When a small white-and-red Cessna Grand Caravan plane took off from Moses Lake in Washington state on Thursday, it was flying into history.
The aircraft flew at more than 100 mph to an altitude of around 2,500 feet, made a few turns and then landed after 28 minutes — an otherwise unremarkable journey for a common aircraft.
What made history was under the hood. The eCaravan, as it has been dubbed, is powered by a 750-horsepower electric motor, supplied with energy by more than 2,000 pounds of lithium-ion batteries. Weighing in at over 4 tons, with a wingspan of over 50 feet and room for nine passengers, it's the largest electric plane ever to have flown.
Electric airplanes have been heralded as the future of cleaner, climate-friendly air travel. Electric motors have several advantages over gas-powered engines but one major shortcoming — the batteries that power them.
While significant advances in battery technology have been made in the last 10 years, batteries are still so heavy that electric planes can't be expected to fully replace fossil fuel aircraft in the foreseeable future.
But proponents argue that they don't need to and that the benefits of electric aviation are already real.
Roei Ganzarski, CEO of the Seattle-based electric propulsion firm magniX, which is developing the eCaravan with the flight testing company AeroTEC, said electric aircraft can be better than fossil-fuel propeller planes over distances of up to 1,000 miles, which make up more than half of all passenger flights in the world today.
Airlines today use jets or turboprops for those flights, he noted, "but that's a waste of fuel, it's a waste of emissions, and it's not good for the environment."
"Why not do it electrically, which is also cheaper, as well?" Ganzarski said.
Turboprop Caravan planes are used around the world to carry passengers and haul cargo, and the eCaravan's developers hope their electric version can take on some regional airline routes.
Proponents boast that electric airplanes are quieter, safer and cheaper to run than fossil fuel planes. The half-hour Moses Lake eCaravan flight, for example, used just $6 of electricity – instead of $300 of kerosene – and the gasoline engine of its smaller chase plane was twice as loud.
Electric motors are also lighter than fossil fuel engines, don't need as much maintenance and last much longer before they need to be replaced, Ganzarski said
And as long as the electricity is generated cleanly, electric aircraft create no atmospheric carbon emissions, he added.
The key drawback of electric aircraft is their limited range, which depends on the batteries that they can carry – although a few designs use hydrogen fuel cells, instead. Today's batteries are at least 30 times heavier than an energy-equivalent volume of kerosene, so electric aircraft can make only much shorter flights.
The eCaravan has a range of about 100 miles. But a turboprop Cessna Caravan with the same weight of kerosene can fly about 1,500 miles.
Better batteries are on the way. Materials scientist Shirley Meng of the University of California, San Diego is part of the Battery 500 Consortium working on new battery designs.
Commercial lithium-ion batteries can store about 250 watt-hours of electricity per kilogram, she said, but new designs could double that in a few years – although it depends on how quickly factories can be equipped to make them.
"We don't have mass production capabilities, but on the research front, right now we are hitting 400 [watt-hours]. We're not at 500 yet," Meng said.
Electric aircraft can also take advantage of battery technologies pioneered by electric cars.
New battery technologies from electric cars will soon make their way to electric aircraft, Ganzarski said – although aircraft battery packs are different, they use the same basic designs.