I am trying to figure out what the actual efficiency of solid state hydrogen storage is. So how many kg of hydrogen can you store in a Xcm3 of metal hybride solid state storage. I was trying to find a conversion and only found a metric that was 500NL in a specific device that had some dimensions. Or if anybody knows of good practical solutions that I could refer to, much appreciated. Basically I a trying to find how much volume a 4kg (of hydrogen) solid state storage solution would take? Application is a car. I'm trying to convert an old Audi A2 into a lion + hydrogen. Yes still in the early drawing board, but I have the car.