I'm envisioning submarines just cruising around doing normal things, taking the role of cars, trucks, RVs. I'm trying to estimate how much energy they would need.
https://en.wikipedia.org/wiki/List_of_submarine_classes_in_service leads to a lot of page with specifics on the horsepower and size of various submarines. I'm very surprised by how much energy they use: e.g. the S-80 Plus Class carries 32 people and uses 7400kW (that's 231kW per person!)
Is submarine propulsion (or life-support, or some vital system) inherently really power-hungry? Or is that juice going to weapons-systems etc.?
Food for thought: http://ihpva.org/submersible.htm