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.

The rising share of renewable energies leads to increased fluctuations in electrical power supply. One possibility to shift the surplus energy based on demand is a Carnot battery (CB). A CB uses a heat pump or resistance heater to convert and store thermal energy into electrical energy. Later, the stored thermal energy is converted back into electrical energy using a heat engine. This study investigates a CB with a two-zone tank for thermal energy storage. A transcritical process with ${\mathrm{CO}}_2$ is applied for charging, while discharging employs a transcritical process with ${\mathrm{CO}}_2$ and six refrigerants operating in a subcritical process. The transcritical process with ${\mathrm{CO}}_2$ and the four most promising subcritical processes are compared regarding round trip efficiency and levelized cost of electricity (LCOE) depending on the pinch points 5 K and 1 K in the heat exchangers. Additionally, the technology readiness level (TRL) is determined for these configurations. The results show round-trip efficiencies between 11.3% and 33.5% and LCOEs ranging from EUR 0.95 ${\left(\mathrm{kWh}\right)}^{-1}$ to EUR 2.09 ${\left(\mathrm{kWh}\right)}^{-1}$ for the considered concepts with TRLs of up to six.