Compile / Wenlong
Curbing carbon emissions requires electrification of transportation, but so far most innovation has only been in the automotive industry. In a recent nature energy article, researchers from Lawrence Berkeley National Laboratory and the University of California set their sights on another key industry — freight trains. In fact, the policy of railway electrification has always existed, but the solution proposed by the research team is not to use traditional overhead lines, but to use batteries.
(Image source: Alamy Stock Photo)
According to data from the International Energy Agency, carbon dioxide emissions from China's transportation industry accounted for 10.2% of China's total national emissions in 2018, which is an industry in urgent need of breakthroughs in the three key industries of energy conservation and emission reduction. In railway transportation, although passenger trains such as high-speed rail trains have been basically electrified, freight trains still use diesel as the main driving force. Rail transport, because it is cheaper than road transport, is naturally ideal for the reliable transport of large containers over long distances.
Similar to china, U.S. rail freight runs almost entirely on polluting diesel, with an estimated 35 million tons of CO2 air pollution emitted annually, which will cause about 1,000 premature deaths and about $6.5 billion in health damage costs. On the other hand, improved battery technology coupled with the advantage of cheap renewables will soon allow battery power to compete with diesel fuel, powering freight trains. As a result, Natalie Popovich and colleagues made recommendations to support the U.S. transition to battery-electric railroads and analyzed the feasibility from technical and economic perspectives.
You can travel up to 241 km on a single charge
Currently, electrification in the railway sector means the installation of overhead line equipment – cables that carry electrical energy along the entire line, connected to mobile locomotives equipped with electric motors via pantographs. This not only requires an intensive capital investment proportional to the length of the tracks, but also makes it impossible for electric locomotives to operate on the remaining non-electrified parts of the track network. As battery prices continue to fall, making it easier for consumers to get electric vehicles, researchers have also been studying the possibility of using batteries in rail transportation.
The team calculated that using current battery technology, assuming lithium iron phosphate (LFP) batteries, it is feasible to build a single-cell battery trolley capable of powering a Class I freight train (with an average daily range of 241 kilometers) while also surpassing the energy efficiency of diesel trains.
Using known LFP battery data, assuming the battery achieves the current optimal energy density, a single car can accommodate 14 MWh batteries and can travel 241 kilometers on a single charge. The total weight of the 14 MWh battery plus the inverter is about 114 tons, which is lower than the railway weight requirement; the total volume of the battery is about 39 m3, plus the inverter volume of 13.7 m3, which is about 40% of the volume of the standard single car (129 m3). Therefore, in terms of weight and volume, it is feasible to achieve a range of 241 km using a single carriage equipped with a 14 MWh battery and inverter. Battery freight trains consume 5 percent more energy due to increased battery weight, but it is still about half the energy consumption of diesel trains due to the high efficiency of all-electric drives.
As for the choice of batteries, lithium ferrous phosphate (LFP) batteries have a longer cycle life and lower temperature than nickel-manganese cobalt oxide (NMC) batteries, are cheaper than lithium titanate (LTO) oxide and can operate over a wide temperature range. While RTOs have the advantage of extremely fast charging over LFP, LFP batteries can also be fully charged in less than half an hour, and trains can also be quickly charged or replaced with recharged batteries at stops along the way.
$94 billion could be saved over 20 years
However, technical feasibility is one thing, economic feasibility is another, and if proven, battery electrification could be a promising route for decarbonizing rail freight. Popovich and colleagues also looked at this aspect, and their results show that cheap renewable electricity and the environmental costs of fossil fuels at battery prices below $100 per kilowatt-hour make batteries competitive with diesel in terms of total cost.
It is worth noting that the components of the total cost of ownership of battery locomotives are fundamentally different from those of internal combustion locomotives: in the latter, operating expenses (especially fuel) are the main costs at present; in the former, the main costs are the capital expenditure of the battery itself and charging infrastructure, while energy is much cheaper. This means that the upfront costs will be higher, even if the total cost of ownership is competitive.
(Based on the total cost of ownership required to reach diesel parity, the all-inclusive electricity price)
The calculations show that in order to be on par with the average U.S. diesel price (US$0.66/L), the electricity price must reach US$ 0.072/kWh and the battery cost must be lower than the US$100/kWh battery. While the average industrial electricity price in the U.S. is US$ 0.064/kWh, the latest LFP technology is priced at US$100/kWh. The calculation does not include infrastructure costs, nor does it include environmental costs. Switching to battery power propulsion would save $44 billion when considering standard pollution reductions and $94 billion when using CO2 as the reduction standard. The main determinants of economic returns are station utilization and diesel prices.
There are two main challenges
However, there are still many challenges to be solved before batteries can power trains.
On the one hand, it is difficult to establish a fast charging infrastructure in sparsely populated areas. This is important because Popovich and colleagues found that charging infrastructure is an important part of the total cost of ownership of battery packs. In the initial stages, slow charging by replacing the battery may be a preferable deployment strategy.
(Energy price for 72 MW charging station at different usage rates)
However, the centralized nature of freight rail operations and dispatches can reduce costs by enabling high utilization of fast-charging infrastructure. The researchers estimated the cost of a 72 MW charging station, estimating that the levelized cost of electricity plus charging is between US$0.185/kWh and US$0.185/kWh.
The charging station can charge eight cars at a time, and since these costs are shared by the number of trains using the charging station, stations with larger trips have the potential to be the most cost-effective locations.
A recurring uncertainty is the evolution of battery price and longevity. Even as batteries become cheaper, they cannot be cheaper than the value of their raw materials. Popovich and colleagues reiterated their analysis of several battery cost levels, confirming that their results hold true in all but the most pessimistic cases.
For zero-emission rail transport, Popovich and colleagues not only pointed to the economically viable route of battery freight trains, but also proposed other solutions, such as biodiesel or hydrogen. These energies can store more energy in less time, but their techno-economic viability needs to be assessed in a similar way. It is undeniable that with the innovation of battery technology and other ways of decarbonization, the railway industry is moving towards interesting times.
For reference:
https://techxplore.com/news/2021-11-battery-powered-economically-viable.html
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