Hi Groucho,
I guess it works by having a combustion engine that only needs to develop the power equivalent of MCT. The electric motor + battery + combustion engine would only need produce take off thrust for up to say 10 mins.
How much electrical power is required
260 kW.
where could it be generated?
by the combustion engine.
See
Rolls-Royce Marine Olympus - Wikipedia, the free encyclopedia
RR Gas turbine Olympus and Tyne engines are commonly used to generate electricity on ships.