Can Tesla Batteries Perform as Much Work as Diesel?

Twitter’s snapshot format provides an intriguing glimpse of Musk’s latest vision. In April, Musk promoted two new intriguing Tesla truck concepts; a semi-tractor and a pickup.

What is so intriguing about Elon Musk’s amazing new semi-tractor proposal, is how the physics of energy storage and the economics of trucking argue very persuasively against the idea; but physics major Musk pushes on anyway. If Tesla has solved the problem of battery energy storage limitations, that is a breakthrough!

Deep-dive into the physics and economics of diesel-powered hauling.

Unlike cars, trucks only exist to earn revenue from hauling freight. The more cargo they efficiently carry, the more they earn. Trucks carry as much as 150% of their own weight in rate paying cargo. Cars, by comparison, normally carry one or two occupants which is only 5-15% of the vehicle’s weight.

The trucking industry with over 100 years of experience meeting the demands of its customers, knows how to get the job done efficiently. The trucks that you see going down the highway, how they are equipped and how their logistics are managed, is the result of a competitive market finding the most cost efficient way to deliver a service profitably.

Trucks have a great deal of operating range. They are be able to endure extreme conditions like North Dakota winters, Arizona summers and bad roads. They compete fiercely on cost efficiency. Commercial trucks’ useful life must be a million miles, or even millions of miles.

Semi tractors cost between $80,000 to $150,000. Trucks that are being used for short hauls and less heavy loads are at the low-end, and high-powered long haul trucks with sleeper cabs are on the high end of the range. Fuel consumption averages about 6 mpg. Fuel efficiency research for heavy trucks (Class C) has seen results of nearly 10 mpg.

Trucks are heavy, but weight-limited, and for good reason. The weigh stations on the side of the interstates are there to catch overweight trucks. The conventional 18-wheeler is limited to a total weight of 80,000 lbs. This is primarily to control wear and tear on roads and bridges. Heavy trucks are hard on the transportation infrastructure and they pay a lot of road taxes to compensate for that.

This is the architecture of diesel powered semi-tractors; the industry Elon Musk is intimating he has innovations that will disrupt.

Why Diesel?

The technical enabler of today’s trucking industry is diesel fuel. The equipment and the capabilities of the industry have all evolved around diesel not gasoline, not batteries and not compressed natural gas, but lowly diesel. For several reasons, diesel engines were found, many decades ago, to be the best engine and fuel for trucks.

It begins with diesel fuel, which has an exceptional quality. It is not generally known but gallon for gallon and dollar for dollar, diesel fuel is the absolute best source of stored energy available. It is safe to handle and cheap to manufacture. It is efficient to store. It is the ideal fuel for the load-hauling industry.

For example, one gallon of diesel fuel stores 38 kilowatt hours of energy. Diesel has 113% the energy density of gasoline and 140% the energy density of propane. It has 27 times the energy density of lithium ion batteries. Diesel fuel weighs only 6 lbs./gallon and that single gallon stores 38 kilowatt (kwh) hours of energy. Diesel stores over 6 kwh of energy per pound. In the Wikipedia table below, lithium ion batteries scored dead last in energy density and diesel scores first, among fuels.

Diesel engines are inherently more fuel efficient than gasoline engines, require less maintenance, have more low-end power. They also have a much longer service life. There are very good reasons why diesel-powered tractor trailers are the industry’s primary configuration.

Trucks do heavy work and work is powered by energy. Physics major Elon Musk would be familiar with the concept that work is equivalent to energy consumed over a period of time. The term ‘work’ was introduced in 1826 by a French mathematician, Coriolis, who was quantifying the same problem of energy and work equivalence.

A fully loaded 80,000 lbs. tractor trailer can carry enough fuel to haul its load well over 1,000 miles before refueling. The cost to fill that tank of fuel without road taxes is about $500. Since diesel is so light weight, the truck can still carry 44,000 lbs. of rate-paying cargo and stay under the government mandated 80,000 lbs. maximum.

Hauling 44,000 pounds is work and that is where the physics of diesel’s profound energy storage ability meets the economics of trucking. The weight of the stored energy (diesel fuel) in a semi-tractor infringes little on the ability of a Class C truck’s ability to carry freight and is relatively inexpensive. Light diesel fuel loads are a big part of the economics of diesel and trucking.

To show how steep a threshold Tesla must cross to challenge diesel powered trucking, consider how much energy a truck consumes. How much energy does a truck use to drive 600 miles? At 6 mpg, it uses 100 gallons of diesel. 100 gallons of diesel contains 3800 kwh of energy. Put another way, a diesel-powered tractor-trailer consumes 3,800 kwh of energy to move 80,000 lbs. How will a battery-powered Truck carry that much energy? We’ll break that down in the following section.

Tesla’s Intriguing New Semi and Energy Efficiency

Musk tweets. The world listens. The stock market buys the shares. On April 13, Musk tweeted that this coming September, Tesla will announce details of an intriguing battery powered semi-tractor. Here are the challenges Musk intimates Tesla will overcome.

Tesla’s Giga Factory offers state-of-the-art 210 kwh batteries on their website. They are designed for fixed installations. They are quoted as costing $89,000 each and weigh 3,575 lbs.. This is on the Tesla website.

How much work can batteries power? We saw that the diesel rig consumed 3800 kwh of energy to haul its load 600 miles. How can Tesla do that amount of work or improve on that? First, Tesla’s electric truck would be more energy efficient than an internal combustion diesel. It has regenerative brakes for one thing, that convert braking energy back into electricity. This feature adds efficiency, but over the road trucks aren’t using the brakes often, so that is limited.

Electric motors have less energy losses than a diesel engine. A battery-powered electric truck could likely do at least twice as much work per kwh of energy consumed than a diesel powered truck, but not much more than that. And as research has shown, future diesel-powered trucks will get much better energy efficiency, but for now, let’s generously assume a savings of 65% on kwh consumed.

The Tesla semi-tractor will consume about 1520 kwh of electricity to move 80,000 pounds 600 miles. Can Tesla’s battery powered semi-tractor do this? Can it carry this much stored energy?

Energy Storage is the Biggest Hurdle

First, Tesla’s truck with a 600-mile range needs a storage capacity of at least 1520 kwh. That is more than seven of their 210 kwh batteries. They need more than seven though. They need extra range for contingencies, such as wrong turns or heavy winds. Assume they need 8 batteries.

Also, it isn’t clear that electric vehicles start with fully-charged batteries. There is very little discussion about this, but lithium ion batteries lose capacity over time. As one mechanic told me recently, “They never talk about how many Toyota Prius’s are gas engine only now.”

Aging cell phones lose charging capacity and so do car batteries. One of the reasons large lithium ion batteries are so expensive is they have elaborate control systems in them to keep them from overheating, draining too fast, spiking voltage and even from catching fire.

Batteries lose charge capacity. Some of the literature indicates that both fully charging and fully discharging hastens this loss. More on that later and add one more battery to account for less than 100% charging. Now the truck has 9 batteries.

How Much do Tesla Batteries Weigh?

Remember, the reason trucks exist is to haul weight. Nine Tesla 210 kwh batteries at 3,575 lbs. each weigh about 32,000 lbs. Compare that to the weight of 100 gallons of  the super-great energy storage medium diesel at 600 lbs.  How can Tesla make up for the loss of about 31,000 lbs. of payload?

For one thing, Tesla truck’s power train will be lighter than that of diesel trucks. The weight of the motor and transmission on a diesel truck is about 4,000 lbs. On the Tesla, add in regenerative braking systems on the wheels and the motor and transmission setup and you probably are still lighter than that. This powertrain doesn’t exist yet, so it is only speculation. But it will probably weigh 1,000 to 1,500 lbs. less than the heavy truck diesel powertrain. Not enough savings to make up for the weight in batteries.

The Tesla truck is still 30,000 pounds heavier than the diesel semi-tractor. Are there other strategies open to Tesla to make their truck competitive with a diesel truck?

Maybe they can be more aerodynamic than a diesel? No. A diesel can be just as aerodynamic. Maybe they can be even more efficient than a diesel? Diesel’s actually have much more room for efficiency gains than electric motors. Diesels can probably make up ground in that respect.

The problem then remains, a Tesla semi-tractor will weigh tens of thousands of pounds more than a diesel and thus lose revenue from hauling much less freight.

Maybe Tesla trucks can just be used for short haul? Well maybe they can, but then you are comparing them to the less expensive $80,000 diesel trucks. You still need four or five batteries to get 250 miles range from a short-range Tesla truck. That truck still weighs 15,000 more than the diesel truck. It is also much more expensive. Each battery alone costing more than a short-haul diesel semi-tractor.

Battery Useful Life and Charging Examined

We all see battery storage deteriorate in our cell phones, but Tesla has not been definitively forthcoming on the issue of battery useful life. Batteries are about half the cost of a Tesla car, so it matters a great deal how long a useful life the battery has. Especially since cars do 1/20^th the work a truck does. Trucks need 20 times more available battery energy.

The nine 210 kwh batteries the Tesla semi needs are being quoted as costing $89,000 each or $800,000. They better last many years. Will they?

It has been shown on Tesla’s, Chevy’s and Nissan’s electric vehicles (EV), that supercharging or rapid charging, fully discharging and even fully charging all contribute to battery storage deterioration. Controlling heat, slower charging rates and not fully charging or fully discharging are all strategies being used to extend the useful life of expensive batteries. Losing storage capacity is a big problem if the battery is half the vehicle’s cost.

The operating environment of a truck can be very harsh and this is a particular problem for the Tesla truck concept. Tesla’s own car battery warranty is voided by exposure to extreme heat or extreme cold. Tesla’s battery warranty covers failure but isn’t explicit about guaranteeing against declining storage efficiency. What is the storage capacity decline rate to be expected from these batteries? That isn’t laid out either.

From user reports I have read, a good battery storage capacity decline experience in a car would be to still have 85% after three years. But it isn’t just age, discharge/charge cycles matter more. Trucks are driven 5 – 10 times more miles than cars and will undergo many more charging cycles. If the truck in this example was driven 500 miles/day or 125,000 miles/year it would be recharged 250 times. The truck is going to age its batteries much quicker than a car will.

A good battery storage outcome for a Tesla truck after only three years might be 70% capacity. A not so good one might be 50 – 60% capacity. That makes a Philly to Pittsburgh trip very risky.

Replacement of the batteries would be looming. At $800,000 just for batteries, it is cheaper to buy a new truck.

It doesn’t seem either the battery/energy storage cost or the lifespan of the batteries is going to compete with diesel. This seems obvious, so one can only assume Elon Musk and Tesla have a very big breakthrough in the works to float the idea they will be building semi-tractors.

The reality of trucking operations is the optimal doesn’t always happen. Diesel trucks can handle that. Will Tesla’s semi respond well to lessthan optimal battery usage and charging? Will they be useful in the north in the winter or in the hot arid southwest in the summer? Those are other considerations.

Here is a financial comparison table based on best information guesses.

Estimating the Financials

Note on Recharging Costs:

The electricity cost is lower than the diesel fuel cost. However, the expense of a charging station, the long downtime and labor costs of recharging an electric truck are higher. Recharging 1500 kwh of power into the truck’s batteries requires many hours at a charging station, at least 8 hours. This means each truck must have its own parking spot with its own high-capacity charging station, which is another cost.

Energy Storage is the $Trillion Transportation Question

Weight:  As efficient, cheap and lightweight as diesel is at storing energy, batteries are the opposite. Tesla’s 210 kwh battery weighs 17 lbs. for every kwh stored. Diesel weighs 2.2 ounces per kwh stored. Converted for efficiency, 8 lbs. of battery will give the available energy to do the same work 2 ounces of diesel will do.

Range:  A single 210 kwh battery will give a loaded tractor-trailer only 75 miles effective range. Assume 300 miles is a bare minimum range. That requires 4 batteries, which reduces payload by over 13,300 pounds versus a diesel truck.

Cost: A single 210 kwh battery costs more than a basic short-haul diesel powered semi-tractor that has a useful life of over 1 million miles and can be adapted to many environments and operating conditions.

The cost of diesel is $2.50/gallon with road taxes deducted. Electric trucks will pay road taxes, which are typically $12,000/year. Investment bankers and Tesla who are pitching shares will leave out this important operating cost. They will also probably not mention the actual cost of recharging trucks as well.

Storage Capacity degradation: Like lithium ion cell phone batteries, electric vehicle batteries lose charge capacity. Useful life is measured in time and the number and depth of charging cycles. Tesla has intentionally avoided providing hard information on battery life.  Tesla sells supercharging as a solution to slow charging but it is believed that rapid charging and deep discharges significantly shorten battery life. What is  a battery’s useful life?

Presumably fleet managers keep their capital investment working as much as possible and full recharging cycles would be daily. How long would a truck battery undergoing rigorous duty provide sufficient power? The evidence is after only three years, the batteries would probably be down to 75% or less capacity.

Tesla’s Options

Can the cost, weight and performance of a Tesla battery be improved upon? Yes, but the truck battery must be structurally strong, built to endure severe shocks and environmental extremes; all of which will add cost and weight back in. For now, you can’t assume a lower cost. The quoted cost for the 210 kwh battery is $423/kwh. The quote for a 14 kwh battery is $393/kwh.

To limit the problem of heavy and expensive batteries, can Tesla position trucks as short haul? Yes, but they still aren’t admitting heavy costly batteries shrink the payload and cost more than a single truck. Short haul diesel trucks are the cheaper ones on the price scale. As little as $80,000, and they are still more flexible and last longer than the batteries on a Tesla truck.

One technical advantage electric vehicles have is brake energy recapture. Over the road trucks aren’t on the brakes that much but local delivery trucks use their brakes constantly. UPS trucks, for instance, would recapture brake energy, not lose energy at stop lights. They could return to their fleet base every day for recharging and may have payloads that are light enough to allow the use of Tesla’s heavy batteries and remain under weight limits. The way UPS uses its delivery trucks is very favorable to the advantages of EV. But is it economic for them?

If UPS were to be ready to deploy EV trucks in size, observers will know the economics and technical performance of a Tesla truck were real. It is unlikely UPS will be placing these orders despite having the scale, fleet management advantages, and ability to capture the brake energy recycling advantage of this technology. The economics of battery powered haulage are likely still not there.

What are they thinking of?

Elon Musk dual majored in Physics at an Ivy League university. The physics of battery energy storage, weight, cost and capacity degradation are central to the technical problem of Tesla cars; and  in the proposed Tesla truck.

Until now, the shortcoming of energy storage in lithium ion batteries hasn’t been so obvious since a car’s payload is a small part of the total weight. No one loads up a model S with five large passengers and luggage and reports on the change in the car’s battery range.

Truck payloads, however, aren’t 10% of their weight like cars. Trucks carry up to 150% their weight. The sheer amount of work they do and energy they expend puts a huge demand on the energy storage system. Diesel copes with it easily, batteries not so much.

Has Elon Musk solved the biggest technical problem of the EV industry? Or is he overreaching and putting a spotlight on how far they really are from solving the energy storage problem?

What exactly are Tesla and Musk going to show us with their intriguing new Tesla semi-truck?