Of course those inefficiencies multiply. You generate hydrogen at 30/40% efficiency. You generate methane from that at a similar efficiency. Then you compress i

Of course those inefficiencies multiply. You generate hydrogen at 30/40% efficiency. You generate methane from that at a similar efficiency. Then you compress it ... which takes energy. You ship it around. Which takes energy. Then you burn it at 40% efficiency. Numbers rounded up here. Real world efficiencies are worse. Multiply all of that and you end up with efficiencies of a few percent. Nice that it can be done at great cost but there are a lot of things that are probably more efficient and cheaper.