The move to production of green ammonia using hydrogen produced from renewable energy raises the need to manage a variable production of hydrogen with a demand that has traditionally been constant 24/7. Whilst ammonia plants have some ability to ramp production rates, there are limits to this and any operation at reduced capacity will mean that their annualized cost recovery must be amortised over reduced production. Thus there is an apparent need for buffer storage corresponding to one or two days of hydrogen feedstock. This talk will introduce a new approach to underground storage of hydrogen that is being commercialized by www.ardentunderground.com . It involves the adaptation of blind bore shaft drilling from the mining industry to produce modular lined rock caverns. Diameters of 3 to 5 m and depths down to 500m offer the potential for high pressure storage of 50t or more per shaft, with multiple shafts offered larger capacity.