Videos of Electric and Hybrid electric plane designs from Boeing, EADS and NASA

Technology Review – Boeing has a concept for hybrid airplanes the size of 737s, which can seat more than 150 passengers, although it’s unlikely these will come into service before 2030. EADS, the parent company of Airbus, has also developed a conceptual design for passenger airplanes that fly exclusively on electricity, although the range of these aircraft would be limited.

“A few years ago, the idea of flying an airplane on batteries was a joke,” says Marty Bradley, a principle investigator for advanced aircraft concepts at Boeing Research and Technology. While batteries and electric motors are efficient and quiet, batteries tend to be big and heavy, storing far less energy than liquid fuels.

Two things have changed. The amount of energy that batteries can store is steadily improving, and this looks likely to continue as they’re developed for use in portable electronics and electric vehicles, Bradley says. Meanwhile, the technologies needed to integrate batteries and electric motors with conventional engines are getting smaller, lighter, and more efficient. Siemens demonstrated an earlier version of its hybrid airplane in 2011, but it was too heavy to be practical. For the new plane, Siemens decreased the weight of the electric motor, power electronics, and gears by 100 kilograms to bring its cargo and passenger capacity up to the level of similarly sized small planes.

How fast electric propulsion is adopted depends mostly on the development of the batteries. EADS’s electric airplane plans call for a battery that can store 1,000 watt hours per kilogram, which is about five times more energy than a typical lithium-ion battery. New battery chemistries like lithium-air and lithium-sulfur could provide more capacity.

The lithium/air couple has a theoretical energy density that is close to the limit of what is possible for a battery (~10,000 Wh/kg). Polyplus primary Li/Air technology is nearing commercialization and has already achieved specific energies in excess of 700 Wh/kg (~ 2 Ah cells). Rechargeable Li/Air technology, also based on the protected lithium electrode, is still in development, but is expected to achieve much higher energy density than commercial Li-ion chemistry.

Three examples of the new molten air batteries were demonstrated. These are the iron, carbon and VB2 molten air batteries with respective intrinsic volumetric energy capacities of 10,000, 19,000 and 27,000 Wh/liter. These compare favorably to the intrinsic capacity of the well known lithium air battery (6,200 Wh/liter) due to the latter’s single electron transfer and low density limits.