Four Ways to Store Large Quantities of Hydrogen

Hydrogen can be stored in underground caverns or geological structures in one of four ways. The easiest way to store hydrogen is in salt caverns. These are created by injecting fresh water or water with low salt content into a well down to a salt geological layer, with the extraction of salt-saturated brine. The caverns measure between 50 and 100 metres in diameter and up to several hundred meters tall where the salt formation is thick enough. Salt caverns are not lined, as the salt itself acts as a sealant. This type of storage is suitable for storing hydrogen at extremely high pressures where the salt layer is deep enough. The second way to store large quantities of hydrogen is to inject pure hydrogen or a hydrogen-methane mix into porous rock, in a depleted oil or gas field, or an aquifer. The hydrogen content may vary from a few per cent to 100 per cent. Reservoir and biochemical testing/modelling are to be performed accordingly. The hydrogen-methane mix can be withdrawn and injected into the network. Alternatively, hydrogen can be separated from methane at the well head, for example using pressure swing adsorption technology. Hydrogen can also be stored underground by converting it into a liquid carrier, such as ammonia, which can then be stored in a Lined Rock Cavern. A liner is required to prevent contact between ammonia and water. The pressure and temperature are adapted to optimise the entire supply chain. The advantage of using ammonia is that proper storage conditions can be fulfilled without the need for excessive pressure or temperature. Lastly, hydrogen can be stored underground by directly injecting it into a Lined Rock Cavern. This may take the form of compressed storage (gaseous hydrogen) or cryogenic storage (liquid hydrogen), the choice once again depending on the supply chain as a whole. A liner is required owing to extremely high pressures or extremely low temperatures. It should be noted that storing hydrogen in a Lined Rock Cavern involves a few technical difficulties that have yet to be resolved. These four underground hydrogen storage techniques differ in terms of their technology readiness level (TRL) and cost. All four will likely be required in the coming years to satisfy the needs of a booming market.

Parametric Study of a Long-Duration Energy Storage Using Pumped-Hydro and Carbon Dioxide Transcritical Cycles

The urgent energy transition needs a better penetration of renewable energy in the world’s energy mix. The intermittency of renewables requires the use of longer-term storage. The present system uses water displacement, in a lined rock cavern or in an aerial pressurised vessel, as the virtual piston of compressor and expander functions in a carbon dioxide heat pump cycle (HPC) and in an organic transcritical cycle (OTC). Within an impermeable membrane, carbon dioxide is compressed and expanded by filling and emptying pumped-hydro water. Carbon dioxide exchanges heat with two atmospheric thermal storage pits. The hot fluid and ice pits are charged by the HPC when renewable energy becomes available and discharged by the OTC when electricity is needed. A numerical model was built to replicate the system’s losses and to calculate its round-trip efficiency (RTE). A subsequent parametric study highlights key parameters for sizing and optimisation. With an expected RTE of around 70%, this CO2 PHES (pumped-hydro electricity storage) coupled with PTES (pumped thermal energy storage) could become a game-changer by allowing the efficient storage of intermittent renewable energy and by integrating with district heating and cooling networks, as required by cities and industry in the future.

Hydrogen Permeability of Epoxy Composites as Liners in Lined Rock Caverns—Experimental Study

Energy production from renewable energy sources is not stable and any fluctuations in energy productions need to be eliminated with underground energy storage. Demand of underground gas storage will be increasing, due to the switching to green energy, while the availability of underground storage sites, especially salt caverns suitable for hydrogen storage, is limited. The purpose of this paper is to compare the hydrogen permeability of different materials and select a proper liner material for hydrogen storage in Liner Rock Caverns or post mine workings. A variety of materials, like concrete, polymer concrete, epoxy resin, salt rock, and mudstone, were tested for gas permeability/hydrogen diffusion, using the combined Steady-State Flow/Carrier Gas methods. Results are shown in different units, providing the opportunity to compare the results with literature data. The permeability value of investigated epoxy resin is comparable to the salt rock (after creep process), which makes the epoxy resin a promising sealing liner for hydrogen and potential substitution of stainless-steel in Lined Rock Cavern (LRC) gas storage.

Geochemical monitoring of deionized seawater injected underground during construction of an LPG rock cavern in Namikata, Japan, for the safety water curtain system

An underground liquified petroleum gas (LPG) storage facility was constructed between 1998 and 2006 in Namikata, Imabari City, Ehime Prefecture, Japan, to increase domestic LPG stockpiles. The most important issue during construction and operation of this facility is gas leakage prevention. To thwart water leakage, the water curtain system was constructed according to design standards, and a large amount of deionized seawater (seal water) was continuously injected into the rock mass around the cavern to keep the water level constant during both construction and operation. It is possible to distinguish three end member waters (existing groundwater, seawater or fossil seawater, and seal water) using the salinity and isotope (δ18O) difference because seal water injected underground has almost the same δ18O value as seawater. In this study, continuous observation is carried out using the geochemical techniques for flow analysis with a mixing ratio of three end members in the initial construction period (April 2005 to March 2006) of the LPG underground storage facility. It is determined that existing groundwater and seawater originally distributed in this region are partly replaced by seal water in the cavern.