Lined hard rock cavern storage

Lined hard rock caverns are artificial structures consisting of caverns created in metamorphic or igneous rock in geographical areas where salt or depleted fields cannot be exploited. The caverns are lined with a layer of concrete to create smooth walls, which are then lined with steel. Because they are carefully lined, hard rock caverns have no risk of contamination and can be operated at higher pressures than other structures, but steel embrittlement due to hydrogen exposure must be avoided. Hard rock caverns can experience several injection and withdrawal cycles per year, making them well suited for peak load purposes. They require relatively little cushion gas, but are expensive to develop. The construction process is mature, such as rock excavation, but the development of hydrogen-resistant liners and leak-free connections is challenging. Compared to salt caverns or depleted fields, rock caverns are developed at shallower depths (up to several hundred metres) and require shallow basement rock, which is not always available.