“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

## Wednesday, December 27, 2017

### Charging the Tesla class 8 semi

This is my third post regarding the Tesla class 8 truck. The first covered the range claim and the consequent weight ramifications. The second covered the cost. And, of course, the numbers were my estimates only. In this post I'll consider the charging situation.

The "poster" claim is that charging stations will enable the 500 maximum mile range truck to charge sufficiently for a 400 mile range in 30 minutes. In my first Tesla truck post I estimated that the battery pack capacity to enable a range of 500 miles would need to be about 1,145 kWh (kilowatt hours) so 400 miles would need about 915 kWh. To deliver this energy in 30 minutes requires power to be delivered at 1,830 kilowatts, that is, 1.83 mW (megawatts). And battery charging isn't 100% efficient, so we'll say 90%. Now we need to deliver energy at a rate of just over 2 megawatts!

The current inventory of Tesla Superchargers for the Models X, S, and 3 deliver energy at a rate of up to 140 kW, about 8% of the required power for a "Megacharger" for the 30 minute/400 mile charge for a Tesla semi. Now, Elon Musk has hinted on Twitter of much higher charging rates, hinting that the megacharger's rate will be far in excess of 350 kW.

Elsewhere, rates on the order of 1.6mW are discussed in the main article here, and the comments are interesting as well. There is discussion of the solar charging aspect, even to the extent of putting solar panels on the roofs of the trailers to be hauled by the semi, something that I may take up in a subsequent post.

There are several concerns with respect to delivering energy at the rate of 2 mW. First, what will such a charge actually cost?Second, how will such power be delivered given that multiple trucks will be charging simultaneously? Third, will a battery pack hold up under such charging rates, presumably applied on a daily basis?

While the first question might seem like a no-brainer advantage for the Tesla, we'll take a look anyway. It's true that, at about 2 kWh/mile and a typical industrial rate of $0.0692/kWh, the implied rate of about$0.14/mile for energy looks very favorable in comparison to 1/7 of a gallon of diesel at $2.93/gallon yielding$0.42/mile. But the infrastructure for delivering diesel fuel to trucks is long since built out and the capital costs fully recovered. The Tesla megachargers are merely hypothesized, not built out and paid for. Unfortunately, I have no idea what Elon Musk has in mind with respect to what he'll build, where he'll build it, and how he'll recover its costs. He does say, in his introductory video, that there are "guaranteed low electricity rates for Tesla." But, one way or another, the infrastructure will have to be paid for. Call it a wild card.

What about question number two? Musk has mentioned solar power for the megacharger stations, but that doesn't necessarily imply a solar roof over a few acres at every truck stop. It could just as easily mean offsetting grid supplied electricity at truck stops with solar electricity offsets at favorable locations. Musk makes somewhat contradictory statements when he discusses recharging at destinations while trucks unload and/or at the truck's base while loading. Whether he's discussing a megacharger at such locations (so that the truck owner would own or lease the charger) or whether he's discussing standard charging isn't clear.

He also discusses being able to take the trucks "anywhere in the world," implying that charging facilities will be ubiquitous. Again, whether all of these facilities would be megachargers isn't made clear. Another possibility would be having a premium charge for the megacharger. Again, details aren't available. Thus, I have insufficient information to speculate in detail.

But I do have to look at one aspect. Here, we find that something like two million tractor trailers are registered in the US. I'll just speculate (really, guess, though I hate guessing) that something like 1.5 million are actively earning money for their owners by hauling freight. I'll also use the estimation that each such truck drives about 45,000 miles per year.

Now, if Tesla were to replace 10% of the semi truck fleet, their trucks would travel 45,000 * 150,000 or 6.75 billion miles/year. At 2 kWh/mile, they'd use 13.5 billion kWh or 13.5 gWh (gigawatt hours)/year of electrical energy. As an aside, this rate represents an average power of a bit over 1.5 mW, though the rate will obviously vary hugely. Nevertheless, this hardly seems like a large strain on the US electrical grid. Discovery Network's Science Channel is currently replaying all of the Mythbusters episodes from the original crew's 14 seasons so I'll echo their nomenclature and call it "PLAUSIBLE."

Both for the reason that this post is already plenty long and the reason that I'm still doing some reading on the effects of consistent extremely high charge rates on Li ion batteries, I'll defer to a subsequent post on that topic and end this post here.

## Sunday, December 17, 2017

### Tesla class 8 truck, part 2

 Image credit: Matchmakerlogistics.com
In my previous post I estimated the weight penalty imposed by the need for a battery pack that will enable the Tesla Truck to have a range of 500 miles. Next, I'll take a look at the pricing situation.

As most know, battery packs of the size to supply energy to road vehicles are very expensive. In fact, in the opinion of many, the U.S. Government subsidy is the only reason the BEVs (battery electric vehicles) have sold as well as they have, especially in the relatively lower price classes such as those occupied by such cars as the Chevrolet Bolt, the Nissan Leaf, and the Honda Clarity EV.

It's not easy to get a handle on the price of a battery pack, but synthesizing various sources, it seems likely that battery packs from the Gigafactory will cost Tesla something like $150/kWh in the 2020 time frame. That would put the cost of the estimated (by me) 1,145 kWh pack for the claimed 500 mile range at$171,750. We see here though that
The electric semi trucks will run between $150,000 and$180,000, depending on range, with a fancy "Founders Series" of semis coming in at $200,000. It's not an easy thing to figure what the cost of a semi truck cab, wheels, etc. (i.e., the entire semi minus the engine and transmission) is but I've tried to get a handle on it by looking at some pricing of so-called "glider kits." Here, I found that a rolling glider could cost from$75,000 to $97,000. Assuming something like a 20% markup, the cost to produce the glider would be$60,000 to $77,600. Using the lower number, Tesla might spend$60,000 on the body, frame rails, axles, etc.

Next, my understanding is that the Tesla truck will utilize four 192 kW permanent magnet electric motors (the same as the Tesla Model 3 motor). I've found it to be EXTREMELY difficult to get an accurate estimate for the cost of such a motor, here we find a source to purchase Tesla 3 drive units  (Tesla motor, inverter, gear box, dash display and control unit, throttle pedal, and two axles) for $11,900. I'll estimate that the markup is 50% and so the cost of the unit is$7,933. I'll further estimate that the parts needed for all four motors (since we won't need four throttle pedals, etc.) represent 2/3 of the cost, so three of the units cost 3*(2/3)*$7,933 or$15,866. Add the full $7,933 for the fourth unit to get a total cost of$23,799 for the entire set. Call it $24,000. So we have an estimated cost to Tesla of$171,750+$60,000+$24,000=$255,750. And there's no question that I've left a few things out. And, assuming that Tesla would like to make a profit of, say, 20%, the price out the door would be$306,900. That's over 70% higher than the cited price of the 500 mile range truck. Where may I have gone wrong? Conversely, if Tesla is selling a 500 mile range truck at $180,000 and is making some incremental profit on the sale then their cost would be, at most,$150,000 using the same 20%. And this doesn't include the subsidy that Tesla is offering for charging (I'll take up charging in a subsequent post).

It's unlikely that the cost of materials (aluminum, steel, plastic, carbon fiber, etc.) will decrease sufficiently to reduce Tesla's cost by something like 40%. My conclusion is that they are banking on some combination of manufacturing efficiencies, economies of scale, and improvements in the actual battery chemistry to reduce the cost per kilowatt hour of their battery packs.

In order reduce the cost of a truck by some $100,000 (turning now to very round numbers) by reducing the cost of a battery, the cost would need to come down to somewhere in the$63/kWh. Below we see a graph of costs projected out to 2030. And, while the cost has come down considerably and is projected to continue to do so, I've not found a credible projection that hits anything close to $63/kWh even out 13 years, let alone three years. WebPlotDigitizer quickly shows that the projection is for$170/kWh in 2020 and $75/kWh in 2030. Note that my calculation above used$150/kWh!