Off-Design Analysis of a TES-Based Electricity Energy Storage System

Abstract

Carnot battery is considered one of the most promising technologies for large-scale electricity storage. Among the available configurations, the so-called Integrated Energy Storage System (I-ESS) developed by the University of Padova research group allows the use of components of unused gas turbine power generation units for storage purposes. In particular, during low-demand hours, the electricity generated in surplus by, e.g., wind and solar, is used in an electric heater to heat up the air sucked by a fan. When air passes through the tank composed of a packed bed of solid material, it heats the bed itself. Therefore, excess electricity is stored as sensible heat in the storage material. Air then leaves the tank and is released into the atmosphere. During peak demand hours, the heat stored in the packed bed is extracted and converted again into electricity using a modified gas turbine in which the combustion chamber is bypassed and replaced by the storage tank. Having established that the I-ESS configuration can compete with the other large-scale storage technologies, the focus of this work is on the I-ESS off-design performance during the discharge phase. An investigation that still lacks in the literature. To predict the behaviour of the plant in part-load, the characteristic curves of the turbine and the compressor are implemented into the mathematical model of the I-ESS. In this way, the influence of key parameters such as pressure ratio, turbine inlet temperature, and generated power is analysed for the different state of discharge of the tank. The parameter that most affects the discharge time is the temperature of the tank. In fact, for a temperature of 1200 K, the total discharge time is up to 35 h. The discharge efficiency reaches 25.3%.