…Though airlines are not going to be buying solar-powered aircraft anytime soon, engineers are already investigating many of the technologies that let Solar Impulse 2 fly around the world: lightweight materials for cars, foam insulation for refrigerators and buildings, efficient power management for electronics. But researchers say it’s going to be much harder to reduce carbon emissions from commercial aircraft in a practical way.
“The current aircraft are pretty near what the laws of physics allow in terms of thermodynamics of the engine,” said Paul Peeters, an associate professor of sustainable transport and tourism at NHTV Breda University of Applied Sciences in the Netherlands.
Even without climate concerns, aircraft engineers are constantly looking for ways to save fuel, since every pound of fuel subtracts from the number of paying passengers on board or from the amount of cargo. “The payload of an aircraft is directly a function of fuel efficiency,” Peeters said.
When it comes to commercial airliners, incremental is huge
Plane builders have already picked most of the low-hanging fruit in fuel efficiency, so now many designers are chasing marginal improvements through lighter materials and better aerodynamics.
A zero-emissions airliner or a carbon-neutral aircraft is theoretically possible, but it would require a drastic technology leap that is likely decades away, Peeters said.
Electric motors are inherently more efficient than combustion engines, but batteries have only the fraction of the energy density of fossil fuels, taking up more space and adding more weight for much less power. A fuel cell-powered aircraft could be possible, but it would require more than a decade of research and development along with significant financial backing from the aerospace industry.
Peeters cited the case of the Boeing 787 Dreamliner. The aircraft uses lightweight materials and better engines for a 20 percent fuel savings (ClimateWire, June 21, 2013). The design was an incremental improvement, but it still took 12 years to develop and hit some snags with its new batteries that led to a worldwide grounding of the fleet (ClimateWire, Dec. 18, 2014).
A carbon-neutral biofuel would be an easier drop-in improvement, but costs are currently much too high for notoriously frugal airlines. Meanwhile, the demand for air travel is growing year on year by roughly 5 percent. “We need policies to contain that,” Peeters said. “Otherwise, I don’t see any way to reduce the emissions or get them flat.”
Developing a ‘mindset,’ not technology
In May, Peeters co-authored a paper in the journal Transportation Research Part D: Transport and Environment titled “Are Technology Myths Stalling Aviation Climate Policy?”
The paper argued that proposed technology fixes for aviation have undermined the push to limit aircraft emissions, allowing lawmakers leeway to wait for a solution instead of making the hard choices to tax and regulate the industry right now.
“There’s also the problem that oil is extremely cheap right now, so some of the imperative is falling out in that respect,” said co-author Scott Cohen, head of the Department of Tourism and Events at the University of Surrey in the United Kingdom. In addition to policy fixes, cutting greenhouse gas emissions at a meaningful level would likely require rethinking how people approach air travel altogether.
If flying is the only option, then spring for a direct route instead of connection, he said. Passengers also have the option of buying voluntary emissions offsets for their air journeys, but Cohen cautioned that offsets should not be used as an indulgence, where they may have the rebound effect of encouraging more air travel, guilt-free.
Nevertheless, research agencies like NASA and aerospace firms are studying electric propulsion and hybrid power plants for aircraft in efforts to reduce greenhouse gas emissions (ClimateWire, April 12).
And conscientiousness may be Solar Impulse’s biggest impact on aviation. “The learning, in the end, is more about developing the right mindset and not so much about developing the right technology,” said the pilot of the flight. Click here to view a video of the Solar Impulse 2 landing in Abu Dhabi.