PUSH-CCC technology as a whole will be validated to TRL4, through the WP4, into the cavern lab, mainly including control and operation tests; thermal loss tests in the process; energy balance tests (for different conditions, control strategies, T & P) with outputs of thermal efficiency of heat exchange processes; volumetric storage capacity efficiency; electrical efficiency of the charge-discharge process. The cavern will be initially fully filled in with compressed air, to make sure no leaks are produced and that the mountain rock structure is perfectly able to withstand the cavern interior pressure with no landslides or damages. To confirm it, an auscultation system will be designed and installed to monitor the structure performance. Once confirmed cavern performance, membrane experiments will take place. The lab will be equipped with thermographic cameras and air composition analysers to try to detect any possible damage to the membrane before it is extracted. Technological targets: i) Average round-trip efficiencies >= 80 %; ii) Levelized cost of storage (cost of input energy 0,1 $/ KWh) <= 150 $/MWh; iii) Cyclability >= 15.000; iv) Very wide geographical availability worldwide; v) 10 kTn CO2 capture from atmospheric air per year for an standard 500 MW plant.