This is what’s keeping electric planes from taking off

Startups are exploring how electric planes could clean up air travel, which accounts for about 3% of worldwide greenhouse-gas emissions. The problem is that today's electric aircraft could safely carry you and about a dozen fellow passengers only around 30 miles, according to a recent analysis.

The limiting factor is the battery, in particular the amount of energy that can be stored in a small space. If you've folded your legs into a cramped window seat or been charged extra for overweight luggage, you're probably familiar with the intense space and weight constraints on planes.

Today's batteries don't have the energy density necessary to power anything but the lightest planes. And even for those, the trip will be about as far as a long bike ride.

Batteries have been packing more power into smaller spaces for about 30 years, and continuing improvements could help electric planes become a more feasible option for flying. But they're not there yet, and ultimately, the future of electric planes may depend on the future of progress in battery technology.

Powering up

The prospect of electric flight is appealing in many ways. Aviation contributes a growing share of the global greenhouse-gas emissions that cause climate change, and battery-powered planes could help speed decarbonization in a growing sector.

The emissions reductions could be significant. A battery-powered plane charged with renewable energy could produce nearly 90% less in emissions than today's planes that run on jet fuel, says Jayant Mukhopadhaya, a transportation analyst at the International Council on Clean Transportation (ICCT). (Remaining emissions are largely from producing the battery, which likely would need to be replaced each year for most planes.)

Batteries are also an efficient way of using electricity. In an electric plane, about 70% of the energy used to charge up a battery would actually power the plane. There are some losses in the battery and in the motor, but this efficiency is high compared with other options being considered to decarbonize flight. With hydrogen and synthetic fuel, for example, efficiencies could be as low as 20 to 30%.

Given the potential, a number of startups are hoping to have small electric planes making relatively short trips before the end of the decade.

Heart Aerospace, a Sweden-based startup, is among the companies attempting to capitalize on the promise of batteries to commercialize electric planes. Their 19-seat planes will start flight tests in 2024 and could be flying commercially by 2026, according to CEO Anders Forslund.

Our goal is to create the most affordable, fastest, greenest way of getting around the world," Forslund says.

The company plans to start in niche markets-like hopping across fjords in Scandinavia. These routes are difficult to replace with ground transport, and in some countries, like Norway, they could be subsidized by the government.

Forslund says that these trips are just the beginning, though, and the goal is to expand regional flying globally. Even with current battery technology, the company claims, its planes could be able to fly about 400 kilometers, or 250 miles. That's about the distance between New York City and Boston or Paris and London.

The battery requirements to fly even these short trips are pretty substantial. Heart's 19-seat planes will carry about 3.5 tons of batteries on board, for a combined capacity comparable to that of eight to 10 electric vehicles.

Wright Electric, a US-based startup, is aiming for even bigger planes. The company, which plans to retrofit 100-seat aircraft with batteries for short routes, also anticipates flying by 2026.

Turbulence

Some in the industry are skeptical that such planes could be successful without major improvements to batteries. The battery technology is just not there yet," Mukhopadhaya says.

In a recent report by the ICCT, Mukhopadhaya and his colleagues found that the range of electric aircraft would be severely limited with existing energy storage technology. We were surprised by how terrible the range was, frankly," he says.

Using estimates for current battery densities and plane weight restrictions, the analysts estimated that 19-seat battery-powered aircraft would have a maximum cruise range of about 260 km (160 miles), significantly less than the company's claim of 250 miles.

Forslund argues that estimates by outside observers don't give a true picture of the company's technology, since they're not privy to details about its battery pack and plane design. (The company plans to design its own aircraft rather than retrofitting an existing model to run on batteries.)

Reserve requirements could severely limit the true range of electric planes. A plane needs extra capacity to circle the airport for 30 minutes in case it can't land right away, and it must also be able to reach an alternative airport 100 km (60 miles) away in an emergency.

When you take all that into account, the usable range of a 19-seat plane goes from about 160 miles to about 30 miles. For a larger aircraft like the 100-seat planes that Wright is building, it's less than six miles.

That reserve requirement is ultimately the killer," says Andreas Schafer, director of the air transportation systems lab at University College London.

Future of flying

Ultimately, Schafer says, the future of electric planes depends on the future of battery improvements.

According to the ICCT analysis, batteries would need to basically double in energy density to enable the short routes that startups are aiming for. That improvement likely approaches the limit of lithium-ion batteries, which are used today for EVs and consumer electronics. Even with this sort of progress, electric aircraft could only displace enough aircraft to cut less than 1% of emissions from the aviation industry by 2050.

In order for electric planes to play a more significant role in decarbonizing air travel, energy density may need to quadruple, Schafer says. This could require novel types of batteries to reach commercialization.

Meanwhile, other technologies like alternative fuels and green hydrogen have much higher energy densities, so they're a more likely candidate for longer flights, provided that they can be produced economically at scale.

Electric planes could take to the sky soon, maybe even before the end of the decade. But they probably won't be able to take very many of us very far. For now, unless there's a fjord in the way, you might want to just ride a bike or take the train.