You have got this wrong.
By "diesel electric" you are referring to a power system that has a generator, an electrical power line, and a remote motor. The reason why they do this is to avoid the mechanical engineering involved in coupling a big motor to a big prop. Also, the generator serves a power for the ship also, BUT IT IS RUNNING ALL THE TIME!!!! Diesel electric trains do it too, and for reasons of coupling also, particularly with multiple drive wheels on the loco.
What they are referring to is... and I quote...
"Picture yourself in pristine lagoons and allow the power of the sun, tides and wind to replenish your cruising. Motor away from distant fuel docks of unknown diesel quality without bating an eye. Remove your portion from our oil burden while silently cruising into distant harbors. Live the Solidnav shift, change your world. "
This is charging a battery, then running constant loss on the battery, and no-doubt having to compete with the sort of energy delivery I calculated.
Is that what you mean by "diesel electric"? ...because that is not what ships have and not what trains have.
Where does the energy I describe come from?... does anyone plan to store even a fraction of that in a battery bank???. How far would you get before you have to start the diesel to drive the prop. When you do, you would be much better to save energy a-plenty by joining the prop to the motor by a shaft and dump the generator, cabling, and motor.
There is just not enough energy stored in the battery bank, this side of sanity.
For a submarine submerged it can work for a while... another type of "diesel-electric"... but have you ever seen the battery bank on one of those beasts?