So lets see: To produce 1kg of Hydrogen by electrolysis
takes 180-200MJ of energy using the best known techniques.
The resulting hydrogen has a calorific value of 141.8MJ
Taking the hydrogen (and oxygen) and running it through a fuel cell
has a practical efficiency of ~36%. Citation: https://en.wikipedia.org/wiki/Fuel_cell#In_practice
Dang, sounding a lot like an ICE....
So overall efficiency is (141.8*0.36)/190 =26.8%
We are missing parts
of the puzzle though. Seawater is hardly a good electrolyte, so one would first have to do reverse osmosis
then make up a suitable electrolyte, manage the condition of the anode and cathode. Find a way to reliably separate hydrogen and oxygen, compress both gasses into storage tanks
which would have to be large if pressures are not to be excessive. Then you need all the unobtanium - the fuel cell which is generally loaded with a lot of platinum
It just seems like it would be much more practical to drive the propulsion
motors directly using PV panels
and use excess to charge good quality batteries which can run the motors overnight, possibly at reduced power. If you consumed diesel overnight with the batteries adding to available power one would still achieve very good efficiency, especially in northern climates where heat recovery from the genny can provide the heating
needed for the interior
, hot water
etc. In this scenario one could maintain cruise
speed through the night. So put a lot of miles under the keel
every 24 hours.
Originally Posted by Chotu
Depending on the efficiency, it would be really cool to have a huge hydrogen tank and make H2 from sea water via wasted solar
Imagine large arrays on Catamaranís being put to full use making hydrogen for propulsion after they met house demands.
A big tank could be slowly filled and then used when needed.