The next time you’re staring out a plane window during takeoff or landing, give the airport a scan. You’ll see hangars and other support buildings and, of course, the terminal. But mostly, you’ll see lots of empty space. Airplanes, as many aeronautical engineers have noted, like open spaces—for obvious reasons, including not getting along with trees.

You know what also likes open spaces? Solar panels, which abhor the shade of not only trees but also tall buildings. So why aren’t we covering our airports—dedicated spaces that can’t be used for anything other than the business of air travel—with solar arrays? Well, it turns out that airports not only have a lot of empty space, they also have a lot of rules.

But let’s talk about their potential first. New research out of Australia shows how massively effective it would be to solarize 21 airports in that country. Researchers scanned satellite images of the airports for open roof space, where solar panels best avoid shadows, and found a total of 2.61 square kilometers, or 1 square mile, of usable area. 

For comparison, they also scanned satellite imagery and found 17,000 residential solar panels in the town of Bendigo, just north of Melbourne in southern Australia. The researchers calculated that the airports could potentially produce 10 times the amount of solar energy as those 17,000 residential panels—enough to power 136,000 homes. Perth Airport alone would generate twice as much as Bendigo. (Perth is very sunny, and the airport has lots of big buildings.) They further calculated that solarizing all 21 airports would reduce greenhouse gas emissions by 152 kilotons a year, the equivalent of pulling 71,000 passenger cars off the road.

With their plentiful sunshine, Australians are sitting on the energy equivalent of a gold mine; large swaths of blank rooftop space in airports provide an opportunity to centralize solar energy production. Installing panels house by house is great—and no one is saying we should stop, because we need all the solar power we can get. But commercial panels are bigger and more efficient, so they can generate more power. Plus, residential roofs come in all shapes and sizes, making them more difficult to work with than a commercial roof, which is usually flat. “Just imagine the labor to install on all the different shapes of residential buildings,” says Royal Melbourne Institute of Technology geospatial scientist Chayn Sun, the corresponding author on the new paper describing the modeling in the Journal of Building Engineering. “Compare that with flat-roof, low-rise airport buildings.”

Solarizing airports could potentially power the airport itself and even export energy. “Not only can they be self sufficient, they may have excess electricity they can send to the grid to supply the surrounding area,” says Sun.

While paneling these roofs may be efficient, it still won’t be easy. In the United States, for instance, the Federal Aviation Administration requires that airport officials prove that their new panels won’t produce glare, firing sunlight into the eyes of pilots and the air traffic controllers in the tower. (That shouldn’t be a problem, thanks to coatings on modern solar panels, but it’s still something officials have to take into account in their planning.) The FAA also wants to be sure that the panels don’t interfere with radar communications at the airport.

Also, mounting panels on existing roofs could require a retrofit, which will add to costs, says Scott Morrisey, senior vice president of sustainability at the Denver International Airport, aka DEN. But when building new structures or expanding terminals, solar capacity can be engineered right into the plan. “The fact that you are designing and integrating solar into that building makes it a lot more cost-effective than going back and trying to retrofit older buildings,” says Morrisey.

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