Electric Semi-truck: yes, the size matters

Once again, Mr Elon Musk makes virtuosic use of modern Marketing with his last social buzz epidemic on his new electric semi-truck.

Whatever you are a fan or you dislike his manners, we all need to admit that he provokes the automotive industry business and encourages debate, thinking and innovation to push us further for better development.

One absolute major question that I am trying to answer and that I have found everywhere is "what is the size of the battery?". So, I have asked: "Alexa: what is the weight of the battery of the next Tesla truck?"

... apparently, technology is not always the solution and I have had to explore this question by myself and found a lot of contradictory information ...

Here is a summary of what I have found as so far ...I am really not a battery specialist so I imagine that some of you will soon throw me in the face some electrical cells ... Please note that my objective in this article is "only" to create a collaboratively debate around this question.

First some fact / announcement about the Tesla truck:

• Mileage autonomy = 500 miles
• Tesla touts $200K saving in fuel costs over a million miles.
• Charging time in about 30 minutes

1. About the size of the battery

Today's automotive Li-ion batteries typically get 1500 cycles and with a 500 mile battery, that would translate to 750,000 miles. So these batteries will last for the life of a truck and this would be a one time cost.

1.1: Assumption based on today Tesla S

I am aware that the assumption here below is probably wrong. Nevertheless, assuming an Homothetic transformation between a Tesla S and a truck allows me to ballpark define the "worst case scenario" corner of this estimation.

Based on Tesla S (85 kWh battery weighing 0.544 tons, 2.1 ton weight vehicle, 265 mile range), a 50-ton truck for a 500 mile range (around 35 ton load carrying capacity) would need a battery of about 3,500 kWh. If one based on a lithium ion batteries (energy density 240 Wh per kg), this gives around 15 tons…

1.2: Assumption based on US fuel economy specs

2025 fuel economy specs is about 7.5 mpg. With approximately 50% Engine efficiency (but of course it is just the order of magnitude, at this stage the real value does not really matter), for 500 miles, this translates to about 25,000 MJ of energy transferred (one may assume battery to wheel efficiency of 90%). 

This leads to a battery of about 1 MWh 

1.3: Assumption based on “extrapolation” of Tesla's figure

Tesla said “Less than 2 kWh per mile“ energy consumption. Probably to achieve this level, Tesla assumes that most purposes weight plays a small role in overall energy requirement (as rolling friction plays a minor role and one can recover most of the energy lost for transients via regenerative braking). But in this case, one may challenge the comparison with conventional trucks since breaking recovery would also expand.

Under this assumption, one can assume 120 kW to move the truck along at cruise speed. Please note that this number is lower than the current state closer to 150 kW. This reduction assumes lower drag resistance and friction combination. Nevertheless, this figure seems possible when comparing to the last Supertruck program.

For 500 miles, it means about 1 MWh of storage.

1.4: Comparison with the Daimler electric truck

The Daimler / E-Fuso is 6 high voltage lithium ion battery packs with 420 V and 13.8 kWh for carrying 11 tons of cargo for 220 miles.

Adapting the same approach, this would lead to about 1 MW.h

Hypo 1.2, 1.3 and 1.4 give the same range of about 1 MW.h. Taking contingency of about 20% higher than that as the full capacity of the battery (due to the fact that completely empty battery is not something you would like), this gives a weight of about 6 tons.

Summary: the battery would be between 6 tons (optimist option) and 15 tons which would be between 15% and 30% of the vehicle weight.

2 - Cost of the battery:

Battery cost introduces again a lot of uncertainties:

• Cose given by GM for the Bolt battery pack = $145/kW.h
• Most optimist prediction = $100/kW.h

Summary: this means a price between $100K and $400K.

Please keep in mind that this cost would be upfront of any saving of fuel   

Interestingly, Tesla touts $250K saving in fuel costs over a million miles. If we assume 7.5 mpg diesel truck; 3$ Diesel and 12 cent electricity, it gives us a saving of about $250K over a million miles (over which you need to invest in-front at least $100K). So the total of about $150K seems possible...

3 - About the charging:

Everyone would probably agree that the bottom line in all of this is the charging infrastructure (availability and time). If it is a real challenge for electric cars, it just gets lot worse for trucks.

If we want to charge this truck in half an hour, we would need between 2 MW and a 6 MW charger and possibly an electrical transformer nearby. This will put enormous constrain on the infrastructure for charging…

4- Think outside (the battery) box

In addition of all the technical requirement, Musk's electric truck will have to be challenged from a customer acceptance point of view. Ecological but also economical and political tension will also stretch the future of this innovative truck. Nevertheless, no one can really know what is going to happen and only time will define without doubt if Mr Elon Musk was here a visionar or a dreamer...