Electrification is having a moment. Electric cars are finally in fashion. Electric buses are replacing traditional buses all over China. And there are a number of electric trucks, motorcycles, and even more scooters coming in the very near future.
So why don’t we have electric airplanes yet?
If there’s any vehicle that needs to be electrified, it’s jet engine aircraft. According to the EPA, the aviation industry was responsible for about 2.5% of total CO2 emissions in 2018. If it were a country, aviation would rank sixth in the world in national CO2 emission standings, sandwiched between Japan and Germany. The United Nations estimates airplane emissions will triple by 2050 as a result of increased demand for flights.
Electric planes would reduce greenhouse emissions which is great for the planet. And since electric engines have dramatically fewer parts than jet engine aircraft, they’re easier to maintain, quieter and offer a smoother ride. Plus, they require less runway, allowing regional airlines to expand the cities they serve.
So again: why don't we have electric airplanes given all their benefits? The answer boils down to two words – specific energy.
The Energy Problem
Specific energy is energy per unit mass. Think of it as the amount of energy that can be extracted out of every kilogram of an energy source. Jet fuel provides 12,000 watt hours per kilogram. But today’s most advanced lithium ion batteries provide a scant 250 W h/kg.
An electric Boeing 737 would require at least 800 W h/kg to make a trip from Chicago to New York City. Unfortunately, adding more batteries won’t do the trick because it adds more mass to the aircraft, which would require more batteries to compensate, adding more mass in an endless loop.
Battery technology continues to improve each year, with the specific energy of lithium ion batteries increasing 3 to 4 percent annually. But at this rate, we won’t have an 800 W h/kg battery for about 30 years, barring a huge breakthrough in battery technology.
We hate to say it, but don’t expect to board a commercial cross-country electric flight anytime soon, or even in your lifetime. However, shorter regional trips, in theory, could be serviced by small electric aircraft. And current batteries provide enough energy to power lightweight airplanes up to 650 miles, or the distance from Los Angeles to San Francisco.
Electric Aircraft Coming Soon
Eviation, based out of Israel with U.S. headquarters in Arizona, already has 150 orders for its nine passenger electric plane Alice. The aircraft has a cruise speed of only 260 knots (300 mph) but can make trips of 650 miles. According to the company, each hour of flight would necessitate a 30-minute charge.
MagniX out of Redmond, WA is going the retrofit route, converting seaplanes into all-electric vehicles by replacing the engine with a 750-horsepower motor. The seaplanes will have a range of roughly 100 miles, which is ideal for its partner Harbour Air. The Canadian charter airline typically flies short routes between 40 and 62 miles that last up to 25 minutes.
And just as the Toyota Prius hybrid bridged the gap between traditional and electric automobiles, hybrid planes are expected to the same, filling the space until suitable batteries are engineered.
L.A.-based Ampaire is transforming existing passenger planes into hybrids with a combustion engine in the nose and an electric engine in the tail. The startup projects FAA certification for its Electric Eel aircraft in 2021, and is entering flight trials on commercial routes with Mokulele Airlines in Hawaii this year.
Airbus is set to debut its hybrid-electric airplane, the E-Fan X, next year. In engineering the prototype, the company replaced the aircraft’s four jet engines with a massive 2MW electric motor.
Then, there are all the electric vertical takeoff and landing (eVTOL) aircraft currently in development. These small air taxis are intended for urban transit so they don’t have the same energy requirements that an electric Boeing 737 would have. Joby Aviation, Ehang, Lilium, and Volocopter are all startups working on bringing eVTOL aircraft to market within the decade.
It’s possible that scientists will discover a new battery chemistry that packs the energetic punch a typical commercial airplane requires for cross-country travel, but don’t bet on it. Chances are you’ll sooner hop on an electric flying taxi to take that next weekend getaway – it might sounds futuristic, but it’s more likely than you think.