Dynamic Modelling of a Brayton PTES System

Abstract

Abstract The need for storage capacity is continuously increasing due to the progressive penetration of renewable energy sources in the power grids. New storage technologies for large-scale applications are emerging in this context, among which Pumped Thermal Electricity Storage (PTES) is a promising alternative. PTES is based on closed Brayton cycles: a Brayton heat pump is operated in the charging phase, using the off-peak electricity to transfer heat between two reservoirs. A Brayton heat engine is operated between the same reservoirs in the discharging phase, producing electric energy. The purpose of grid-scale storage facilities is to provide flexibility to the grid. Therefore, the proposed technologies must effectively operate in part-load conditions and quickly react when the load must be adjusted. In this study, the transient response of the Brayton PTES technology is studied, with particular emphasis on its off-design operation and control strategy. To this end, a detailed thermodynamic model of the system is developed. Particular attention is given to the sizing of the components relevant to the control. Furthermore, a control strategy suited for the power regulation of closed Brayton cycles, the Inventory Control, is investigated, and implementation is proposed. As it resulted, the system can operate in part-load with negligible performance degradation and is characterized by a rapid transient response. Therefore, Brayton PTES resulted as a promising storage technology for grid-scale applications.