Where are the current locations of operational CAES sites?
There are currently two grid-scale CAES facilities in operation: Huntorf CAES, constructed in 1978 in Germany as well as McIntosh CAES, constructed in Alabama in 1991. There are also several commercial CAES demonstration projects either in operation or under construction.
What is the difference between traditional CAES and G-CAES?
G-CAES is an adiabatic CAES technology, meaning no additional energy must be added the the system. In a traditional diabatic CAES system, heat must be added in the form of natural gas.
Isn't CAES passé? If it is so great, why have I not heard about it in discussions of energy storage?
Diabatic CAES is a relatively old technology that has largely stuck to the background. Most of the money spent on energy storage R&D gone to much more in-vogue technologies such as batteries and flywheels and a lack of recent CAES projects have pushed it to the periphery of the discussion.
Why would someone looking to incorporate energy storage into their electricity system choose G-CAES over batteries?
There are multiple battery technologies out there, but they all have their problems. Lithium-ion batteries typically have a poor energy:power ratio alongside persistent issues due to state-of-charge limits, end-of-life costs, and system degradation over time. Flow batteries have an inverse linear relationship between open circuit voltage and state-of-charge meaning that round-trip-efficiency depends on state-of-charge. G-CAES has an exceptionally good energy:power ratio making it excel at long duration energy storage, does not need components replaced regularly like lithium-ion batteries, has consistent charge and discharge rates, boasts full depth-of-charge capabilities, performance degradation similar to a gas turbine system, and perhaps most importantly a far lower capital cost than similar duration batteries.