Running Heavy-Duty Transport on Batteries

Running Heavy-Duty Transport on Batteries
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California is mandating a statewide shift to all-electric medium- and heavy-duty trucks, starting in 2024, with the goal of reaching 100% of all new sales, wherever feasible, by 2045.

Summary: Even though a battery electric long-distance heavy-duty truck is technically feasible, it is not practical. The battery capacity needed is very large. The capacity of the truck to carry goods will be reduced, the cost will be high, and the charging time will be too long. It would also require significant up-front costs from a fleet operator to install the required charging infrastructure. Energy consumption per unit of load carried will increase because of the reduced payload capacity. It is also not zero CO2 and would have serious environmental impacts on human health and water requirement and toxicity associated with mining for materials and battery manufacture, though these impacts are exported from where the truck is used.

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Battery electric vehicles (BEVs) are not “zero emissions” vehicles. Mining for the necessary metals and the manufacturing and recycling of batteries are estimated to contribute 75–120 kg CO2 eq/kWh of battery capacity, assuming that battery manufacture is with fossil-free electricity [1]; it could be as high as 200 kg CO2 eq/kWh if the energy used is not sufficiently decarbonized, according to an earlier report in 2017 [2,3].

Even if the electricity used is generated from renewables like wind and solar—as it is likely to be in California in the future—the energy to run the BEV is not necessarily zero carbon [2,3]. This is because even when the average carbon intensity of power generation is very low, the extra electricity demand from BEVs has to be met with marginal (backup) electricity generation, which can quickly respond to changing demand and usually relies on fossil fuels, especially if nuclear power is not in favor, as is the case in California.

The impacts on human health, as measured by the human toxicity impact (HTP) of BEVs, mostly arise from the production of metals needed for batteries [4,5] and are estimated to be three to five times worse than for similar-size internal combustion engine vehicles (ICEVs), where they come from exhaust gas emissions. There are also significant impacts on water toxicity. The larger the battery, the worse these impacts, which are currently exported to countries where the mining takes place (such as the Congo) and are largely ignored; this should not be acceptable as the number and size of batteries increase.

Let’s first look at the CO2 emissions embedded in the truck battery. Consider a heavy-duty 80,000-lb (36-metric-ton [MT]) Class 8 truck in the U.S. with a 500-mile range, such as the Tesla Semi truck. It requires a lithium ion battery capacity of 1,000–1,100 kWh [2], and its embedded CO2 emission from manufacture would be around 102 MT, taking average values. In the U.S. Supertruck program, a Class 8 truck running on diesel has already reached 10.7 mpg, or 0.95 kg CO2/mile. So a diesel semitruck will have covered over 107,000 (102,000/0.95) miles before the electric truck can catch up to pay back the CO2 debt associated with its battery manufacture. After that period, the electric truck, if it is run on a renewable electricity grid, might produce lower CO2 than the diesel truck but will not be zero CO2.

Next let’s look at the performance penalty of a BEV semitruck. We assume values of 180 Wh/kg and $125/kWh for the energy density and cost of the battery pack—35% and 20% better than current average values, respectively. For reference, the 85-kWh battery on a Tesla S takes 75 minutes to charge fully on the 120-kW Tesla Supercharger. So the semitruck battery will weigh at least 5.5 MT, compared with about 1.3 MT for a typical diesel engine for such a truck, reducing its load-carrying capacity by at least 4 MT; it will cost at least $125,000, while an entire Class 8 truck costs about $100,000; and with the Tesla Supercharger, it would take about 14 hours to charge. If there is a depot that is charging 10 such trucks simultaneously, it would need to install a central charging capacity of 1.2 MW, which would entail significant up-front costs to the hauler for the transformer and the connection to a high-voltage grid. Each such battery will also require 2,800 MT—500 times its weight—of earth, on average, moved to access the metals required [6].

Heavy-duty goods vehicles are much heavier than passenger vehicles and have a much longer range, compared with passenger BEVs, because they carry a lot of payload over long distances. Hence they use much more energy, compared with passenger cars; and if they are to be battery-driven, the battery must store large amounts of energy. This requirement translates into a battery weighing several tons, incurring at least a 4-MT weight penalty, compared with a conventional truck. 

In summary, the low energy density of battery storage compared with the chemical energy stored in hydrocarbon fuels renders passenger BEVs costly but—given some limitations on range, for example—practical. For trucking, however, the weight, restricted range, and charging time render BEV operations prohibitive.

 

Dr. Gautam Kalghatgi is a Visiting Professor at Oxford University (Engineering Science) and Imperial College London (Mechanical Engineering).

 

References

  1. Emilsson, E., and L. Dahllöf. “Lithium-Ion Vehicle Battery Production.” IVL, 2019.
  2. Kalghatgi, G. T. Applied Energy 225 (2018): 965–74.
  3. Hausfather, Z. “Fact Check: How Electric Vehicles Help to Tackle Climate Change.” Carbon Brief, 2019.
  4. Baes et al. Future of Batteries. Arthur D Little. 2018.
  5. “Commodities at a Glance: Special Issue on Strategic Battery Raw Materials.” 2020. Chap. 5.
  6. Mills, Mark P. “Mines, Minerals, and ‘Green’ Energy: A Reality Check.” Manhattan Institute. 2020.

 



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