How the World Really Works: A Scientist’s Guide to Our Past, Present and Future

by Vaclav Smil

How soon will we fly intercontinentally on a wide-body jet powered by batteries? News headlines assure us that the future of flight is electric—touchingly ignoring the huge gap between the energy density of kerosene burned by turbofans and today’s best lithium-ion (Li-ion) batteries that would be on board these hypothetically electric planes. Turbofan engines powering jetliners burn fuel whose energy density is 46 megajoules per kilogram (that’s nearly 12,000 watt-hours per kilogram), converting chemical to thermal and kinetic energy—while today’s best Li-ion batteries supply less than 300 Wh/kg, more than a 40-fold difference.79 Admittedly, electric motors are roughly twice as efficient energy converters as gas turbines, and hence the effective density gap is “only” about 20-fold. But during the past 30 years the maximum energy density of batteries has roughly tripled, and even if we were to triple that again densities would still be well below 3,000 Wh/kg in 2050—falling far short of taking a wide-body plane from New York to Tokyo or from Paris to Singapore, something we have been doing daily for decades with kerosene-fueled Boeings and Airbuses.