Thermodynamic assessment of cryogenic energy storage (CES) systems in cogeneration regime

This article demonstrates that Cryogenic Energy Storage (CES) systems benefit from a high round-trip efficiency, applying cogeneration concepts to the charging and discharging operating regimes. CES systems are an emerging technology that can mitigate the power grid instabilities in an adverse scenario of high penetration of intermittent sources. We evaluate this novel concept using mass, energy, and exergy balances. We perform numerical simulations and find that the specific liquid yield is 21.4% higher than that reported for other CES systems. The optimization analysis shows that the exergy efficiency is as high as 85.2% whereas the base CES, with no cogeneration, is 50.3%. For the integrated charging and discharging processes, the round-trip efficiency is 41.9%, for the cryogenic tank capacity of 200 t, which is higher than that reported in the previous studies. The optimum values of electrical efficiency and exergy density of the proposed cycle operating in the discharging regime are 81.0% and 123.7 kWh/m³, respectively. In general, the simultaneous operation of the charging and discharging phases in the proposed CES cogeneration system improves the main indexes and indicators. Readers can also benefit from a novel exergy methodology to estimate the efficiency of CES systems.