Please read my other reply published nearby: we are not embarked into an efficiency race. Efficiency (of any renewable-source based system) is a mean, not an end.

As for efficiency: https://www.vicat.com/news/vicat-schlumberger-new-energy-cea...

https://www.sciencedirect.com/science/article/pii/S187661021...

> Salt cavern storage doesn’t change the math

"Total on- and offshore European hydrogen storage potential estimated at 84.8 PWhH2." is pretty significant and pertinent.