Electric trucks, chapter 2: Motor

[in the blog series: Electric trucks: economically and environmentally desirable but misunderstood]

By Auke Hoekstra

 

Chapter 1
Energy supply

Chapter 2
Motor

Chapter 3
Energy storage

Chapter 4
Energy delivery

Diesel

Fuel

<30% efficient

Gasoline tank

Gas stations

Electric

Electricity

>85% efficient

Battery

Chargers

 

In the previous chapter we saw that the electric motor is our only realistic sustainable option. Fortunately it can also be cheaper. In this chapter we find out how the advantage in vehicle cost, maintenance cost and energy cost puts the electric truck at a strong advantage. The graph visualizes the result. In the next chapters we will calculate what part of this advantage is lost by having to buy expensive batteries and because the charging infrastructure needs to be build and maintained.

 

Electric engines are cheaper, lighter, stronger and easier to maintain

Electric engines are compact and will make an engine compartment unnecessary. Per the IEA report: “Furthermore, electric motors can be mounted either in the drivetrain before the transmission to provide energy to the driveshaft and then to the axles, or they can be installed directly in the wheelers of a truck or trailer. This can further improve the efficiency of translating energy to work at the wheels, although trucks operating at highway speeds generally need a transmission.”

Also important: electric drivetrains are about 3x lighter and 2x cheaper than conventional drivetrains [1]. Finally efficiency hardly suffers when the motor is larger. So just like a Tesla Model S, a truck can have great acceleration and great efficiency at the same time. Tesla’s CEO Elon Musk even made the bold claim that the Tesla’s heavy truck prototype (using a cheap Model 3 motor in multiple axles) “drives like a sports car”.

The IEA report assumes that in the long run an electric motor can have a USD 30,000 lower sticker price (i). Let’s assume that in 2025 about USD 20,000 of that promise is realized. That brings down the vehicle cost per kilometer from USD 0.36 to USD 0.34 (ii).

Maintenance can also be lower. From proprietary Dutch research passenger cars we know that maintenance of full electric vehicles is already about one third. Basically the drivetrain needs zero maintenance and the brakes need hardly any maintenance. Most of the remaining maintenance is tires.

For diesel trucks the IEA assumes USD 0.18/km in maintenance (iii). From other sources we know tires and rethreading for a heavy truck costs about USD 0.04/km [2]. If we assume the remaining USD 0.14 can be halved (a very conservative assumption knowing that the motor needs no maintenance) we arrive at USD 0.11 for electric motor maintenance.

The efficiency of electric motors lowers the energy cost

The most important advantage of the electric motor is that it’s about three times more efficient. Let me quote the IEA report: “When driving on an uncongested highway, a modern truck can achieve efficiencies from the engine to the wheel of no higher than 30%, while electric trucks can reach powertrain-to-wheel efficiencies of as high as 85% or more.” To which I’d like to add that electric trucks keep that efficiency when driving through the city or on congested highways while the efficiency of combustion engines drops to even lower levels. The end result is that a truck uses 4 kWh/km while an electric truck uses 1,5 kWh/km (iv).

The price for electricity in the IEA report is less clear because the numbers don’t add up (v). Also I want to do the calculation in a bit more detail. So let’s start from scratch and do it right. The table shows the most important price components of diesel and electricity in the EU.

Price/kWh

Production

Distribution

Taxation

Total

Diesel

USD 0.047 (vi)

USD 0.02

USD 0.065 (vii)

USD 0.135

Electricity

USD 0.045 (viii)

USD 0.02-USD 0.09

USD 0.001- USD 0.12 (ix)

USD 0.07-USD 0.26

Tax is a thorny issue because it varies so wildly and because it is only partly related to CO2 emissions (of which Diesel emits around 3,23 kg per liter (x) or 323 gram per kwh). But because electric vehicles use so little energy it actually doesn’t matter very much. So I propose we give electricity a tax of USD 0.065: the same as diesel, even though this energy is much cleaner.

I’ve chosen the base year of 2025 for the rest of our analysis. That gives us the graph we already saw at the start of this chapter:

So the fully electric truck is significantly cheaper when you just look at motor, maintenance and most of all energy. But will it be possible to store all the energy needed in a battery? Let’s find out in the next chapter.

-----------------------------------

Footnotes

[i] The report states that the added cost of an heavy electric truck with 400 km range will fall from USD 250,000 with batteries costing USD 350/kWh to USD 40.000 with batteries costing USD 100/kWh. Since the cost of the motor is dwarfed in the first scenario this teaches us that a 400km range truck needs 715 kWh in the IEA scenario. Even if efficiency increases reduce that to 700 kWh it would still cost USD 70,000 with USD 100/kWh batteries. Hence there is also a USD 30,000 somewhere and that can only be the drivetrain. It doesn’t seem like a crazy number to me by the way.

[ii] The IEA tells us it depreciates the vehicle with 58% in five years. Question what is assumed for personnel cost. If you add USD 110,000 to the above depreciation you get exactly the right value for all the scenarios regarding vehicle cost. So that is how I calculate vehicle cost: USD 110,000/500,000km + 0.58*vehicle_cost/500,000km.

[iii] Actually it’s USD 0.17 in 2015 and USD 0.20 in 2050. The maintenance increases because more efficient trucks have more bells and whistles. We are interested in 2025 so I stay closer to the 2015 number.

[iv] The report states: a truck is at most 30% efficient and an electric vehicle is at least 85% efficient. That is 0.85/0.3=2.83 times better. Energy use of a diesel truck is around 40l/100km or 4kWh/km and 4/2.83=1.4kWh/km. Because I think that is slightly optimistic I round it up to 1.5 kWh/km.

[v] The report says it assumes “an electricity price of USD 0.17 in all regions and all cases”. You would assume that’s a price/kWh but the CAT-ERS truck uses USD 0.17/km. However it cannot be USD 0.17/km exactly because the CAT-ERS also runs 1/5 of its km on diesel so the price per full electric km is USD 0.21. Based on efficiency calculations in the report the truck should use about 1.4 kWh/km. The report states: a truck is at most 30% efficient and an electric vehicle is at least 85% efficient. That is 0.85/0.3=2.83 times better. Energy use of a diesel truck is around 40l/100km or 4kWh/km and 4/2.83=1.4kWh/km. But USD 0.21/km with an energy use of 1.4kWh/km would imply an energy cost of USD 0.15/kWh. And the drones flying around in the report (page 72) use electricity at USD 0.1/kWh.

[vi] If you take the slightly different energy density in the US and EU into account the base price of diesel and gasoline is almost exactly the same on both sides of the Atlantic: USD 0.047/kWh for diesel and USD 0.058/kWh for gasoline and [2].

[vii] Taxes are highly different in the US and EU. In the US the tax is almost the same for diesel and gasoline and averages about USD 0.013/kWh. In the EU the average tax is USD 0.05 for diesel and USD 0.08 for gasoline and the expectation after dieselgate is that diesel will soon be taxed comparable to gasoline [3].

[viii] Wholesale day ahead prices often hover around USD 0.035/kWh. New fossil power and renewable power is currently around USD 0.05. I expect prices for renewable energy to keep falling so I consider USD 0.045 actually a kind of worst case scenario, even if we have to include some storage. The fact that hydrogen in the IEA report will be produced using USD 0.01/kWh electricity that is available during the cheapest 50% of the time shows that hydrogen is calculating with lower average prices still.

[ix] If you have a large factory you almost no tax for electricity in most European countries. If you are an end user the tax can be up to USD 0.14 in the Netherlands (regardless of the electricity source).

[x] In Dutch the leading source gives 3.230 kg/liter[4]. An international source would be the EIA that estimates 22.4 pounds of CO2/gallon or 2.68kg/l [5]. If you include life cycle emissions (mostly refining) which averages around 20% you would arrive at that same number.

References

[1]          S. Fuchs, J. Laubmann, and M. Lienkamp, “Parametric Modelling of Cost arising from the  Production,  the Operation and the Recycling of  Vehicles,” Conf. Future Automot. Technol. Focus Energy Storage.

[2]          Iain Staffell, “Energy and Fuel data sheet,” 2011.

[3]          “Europe’s tax deals for diesel,” Transport & Environment, Oct. 2015.

[4]          “Lijst emissiefactoren,” CO2 emissiefactoren. .

[5]          “How much carbon dioxide is produced from burning gasoline and diesel fuel?,” US Energy Information Administration. [Online]. Available: https://www.eia.gov/tools/faqs/faq.php?id=307&t=11. [Accessed: 23-Jul-2017].

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