Compressed air storage
Large amounts of energy can be stored as compressed air. A principle as simple as pumped storage, if physics were not involved, because compression of a gas generates heat that is difficult to store and reduces storage efficiency. To store one kWh, more than 4 kWh must be used beforehand.
But there is another way. We work with physics instead of against it. With the method we have developed, almost no heat is generated and almost as much energy is stored out as was previously stored in. We achieve a "Roundtrip Efficiency" of more than 70 %.
Our resources are air and holes. The cavities in which the air is stored can be easily produced in the many salt domes in Northern Europe. Often these cavities or caverns already exist and are not used. The chemical industry needs chlorine and produces it from brine, during the extraction of which large caverns have been excavated. Such sites are, for example, Stade on the Lower Elbe and Epe in Westphalia or Zuidwending in the Netherlands.
The many disused potash mines can also be used for the construction of storage caverns. The mines are flooded with water for stabilization. The water could previously be used to sink caverns in the geologically well-explored salt layers.
Cavern construction has been a proven technology since the 1960s. Natural gas is stored in caverns at pressures of about 250 bar, and most of our national petroleum reserve is also stored in salt caverns. The salt rock is tight and impermeable to gas.
The materials used in a compressed air storage facility above ground are steel for pipes and machinery and concrete for foundations and buildings. Many natural gas storage facilities have proven that a life span of over 50 years is possible. Natural gas storage facilities can be reused as compressed air storage facilities and it is also possible to use the highly pressurized natural gas as a storage medium as well.
Existing natural gas caverns can be used to store electricity. In the cavern storage facilities currently existing in Germany, 200 GWh could be stored, or 60 TWh at 300 turnovers per year, which corresponds to a share of about 10 % of yearly electricity consumption.