By calculating the human and environmental costs of emissions, study authors show a cost-effective range of fully battery-electric propulsion of up to 5,000 km across all vessel sizes, as compared with heavy fuel oil (HFO)
Academics from the University of California at Berkeley and the US Department of Energy’s Lawrence Berkeley National Laboratory have laid out a path that, they say, would enable the economically feasible electrification of more than 40% of global container ship traffic within the 2020s.
With that level of battery-powered propulsion in the sector, CO2 emissions would be cut by 14% in the US fleet alone, curbing air pollution and mitigating its related environmental and public health costs to coastal communities and economies around the world.
"The shipping industry consumes 3.5M barrels of low-grade HFO annually, produces 2.5% of total anthropogenic carbon dioxide equivalent (CO2e) emissions in 2018 and engenders enormous damages from marine eutrophication and ecotoxicity, air pollution and climate change impacts," study authors Jessica Kersey, Natalie Popovich and Amol Phadke wrote.
"By 2050, maritime shipping emissions are projected to contribute as much as 17% of global CO2e emissions. The industry’s outsized contribution to criteria air pollutants – 12% and 13% of global annual anthropogenic SO2 [sulphur oxide] and NOx [nitrogen oxide] emissions, respectively – caused an estimated 403,300 premature deaths from lung cancer and cardiovascular disease in 2020."
Published in the journal Nature Energy, the study’s economic cases are based on a comparison of HFO and batteries and consider both a comparison of current battery, renewable energy and HFO costs as well as a near-future projection that includes expected improvements to batteries’ energy densities and reductions in cost.
Testing the economic feasibility of a battery-electric container ship against an identical slow-steaming, two-stroke diesel-driven version of the container vessel running on very low sulphur fuel oil (VLSFO 0.5%), the study calculates the vessel’s total cost of propulsion per kilometre by voyage distance.
"For both ship types, we calculate fuel, operations and maintenance costs, as well as the environmental costs of NOx, SO2 and CO2 emissions from direct combustion or grid electricity. For battery-electric vessels, we include the costs of an original and replacement battery set, the opportunity cost of forfeiting TEUs to the battery system and the levelised cost of charging equipment. As we account for the extra cost of the battery energy system separately, we omit the capital cost of the vessel, given that propulsion systems constitute only a small portion of ship newbuild costs and the cost advantage of electric motors relative to marine ICEs," the authors wrote.
Under current economic conditions, known as the baseline scenario, the study found the total cost of propulsion for a battery-electric box ship is lower than that of the HFO-fuelled vessel only on vessels larger than 8,000 TEU over voyages of less than 1,000 km.
"For longer voyages, the additional cost of the battery system, increased power requirements and charging infrastructure outweighs the savings from fuel switching and the efficiency gains of direct electrification," the study said.
But when environmental and human health costs resulting from NOx, SO2 and CO2 emissions are factored in, the cost-effective range of the battery-propelled box ship increases to 5,000 km across all sizes of container ships, given the high emissions rates of HFO.
Emissions costs were calculated based on known emissions from HFO and emissions intensity of the US power grid.
Further, the cost-effective range of battery-driven box ships more than doubled when the study authors used a near-future projection of improved battery energy density and lowered overall costs.
In this scenario, the total propulsion cost for battery-electric container shipping would be lower than that of the HFO-powered vessels at ranges around 3,000 km for all ship classes.
When environmental costs are factored in, the authors said "this range expands to 6,500 km for smaller-capacity ships and up to 12,000 km for the largest ship classes".
The authors pointed out the weight of battery systems required for trans-oceanic travel poses a problem for vessel draughts, but cited bulk carrier designs for heavy cargo such as iron ore as a potential solution to the problem.
The study authors also compared electrification scenarios against replacing HFO with e-fuels including green hydrogen or ammonia and found electrification to be three to five times more efficient.
In their modelling, the authors classified the volume used onboard to house battery systems as an opportunity cost. In the study, they modelled energy needs and emissions for eight container ship size classes and total cost of propulsion for 13 major world trade routes to develop 104 individual models incorporating both ship size and route length for use as comparison points for existing box ships.
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