An alternative sequence of operation for Pumped-Hydro Compressed Air Energy Storage (PH-CAES) systems

In a previous publication, entitled “Experimental study of a PH-CAES system: Proof of concept”, we presented results of an innovative solution for energy storage that uses only air and water as working fluids, named PH-CAES (Pumped-Hydro Compressed Air Energy Storage). Differently from a conventional CAES that operates with air turbines and air compressors, the PH-CAES uses a pump to compress water against air, and a hydraulic turbine to generate power. In the time of the aforementioned publication, it was possible to see that with a suitable thermodynamic cycle the PH-CAES could reach a high round-trip efficiency. Since then, we have worked on this cycle, and in this article we share the progress we have made. We redefined the sequence of charging and discharging aiming to provide constant power output. We present here simulations based on the balance of energy and entropy for transient regime, also used datasheets to simulate the pump characteristics. The maximum round-trip efficiencies were approximately 42%. We show that this is a relatively high round-trip efficiency, when compared to other CAES systems, which usually depend on multiple heat exchangers, burning fuel or an external heat source, validating thus, the technical relevance of the proposed solution.