For electric aircraft, the battery is at the core. The problem is that once you go beyond light aircraft, batteries are no match for jet fuel, which has 50 times the power density of today’s batteries. This means that both fully electric and hybrid-electric propulsion will not be viable anytime soon for large, long-range aircraft, according to Tim White, Collins Aerospace president for power and controls. “Electric propulsion trades more favorably for smaller aircraft.”
For example, all-electric propulsion for a 12-passenger aircraft flying a 500-nm mission would require battery power density capability to improve by a factor of approximately six times, says White. “We expect this to continue to improve, since so many companies are investing in battery research and development,” he says. “In fact, current projections show the power density of batteries improving by a factor of three times over the next 10 years.”
Lithium-ion provides the highest gravimetric and volumetric densities available today, reports Nikhil Sachdeva, a senior consultant at aerospace consultancy Roland Berger.
“The technology has improved rapidly over recent years due to investment by automotive players to develop electric vehicles (EV),” he says. “Future production of EVs is also expected to lead to continued advancement in technology, improvement in densities and reductions in cost.”
Sachdeva adds that today, the best-in-class Li-ion batteries can achieve upward of 300 Wh/kg, which is possibly enough for small aircraft. “Our estimates suggest a regional aircraft would need a battery with a gravimetric density of 500 Wh/kg at the pack level to achieve a range comparable to today’s levels.”
MTU states that if battery-storage capacity continues to improve, smaller, short-range regional aircraft, powered by electric engines could enter service in about 30 years. For a limited-range, single-aisle aircraft the size of an Airbus A320, battery energy capacity of over 2 kWh/kg will be required, along with motors based on high-temperature semiconductors. Currently, battery energy density is about 0.25 kWh/kg, although the potential is there to increase density to 1 kWh/kg, based on laboratory-scale concepts, MTU says.