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How Superconductors Are Enabling Electrification Of Transport Beyond The Car

How superconductors are enabling electrification of transport beyond the car

Global electric car sales are surging based off the public concern for greenhouse gas emissions [1]. Transport makes up 14% of global emissions, however, this isn’t confined solely to road vehicles. International aviation and shipping account for more than 2% globally each [2].

So the big question is can we also electrify aviation and shipping? What materials and technologies exist that could even make this possible?

The big difference in electrical motors for aircraft and shipping compared to those for electric vehicles is that they have much more extreme requirements in terms of weight and power output. So conventional electric motors composed of copper, iron and permanent magnets, which suffice for electric cars, just won’t do if we want to get an airliner off the ground.

High-temperature superconductors

High-temperature superconductors (HTS) are making high power, low weight motors possible. HTS materials lose their electrical resistance below a superconducting transition temperature. For conventional superconductors these transition temperatures are so low that they need mostly to be cooled using liquid helium (-269 °C). HTS on the other hand operate at comparatively high temperatures and can be cooled using liquid nitrogen (-196 °C), a cheap and abundant coolant. As discussed in a previous article, multiple manufacturers have developed methods for producing HTS wire, the price of which is even approaching that of copper [3].

Electric cargo ships

So how do HTS fit into the world of transport? One of the main constraints in constructing ever larger cargo ships is the size and complexity of the propulsion system. Electric ship propulsion has been around since the 19th century, however has mostly been limited to small vessels [4]. HTS wire can conduct the same current as a copper cable in about one tenth of the cross section [5]. So when used to replace copper windings and permanent magnets, HTS wire provided a huge volume reduction and can create much higher magnetic fields. This allows for much more compact, higher power electrical motors.

Another major advantage of replacing copper with HTS in motors is the absence of resistive heating during operation, meaning that only a very small cooling power is required once the superconductor is below its transition temperature. Of course, one of the major challenges is always how to implement a cryogenic system required to cool rotating HTS coils. This, however, is a challenge engineers have risen to. Over the past few decades, several manufacturers have been constructing and testing powerful HTS motors with the high torque required in marine propulsion. Siemens, for one, has demonstrated a motor with a power of 4 MW [6] and AMSC, a 36.5 MW system [7].

How superconductors are enabling electrification of transport beyond the car
Figure 1: AMSC's 36.5 MW HTS ship proulsion motor provides over 100 tonnes of weight reduction [8].

Getting HTS off the ground

When it comes to aviation, electric aircraft seem even farther fetched than electric ships. The work put into HTS ship motors over the years, however, has demonstrated that the advantages HTS bring to motor technology are even more applicable to aviation. Aircraft have very strict weight requirements, which is evident in the industry’s interest in additive manufactured components (as well as some less technological ideas, such as one Japanese airline even asking their passengers to relieve themselves before boarding [9]). Reducing fuel consumption is therefore not only essential for reducing emissions, but is also a massive financial driver. Add to that the benefits of reduced noise and air pollution and electrification of aviation becomes very attractive to the industry.

Figure 2: The E-Fan X hybrid-electric flight demonstrator, a joint project between Airbus, Siemens and Rolls-Royce which will have one of the four gas turbine engines replaced by a 2 MW electric motor. It is planned to fly by 2020 [12].
Figure 2: The E-Fan X hybrid-electric flight demonstrator, a joint project between Airbus, Siemens and Rolls-Royce which will have one of the four gas turbine engines replaced by a 2 MW electric motor. It is planned to fly by 2020 [12].

Developments for passenger electric aircraft are already in full swing, with multiple companies working on prototypes including Airbus, Wright Electric and Zunum Aero [10]. These are mostly hybrid concepts which will demonstrate electrical machines work in tandem with turbine engines for propulsion. In such a configuration that HTS motors are likely to make significant contributions. Looking beyond this, NASA have laid out plans to develop the N3-X aircraft. This should provide a 70 % reduction in fuel consumption by using two gas-driven HTS generators to power the distributed HTS motor-driven fans [11].

How superconductors are enabling electrification of transport beyond the car
Figure 3: NASA's N3-X, an aircraft designed to be propelled via HTS motor-driven fans, powered by HTS turbogenerators mounted on the wing tips [13].

With great power comes superconductivity

Despite the advantages, in reality the adoption of HTS in propulsion has been slow. Most probably this is down to the complexities of the technology and the associated developmental costs.

Nevertheless, the advancements made in exploiting HTS material properties since their discovery in the 80’s has been immense. Effort is still required to implement HTS motors on a large scale, yet, especially in the case of aviation, ambitious development goals have never stood in the way of progress.

As pressure increases to reduce emissions in transport, HTS won’t just offer improvements on conventional devices but will a key enabling technology.

"I am keen for readers to look at materials with the same fascination I do and to see how they will impact our future".
benjamin_stafford
Benjamin Stafford
Ph.D. in Physics

References:

[1] “Global Plug-in Sales for Q1-2018”, EV Volumes, 2018 [Online]. [Accessed Jul. 12, 2018].
[2] Fifth Assessment Report, “Climate Change 2014: Mitigation of Climate Change”, Intergovernmental Panel on Climate Change, 2014.
[3] M. Noe et al., “Common Characteristics and Emerging Test Techniques for High Temperature Superconducting Power Equipment,” CIGRE Brochure, 664, 2015.
[4] R. Kantharia, “Electric Propulsion System for Ship: Does it have a Future in the Shipping?”, Marine Insight, Sept. 11, 2017, [Online]. [Accessed Jul. 12, 2018].
[5] THEVA Pro-Line TPL2100 Technical Data Sheet, THEVA Dünnshcichttechnik GmbH, Jul. 2016, [Online]. [Accessed Jul. 13, 2018].
[6] W. Nick et al., “Test results from Siemens low-speed, high-torque HTS machine and description of further steps towards commercialisation of HTS machines,” Physica C, 482 (2012).
[7] J. Buck J et al., “Factory testing of a 36.5 MW High Temperature superconducting motor,” ASNE Day Symp., 2007.
[8] B. Wang, “36.5 Megawatt superconducting motor Successfully Tested at Full Power,” NextBigFuture, Jan 30, 2009, [Online]. [Accessed Jul. 16, 2018].
[9] P. Hollinger, “Airlines bid to beat their weight problem”, Financial Times, Dec. 14, 2016, [Online]. [Accessed Jul. 13, 2018].
[10] E. Gaj, “The electric aircraft is taking off”, TechCrunch, Jul. 8, 2018, [Online]. [Accessed Jul. 13, 2018].
[11] Press release, “Airbus, Rolls-Royce, and Siemens team up for electric future Partnership launches E-Fan X hybrid-electric flight demonstrator,” Airbus, 28 Nov. 2017, [Online]. [Accessed Jul. 16, 2018].
[12] K. S. Haran et al., “High power density superconducting rotating machines—development status and technology roadmap,” Supercond. Sci. Technol. 30, 2017.
[13] E. Goldstein, “NASA: Leading a Transition to Low-Carbon Propulsion,” Defense Media Network, 3 Apr. 2015, [Online]. [Accessed Jul. 16, 2018].

*This article is the work of the guest author shown above. The guest author is solely responsible for the accuracy and the legality of their content. The content of the article and the views expressed therein are solely those of this author and do not reflect the views of Matmatch or of any present or past employers, academic institutions, professional societies, or organizations the author is currently or was previously affiliated with.

2 Comments Add New Comment

  1. Has there been any consideration given to a more streamlined, modern, helium-filled dirigible type aircraft where most of the energy needed to lift its mass is provided by the helium gas? This would seem to require a lot less motive force being wasted on providing lift, which would make electric power much more feasible.

    1. It’s certainly an interesting idea. I’ve not yet heard of anyone in that field in connection with HTS. Unfortunately, I find it unlikely that the lower speed would make it competitive with passenger airliners or that the lower loads would make it competitive with ocean shipping.

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