Is this the face of the future? The Viking Princess which entered service in 2012, was upgraded in 2017 to incorporate a battery power system, which is said to have resulted in a 30% fuel saving. It is a platform ship, so one assumes that when it is out at the offshore installation and maintaining station for cargo work it uses the battery power, since it would be probable that the main engines would be producing more power than would be required. I can see that there might be problems with this approach, but probably they have worked it all out.

Photo taken the other day as the ship was in the channel at Aberdeen and posted here on 3rd May 2019.