"Increasing renewable energy systems, while sharing an electric power generation and supply infrastructure, raises the need to develop sufficient energy storage capacity. This is essential to balance fluctuating power feed-in from these inherently variable power sources. Among several options being researched in Northern Germany is adiabatic (no heat exchange) compressed air energy storage in underground salt formations, and especially in naturally formed caverns. These structures, which have an average size of 500,000m3, offer a storage capacity between 2.02–2.73 kWh/m3. Total capacity for adiabatic energy storage in Northern Germany is estimated at 800–2500 GWh. The energy storage efficiency depends on the technology applied and is estimated in the range of 50%–70%. However, there are competing uses for these caverns – underground CO2 capture and the long-term storage of nuclear waste."
--Renewable Energy World, March 12, 2009
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