Analysis of low‐temperature pumped thermal energy storage systems based on a transcritical CO₂ charging process

Abstract

Pumped thermal energy storage (PTES) is a technology for intermediate storage of electrical energy in the form of thermal energy. In this work, PTES systems based on a transcritical CO2 charging process are investigated. A two‐zone water storage tank with a storage temperature of 115°C is used as thermal energy storage. For discharge, an Organic Rankine Cycle (ORC) and, alternatively, a transcritical CO2 heat engine are investigated. The considered concepts are modelled and simulated as stationary processes using the EBSILON Professional software. The scaling is based on an electrical input power of 5 MW. Using an ORC with the working fluid R1234yf for the discharging process results in the highest round‐trip efficiency of 36.8%. The component costs of the different configurations are estimated using cost functions. On the basis of this, the levelized cost of storage (LCOS) is calculated. The configuration with the ORC as the discharging process has the lowest LCOS of 59.2 €cents (kWh)−1. In addition, the technological maturity is determined using the technology readiness level scale. There are no prototypes of the investigated PTES systems yet. Therefore, further investigations must be carried out to implement the technology in the future.

Thermodynamic, Economic and Maturity Analysis of a Carnot Battery with a Two-Zone Water Thermal Energy Storage for Different Working Fluids

“…Bodner et al [11] investigated a transcritical process with CO 2 as the working medium in combination with a subcritical process with R1234yf as the working medium. A two-zone storage system was used.…”

“…The presented literature evaluated the concepts based on their round-trip efficiencies. While a few studies also investigated economic aspects in more detail [9,[11][12][13], the others did not examine costs closely [6,7], or costs were not part of their research [4,5,8,10]. Only the study of Bodner et al [11] considered the technology readiness level (TRL) as a measure to evaluate the corresponding systems.…”

“…While a few studies also investigated economic aspects in more detail [9,[11][12][13], the others did not examine costs closely [6,7], or costs were not part of their research [4,5,8,10]. Only the study of Bodner et al [11] considered the technology readiness level (TRL) as a measure to evaluate the corresponding systems. To take economic and practical questions into account, this study determines the LCOE and the TRL in addition to the round-trip efficiency for each promising configuration.…”