Power-to-hydrogen is often attacked for being inefficient, but the alternative presented by the anti-hydrogen people for dealing with seasonal variations and long dark-calm periods is to just overbuild solar and wind massively -- in which case, most of the time power from these is just being curtailed. Apparently using this excess power with 0% efficiency is preferable to using it with nonzero efficiency making hydrogen.
The issue is that hydrogen makes no sense except for transportation fuel, where it also makes no sense. There are other options for stationary energy storage, and hydrogen is amongst the worst. i.e. if we can tolerate high losses, iron-air flow batteries are a much more reasonable option[1]
The thing is you pay for all of that pretty heavily - it's all more expensive with other drawbacks, but it's not nearly the complete pain that handling hydrogen is.
For long term energy storage, minimizing the capital cost of energy storage capacity is paramount. Round trip efficiency is not.
On that relevant metric, hydrogen is very hard to beat, particularly if proper geology is available (salt formations for solution mined storage cavities). Costs less than $1/kWh are possible.
Artificially heated geothermal may be competitive on that metric, but its RTE is likely to be even lower.
Yup, or things like sulphur thermal storage[1]. Also, hydrogen is pushed heavily by the fossil fuel industry, as it will provide another out for all their methane reserves (via steam reforming).
