Compressed Air Energy Storage - CAES
It is not immediately obvious that energy can be stored by the compression of a gas. However this can be illustrated for example when inflating a balloon. A small wind turbine could be operated with the airflow and venting of air power, where the tension of the rubber helps in addition. It would therefore be a logical next step to compress a gas such as for example air in large cavities, and thereby storing energy. To compress the gas a compressor is required. The compressors require power which can be delivered through either solar panels or wind turbines or both.
Large caverns can be built in geological formations of salt. Such salt caverns are being used in FRG for the storage of petroleum and natural gas. The storage of natural gas takes place at pressures of about 250 bar, the caverns are located at depths of 1000 to 2000 m and have a geometrical volume of approximately 500,000 to several million m3. The entire volume of gas storage in salt caverns in Germany is 14 billion standard cubic meters  which corresponds to a geometrical volume of approx. 70 million m3, where an average storage pressure was assumed by 180 bar. "Pressure energy stored" corresponds to approximately 350 TWh, it should be noted that also the energy stored in the cushion gas is included in the afore mentioned number. Cushion gas is the gas portion that is required for the process but due to technical constraints, such as minimum allowed pressure, these cannot contribute to the stored active inventory.For comparison, the net electricity generation, i.e. the current that actually comes out of the socket, amounted in 2016 to 548 TWh . These figures show that with an appropriate technology, the existing potential of cavern storage can provide a massive contribution to the energy revolution.