The relevance of energy storages for an autarky of electricity supply ...

they have large capacities and react slowly on discharge rates. Depending on the size
of the geological structure, physical conditions and depth such storages can have
capacities between hundred cubic meters and some billion cubic meter – around half
of it can be discharged. The maximum pressure for these storages are 60 – 80 bar.
Aquifer storage is considered to be the most cost effective. (Neupert, 2009;
Rummich, 2009; Alamri, 2009)
Cavern storage
Caverns are big natural or artificial underground holes, which are used to store
natural gas or liquid hydrocarbon. Artificial caverns in rock salt are most common, as
they do not need any further sealing. Water is pumped into it, which transports the
natural brine to the surface. Nowadays it is possible to reach a depth of 3000 m, a
diameter of 60 – 100 m, heights of some hundreds of meters and a volume of about
800,000 m 3 . Liquids or liquid gas is filled into it and the brine is pumped out from
the basement. Due to the low specific weight, liquid hydrocarbons are always on top
of the brine and do not undermine the salt dome. To discharge the liquid, again brine
is pumped into the cavern. To store gas, the natural brine is first pumped out
completely. Afterwards the gas is pumped into it under certain pressure. To
discharge gas, the overpressure in the cavern is used. Contrary to the pore-space
storage, the pressure in the cavern is changing with the filling level. As the salty
walls of the caverns are also leak-proof for gas, no losses occur. The maximum
pressure depends on the depth of the storage and can be higher than the hydrostatic
head. Nevertheless, it should not exceed the rock pressure at the given depth. Holes
from the mining industry are usable for liquids or liquid gas. (Neupert, 2009;
Rummich, 2009)
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