There's some important information missing from this article. How much methane was in the mixture? By what calculation is the density of Hydrogen 40kwh/kg? Sh

There's some important information missing from this article. How much methane was in the mixture? By what calculation is the density of Hydrogen 40kwh/kg? Shouldn't that be closer to 33kwh? 17 kWhr/kg of electricity per kg is a pretty great number, but impossible to know if that's a real improvement without knowing how much methane had to go in to it too.