“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!

## Saturday, February 18, 2017

### Once again with Pavegen

(Note: the zombie image applies both to my blog and to the subject of this post.)

Pavegen, a Company that I've looked at before (see here and here) is still around and, apparently, thriving. Pavegen designs, manufactures, and installs tile systems that generate electricity via footfalls as pedestrians walk over them. Despite my lack of posting, I've not lost interest in all aspects of energy and, in perusing the web, I happened upon their new site. They've developed a new tile design and quite a presentation. The link is to a 49 minute video!

I thought I'd keep an open mind and evaluate it, despite my expressed disdain in the previous posts. Getting started, I found a couple of troubling things. At the 19:15 timestamp in the video, CEO and Pavegen inventor Lawrence Kemball-Cook states that the new Pavegen tiles are "200 times as efficient." Later, at the 28:10 timestamp, CTO Craig Webster states that Pavegen is capturing "about 20 times more energy per footstep" than the previous version of the Pavegen tiles.
 Image credit: Pavegen

Well! First, an order of magnitude discrepancy in the claims is hardly something to ignore. But let's use Webster's claim of 20 times, since he's the CTO. Kemball-Cook walks across the tiles to demonstrate the data gathering capabilities of the tiles and the screen shows steps and energy generated (see the graphic at right, click to enlarge). It shows that Kemball-Cook has generated 65 Joules in 14 steps, or about 4.6 Joules/step. As an aside, some quick and dirty calculations with appropriate estimates leads me to conclude that he's generating at something like 8 watts.

In my second Pavegen post (this current one is my third) I estimated that the previous generation of Pavegen tiles generated somewhere between 3.5 and 7.2 joules per footfall (the lower from my estimates, the higher from data generated by a Pavegen installation). I'm hard pressed to see an increase of 20 (let alone the ridiculous 200) times in efficiency of energy conversion. Kemball-Cook and Webster both tout the efficiency of the new triangular shape and its ability to capture energy over 100% of the area of the tiles vs. the previous square tiles but that is, in no way, sufficient to justify their claim.
 Image credit: Pavegen

I assumed from previous information that the mode of energy conversion was piezoelectricity. but it's clear from the Pavegen video that this is not the case, at least in this incarnation. Rather, it appears that a footstep spins a small flywheel that operates as a generator. Each vertex intersection of the triangular tiles rests above such a generator. I will concede that it's a very clever design.

Kemball-Cook and his team have big plans for the Pavegen system. Jeff Martin, CEO and founder of Tribal Planet, apparently has formed a partnership with Pavegen and, through the use of smart phones, anticipates that malls, stores, stadiums, etc. could track the energy delivered through the footsteps of a customer and then provide discounts, loyalty awards, etc. to the customer. Or, one could "donate the energy" to some developing world person who needs it. The mechanism for such a transfer isn't described.

But, as I stated in the previous post, I take about 5,000 steps on an average day. If each step were captured, I'd generate (if I weigh the same and walk similarly to Kemball-Cook) 4.6*5,000= 23,000 joules, or 0.0064 kilowatt hours. In my city of Anaheim, CA, that would be worth a little under eight hundredths of a penny. And, to reiterate, that's not my trip to Target, that's my walking for an entire day. The cost of a Pavegen tile isn't stated, but Kemball-Cook does state that Pavegen's goal is to bring the price close to that of a standard tile through mass production.

There's no doubt that the tiles do generate electricity, probably at the rate of around 8 watts for each walking adult. And there's no doubt that that level of generation can be used for area lighting or similar. But the energy isn't free, it's energy added to that of walking without the tiles. Now, it may be the case that in the generally overweight United States (I can't say about England, the home of Pavegen), having people spend more energy to walk might be desirable.

In any event, at the outset of the video, Kemball-Cook mentions that lighting accounts for nearly 20% of all electricity generated world wide and, after saying that he didn't know that, doesn't say anything further about it. He leaves the impression that he'll show that Pavegen tiles can alleviate the need for mains power for that use. Umm... no.

In my office, there are about 32 people. Most don't walk around as much as I do but let's assume that they do. Most of my walking is at work, say 4000 steps over nine hours. This rate, at 4.6 joules/step, equates to 0.6 watts or so. If all 32 people in my office did the same, it would be 19.2 watts. That wouldn't light one of the four fluorescent tubes in my office, let alone the entire 12,800 square feet of the floor we occupy. It's true that LEDs would do better but there's no chance that 19 watts would come close. And that generation, in a work day, would be about 0.017 kilowatt hours, worth less than two cents.

Pavegen has a fascinating gimmick and a clever design, but it won't put a dent in electricity use. And the electricity comes, ultimately, from the sun. We eat the plants and animals, and fertilize them with products of sunshine from millions of years ago to give us the energy to
pump the Pavegen tiles.

Update: There's significant discussion at the website of the ability of the tiles to generate data and wirelessly transmit it. This could be used to determine traffic patterns in stores, malls, museums, etc. and to locate "hotspots" for patron activity. I strongly suspect that, after the "gee whiz" factor of the trivial energy output wears off, such data will be the real value (or, as my close friend and associate, Dr. Boris Stein, would say, "the dry residue"). Were I an officer at Pavegen, I'd offer a cheaper option of the tiles without the generators to be sold for the data gathering capability.