**4. Conclusions**

This paper presents the state-of-the-art of cryogenic energy storage with regards to air liquefaction processes, thermodynamic parameters and cold storage configurations. Six air liquefaction processes within the charge unit of CES were investigated and results obtained from the exergy-based analysis were compared. The effect of cold storage integration on different liquefaction processes was firstly quantified.


**Author Contributions:** Conceptualization, investigation and data curation, S.H.; methodology, G.T.; software and validation, S.H. and F.M.; formal analysis, S.H. and T.M.; writing—original draft preparation, S.H.; writing—review and editing, T.M. and G.T.; supervision, T.M.; project administration, T.M.

**Funding:** Sarah Hamdy acknowledges the financial support of the Federal Ministry of Education and Research (BMBF—Bundesministerium für Bildung und Forschung) under the Transnational Education project (ID 57128418) of the German Academic Exchange Service (DAAD).

**Conflicts of Interest:** The authors declare no conflict of interest.
