&gt; Currently some companys consider, forging giant conrete containers, sink them out in the ocean, and pump them dry when there is a energy surplus.<p>Compressed Air Energy Storage (CAES) is nothing new per se. CAES plants have been operational in Huntorf, Germany, since the late 1970s and in McIntosh, Alabama, since the late 1990s.<p>The problem with current technology CAES is that it is not energy-efficient (around 30% for the existing installations, though there&#x27;s room for improvement) and not carbon-neutral. The underlying problem is that compressing air generates heat, which is then dissipated; however, that means that during decompression, the air has to be reheated, usually with natural gas.<p>There are currently projects underway with both Adiabatic [1] and Isothermal [2] CAES to improve efficiency and make the process carbon-neutral. Google &quot;SustainX&quot; and &quot;ADELE RWE&quot; for examples of current projects.<p>[1] <a href="http:&#x2F;&#x2F;energystorage.org&#x2F;advanced-adiabatic-compressed-air-energy-storage-aa-caes" rel="nofollow">http:&#x2F;&#x2F;energystorage.org&#x2F;advanced-adiabatic-compressed-air-e...</a><p>[2] <a href="http:&#x2F;&#x2F;energystorage.org&#x2F;energy-storage&#x2F;technologies&#x2F;isothermal-caes" rel="nofollow">http:&#x2F;&#x2F;energystorage.org&#x2F;energy-storage&#x2F;technologies&#x2F;isother...</a>