In two words: It's not.
A lot of websites are showing images of a 367-foot-long hydrogen powered superyacht, calling it "eco-conscious." In the press release, designer Sander Sinot says, "Our challenge was to implement fully operational liquid hydrogen and fuel cells in a true superyacht that is not only groundbreaking in technology, but also in design and esthetics."
AQUA is fueled by hydrogen, a unique concept which represents a significant progression towards achieving a new balance between nature and technology. The system is based on the use of liquified hydrogen, stored at -253°C in two 28-ton vacuum isolated tanks.
The liquified hydrogen is converted into electrical energy by proton exchange membrane (PEM) fuel cells, with water being the only by-product. All parameters in terms of output, system layout, range and physical dimensions where translated to a complete hydrogen / electric based system.
There are, of course, a number of problems with this, the first being that hydrogen is not a green fuel if it is made via steam reformation of natural gas, which 96 percent of the world's hydrogen is right now. Or the question about the upfront carbon emissions that come from building a yacht this size, both of which appear to be ignored by those calling this boat eco-conscious.
But also overlooked is the energy required to make liquid hydrogen. It has to be compressed to 13 times the earth's atmosphere and then cooled to 21 degrees Kelvin, or -421 degrees Fahrenheit. It takes a lot of energy to run the compressors; Praxis, a manufacturer of Liquid Hydrogen, says it take 15 kWh of electricity to make a kilogram of the stuff.
Hydrogen contains 142 megajoules of energy per kilogram; that's 39.44 kWh. So just making it liquid takes up 40 percent of its energy. And that doesn't count the energy required to make the hydrogen from natural gas (because almost nobody is making it through electrolysis) or the losses from storage (about one percent per day). About the only thing that makes less sense than running a boat on hydrogen is running it on liquid hydrogen.
It is pretty, though.