Renewable energy storage in geological formations

Abstract

With the transition to renewable energies and, above all, strongly fluctuating electricity from wind and solar energy, there will be a need for energy storage in the future. For central grid-scale storages, underground geological storage, similar to those already used for fossil fuels, is in the first place under review. Compressed Air Energy Storages have already been successfully used to provide minutes to hours reserve. For storage capacities in the day to week range, storage is required on a chemical rather than a mechanical basis, through either the conversion of electricity into pure hydrogen (H 2) or the generation of mixtures of natural gas and synthetic methane. The latter-the so-called power-togas optionallows the use of the existing gas infrastructure. A likely first choice for the storage of H 2 or H 2-SNG mixtures are man-made salt caverns. The suitability of porous rock storage (depleted hydrocarbon reservoirs or water-bearing reservoirs-aquifers) is still under investigation. Interest in porous rock storage options arises, inter alia, from the fact that many regions of Europe lack suitable salt deposits. Favorable salt deposits exist in the UK, notably in the Cheshire Basin to the west and in eastern England, with six salt cavern-hosted facilities operated as natural gas storages. In any case, underground gas storages are characterized by high safety and low environmental impact.

Estimating available salt volume for potential CAES development: A case study using the Northwich Halite of the Cheshire Basin

“…The Triassic Northwich Halite Member (NwH), is the main sequence of bedded halite widely exploited for brine production and rock salt, and is the host to recently constructed solution-mined gas storage caverns in the Cheshire Basin (Figures 2&3; [6,28,29,30]). The operational gas storage facilities demonstrate the capability of large caverns (~50 m radius and up to 130 m in height) in the halite beds to store gas at high pressure.…”

“…The operational gas storage facilities demonstrate the capability of large caverns (~50 m radius and up to 130 m in height) in the halite beds to store gas at high pressure. Further gas storage caverns are planned at King Street [31] and immediately south of Stublach at the Keuper Gas Storage site (Table 2; Figure 2; [6,32,33,34]).…”

“…Underground geological storage can be through the use of: salt caverns [6] (see below); porous rock, either depleted hydrocarbon fields or aquifers, e.g. the aquifer tests at Sesta in Italy [7,8] and Pittsfield and Iowa, both in the US [9,10,11,12]; abandoned mines/purposely mined voids e.g.…”

“…These operational plants demonstrate that CAES is viable in solutionmined underground salt caverns, either constructed specifically for compressed air storage, or which remain following cessation of brining operations. In the UK, one CAES plant is currently being planned using salt caverns constructed some 1500 m below ground at Islandmagee, near Larne in Northern Ireland (Figures 1 & 2; [6,23,24,25]).…”

Mechanical Systems for Energy Storage – Scale and Environmental Issues. Pumped Hydroelectric and Compressed Air Energy Storage

“…They are not only stable for very long periods of time, but halite is gas tight with no cavern pressure losses over often extended periods of storage (months), and are also inert with respect to liquid and gaseous hydrocarbons, as well as to oxygen and hydrogen. 171 Salt caverns are constructed by a process known as solution-mining: water is pumped via cased boreholes into salt deposits deep underground, dissolving the salt to create a cavity and brine as a by-product. The brine is extracted, with the process continuing until the cavern is the required size and shape.…”