In the future, airplanes might start running on CO2 that is sucked from the air and transformed into jet fuel using nothing but sunshine and water.
Researchers at the EU-funded SOLAR-JET project recently proved that at least the second part of the process is possible: A super-hot solar reactor can convert CO2 into synthetic gas, and then the gas can be turned into kerosene to fly a plane.
The machines could actually use CO2 from any source, like the emissions captured from a power plant. But the researchers think the best source might be the air.
"We're looking at the long term—the future challenges of aviation and potential solutions," says Andreas Sizmann, who is coordinating the SOLAR-JET project. "In the short term, we have many sources of CO2. But we hope in the future we will have fewer conventional power plants. And then the main source of CO2 could be the air."
The researchers' solar-powered process could eventually be used to make renewable forms of other types of fuel, like diesel or gasoline, and even plastics. But they're especially interested in what the technology could mean for the future of flight.
"With solar kerosene, we have a fuel that fits perfectly in the current aviation system," says Sizmann. "We don’t have to change the airplane, we don’t have to change the airport, we don’t have to change the infrastructure. It just fits."
The resulting "solar" fuel would work exactly like a non-renewable version made from natural gas, so it's already proven to be safe. Unlike some alternative fuels, which would require redesigning aircraft, it can be used as it is. And unlike electric planes, which have the challenge of carrying heavy batteries, it wouldn't affect the way the plane flies.
The technology might be ready to use in a decade or so. It will require that the researchers improve the efficiency of the process, and the viability will ultimately also depend on the source of the CO2. Other research teams are working on ways to efficiently capture CO2 from the air.
The biggest catch is the cost of the technology. For such a crazy plan to fly, emitting CO2 from traditional fossil fuels will have to have a price to polluters. "It’s the economics that matter in the long term, because the economics determine whether these things are built or not," says Sizmann. "Will CO2 cost $5 a ton or $100 a ton?"
Ultimately, if it's used, the technology would make flying carbon neutral—the plane would still emit CO2, but then the same amount of CO2 would be taken from the air to power the next flight.