Delbrueck's move from the utility, which was spun out from E.ON in a 2016 stock market listing, follows a string of high-profile hires at Munich-based Lilium, which has raised more than $100 million in two funding rounds so far.

"Obviously to build mass production of the Lilium Jet, further financing at some point will be needed," Delbrueck told Reuters.

Lilium, founded in 2015 by four graduates from the Technical University of Munich, is working on a prototype aircraft powered by 36 electric jet engines mounted on its wings via 12 movable flaps.

It still needs to win certification that its air taxis are safe, and then plans to launch commercial production.

The aircraft would have a range of up to 300 km (186 miles) and a cruising velocity of 300 km/h. It is designed to take off and land vertically, and carries a 'whole-aircraft' parachute as an additional safety feature.

The company, backed by investors Atomico, Tencent, LGT and Obvious Ventures, aims to launch commercial air taxi services by 2025.

It would offer Uber-style rides on demand to people who want, for example, to beat city traffic to get to the airport.

(Reporting by Douglas Busvine; Editing by Ludwig Burger and Jan Harvey)