Tesla electric truck – too good to be true?

by David Cebon on 26th November 2017

Tesla electric truck – too good to be true?

Tesla’s claims for its new electric truck require some scrutiny.  Tesla claims that the new truck will have a range of 800kms and an energy consumption of 1.25kWh/km.  Running 800km will therefore require 1000 kWh of energy: in practice a 1300 kWh battery.  Suitable lithium-ion batteries for electric vehicles cost $150/kWh today and are expected to fall to $100/kWh by 2021.  This suggests a 2021 battery cost of $130,000: approximately equal to the current average price of new heavy truck in the US (in the Class 8 category).

The specific energy of lithium-ion batteries is 0.1 kWh/kg – 0.25 kWh/kg.  So the weight of a 1300 kWh battery will be between 5.2 and 13 tonnes.  A US Class 8 truck has a maximum gross weight of 36 tonnes, 8 tonnes less than the equivalent UK lorry.   In weight terms, US trucks are inefficient by international standards.  US carriers must therefore use their maximum payload of 21 tonnes very effectively.  The weight of the battery in an electric truck is likely to constitute 25% to 60% of this available payload. Even after allowing for the absence of a fuel tank and lighter electric engine this payload penalty will deter many potential users…  A fleet operator might require 4 electric trucks to carry the same load as 3 diesel-powered vehicles.

Here is another aspect of the problem:  If these trucks are to be charged in 30 mins as Tesla claims, the power required for each vehicle is about 3MW.  Each medium sized distribution centre (DC) /warehouse would have to charge about 20-30 vehicles at a time (while they are loading). This means that each would require a substation able to deliver 60-90MW.  That is sufficient capacity to power a city of 100,000-160,000 people (using an average  figure for 0.56 kW/capita).  That is, each DC would need a substation able to power a city about the size of Cambridge.

But… one word of caution here.  Tesla is clearly misguided about the battery, but they are not necessarily wrong to look into the possibility of electric trucks. An electric truck that is charged while in motion is reasonably doable.  Siemens have developed and trialled an overhead wire system ‘eHighway’ which achieves this with a relatively low infrastructure cost.  See https://www.siemens.com/global/en/home/products/mobility/road-solutions/electromobility/ehighway.html  Such a system could power a truck like the Tesla with a smart pantograph on the roof.  As long as DCs are close to the motorway/trunk road network (which they often are), then only a modest battery (less than 100kWh) would be needed to get the vehicle from the motorway to the DC at either end*.  This would be a feasible way to electrify long-haul road freight in some locations – eg in the UK, or along the eastern seaboard of the USA.

Elon Musk promises that his electric truck “will blow your mind clear out of your skull and into an alternate dimension”.  However, in the real world, a vehicle offering at most 3/4 of the payload for double the capital cost does not seem a very attractive proposition for the road freight industry.  Nevertheless, electric trucks are worth debate for the long term future.

Here are some further references to this debate in: Prime Mover Magazine and Diesel News

* Nicolaides, D, Cebon, D and Miles J.  ‘Prospects for electrification of road freight’, accepted for publication in IEEE Systems.  Published online 21 April 2017. DOI: http://dx.doi.org/10.1109/JSYST.2017.2691408

Update 4 Dec 2022: Now that the Tesla Semi has finally appeared, you can compare my numbers in this blog (from 5 years ago) with the reality. Follow this link for the actual numbers. You will see that I wasn’t too far out…