Where coverage of reducing the amount of carbon dioxide in our atmosphere is concerned, the big headlines often go to big names backing big solutions. Artificially sucking carbon out of the air, and covering the entire the entire sky in a shroud of sun-reflecting aerosols, have garnered quite a lot of press for technologies that don’t really exist yet. But plenty of people are looking at practical ways to eliminate emissions from the most challenging sources, instead of accepting that their emissions must continue indefinitely. The emissions source that poses the biggest challenge is the airplane. The quest to develop emissions-free airplanes doesn’t get a whole lot of attention. Perhaps people assume that it’s going to be too hard, even though large-scale carbon removal or dust-spreading are not any more technologically feasible right now. (On a more cynical note, artificially removing carbon dioxide or filling the stratosphere with particles allows for the possibility of fossil fuels continuing to burn — while if airplanes don’t need fossil fuels, what does?) However, there are some interesting recent articles on emissions-free airplanes that give a good assessment of what can and can’t be done presently, and what the obstacles for future development are.
One article published by Energy Monitor in May talks about a western Canadian seaplane company called Harbour Air. They have been making regular test flights of a prototype commercial electric airplane since 2019, and they have recently announced a partnership with a battery supplier. Their long-term goal is to fully electrify their fleet. What makes this article particularly interesting is the way Harbour Air CEO Greg MacDougall (who doubles as the test pilot) discusses the logistical hurdles. These hurdles include mundane things like obtaining certification from the Canadian government, but they also include weight- and space-efficient heat shielding for the batteries (with airplanes, every pound and cubic foot counts a lot), to the advantages of retrofitting old aircraft over building new ones.
In other news, NASA is openly soliciting demonstrations of electric flight. Cross-country jet flights won’t happen tomorrow — the needed battery power is not only too heavy at present, it would take up the whole plane — but smaller electric aircraft traveling relatively short distances are already viable. NASA’s objective is to stretch the carrying capacity of these flights from a few people to up to a hundred by the end of the decade. Green air technology is still very young, and NASA wants to see who has the best ideas.
I also decided to take a look into what people have done with solar-powered flight, and I found a couple of good articles on the subject. The first was published just this January. It begins by acknowledging the accomplishments of two Swiss aviators who crossed the globe in a solar powered aircraft. But from the perspective of commercial flight, there is a major drawback: the plane’s maximum speed was 75 km/hr, or 47 mph — slower than a car at highway speed, and much slower than a jet. The plane also needed batteries accounting for 25% oof the plane’s weight to keep running at night. Factor in trying to fly when the sky is not crystal clear, and there are some major hurdles that need to be overcome. The second article is a response to a question posed to the faculty at the MIT School of Engineering. There are a couple of engineering issues if you wish to maximize the energy that solar panels generate. The first of these is that the angle that the sunlight makes with the panels is a lot more variable than it would be for a stationary object. The second is that the energy need to maintain cruising speed varies with the cube of the speed (i.e., if you double the speed it will take eight times as much energy to maintain it). Third, and perhaps most obviously, is that flights powered entirely by solar energy would be limited by the weather. So while solar planes can be and are used for applications like data collection that can be done at low speeds and high altitudes, commercial flights relying solely on the Sun for power are not likely. But solar power can still conceivably be used in tandem with other energy sources.
For some small-scale applications, like island-hopping along the Pacific Coast in Canada, emissions-free airplanes are already viable enough to start carrying passengers. But commercial jet travel without emissions remains a daunting obstacle. My guess is that short-range flights for business trips will eventually be phased out in favor of high-speed rail; the technology exists, and the trains are as clean as the energy that powers them. Mid-range flights, on the order of 500 to 1000 miles, will require a significant improvement in the energy density of the batteries. People are working on that, and NASA’s interest speaks for itself, but the technology does not exist now. As for longer flights, solar might have a supportive role to play. The planes would have to get to a high altitude, much like what has been proposed for a new generation of supersonic jets. Going above the ozone layer would not only reduce the air drag that a plane would need to overcome in order to maintain speed, but it would also give solar panels access to the UV radiation that gets absorbed in the ozone layer. That could reduce the burden on the batteries significantly, but as I said before, the energy density of the batteries will still need to increase substantially for this to become feasible. (And, obviously, such flights couldn’t happen at night).
One thing that people need to keep in mind with airplanes, though, is that they account for only 2% of total global emissions of carbon dioxide. If we seriously act to make electricity generation emissions-free over the next 15 years and electrify our other sources of transportation as well, we will have nearly solved the climate crisis. And hopefully, by the end of that time, low- or no-emissions flights will be much closer to becoming a reality.
