Zero-dimensional model of a pumped heat energy storage system with reciprocating machines

• Published in: Applied energy 2024-10, Vol.372, p.123764, Article 123764
• Main Authors: Wener, Natalia, Martinez-Boggio, Santiago, Favre, Federico, Curto-Risso, Pedro
• Format: Article
• Language: English
• Subjects: Energy storage; Heat transfer; Reciprocating machines; Renewable energy
• ISSN: 0306-2619
• DOI: 10.1016/j.apenergy.2024.123764

The technology of Pumped Heat Energy Storage allows for the storage of large amounts of electrical energy, which is currently crucial due to the worldwide use of renewable energy sources (intrinsic and highly variable). In these systems, electrical energy is used to feed a heat pump cycle (charging phase) that exchanges heat with two thermal reservoirs, storing part of the input energy in the form of thermal energy. This energy is then supplied to the grid through a power cycle (discharging phase) when needed. This article presents a zero-dimensional model of a Pumped Heat Energy Storage system that uses a numerical zero-dimensional model for the reciprocating machines and an analytical model for the heat exchangers. By feeding the model with the operating point data (rotational speed of the reciprocating machines, pressure at a point in the system, fluid temperatures in the reservoirs, and mass flows of the thermal fluids circulating through the heat exchangers) and the geometric dimensions of all the machines, the steady-state evolution of the system can be obtained as result and also the powers of the reciprocating machines and heat exchanged with the thermal reservoirs, circulating mass flow of the working fluid, inlet and outlet temperatures and pressures of each machine, and the round-trip efficiency of a certain configuration, among others. Evaluating the coupling of the machines in a particular setup an overall efficiency of around 36% was calculated for the condition with the maximum local performance coefficient. Analysing the dependency between the stages of charge and discharge an operating condition that improved this value up to an efficiency of approximately 40% was obtained. Both values are conditioned for the use of molten salt, particularly its high melting temperature, which imposes higher temperatures at the expander inlet thus decreasing the overall efficiency of the system. •Advanced Modelling for PHES: Zero-dimensional model for comprehensive analysis.•Tailored Efficiency Analysis: Precise efficiencies for system configurations.•Optimal Operation Insights: Beyond COP for higher system efficiency.•Renewable Energy Integration: Valuable insights for sustainable energy systems.