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All-electric aircraft – are we far from an environmental utopia?
Recently, the CEO of Tesla Motors, Mr. Elon Musk, has introduced Tesla’s batteries for home and business usage, fostering a clean energy ecosystem and amplifying its efforts to accelerate the move away from fossil fuels towards a more sustainable energy future. The new 10kWh lithium-ion battery pack comprises a liquid thermal control system and software which receives dispatch commands from a solar inverter. Although the relatively modestly priced ($3500) unit is still to win over some sceptics, its potential implications for multiple industries is already a hot topic amongst technology aficionados worldwide. For instance, subject to further developments, the new battery may become the next big step in aviation, where the possibility to integrate aircraft electrical components could be the answer to many pressing environmental concerns.
The idea of using electric energy for aviation has always been extremely popular among environmentalists, and electric aircraft have set some previously unimaginable records in energy efficiency and eco-sustainability. As for now, electrical propulsion systems are being increasingly used on smaller jets.
According to Sylvie Gauthier, the Director of Product Development Engineering at Bombardier, the current features of all electric planes have very limited autonomy. For example, an Airbus e-fan aircraft, with two electric motors totalling 60 kW of power, generates just enough power for one hour flight at a cruising speed of 160 km/h and takes one hour to recharge. With this in mind, using such or similar technology on large jets will be quite a challenge, considering the need to manage high electrical loads on-board and maintain enough power storage to run the machines. And yet, despite the difficulties, there is plenty of enthusiasts who do believe in such projects.
“There is no doubt that the future of aviation is electric. Compared to the currently used technologies, electric propulsion is probably superior in all aspects but one – it still needs further development until we can reach the same level in the commercial sector. In addition, the use of electric propulsion is at the moment only possible on certain types of planes, for certain purposes… However, I am certain that the first 10 or more new seated aircraft, which are to be designed in the following years, will already have elements of electric propulsion – at least partially,” shares Taja Boscarol, representing the Pipistrel team from Slovakia, the creators of a two-seat electric Pipistrel Taurus Electro Aircraft.
Meanwhile, many experts argue that one of the biggest obstacles at the moment is the technologies limiting the weight of batteries or production of energy during flight. Although for some types of aircraft such obstacle is no longer an issue (electric gliders, electric training aircraft), in the field of airline transport there are still quite a few challenges regarding energy efficiency and wireless transmission of energy during flight. In order to be aviation compatible, the next generation of batteries needs to deliver a whopping amount of power while being simultaneously smaller, safer and lighter than lithium-ion ones available today.
In the meantime, some industry representatives are more sceptical than others, stating that in order to successfully implement the project, there has to be a complete re-arrangement of aircraft design with absolutely new technologies. Professor Peter Malkin, currently leading the Electrical Power Group at Cranfield in its quest to discover new application areas in Novel Energy and Transport Applications, has been studying Hybrid Electric Aircraft in close collaboration with Airbus, Rolls-Royce and NASA for quite some time now. The professor has stated that he does not see large battery powered aircraft being viable in the foreseeable future.
“Certainly, the Hybrid Electric propulsion system which allows the use of distributed propulsion systems is definitely a way forward, with NASA experimental models showing over 70% gains in energy efficiency. These are massive gains but it requires a complete re-design of aircraft. Furthermore, these aircraft will require superconducting electrical power systems. These, in turn, will need cryo-cooling systems to run them, but we are proposing the use of cooling fluids such as LNG or liquid Hydrogen. These will then also be used as fuel, further reducing emissions. For LH2 this would produce zero CO2, but it is expensive. LNG, on the other hand, is still much cleaner than jet fuel and comes at about half the price,” explains Peter. “These results would have a major impact on global warming – possibly greater than any renewable energy systems. However, to make any of the aforementioned possible, we need to secure massive investment into the Aerospace industry and implement what would probably constitute the biggest change since the introduction of the jet engine. Understandably, the industry is very cautious about this technology.”
At the moment such batteries are not being considered by Bombardier either. “Electric batteries as an energy source is not what we are currently looking into, as it is limiting in terms of individual component efficiency and layout for airframe/engine integration. The electrical power demand of a Boeing 787 is nearly 1MW, twice as much as the one of a way larger Boeing 777. It is therefore necessary to optimize the power within the aircraft, and batteries are not an option,” continues Sylvie Gauthier. “More Electric Aircraft (MEA) technologies have the biggest potential for achieving superior performance. The 787 is the first MEA commercial aircraft. With the progress in integration and component efficiency, we can expect that this technology will only pop up in all aircraft segments, regional, narrow-body and large-body jets after 2020. However, these aircraft will still be powered by fuel engines.”
However, Frank Anton, the head of eAircraft at Siemens Corporate Technology, is convinced that the use of hybrid-electric drives in regional airliners with the capacity of carrying 50 to 100 passengers is a real medium-term possibility. Researchers at Siemens have created a new prototype electric motor which weighs in at just 50 kg (110 lb) and is claimed to produce about 260 kW (348 hp) at just 2,500 RPM. With a quoted power five times greater than any comparable powerplant, the new motor, specifically designed for aircraft, promises enough grunt to get planes with take-off weights of up to 1800 kg (2 tons) off the ground.”This innovation will make it possible to build a series of hybrid-electric aircraft with four or more seats,” says Frank Anton.
The largest drawback of electrically-powered vehicles so far has been the on-board energy storage system – namely, its cost. However, the investment is surely to pay off. Pipistrel has recently presented its comparative study analysing the financial benefits of operating an electric-powered versus petrol-powered aircraft. Based on the results, the former can deliver up to 27 times the cost savings. The price of operating the Pipistrel Alpha Trainer, including lubrication and obligatory services, is approximately 27 $/hour. Flying with electric propulsion costs 1 $/hour. This is such a significant difference that the higher initial investment into an electric aircraft pays off in less than 400 hours of flight.
Moreover, Airbus claims that a typical flight on e-fan will only cost about $16, whereas a comparable gas-powered plane would suck down $55 worth of fuel. These planes could lower the cost of entry to aviation, at least as far as fuel is concerned, and one day small electric or hybrid Airbus aircraft could become the standard commuter plane for frequent flyers. The Airbus Group’s ultimate goal is to produce a 70- to 80-person hybrid-electric commuter jet with three hours of range in the 2050 time frame.
The main technological barrier that must be overcome is the energy density of batteries. It measure the amount of power which can be generated from batteries or other alternative energy sources. Thus, the development of electric aircraft depends not only on the speed at which the battery technology is refined, but also on how fast the electrical equipment (motors) can be further improved. As stated by Peter Malkin, the cryogenic technology is not yet fully practical and still requires decades of testing. In any case, given the enthusiasm and quality of the existing developments, it is likely that someday, with the help of electric technology, the future of aviation in the larger airlines’ segment will become not only cost-effective but also really environment-friendly.
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