Adding Carnot battery functionality to combined-cycle gas turbine power and cogeneration plants

This study assesses how combined-cycle gas turbine (CCGT) plants, especially in combined heat and power (CHP) operation, can be retrofitted as Carnot batteries by integrating high temperature power-to-heat (P2H) unit and thermal energy storage (TES) between the gas turbine (GT) and the steam bottoming cycle. A generic dual-pressure CCGT-CHP configuration with an optional duct burner is modelled with added packed bed TES concept (igneous gravel, ≈600 °C hot side), electric heaters and integrating air loop. The concept leverages the existing heat recovery steam generator (HRSG) for TES discharge, minimizing the added technology and costs. The study therefore extends previous power-only CCGT storage concepts by combining HRSG reuse with a systematic CCGT-CHP multi-mode analysis. A comprehensive matrix of operating modes is constructed to quantify electricity, heat, and CHP efficiencies across GT-only, GT + TES charging, electric charging, TES-only discharge, and hybrid GT + TES discharge operation. For the reference case (≈50 MW e GT; ≈79 MW e CCGT), the complete electrically charged P2H2P pathway reaches 33% electrical round-trip efficiency, whereas CHP-oriented discharge reaches near-complete (>95%) first-law utilization of stored heat as power and delivered useful heat. Sizing is shown for nominal 12 h full discharge duty and ≈1%/day heat loss. A module-costing based estimate indicates a retrofit CAPEX on the order of $6–16 M depending on electric heater power and storage duration, with indicative unit costs of ≈41 $/kWh e for pure P2H2P operation ≈14 $/kWh for CHP operation.