Intro<\/u><\/b><\/p>\n
Who says lightning never strikes twice?<\/p>\n
Last week, I wrote an article regarding the difficulty of charging a hypothetical all-electric US vehicle fleet with today\u2019s electric grid<\/i><\/a>. But as before, part of a comment to that article<\/i><\/a> made by longtime TAH reader rgr769<\/i> caught my eye \u2013 and made me wonder:<\/p>\n . . . . I would still like to see an EV Freightliner or Mack tractor pulling a fully loaded trailer uphill. Also, can anyone imagine the size of the battery packs to make that happen or how long it would take to charge them. . . . .<\/p>\n<\/blockquote>\n Well, longtime readers can probably see what\u2019s coming – again. (smile) Yeah, I decided to take a reasonably \u201cquick and dirty\u201d look at that too, and also answer the questions rgr769<\/i> implicitly asked regarding such a hypothetical EV semi\u2019s battery pack.<\/p>\n Consider yourself forewarned. And yes, as in the previous articles there\u2019s some math involved. But just as before, the math again turns out to be pretty straightforward and simple.<\/p>\n And before anyone asks: no, I didn\u2019t collude with rgr769<\/i> (or pay him a retainer) to induce him to make that comment. This is a legitimate pure coincidence; he just happened to raise another question that made me go, \u201cHmm?\u201d<\/p>\n \u201cAnyway, that’s my story and I’m stickin’ to it.\u201d (smile)<\/p>\n BLUF (Partial): Yeah, We Could Likely Build It Today<\/u><\/b><\/p>\n So, could we build an EV semi-tractor (hereafter I\u2019ll refer to either the semi-tractor or semi-tractor-trailer combinations as a \u201csemi\u201d) that would climb hills as well as a conventional diesel-powered one? Best I can tell, yes we could \u2013 and fairly easily. After all, we’ve been powering trains with electric motors for literally decades.<\/p>\n Here’s one possible way. Per Source 1, a conventional semi\u2019s diesel engine typically produces between 400 and 600 horsepower (hp) and between 1,200 and 2,000 ft-lb of torque. Per Source 2 the motor in the original versions of the Tesla Model 3 produced 258 hp and 317 ft-lb of torque (later improvements raised that to 283 hp and 330 ft-lb of torque) \u2013 and those motors are not particularly large<\/i><\/a> (the linked photo shows the motor\/rear axle assembly from a Tesla S vice a Tesla Model 3). <\/p>\n Use appropriate multiples of variants of those motors (4 to 6) and synchronize them (easily done), and I\u2019m reasonably sure such a design could generate the horsepower and torque needed. With some moderate redesign to up the horsepower to around 400 and the torque to around 450 ft-lb, you might even be able to mount four of them in or near the semi-tractor\u2019s drive axle assemblies where differentials would normally be located and use one per drive axle, using electronics to precisely control speed and eliminate the need for differentials entirely.<\/p>\n However, those motors would require electricity to operate. Since we’re talking an EV semi, we’re talking stored electricity \u2013 and thus a battery pack. How much stored energy? Glad you asked. Let’s figure that out.<\/p>\n EV Semi: How Much Power Required?<\/u><\/b><\/p>\n How much power does a semi require to keep rolling at highway speed? At a constant speed on perfectly level ground in calm conditions, the power requirement for a semi is minimized. The weight of the load no longer is much if any of a factor; a heavy load might add a bit to drivetrain and axle friction, but I\u2019d guess any such addition would be very small. Rather, the power needed for steady state operation on level ground when it\u2019s calm is dominated by 4 items: aerodynamic load, rolling resistance, accessory load, and drivetrain load – with the first two being far larger than the last two. (If you\u2019re interested, Source 3 explains each of those terms in some detail.) For a typical semi from about a decade ago, per Source 3 those loads were as follows:<\/p>\n \nTypical Semi Power Requirements, constant 65MPH, level ground\/no wind, circa 2010<\/u><\/p>\n Aerodynamic load \u2013 114 hp Total Power Required \u2013 214 hp\n<\/p>\n<\/blockquote>\n As you might have guessed, these loads \u2013 which represent the power needed merely to keep rolling at constant speed on perfectly level ground with zero net headwind \u2013 are the primary reason why semis on average get around 6.5 MPG (Source 4).<\/p>\n You may have noticed more use of wind deflectors and skirting on semis over the past decade. Those are an attempt to reduce the aerodynamic load component, and thus save fuel. <\/p>\n Let\u2019s assume our hypothetical EV semi achieves a 20% reduction in both aerodynamic load and rolling resistance (more streamlined design and better tires). Let\u2019s assume a 50% reduction in accessory load (on-demand only vice constant drive by vehicle engine wherever possible \u2013 but I\u2019d guess that\u2019s about it in terms of a reduction; for an EV, heat\/lights\/instruments\/AC also consume battery power, and drivers are going to need those regardless). And since the transmission and other drivetrain components are greatly simplified in an EV (Tesla uses a 1-speed 9:1 reduction gear in the Tesla 3), let\u2019s assume a 75% reduction here too. That yields the following:<\/p>\n \nHypothetical EV Semi Power Requirements, level ground\/no wind, constant 65MPH<\/u> <\/p>\n Aerodynamic load \u2013 91.2 hp Total power required \u2013 158.6 hp\n<\/p>\n<\/blockquote>\n So, what\u2019s that in terms of kW \u2013 and, more importantly, in kWh, which is a measure of energy stored as battery capacity? That\u2019s actually pretty straighforward to calculate.<\/p>\n One horsepower is approximately 746 watts. So 158.6 hp is equivalent to 118.315 kW, give or take a bit. <\/p>\n Unfortunately, this figure is somewhat optimistic. The power for three of the categories above (aerodynamic load, rolling resistance load, and powertrain load) is mechanical power, and would all be provided through the operation of the hypothetical EV semi\u2019s drive motors \u2013 and while electric motors are quite efficient, like all other energy conversion devices they\u2019re not 100%<\/i> efficient. (The fourth, accessory load, would be a direct electrical load on the battery and therefore shouldn\u2019t require much if any adjustment for electric motor inefficiencies with proper design.) Per Source 5, the highest laboratory demonstrated efficiency for an electric motor to date appears to be 96.5%. Let\u2019s back off that a touch and assume 95% efficiency for the drive motors. (I’d guess this likely somewhat optimistic, but it could be pretty close.) This yields a total power requirement of <\/p>\n ( ( (91.2 + 54.4 + 3) hp \/ .95 ) + 10 hp ) * 0.746 kW\/hp = 124.15 kW<\/p>\n Again: this is the power required merely to maintain a speed of 65 MPH on perfectly level ground in calm conditions<\/i>. It doesn\u2019t account for hills.<\/p>\n At 65 MPH, traveling 1 hour means you go 65 miles. Since a kWh is 1 kilowatt used for a period of one hour, that means we\u2019d need at least 124.15 kWh of stored electricity – that is, at least 124.15 kWh of battery capacity – for each 65 miles driven under those conditions. We\u2019d need more if hills were involved.<\/p>\n How much more? Well, here we go. Now we need to consider the vehicle\u2019s weight and just how much climbing is involved.<\/p>\n How Hills Affect Energy Usage<\/u><\/b><\/p>\n Climbing hills takes additional energy. This is because you\u2019re adding gravitational potential energy to the vehicle and load by raising its altitude with respect to the earth\u2019s center of mass.<\/p>\n However, electric (and hybrid vehicles with battery packs) can recover some of this energy when they descend by using what\u2019s called regenerative braking. In regenerative braking, a portion of the vehicle’s kinetic energy otherwise lost during braking is used to generate electricity, which can then be used to recharge batteries. That means that some of the extra energy used during a climb can be later recovered during descent and used to recharge the vehicle\u2019s battery. (Conventional vehicles also do this in a limited sense as well; they use far less fuel going downhill than they do on level ground to maintain speed, and in many cases gain speed. They just can\u2019t store any of that excess energy for later use.) <\/p>\n Unfortunately, regenerative braking is also an energy conversion process. And like all other energy conversions processes it\u2019s not 100% efficient either. Source 6 indicates that regenerative braking for the electric vehicles on the road today is between 16% and 70% efficient. So if an EV climbs a hill and then descends to its original elevation today, it will end up with a minimum net loss of somewhere between 30% and 84% of the energy it used to make the climb. And remember: this energy used to make the climb was in addition to the energy needed to keep moving at a constant speed. Further, the additional energy loss occurs each and every time an EV climbs and then descends<\/i>; the amount of energy lost is determined by the total vertical distance climbed and descended and the efficiency of that vehicle’s regenerative braking. <\/p>\n As you might expect, there\u2019s ongoing research in improving regenerative braking efficiency. Below, I\u2019ll give designers the benefit of the doubt and use 85% for regenerative braking efficiency. That\u2019s probably a bit high, but IMO it\u2019s at least within the realm of the possible without making use of either pentagrams or unicorns. (smile)<\/p>\n Now, let\u2019s consider a couple of examples and see how much energy loss we\u2019re talking about.<\/p>\n Example 1<\/u>: A single climb of 1,000\u2019 elevation and a matching descent by an EV with 50,000 lb Gross Vehicle Weight (GVW). (FWIW: 50,000 lb is far below the maximum GVW limit for a semi in the US. Per Source 13, the minimum GVW limit for federally-funded highways appears to be 80,000 lb; some states allow far more.)<\/p>\n We\u2019ll do this in three steps. First, we\u2019ll calculate \u2013 in kWh \u2013 how much energy is required over and above constant-speed driving on level ground with no wind<\/i> for the vehicle to climb the hill. Next, we\u2019ll calculate 85% of that figure and assume that is returned to the EV\u2019s battery pack (some additional energy might be lost if regenerative braking isn’t sufficient to keep speed under control and conventional friction braking also must be used). The difference between those two numbers is the minimum net lost energy due to the climb and descent.<\/p>\n This is easiest done if we first convert weight and altitude gained to metric units. 50,000 lbs is approximately 22,700 kg; 1,000\u2019 is approximately 304.8 meters. Per Source 7, gravitational potential energy can be calculated as PE = mGh<\/strong>, where PE<\/strong> is the gravitational potential energy; m<\/strong> is the mass of the object involved; G<\/strong> is the Earth\u2019s gravitational constant (9.81 m\/sec^2); and h<\/strong> is the change in the object\u2019s altitude (a negative value for h<\/strong> implies the object is being lowered vice raised and is thus is releasing gravitational potential energy vice acquiring it). Since we\u2019re raising the vehicle (climbing a hill), the vehicle is gaining gravitational energy; we therefore must consume additional energy to make the climb. Allowing for 95% motor efficiency, the additional energy required is thus<\/p>\n ( 22,700 kg * 304.8 m * 9.81 m\/sec^2 ) \/ .95 ) = 67,874,997.6 J, or about 67.875 MJ<\/p>\n One kWh is equal to 3.6 MJ. So the additional energy required to make the climb, expressed in kWh, is 18.854 kWh. <\/p>\n Sidebar<\/u>: How about the additional horsepower required? That can also be fairly easily calculated. For a 5% slope, at a constant 65MPH such a climb would take about 3.5 minutes. Expending 18.854 kWh over a period of 3.5 minutes would require an increase in power above the normal cruising power of <\/p>\n ( 18.854 kWh \/ ( 3.5 min \/ 60 min\/hr ) = 323.21+ kW, or about 433.26 hp<\/p>\n The four hypothetical 400 hp \/ 450 ft-lb torque electric engines on a EV semi would have more than enough horsepower reserve, and would collectively have around 1,800 ft-lb torque. That seems to be enough extra horsepower. I’m not going to check the torque, but 1,800 ft-lb is near the upper end of what conventional semis have today. I’d guess that would also be enough.<\/p>\n FWIW: since conventional semi engines typically have a power output of between 400 to 600 hp and between 1,200 and 2,000 ft-lb of torque, this additional power requirement for such a 5% climb explains why loaded conventional semis have difficulty on long hills.<\/i><\/p><\/blockquote>\n Assuming that we now descend 1,000 ft and that regenerative braking is 85% efficient, a maximum of 16.026 kWh will be returned to the vehicle\u2019s battery pack by regenerative braking. That means the net energy loss due to the climb and descent of the vehicle is at least the difference between these two figures, or 2.838 kWh.<\/p>\n No, that doesn\u2019t seem like much. But when driving, you\u2019re likely doing far more climbing and descending than you realize.<\/p>\n Example 2:<\/u> Same vehicle driving over gently rolling terrain <\/p>\n OK, let\u2019s take that same vehicle and drive it on almost \u2013 but not quite \u2013 level ground with no net change in altitude for one hour. Here, let\u2019s assume the entire trip consists of alternating segments of 0.5% slope (e.g, a 6-inch elevation change every 100\u2019) 2,000 feet in length going uphill followed by a matching 0.5% 2,000\u2019 slope downhill for the entire 65 miles. This is terrain where one climbs and descends 10 feet roughly every 3\/4 mile – very gently rolling terrain.<\/p>\n In one hour, the vehicle would drive (65 miles * 5,280 ft\/mile) = 343,200 feet. Every 4,000 ft, the vehicle would climb \u2013 and then descend \u2013 10 feet. It would therefore repeat the climb\/descent 85.8 times in 65 miles.<\/p>\n That means the vehicle would climb and descend 858 feet \u2013 even though the net result is zero change in altitude. The vehicle thus would lose 85.8% as much additional energy (due to those repeated gentle climbs and descents) as a vehicle that had climbed, then descended a single 1,000 ft hill. For an EV semi weighing 50,000 lbs gross, that works out to the use of an additional 2.435 kWh of battery capacity during that hour\u2019s driving. And that\u2019s for 10′ high undulations with \u201cridge crests\u201d (if you want to call them that) spaced about \u00be mile apart. Most roads have more pronounced hills than that, and many have them more frequently. <\/p>\n What happens if you double the slope in the above example? That doubles the distance climbed and descended \u2013 and thus doubles the amount of extra energy consumed. Ditto if the undulations are twice as frequent but have same altitude variation. Double both the frequency of undulation and altitude variation? That quadruples the extra energy consumed.<\/p>\n Let me put it in gambler\u2019s language: when it comes to storing energy in a EV’s battery with regenerative braking, \u201cYou can\u2019t win and you can\u2019t break even. \u2018Cause over time the house is guaranteed<\/u> to take its \u2018cut\u2019.\u201d (smile)<\/p>\n So, About That Battery Pack . . . <\/u><\/b><\/p>\n OK, so let\u2019s look at a hypothetical example. Let\u2019s use the same 50,000 lb GVW hypothetical EV semi from the above example. What would you need in terms of a battery pack to drive, say, 5 hours over (as defined above) \u201cgently rolling terrain\u201d at a constant 65MPH with no wind?<\/p>\n Turns out that\u2019s fairly easy to calculate. From calculations done previously, driving this hypothetical EV semi at a constant 65MPH on level ground with no wind requires 124.15 kWh of battery capacity. To account for the gentle undulations in the roadway at the specified GVW, add another 2.435 kWh. That means the vehicle will consume 126.585 kWh per hour driven \u2013 or about 632.925 kWh of battery capacity is needed for 5 hours driving time. (You’d also need to accelerate the vehicle to 65MPH in the first place. But since the kinetic energy of the vehicle at 65MPH works out to be less than 1 kWh and we\u2019re assuming 85% energy recovery due to regenerative braking, I\u2019m neglecting that. Add in aerodynamic losses and rolling resistance during acceleration and I\u2019d guess that getting up to speed would add maybe another 2 or 3 kWh max to the total energy required, and possibly only 1 kWh or so.) <\/p>\n Most likely, a modest amount of extra battery capacity would need to be included to account for the cumulative effect of larger hills, wind, and weather conditions as well as a general safety factor. I\u2019m going to assume a roughly 15% overcapacity is provided \u2013 which means the battery pack would be about 750 kWh. I’ll thus use a battery pack of 750 kWh for the calculations that follow.<\/p>\n That\u2019s equal to 10 Tesla Model 3 extended-range option batteries. (Per Source 2, these batteries have 75kWh capacity, weigh 1,060 lbs, and have a volume of approximately 0.4 cubic meters.). So yeah, you could build something like that. But would it be workable in the real world? And that leads to . . . <\/p>\n \u201cUh, Houston . . . We Have A Problem\u201d<\/u><\/b><\/p>\n More precisely, we have three problems.<\/p>\n First problem<\/u>: charging. A battery that size can be built, but if used for freight hauling it will have to be charged repeatedly; nearly daily would be my guess. And assuming even a 10 hour charge time, a battery with a 750 kWh capacity would require a huge amount of electrical power to charge it. How much? Assuming 92% efficiency for the battery charger (the rationale for that 92% figure is in my previous article concerning EVs linked at the beginning) and completely uniform charging over a 10 hour period, that works out to <\/p>\n ( 750 kWh ) \/ (.92 * 10 hrs) = 81.5 kW<\/p>\n Assuming a power factor<\/i><\/a> of 1 and assuming an invariant load from the charger (these conditions are the best possible case in terms of minimizing the charging current required), per Source 8 that means you\u2019d need a 240v circuit capable of handling at a minimum 339+ Amps \u2013 or a circuit rated around 340 Amps, and probably larger to include some safety margin. Even using 480v 3-phase power, again per Source 8 you\u2019d need 98+ Amps \u2013 or a 100 Amp circuit, and again probably larger to allow for some safety margin. <\/p>\n Oh, and that battery charger is going to get rather hot, too. With a power factor of 1, it\u2019s going to be rejecting most of the energy it doesn\u2019t deliver to the battery as waste heat (the batteries themselves and the conductors connecting the charger to the vehicle will reject some smaller portion of the charging loss). That’s a heat output of roughly 6.5 kW – or the equivalent of between 4 and 5 1500-watt space heaters all operating simultaneously at max output.<\/p>\n Now, large truck stops today have large parking areas. But I don\u2019t think they\u2019re typically big enough to handle 100 or 200 trucks parked, simultaneously, and staying there for 10 hours at a time each while charging their batteries. And I don\u2019t think they\u2019re typically serviced by multi-MW electrical feeds, either (81.5kW x 100 = 8.15 MW). Plus, with 100 trucks each of which is generating 6.5kW of waste heat while charging those huge batteries, well, if you liked summer in Kuwait . . . you just might enjoy walking around that charging yard. (smile)<\/p>\n Yes, you could charge those battery packs slower using far less power. But that means you’d have to swap the discharged battery pack for a fully-charged one daily – and would have to have spares on-hand. At a trucking company’s maintenance facility? That might be possible. (Whether it could be done safely or not is another question. Even a “discharged” 750 kWh battery pack still would contain enough energy to be deadly dangerous if mishandled.) Doing it at a truck stop or hotel parking lot during a nightly rest stop? “Good luck wit dat.”<\/i><\/p>\n Second problem<\/u>: 750 kWh is probably less than half of what you\u2019d really need for long-haul trucking.<\/p>\n Per Federal Motor Carrier Safety Administration (hereafter FMCSA) rules (see Source 10), long-haul truckers are allowed to drive 11 hrs daily within a 14 hour \u201cduty day\u201d window, followed by a mandatory 10-hour \u201coff duty\u201d period (there are numerous other limitations\/restrictions\/exemptions, but that\u2019s the one that\u2019s generally going to be pertinent here). Further, truckers must take a half-hour break from driving during their duty day; this break must occur NLT 8 hour after they begin driving during their duty day.<\/p>\n OK, so let\u2019s consider driving 11 hours at 65 MPH. That\u2019s a touch over 700 miles in one day. <\/p>\n Do long-haul truckers routinely do something close to that, particularly west of the Mississippi where speed limits are higher and traffic is generally less congested than in the Eastern US? That is, do they often drive 10 hours or so at an average speed of 65+ MPH in one day? I\u2019ll go out on a limb here and say, \u201cYou betcha!\u201d \u2013 though I really don\u2019t know that with certainty. But If I\u2019m wrong, I\u2019m sure one of our readers with personal experience working in the field can (and will) correct me. For a long-haul trucker, more miles driven generally means more cash in their pocket. <\/p>\n Bottom line: 5 hours at 65MPH realistically seems to be about half of what would be required for a semi to be used in long-haul trucking. With a multi-hour recharge time, given the maximum 14 hour duty day followed by the 10 hour mandatory off-duty period imposed by FMCSA you\u2019d need the battery capacity to go at least twice as far as that 750 kWh battery pack allows in order for the vehicle to be useful for long-haul trucking. <\/p>\n Third problem<\/u>: weight. A 750kWh battery pack would be equivalent to 10 Tesla Model 3 extended range battery packs. As previously noted, a Tesla Model 3 extended range battery pack weighs 1,060 lbs and has a volume of 0.4 cubic meters, and probably represents about the best EV battery technology mankind currently can produce in quantity. So we could expect a 750 kWh battery pack to weigh roughly 10,600 lbs and have a volume of around 4 cubic meters (think a rectangular cuboid that’s 1m x 2m x 2m, or about 3\u2019 3\u00bd\u201d h x 6\u2019 7\u201d l x 6\u2019 7\u201d w ). <\/p>\n A 1,500 kWh battery pack would be about twice that in terms of size and weight. It would have a volume of 8 cubic meters (e.g., it would have the same volume as a cube 2 meters on a side). That 1,500 kWh battery would also weigh around 21,200 lbs, or roughly 10.6 tons<\/u> \u2013 far more than combined weight of the engine, transmission, fuel tank, fuel, and other fluids used in a conventional semi. (For the record, the 10,600 lbs estimated for the 750 kWh battery pack above also is heavier than the engine\/transmission\/etc . . . in a conventional semi today.) Since GVW limits exist, presumably for good reason, what do you think that battery weight is going to do to an EV semi\u2019s maximum cargo capacity in terms of max allowable cargo weight? <\/p>\n Conclusions<\/b><\/u><\/p>\n IMO, we now have an answer to rgr769\u2019s<\/i> implicit questions. First: yes, it appears technically feasible to build an EV semi that could move loads and make substantial climbs. Building the batteries would be technically possible, and the motor technology (in terms of the required torque and horsepower) appears eminently do-able as well. We\u2019ve been building diesel-electric trains for decades; building a suitable electric motor was IMO never the issue. Whether we could build a battery of sufficient capacity was the key question, and it appears we could.<\/p>\n However, whether such a vehicle would be useful or not is another question entirely. For long-haul freight, the answer today seems to be a firm \u201cNo\u201d, and perhaps even \u201cNo way in hell.\u201d While the battery pack required can at least in theory be produced, at 10.6 tons it would simply be too heavy to be practical. And the power distribution infrastructure to support charging large trucks on the scale required during the FMCSA-mandated 10-hour \u201coff duty\u201d time required for long-haul truckers after a maximum 14-hour \u201cduty day\u201d . . . simply doesn\u2019t exist. Could it be installed? In theory, yes. But I’d guess serious proposals for installing same would likely produce a \u201cYou\u2019re joking \u2013 right?\u201d moment when those proposals were presented to utility company leadership. <\/p>\n Why? Because as demonstrated above, the amount of power required to charge 100 large EV semi\u2019s each having only half the battery capacity needed for long-haul trucking<\/i> simultaneously in 10 hours would be huge \u2013 as in approaching 10 megawatts. Since per Source 14 one<\/u> megawatt of constant electrical power typically can power 400 or more homes, that means you’re talking the equivalent of s medium-sized town’s or small city’s electrical power supply for each 100-EV semi charging lot<\/i> – and you’d need twice that if you had the batteries actually required for long-haul trucking. <\/p>\n Even a small facility that could charge only 10 trucks would need 1 to 2 megawatts of electrical supply, and possibly substantially more if charging EV semi batteries does not draw a constant load. (Real-world data on charging LiIon batteries from Source 9 indicates that the charging load is not likely to be constant.) EV semi charging locations would thus not be terribly common, at least initially. Large trucks would tend to congregate at the few facilities that would be available. And the waste heat generated during charging (around 8% of the power supplied by the electric grid to the chargers) would make such charging yards local \u201chot spots\u201d \u2013 literally.<\/p>\n So, how can current semis do what they do today? Easy \u2013 it’s because of diesel fuel’s high energy density. Hydrocarbon fuels have hugely larger energy densities than LiIon batteries. As an example: per Source 11, diesel fuel has an energy content of 38.6 MJ per liter \u2013 or about 40.53 kWh per gallon. That means a bit over 18.5 gallons of diesel fuel, weighing around 125 lbs, has the same energy content as the electrical energy stored in the hypothetical five-ton-plus 750 kWh LiIon battery discussed above. Even if you only recover a bit over 1\/3 of diesel fuel\u2019s energy content in the form of mechanical or electrical energy, you\u2019d still only need somewhere around 50 gallons of diesel fuel, give or take, to provide the same amount of usable mechanical or electrical energy as a 750 kWh battery pack can store.<\/p>\n Real-world data bears that out. As I noted previously, per Source 4 in the real world conventional semis average somewhere around 6.5 miles per gallon. That means that a hypothetical drive of 325 miles in a conventional semi would require about 50 gallons of diesel fuel \u2013 60 gallons if you want a 20% safety factor. Assuming a weight of 6.65 lb per gallon, the former would weigh somewhat less than 350 lbs; the latter, around 400 lbs. Even after considering the weight of the conventional engine\/transmission\/fuel tank\/other fluids\/associated equipment needed, that represents a significant weight savings over an EV semi using the best current technology; that in turn allows more cargo to be hauled. Plus, replacing that 50 or 60 gallons of fuel (thus adding another 325+ miles of range) takes a few minutes, not literally hours. In fact, it can be done in conjunction with that mandatory half-hour \u201cbreak\u201d required NLT 8 hrs after a long-range driver begins driving for the day – or when the driver makes a longer stop for a meal. Then the trip can continue on until the daily driving hours limit is reached.<\/p>\n Oh, and did I mention you\u2019d need to be able to drive twice that far – and thus would need twice as large a battery (e.g., around 1,500 kWh) – for a hypothetical EV semi to be usable for long-haul trucking? Which in turn means the battery would be twice as large, twice as heavy, and take twice as much power to charge (and reject twice as much heat) during that daily 10-hour “off duty” period? Well, if I didn’t before . . . I guess I just did. (smile)<\/p>\n . . . <\/b><\/p>\n Do EV semis (or somewhat smaller non-articulated EV trucks and buses) have a role? For local use, perhaps. Even that is questionable at present, though. Source 12 indicates that LA and other locations have tried pilot projects involving electric buses and found them to have serious reliability and range issues. <\/p>\n But for long-haul operations, given the current state of technology those hypothetical EV semis appear to be more like the original cast of SNL: \u201cThe Not Ready for Prime Time Players\u201d. IMO it would take a major breakthrough in battery technology along with truly serious upgrades to the electrical grid \u2013 or a change to some technology that generates electrical energy on-vehicle vice storing same in a battery \u2013 to make electric semis\/trucks\/buses feasible for long-distance use.<\/p>\n Or, as country folks might put it: \u201cAin\u2019t enough lipstick in the whole world today to make that<\/i> pig look purdy.\u201d (smile)<\/p>\n ———-<\/p>\n Sources<\/u>:<\/p>\n 1 \u2013 Typical Conventional Semi Engine Power and Torque: https:\/\/www.internationalusedtrucks.com\/semi-truck-horsepower\/<\/em><\/a><\/p>\n 2 \u2013 Wikipedia article, Tesla Model 3: https:\/\/en.wikipedia.org\/wiki\/Tesla_Model_3<\/em><\/a><\/p>\n 3 \u2013 Semi Steady-Speed Power Requirements: https:\/\/www.nap.edu\/read\/13288\/chapter\/7#79<\/em><\/a><\/p>\n 4 \u2013 Typical Semi Fuel Economy: https:\/\/www.arrowtruck.com\/blog\/2016\/06\/21\/manage-your-semi-trucks-fuel-use-with-these-tips\/<\/em><\/a><\/p>\n 5 \u2013 Wikipedia article, Electric motors: https:\/\/en.wikipedia.org\/wiki\/Electric_motor<\/em><\/a><\/p>\n 6 \u2013 Regenerative Braking: https:\/\/www.sciencedirect.com\/topics\/engineering\/regenerative-braking<\/em><\/a><\/p>\n 7 \u2013 CalculatorSoup Gravitational Potential Energy Calculator: https:\/\/www.calculatorsoup.com\/calculators\/physics\/gravitational-potential.php<\/em><\/a><\/p>\n 8 \u2013 RapidTables Kilowatts to Amps Calculator: https:\/\/www.rapidtables.com\/calc\/electric\/kW_to_Amp_Calculator.html<\/em><\/a><\/p>\n 9 \u2013 Battery University, BU-409: Charging Lithium-ion: https:\/\/batteryuniversity.com\/learn\/article\/charging_lithium_ion_batteries<\/a><\/em><\/p>\n 10 \u2013 FMCSA Interstate Truck Drivers Guide to Hours of Service: <\/em>https:\/\/www.fmcsa.dot.gov\/sites\/fmcsa.dot.gov\/files\/docs\/Drivers_Guide_to_HOS_2016.pdf<\/em><\/a><\/p>\n 11 \u2013 Wikipedia article, Energy Density: https:\/\/en.wikipedia.org\/wiki\/Energy_density<\/em><\/a><\/p>\n 12 \u2013 Google Cached LA Times Article: \u201cStalls, stops and breakdowns: Problems plague push for electric buses\u201d https:\/\/webcache.googleusercontent.com\/search?q=cache:q9TtqnnFrToJ:https:\/\/www.latimes.com\/local\/lanow\/la-me-electric-buses-20180520-story.html+&cd=1&hl=en&ct=clnk&gl=us&client=firefox-b-1-d<\/a><\/em><\/p>\n 13 – US and Canada Semi Weight and Size limits: https:\/\/www.bigtruckguide.com\/semi-truck-size-and-weight-laws-in-the-united-states-and-canada\/<\/a><\/em><\/p>\n 14 – Number of US Homes Powered by 1 MW – https:\/\/www.nrc.gov\/docs\/ML1209\/ML120960701.pdf<\/a><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"\n
\n
\nRolling resistance \u2013 68 hp
\nAccessory load \u2013 20 hp
\nPowertrain load \u2013 12 hp<\/p>\n\n
\nRolling resistance \u2013 54.4 hp
\nAverage Accessory load \u2013 10 hp
\nPowertrain load \u2013 3 hp<\/p>\n
![are not particularly large<\/i><\/a> (the linked photo shows the motor\/rear axle assembly from a Tesla S vice a Tesla Model 3). <\/p>\nUse appropriate multiples of variants of those motors (4 to 6) and synchronize them (easily done), and I\u2019m reasonably sure such a design could generate the horsepower and torque needed. With some moderate redesign to up the horsepower to around 400 and the torque to around 450 ft-lb, you might even be able to mount four of them in or near the semi-tractor\u2019s drive axle assemblies where differentials would normally be located and use one per drive axle, using electronics to precisely control speed and eliminate the need for differentials entirely.<\/p>\nHowever, those motors would require electricity to operate. Since we’re talking an EV semi, we’re talking stored electricity \u2013 and thus a battery pack. How much stored energy? Glad you asked. Let’s figure that out.<\/p>\nEV Semi: How Much Power Required?<\/u><\/b><\/p>\nHow much power does a semi require to keep rolling at highway speed? At a constant speed on perfectly level ground in calm conditions, the power requirement for a semi is minimized. The weight of the load no longer is much if any of a factor; a heavy load might add a bit to drivetrain and axle friction, but I\u2019d guess any such addition would be very small. Rather, the power needed for steady state operation on level ground when it\u2019s calm is dominated by 4 items: aerodynamic load, rolling resistance, accessory load, and drivetrain load – with the first two being far larger than the last two. (If you\u2019re interested, Source 3 explains each of those terms in some detail.) For a typical semi from about a decade ago, per Source 3 those loads were as follows:<\/p>\n\n\nTypical Semi Power Requirements, constant 65MPH, level ground\/no wind, circa 2010<\/u><\/p>\nAerodynamic load \u2013 114 hp\nRolling resistance \u2013 68 hp\nAccessory load \u2013 20 hp\nPowertrain load \u2013 12 hp<\/p>\nTotal Power Required \u2013 214 hp\n<\/p>\n<\/blockquote>\nAs you might have guessed, these loads \u2013 which represent the power needed merely to keep rolling at constant speed on perfectly level ground with zero net headwind \u2013 are the primary reason why semis on average get around 6.5 MPG (Source 4).<\/p>\nYou may have noticed more use of wind deflectors and skirting on semis over the past decade. Those are an attempt to reduce the aerodynamic load component, and thus save fuel. <\/p>\nLet\u2019s assume our hypothetical EV semi achieves a 20% reduction in both aerodynamic load and rolling resistance (more streamlined design and better tires). Let\u2019s assume a 50% reduction in accessory load (on-demand only vice constant drive by vehicle engine wherever possible \u2013 but I\u2019d guess that\u2019s about it in terms of a reduction; for an EV, heat\/lights\/instruments\/AC also consume battery power, and drivers are going to need those regardless). And since the transmission and other drivetrain components are greatly simplified in an EV (Tesla uses a 1-speed 9:1 reduction gear in the Tesla 3), let\u2019s assume a 75% reduction here too. That yields the following:<\/p>\n\n\nHypothetical EV Semi Power Requirements, level ground\/no wind, constant 65MPH<\/u> <\/p>\nAerodynamic load \u2013 91.2 hp\nRolling resistance \u2013 54.4 hp\nAverage Accessory load \u2013 10 hp\nPowertrain load \u2013 3 hp<\/p>\nTotal power required \u2013 158.6 hp\n<\/p>\n<\/blockquote>\nSo, what\u2019s that in terms of kW \u2013 and, more importantly, in kWh, which is a measure of energy stored as battery capacity? That\u2019s actually pretty straighforward to calculate.<\/p>\nOne horsepower is approximately 746 watts. So 158.6 hp is equivalent to 118.315 kW, give or take a bit. <\/p>\nUnfortunately, this figure is somewhat optimistic. The power for three of the categories above (aerodynamic load, rolling resistance load, and powertrain load) is mechanical power, and would all be provided through the operation of the hypothetical EV semi\u2019s drive motors \u2013 and while electric motors are quite efficient, like all other energy conversion devices they\u2019re not 100%<\/i> efficient. (The fourth, accessory load, would be a direct electrical load on the battery and therefore shouldn\u2019t require much if any adjustment for electric motor inefficiencies with proper design.) Per Source 5, the highest laboratory demonstrated efficiency for an electric motor to date appears to be 96.5%. Let\u2019s back off that a touch and assume 95% efficiency for the drive motors. (I’d guess this likely somewhat optimistic, but it could be pretty close.) This yields a total power requirement of <\/p>\n( ( (91.2 + 54.4 + 3) hp \/ .95 ) + 10 hp ) * 0.746 kW\/hp = 124.15 kW<\/p>\nAgain: this is the power required merely to maintain a speed of 65 MPH on perfectly level ground in calm conditions<\/i>. It doesn\u2019t account for hills.<\/p>\nAt 65 MPH, traveling 1 hour means you go 65 miles. Since a kWh is 1 kilowatt used for a period of one hour, that means we\u2019d need at least 124.15 kWh of stored electricity – that is, at least 124.15 kWh of battery capacity – for each 65 miles driven under those conditions. We\u2019d need more if hills were involved.<\/p>\nHow much more? Well, here we go. Now we need to consider the vehicle\u2019s weight and just how much climbing is involved.<\/p>\nHow Hills Affect Energy Usage<\/u><\/b><\/p>\nClimbing hills takes additional energy. This is because you\u2019re adding gravitational potential energy to the vehicle and load by raising its altitude with respect to the earth\u2019s center of mass.<\/p>\nHowever, electric (and hybrid vehicles with battery packs) can recover some of this energy when they descend by using what\u2019s called regenerative braking. In regenerative braking, a portion of the vehicle’s kinetic energy otherwise lost during braking is used to generate electricity, which can then be used to recharge batteries. That means that some of the extra energy used during a climb can be later recovered during descent and used to recharge the vehicle\u2019s battery. (Conventional vehicles also do this in a limited sense as well; they use far less fuel going downhill than they do on level ground to maintain speed, and in many cases gain speed. They just can\u2019t store any of that excess energy for later use.) <\/p>\nUnfortunately, regenerative braking is also an energy conversion process. And like all other energy conversions processes it\u2019s not 100% efficient either. Source 6 indicates that regenerative braking for the electric vehicles on the road today is between 16% and 70% efficient. So if an EV climbs a hill and then descends to its original elevation today, it will end up with a minimum net loss of somewhere between 30% and 84% of the energy it used to make the climb. And remember: this energy used to make the climb was in addition to the energy needed to keep moving at a constant speed. Further, the additional energy loss occurs each and every time an EV climbs and then descends<\/i>; the amount of energy lost is determined by the total vertical distance climbed and descended and the efficiency of that vehicle’s regenerative braking. <\/p>\nAs you might expect, there\u2019s ongoing research in improving regenerative braking efficiency. Below, I\u2019ll give designers the benefit of the doubt and use 85% for regenerative braking efficiency. That\u2019s probably a bit high, but IMO it\u2019s at least within the realm of the possible without making use of either pentagrams or unicorns. (smile)<\/p>\nNow, let\u2019s consider a couple of examples and see how much energy loss we\u2019re talking about.<\/p>\nExample 1<\/u>: A single climb of 1,000\u2019 elevation and a matching descent by an EV with 50,000 lb Gross Vehicle Weight (GVW). (FWIW: 50,000 lb is far below the maximum GVW limit for a semi in the US. Per Source 13, the minimum GVW limit for federally-funded highways appears to be 80,000 lb; some states allow far more.)<\/p>\nWe\u2019ll do this in three steps. First, we\u2019ll calculate \u2013 in kWh \u2013 how much energy is required over and above constant-speed driving on level ground with no wind<\/i> for the vehicle to climb the hill. Next, we\u2019ll calculate 85% of that figure and assume that is returned to the EV\u2019s battery pack (some additional energy might be lost if regenerative braking isn’t sufficient to keep speed under control and conventional friction braking also must be used). The difference between those two numbers is the minimum net lost energy due to the climb and descent.<\/p>\nThis is easiest done if we first convert weight and altitude gained to metric units. 50,000 lbs is approximately 22,700 kg; 1,000\u2019 is approximately 304.8 meters. Per Source 7, gravitational potential energy can be calculated as PE = mGh<\/strong>, where PE<\/strong> is the gravitational potential energy; m<\/strong> is the mass of the object involved; G<\/strong> is the Earth\u2019s gravitational constant (9.81 m\/sec^2); and h<\/strong> is the change in the object\u2019s altitude (a negative value for h<\/strong> implies the object is being lowered vice raised and is thus is releasing gravitational potential energy vice acquiring it). Since we\u2019re raising the vehicle (climbing a hill), the vehicle is gaining gravitational energy; we therefore must consume additional energy to make the climb. Allowing for 95% motor efficiency, the additional energy required is thus<\/p>\n( 22,700 kg * 304.8 m * 9.81 m\/sec^2 ) \/ .95 ) = 67,874,997.6 J, or about 67.875 MJ<\/p>\nOne kWh is equal to 3.6 MJ. So the additional energy required to make the climb, expressed in kWh, is 18.854 kWh. <\/p>\nSidebar<\/u>: How about the additional horsepower required? That can also be fairly easily calculated. For a 5% slope, at a constant 65MPH such a climb would take about 3.5 minutes. Expending 18.854 kWh over a period of 3.5 minutes would require an increase in power above the normal cruising power of <\/p>\n( 18.854 kWh \/ ( 3.5 min \/ 60 min\/hr ) = 323.21+ kW, or about 433.26 hp<\/p>\nThe four hypothetical 400 hp \/ 450 ft-lb torque electric engines on a EV semi would have more than enough horsepower reserve, and would collectively have around 1,800 ft-lb torque. That seems to be enough extra horsepower. I’m not going to check the torque, but 1,800 ft-lb is near the upper end of what conventional semis have today. I’d guess that would also be enough.<\/p>\nFWIW: since conventional semi engines typically have a power output of between 400 to 600 hp and between 1,200 and 2,000 ft-lb of torque, this additional power requirement for such a 5% climb explains why loaded conventional semis have difficulty on long hills.<\/i><\/p><\/blockquote>\nAssuming that we now descend 1,000 ft and that regenerative braking is 85% efficient, a maximum of 16.026 kWh will be returned to the vehicle\u2019s battery pack by regenerative braking. That means the net energy loss due to the climb and descent of the vehicle is at least the difference between these two figures, or 2.838 kWh.<\/p>\nNo, that doesn\u2019t seem like much. But when driving, you\u2019re likely doing far more climbing and descending than you realize.<\/p>\nExample 2:<\/u> Same vehicle driving over gently rolling terrain <\/p>\nOK, let\u2019s take that same vehicle and drive it on almost \u2013 but not quite \u2013 level ground with no net change in altitude for one hour. Here, let\u2019s assume the entire trip consists of alternating segments of 0.5% slope (e.g, a 6-inch elevation change every 100\u2019) 2,000 feet in length going uphill followed by a matching 0.5% 2,000\u2019 slope downhill for the entire 65 miles. This is terrain where one climbs and descends 10 feet roughly every 3\/4 mile – very gently rolling terrain.<\/p>\nIn one hour, the vehicle would drive (65 miles * 5,280 ft\/mile) = 343,200 feet. Every 4,000 ft, the vehicle would climb \u2013 and then descend \u2013 10 feet. It would therefore repeat the climb\/descent 85.8 times in 65 miles.<\/p>\nThat means the vehicle would climb and descend 858 feet \u2013 even though the net result is zero change in altitude. The vehicle thus would lose 85.8% as much additional energy (due to those repeated gentle climbs and descents) as a vehicle that had climbed, then descended a single 1,000 ft hill. For an EV semi weighing 50,000 lbs gross, that works out to the use of an additional 2.435 kWh of battery capacity during that hour\u2019s driving. And that\u2019s for 10′ high undulations with \u201cridge crests\u201d (if you want to call them that) spaced about \u00be mile apart. Most roads have more pronounced hills than that, and many have them more frequently. <\/p>\nWhat happens if you double the slope in the above example? That doubles the distance climbed and descended \u2013 and thus doubles the amount of extra energy consumed. Ditto if the undulations are twice as frequent but have same altitude variation. Double both the frequency of undulation and altitude variation? That quadruples the extra energy consumed.<\/p>\nLet me put it in gambler\u2019s language: when it comes to storing energy in a EV’s battery with regenerative braking, \u201cYou can\u2019t win and you can\u2019t break even. \u2018Cause over time the house is guaranteed<\/u> to take its \u2018cut\u2019.\u201d (smile)<\/p>\nSo, About That Battery Pack . . . <\/u><\/b><\/p>\nOK, so let\u2019s look at a hypothetical example. Let\u2019s use the same 50,000 lb GVW hypothetical EV semi from the above example. What would you need in terms of a battery pack to drive, say, 5 hours over (as defined above) \u201cgently rolling terrain\u201d at a constant 65MPH with no wind?<\/p>\nTurns out that\u2019s fairly easy to calculate. From calculations done previously, driving this hypothetical EV semi at a constant 65MPH on level ground with no wind requires 124.15 kWh of battery capacity. To account for the gentle undulations in the roadway at the specified GVW, add another 2.435 kWh. That means the vehicle will consume 126.585 kWh per hour driven \u2013 or about 632.925 kWh of battery capacity is needed for 5 hours driving time. (You’d also need to accelerate the vehicle to 65MPH in the first place. But since the kinetic energy of the vehicle at 65MPH works out to be less than 1 kWh and we\u2019re assuming 85% energy recovery due to regenerative braking, I\u2019m neglecting that. Add in aerodynamic losses and rolling resistance during acceleration and I\u2019d guess that getting up to speed would add maybe another 2 or 3 kWh max to the total energy required, and possibly only 1 kWh or so.) <\/p>\nMost likely, a modest amount of extra battery capacity would need to be included to account for the cumulative effect of larger hills, wind, and weather conditions as well as a general safety factor. I\u2019m going to assume a roughly 15% overcapacity is provided \u2013 which means the battery pack would be about 750 kWh. I’ll thus use a battery pack of 750 kWh for the calculations that follow.<\/p>\nThat\u2019s equal to 10 Tesla Model 3 extended-range option batteries. (Per Source 2, these batteries have 75kWh capacity, weigh 1,060 lbs, and have a volume of approximately 0.4 cubic meters.). So yeah, you could build something like that. But would it be workable in the real world? And that leads to . . . <\/p>\n\u201cUh, Houston . . . We Have A Problem\u201d<\/u><\/b><\/p>\nMore precisely, we have three problems.<\/p>\nFirst problem<\/u>: charging. A battery that size can be built, but if used for freight hauling it will have to be charged repeatedly; nearly daily would be my guess. And assuming even a 10 hour charge time, a battery with a 750 kWh capacity would require a huge amount of electrical power to charge it. How much? Assuming 92% efficiency for the battery charger (the rationale for that 92% figure is in my previous article concerning EVs linked at the beginning) and completely uniform charging over a 10 hour period, that works out to <\/p>\n( 750 kWh ) \/ (.92 * 10 hrs) = 81.5 kW<\/p>\nAssuming a power factor<\/i><\/a> of 1 and assuming an invariant load from the charger (these conditions are the best possible case in terms of minimizing the charging current required), per Source 8 that means you\u2019d need a 240v circuit capable of handling at a minimum 339+ Amps \u2013 or a circuit rated around 340 Amps, and probably larger to include some safety margin. Even using 480v 3-phase power, again per Source 8 you\u2019d need 98+ Amps \u2013 or a 100 Amp circuit, and again probably larger to allow for some safety margin. <\/p>\nOh, and that battery charger is going to get rather hot, too. With a power factor of 1, it\u2019s going to be rejecting most of the energy it doesn\u2019t deliver to the battery as waste heat (the batteries themselves and the conductors connecting the charger to the vehicle will reject some smaller portion of the charging loss). That’s a heat output of roughly 6.5 kW – or the equivalent of between 4 and 5 1500-watt space heaters all operating simultaneously at max output.<\/p>\nNow, large truck stops today have large parking areas. But I don\u2019t think they\u2019re typically big enough to handle 100 or 200 trucks parked, simultaneously, and staying there for 10 hours at a time each while charging their batteries. And I don\u2019t think they\u2019re typically serviced by multi-MW electrical feeds, either (81.5kW x 100 = 8.15 MW). Plus, with 100 trucks each of which is generating 6.5kW of waste heat while charging those huge batteries, well, if you liked summer in Kuwait . . . you just might enjoy walking around that charging yard. (smile)<\/p>\nYes, you could charge those battery packs slower using far less power. But that means you’d have to swap the discharged battery pack for a fully-charged one daily – and would have to have spares on-hand. At a trucking company’s maintenance facility? That might be possible. (Whether it could be done safely or not is another question. Even a “discharged” 750 kWh battery pack still would contain enough energy to be deadly dangerous if mishandled.) Doing it at a truck stop or hotel parking lot during a nightly rest stop? “Good luck wit dat.”<\/i><\/p>\nSecond problem<\/u>: 750 kWh is probably less than half of what you\u2019d really need for long-haul trucking.<\/p>\nPer Federal Motor Carrier Safety Administration (hereafter FMCSA) rules (see Source 10), long-haul truckers are allowed to drive 11 hrs daily within a 14 hour \u201cduty day\u201d window, followed by a mandatory 10-hour \u201coff duty\u201d period (there are numerous other limitations\/restrictions\/exemptions, but that\u2019s the one that\u2019s generally going to be pertinent here). Further, truckers must take a half-hour break from driving during their duty day; this break must occur NLT 8 hour after they begin driving during their duty day.<\/p>\nOK, so let\u2019s consider driving 11 hours at 65 MPH. That\u2019s a touch over 700 miles in one day. <\/p>\nDo long-haul truckers routinely do something close to that, particularly west of the Mississippi where speed limits are higher and traffic is generally less congested than in the Eastern US? That is, do they often drive 10 hours or so at an average speed of 65+ MPH in one day? I\u2019ll go out on a limb here and say, \u201cYou betcha!\u201d \u2013 though I really don\u2019t know that with certainty. But If I\u2019m wrong, I\u2019m sure one of our readers with personal experience working in the field can (and will) correct me. For a long-haul trucker, more miles driven generally means more cash in their pocket. <\/p>\nBottom line: 5 hours at 65MPH realistically seems to be about half of what would be required for a semi to be used in long-haul trucking. With a multi-hour recharge time, given the maximum 14 hour duty day followed by the 10 hour mandatory off-duty period imposed by FMCSA you\u2019d need the battery capacity to go at least twice as far as that 750 kWh battery pack allows in order for the vehicle to be useful for long-haul trucking. <\/p>\nThird problem<\/u>: weight. A 750kWh battery pack would be equivalent to 10 Tesla Model 3 extended range battery packs. As previously noted, a Tesla Model 3 extended range battery pack weighs 1,060 lbs and has a volume of 0.4 cubic meters, and probably represents about the best EV battery technology mankind currently can produce in quantity. So we could expect a 750 kWh battery pack to weigh roughly 10,600 lbs and have a volume of around 4 cubic meters (think a rectangular cuboid that’s 1m x 2m x 2m, or about 3\u2019 3\u00bd\u201d h x 6\u2019 7\u201d l x 6\u2019 7\u201d w ). <\/p>\nA 1,500 kWh battery pack would be about twice that in terms of size and weight. It would have a volume of 8 cubic meters (e.g., it would have the same volume as a cube 2 meters on a side). That 1,500 kWh battery would also weigh around 21,200 lbs, or roughly 10.6 tons<\/u> \u2013 far more than combined weight of the engine, transmission, fuel tank, fuel, and other fluids used in a conventional semi. (For the record, the 10,600 lbs estimated for the 750 kWh battery pack above also is heavier than the engine\/transmission\/etc . . . in a conventional semi today.) Since GVW limits exist, presumably for good reason, what do you think that battery weight is going to do to an EV semi\u2019s maximum cargo capacity in terms of max allowable cargo weight? <\/p>\nConclusions<\/b><\/u><\/p>\nIMO, we now have an answer to rgr769\u2019s<\/i> implicit questions. First: yes, it appears technically feasible to build an EV semi that could move loads and make substantial climbs. Building the batteries would be technically possible, and the motor technology (in terms of the required torque and horsepower) appears eminently do-able as well. We\u2019ve been building diesel-electric trains for decades; building a suitable electric motor was IMO never the issue. Whether we could build a battery of sufficient capacity was the key question, and it appears we could.<\/p>\nHowever, whether such a vehicle would be useful or not is another question entirely. For long-haul freight, the answer today seems to be a firm \u201cNo\u201d, and perhaps even \u201cNo way in hell.\u201d While the battery pack required can at least in theory be produced, at 10.6 tons it would simply be too heavy to be practical. And the power distribution infrastructure to support charging large trucks on the scale required during the FMCSA-mandated 10-hour \u201coff duty\u201d time required for long-haul truckers after a maximum 14-hour \u201cduty day\u201d . . . simply doesn\u2019t exist. Could it be installed? In theory, yes. But I’d guess serious proposals for installing same would likely produce a \u201cYou\u2019re joking \u2013 right?\u201d moment when those proposals were presented to utility company leadership. <\/p>\nWhy? Because as demonstrated above, the amount of power required to charge 100 large EV semi\u2019s each having only half the battery capacity needed for long-haul trucking<\/i> simultaneously in 10 hours would be huge \u2013 as in approaching 10 megawatts. Since per Source 14 one<\/u> megawatt of constant electrical power typically can power 400 or more homes, that means you’re talking the equivalent of s medium-sized town’s or small city’s electrical power supply for each 100-EV semi charging lot<\/i> – and you’d need twice that if you had the batteries actually required for long-haul trucking. <\/p>\nEven a small facility that could charge only 10 trucks would need 1 to 2 megawatts of electrical supply, and possibly substantially more if charging EV semi batteries does not draw a constant load. (Real-world data on charging LiIon batteries from Source 9 indicates that the charging load is not likely to be constant.) EV semi charging locations would thus not be terribly common, at least initially. Large trucks would tend to congregate at the few facilities that would be available. And the waste heat generated during charging (around 8% of the power supplied by the electric grid to the chargers) would make such charging yards local \u201chot spots\u201d \u2013 literally.<\/p>\nSo, how can current semis do what they do today? Easy \u2013 it’s because of diesel fuel’s high energy density. Hydrocarbon fuels have hugely larger energy densities than LiIon batteries. As an example: per Source 11, diesel fuel has an energy content of 38.6 MJ per liter \u2013 or about 40.53 kWh per gallon. That means a bit over 18.5 gallons of diesel fuel, weighing around 125 lbs, has the same energy content as the electrical energy stored in the hypothetical five-ton-plus 750 kWh LiIon battery discussed above. Even if you only recover a bit over 1\/3 of diesel fuel\u2019s energy content in the form of mechanical or electrical energy, you\u2019d still only need somewhere around 50 gallons of diesel fuel, give or take, to provide the same amount of usable mechanical or electrical energy as a 750 kWh battery pack can store.<\/p>\nReal-world data bears that out. As I noted previously, per Source 4 in the real world conventional semis average somewhere around 6.5 miles per gallon. That means that a hypothetical drive of 325 miles in a conventional semi would require about 50 gallons of diesel fuel \u2013 60 gallons if you want a 20% safety factor. Assuming a weight of 6.65 lb per gallon, the former would weigh somewhat less than 350 lbs; the latter, around 400 lbs. Even after considering the weight of the conventional engine\/transmission\/fuel tank\/other fluids\/associated equipment needed, that represents a significant weight savings over an EV semi using the best current technology; that in turn allows more cargo to be hauled. Plus, replacing that 50 or 60 gallons of fuel (thus adding another 325+ miles of range) takes a few minutes, not literally hours. In fact, it can be done in conjunction with that mandatory half-hour \u201cbreak\u201d required NLT 8 hrs after a long-range driver begins driving for the day – or when the driver makes a longer stop for a meal. Then the trip can continue on until the daily driving hours limit is reached.<\/p>\nOh, and did I mention you\u2019d need to be able to drive twice that far – and thus would need twice as large a battery (e.g., around 1,500 kWh) – for a hypothetical EV semi to be usable for long-haul trucking? Which in turn means the battery would be twice as large, twice as heavy, and take twice as much power to charge (and reject twice as much heat) during that daily 10-hour “off duty” period? Well, if I didn’t before . . . I guess I just did. (smile)<\/p>\n. . . <\/b><\/p>\nDo EV semis (or somewhat smaller non-articulated EV trucks and buses) have a role? For local use, perhaps. Even that is questionable at present, though. Source 12 indicates that LA and other locations have tried pilot projects involving electric buses and found them to have serious reliability and range issues. <\/p>\nBut for long-haul operations, given the current state of technology those hypothetical EV semis appear to be more like the original cast of SNL: \u201cThe Not Ready for Prime Time Players\u201d. IMO it would take a major breakthrough in battery technology along with truly serious upgrades to the electrical grid \u2013 or a change to some technology that generates electrical energy on-vehicle vice storing same in a battery \u2013 to make electric semis\/trucks\/buses feasible for long-distance use.<\/p>\nOr, as country folks might put it: \u201cAin\u2019t enough lipstick in the whole world today to make that<\/i> pig look purdy.\u201d (smile)<\/p>\n———-<\/p>\nSources<\/u>:<\/p>\n1 \u2013 Typical Conventional Semi Engine Power and Torque: https:\/\/www.internationalusedtrucks.com\/semi-truck-horsepower\/<\/em><\/a><\/p>\n2 \u2013 Wikipedia article, Tesla Model 3: https:\/\/en.wikipedia.org\/wiki\/Tesla_Model_3<\/em><\/a><\/p>\n3 \u2013 Semi Steady-Speed Power Requirements: https:\/\/www.nap.edu\/read\/13288\/chapter\/7#79<\/em><\/a><\/p>\n4 \u2013 Typical Semi Fuel Economy: https:\/\/www.arrowtruck.com\/blog\/2016\/06\/21\/manage-your-semi-trucks-fuel-use-with-these-tips\/<\/em><\/a><\/p>\n5 \u2013 Wikipedia article, Electric motors: https:\/\/en.wikipedia.org\/wiki\/Electric_motor<\/em><\/a><\/p>\n6 \u2013 Regenerative Braking: https:\/\/www.sciencedirect.com\/topics\/engineering\/regenerative-braking<\/em><\/a><\/p>\n7 \u2013 CalculatorSoup Gravitational Potential Energy Calculator: https:\/\/www.calculatorsoup.com\/calculators\/physics\/gravitational-potential.php<\/em><\/a><\/p>\n8 \u2013 RapidTables Kilowatts to Amps Calculator: https:\/\/www.rapidtables.com\/calc\/electric\/kW_to_Amp_Calculator.html<\/em><\/a><\/p>\n9 \u2013 Battery University, BU-409: Charging Lithium-ion: https:\/\/batteryuniversity.com\/learn\/article\/charging_lithium_ion_batteries<\/a><\/em><\/p>\n10 \u2013 FMCSA Interstate Truck Drivers Guide to Hours of Service: <\/em>https:\/\/www.fmcsa.dot.gov\/sites\/fmcsa.dot.gov\/files\/docs\/Drivers_Guide_to_HOS_2016.pdf<\/em><\/a><\/p>\n11 \u2013 Wikipedia article, Energy Density: https:\/\/en.wikipedia.org\/wiki\/Energy_density<\/em><\/a><\/p>\n12 \u2013 Google Cached LA Times Article: \u201cStalls, stops and breakdowns: Problems plague push for electric buses\u201d https:\/\/webcache.googleusercontent.com\/search?q=cache:q9TtqnnFrToJ:https:\/\/www.latimes.com\/local\/lanow\/la-me-electric-buses-20180520-story.html+&cd=1&hl=en&ct=clnk&gl=us&client=firefox-b-1-d<\/a><\/em><\/p>\n13 – US and Canada Semi Weight and Size limits: https:\/\/www.bigtruckguide.com\/semi-truck-size-and-weight-laws-in-the-united-states-and-canada\/<\/a><\/em><\/p>\n14 – Number of US Homes Powered by 1 MW – https:\/\/www.nrc.gov\/docs\/ML1209\/ML120960701.pdf<\/a><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"Intro Who says lightning never strikes twice? Last week, I wrote an article regarding the difficulty … So: What About Really Large EVs?<\/span>Read more<\/a><\/p>\n","protected":false},"author":623,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11,98,188,503],"tags":[],"class_list":["post-104560","post","type-post","status-publish","format-standard","hentry","category-economy","category-global-warming","category-reality-check","category-science-and-technology"],"_links":{"self":[{"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=\/wp\/v2\/posts\/104560","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=\/wp\/v2\/users\/623"}],"replies":[{"embeddable":true,"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=104560"}],"version-history":[{"count":0,"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=\/wp\/v2\/posts\/104560\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=104560"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=104560"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.azuse.cloud\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=104560"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}](\"https:\/\/i.ebayimg.com\/images\/g\/FPIAAOSw1h5demAe\/s-l1600.jpg\"){kind=link}