In order to fly a number of single rotor units join up with one another to form a viable aircraft. Individually the units are unable to fly but this changes when they join up and co-operate in order to fulfill their mission.
More details - and videos - can be found here.
Invinity to build 20MWh flow battery in UK
A surprising comment for someone who (I think you´ve said in the past) worked in the industry. National Grid have a variety of reserve service schemes...