To enhance the flexibility of coal-fired power plants

this paper proposes a Carnot battery system retrofit based on a coal-fired power plant. The optimal system configuration is clarified using evaluation criteria of equivalent round-trip efficiency and output power change ratio. System performance and investment of the feasible configurations are explored under different scales of power storage. Finally

the thermodynamic differences with the extracted steam thermal storage integrated electric heater are explored. Results show that the two configurations with live steam or exhaust steam as the low-temperature heat source and the stored heat used to heat the feedwater to generate live or reheat steam are the most promising. The equivalent round-trip efficiency of those two configurations can reach 67.29%~67.77% and 62.03%~ 63.27%

respectively. When the extracted steam mass flow rate ranges from 0~103.8 t/h

the output power change ratio is -30.30%~20.58% and -52.69%~33.30%

respectively. Investment costs are separately 17 598.4 million yuan and 20 461.5 million yuan at zero output power of the power plant. The extracted steam thermal storage integrated electric heater is limited by the pinch point temperature and molten salt solidification temperature

and the equivalent round-trip efficiency is 55.22%

which are lower than the SE1-C1 configuration.