CLEAN ENERGY - Any fuel is just as clean as it was produced
The infrastructure to produce our fuel begins with harvesting renewable energy by wind turbines in regions with good wind resources such as Ireland and the Netherlands as well as solar power plants (especially Concentrated Solar Power) in regions with high sun radiation such as Morocco or Uruguay as well as the Asian countries. For Switzerland (i.e. Basel - Rotterdam) I could also imagine using hydro power plants.
The technical progress and reliability in wind and solar power technology is enormous last couple of years and they are already proven in various large-scale projects - 'ready to buy'. It is technically feasible and becomes now financial attractive as well to produce primary renewable energy for electrolysis instead of using excess energy only as the renewable power plants become cheaper and more various every day. Nowadays, we can produce cheaper electricity by wind power plants than we do by coal/gas or even nuclear power plants.
POWER TRANSFORMATION - GASIFICATION
For the 'short-term' project idea in the beginning, more or less fix routes due to our 'fix' hydrogen infrastructure such as Ireland - Netherland - Morocco, Rotterdam - Basel, Hongkong - San Francisco or Hamburg - Montevideo could be necessary. For a slightly higher price, also 'floating' wind turbines are ready to buy, enabling production of own fuel in all the seven seas.
A century old technology to produce hydrogen by splitting up water molecules which is called 'electrolysis' that is nowadays a pretty advanced technology and is 'ready to buy'.
The hydrogen can be stored compressed at low, medium or high pressure ranging from 20 to several hundred bar and all kind of pressure vessels are ready to buy with safety certification.
Hydrogen can also be liquefied. That liquefaction process can take up to a third of the contained energy, but the total amount of energy the ship could carry in cryogenic tanks would be considerably more. Also this technology is proven and 'ready to buy'.