Pumped heat energy storage with liquid media: Thermodynamic assessment by a Brayton-like model. (15th December 2020)

• Record Type: Journal Article
• Authors: Salomone-González, D.; González-Ayala, J.; Medina, A.; Roco, J.M.M.; Curto-Risso, P.L.; Calvo Hernández, A.
• Is Part Of: Energy conversion and management. Volume 226(2020)
• Publication Date: 2020-12-15
• Subjects: Energy storage -- Molten salts -- Coupled Brayton model -- Round trip efficiency -- Internal and external irreversibilities; Direct energy conversion -- Periodicals; Energy storage -- Periodicals; Energy transfer -- Periodicals; Énergie -- Conversion directe -- Périodiques; Direct energy conversion; Periodicals; 621.3105
• DOI: 10.1016/j.enconman.2020.113540
• Languages: English
• ISSNs: 0196-8904

Abstract

Abstract: A thermodynamic model for a steady state pumped heat energy storage in liquid media is presented: it comprises a coupled Brayton-like heat pump and heat engine cycles connected to a cryogenic liquid and a hot molten salt by counter-flow heat exchangers. The model considers non-isothermal heat transfers between the working fluid and the liquid media and explicitly includes a set of parameters accounting for the main internal and external losses, heat leak, and pinch point effects for both the heat pump (charge) and heat engine (discharge) modes. Specific expressions for the main magnitudes in the charge (as the input power and coefficient of performance) and discharge (as power output and efficiency) modes and the global round trip efficiency have been analytically derived in terms of isentropic efficiencies of the compressor and turbine, pressure losses in the heat exchange processes, effectivenesses of the external counter-flow heat exchangers, and coupling between the working fluid and the storage and cryogenic liquid media. Round trip efficiencies around of 35 − 40 % have been obtained, internal losses being those with main negative influence on the calculated values. The strong constraints imposed by the pinch point effects and liquid media have been analyzed. The model provides a thermodynamic assessment of the main involved processes and their interplay for a selected arrangement (molten salts, cryogenic fluid, and the charge and discharge power blocks) in order to check parametric strategies for thermodynamic optimization and design. These strategies are based on a reduced set of parameters of the overall installation and without the high computational costs of dynamical models. Highlights: Irreversibility effects in pumped thermal energy storage in liquid media. Efficiency limitations from molten salts and cryogenic fluid temperatures. The pinch point constraints strongly the achievable round-trip efficiencies. Not all molten salts allow for maximum efficiency/power operation regimes. Round-trip efficiencies around of 35%–40% are obtained.