same as 1.34 meters per second squared so that tells us the amount of power required in this scenario is about 650 kilowatts or about 870 30 horsepower now I have an asterisk here because this is the absolute minimum you would need to do it you're not taking it into consideration efficiency you're not taking into consideration you know the rotational inertia for all these tires things like that so you're looking at around a thousand horsepower for this thing to be able to do what they claim of 0 to 60 in 20 seconds and yeah the math checks out Tesla's capable of 1000 horsepower uh that all is very possible all right next we get to charging rate this one is very simple and easy to verify so Tesla says they can charge this battery this massive battery uh 70 percent in 30 minutes and so the thing is with battery charging that is simply limited to the cell right so you can have a ton of cells and you can still charge all of them at the same rate you just need more power to do it so it isn't crazy they're already doing you know 70 of a battery charge in 30 minutes so that is not anything to be concerned with uh it is a high level of power that is going going into the vehicle so that 700 kilowatt hours in 30 minutes if you assume a thousand kilowatt hour battery pack which means the charging rate is 1400 kilowatts that's about six to ten times what their current superchargers are doing so they're going to have these semi Chargers uh that are capable of much faster charging rates uh very high power and like liquid cooled sleeves and stuff like that Wild Tech but point is they're going to be pumping a ton of power into that semi to charge it up quickly and it is feasible it still means you know you have to have access to these Chargers in order to do it but the math is very feasible there okay next let's get into cost per mile and we're just going to be looking at fuel versus energy here versus a diesel truck I don't know what the price of this Tesla semi is going to be often that comes down to whatever business they're negotiating with when they're selling it at one point they said 180 000 for this truck who knows point is we can do a little math and see whether or not per mile if any of this makes any sense so if you look at the wholesale price for industrial electricity within the United States it's about nine cents per kilowatt hour if you look at diesel uh wholesale price in the US is about four dollars and twenty cents it seems like uh Elon would recommend diesel in this case if it was actually four dollars and twenty cents but that's price of diesel as of when I'm recording this average for the US wholesale now efficiency Tesla we're going to go with their 0.5 mile per kilowatt hour claim and the average uh Class 8 truck within the United States is getting 5.29 miles per gallon so we're going to say that both of these go for a million miles that's what Tesla says they're going to guarantee their powertrain for and it's not uncommon for one of these diesel vehicles to also travel a million miles in its lifetime it's pretty impressive versus you know production cars how much longer these things last so what is the price in each of these scenarios well for the Tesla you multiply that all out you get a hundred and eighty eight thousand six hundred dollars that you will spend purely on electricity uh and for the diesel you're at 793 950 so if these are the actual prices you're paying for one or the other it's like abundantly clear uh that you should go electric if you have the capability to do it in the charging infrastructure all that so if you can actually get electricity for this price and make it work out yeah it's insane uh to go diesel Tesla in their video said they're going to guarantee seven cents per kilowatt hour for these semi Chargers if they actually do that great take them up on it I have my skepticism that they'll actually be offering that and if you look at retail prices that some of us pay uh for like superchargers within the United States that can be above 50 cents per kilowatt hour and if you were to ever actually they have to pay these prices I mean if you multiply that all out then you're at a million dollars in electricity if you're per kilowatt hour price is 50 Cents so then it favors the diesel if the electricity gets really expensive so as long as you're paying industrial electricity prices great you can make it work out and actually a huge leap even if you need to replace the battery considering you know if the price of the truck is anywhere around here or if you have to replace the entire truck so if the price is anywhere near this and fuel prices and energy prices or anything like that math checks out heavily in favor of Tesla so our final subject do the emissions check out because this is of course what Tesla is pushing for they're saying you know by switching from diesel to Electric you're going to have far better CO2 emissions so if we look at our well-to-wheel CO2 emissions meaning everything required in order to use that certain amount of energy within the vehicle for the Tesla that is 0.53 kilograms of CO2 per kilowatt hour that includes includes transmission losses that includes charging losses so our well-to-wheel number there and then for diesel 12 kilograms of CO2 emitted for every gallon of diesel burned and that includes production of that diesel fuel extraction all that stuff so if we look at the mass contribution of the trucks of course we have you know what does it take in order to create these vehicles and then what does it take to run them so we're going to go with the Assumption of 5000 kilograms of CO2 per ton of vehicle this is not including the battery and then the CO2 emissions of the battery we're going to go with uh somewhat of an average within the industry of 150 kilograms per kilowatt hour Tesla says their number is much better than this about 70 kilograms per kilowatt hour but we're going to go with the higher estimate just to kind of be on the safe side here so if we look at the lifetime emissions of CO2 for these vehicles including production and use we get to the perfect scenario here for Tesla just production and assuming all energy is from renewable resources and you have zero emissions associated with driving then you just have a 175 000 kilograms of CO2 emissions not really achievable uh because you know there's going to be some emissions associated with creating solar power wind power whatever but far lower numbers so it can approach this perfect scenario right here realistically using the average mix of electricity within the United States uh so if we go with average USA we're looking at one million 235 000 kilograms of CO2 emitted to travel those million miles for this vehicle and then finally if we get to our diesel example here uh so our last one diesel we're looking at two million three hundred ten thousand kilograms total uh CO2 emissions so what's a little disappointing to me is that using the average US mix we're only cutting emissions in half that's obviously great I mean it's great to cut emissions in half but it could be a lot more impactful depending on where the energy comes from and so that's kind of the whole point right if we improve the energy sources we can make a huge difference using this technology in emissions reductions so over overall if you look at all the elements of this I was quite surprised that there didn't seem to be some fatal flaw from a theoretical standpoint in the Tesla semi thank you all so much for watching and if you have any questions or comments feel free to leave them below

Channel: Engineering Explained

Views: 1,340,402

Keywords: Tesla Semi, engineering explained, elon musk, diesel, electric vs diesel, electric truck

Id: Uv44W7xa4IU

Length: 18min 12sec (1092 seconds)

Published: Fri Oct 14 2022