The Carnot batteries thermally assisted by the steam extracted from thermal power plants: A thermodynamic analysis and performance evaluation

Extending the operating range of thermal power plants and promoting the application of large-scale electricity storage facilities are feasible ways to accommodate renewable power. This work proposes and evaluates the Carnot batteries thermally assisted by the steam extracted from thermal power plants for (1) improving the round-trip efficiency of energy storage and (2) reducing the minimum load of thermal power plants. Four critical and fundamental issues of such a coupling are investigated considering the detailed off-design characteristics of a case coal-fired power plant: (1) the energy conversion characteristics of the integrated system; (2) the capabilities for energy storage, carbon reduction, and renewable power accommodation; (3) the effects of the variation in the integrated capacity of Carnot battery and the load of power plant; and (4) the steam source selection strategy. As the results show, under the different minimum loads of design, (1) the ability for renewable power accommodation can be improved by 12.4–34.4 MW; (2) the round-trip efficiency of the Carnot battery can be improved to 59.39–114.67% with the cost of a slight reduction in power generation efficiency; (3) the integrated Carnot battery’s exergy efficiency is increased by 52.84–67.31% compared to the standalone but still low. In a 24-hour operation case study, 1.26% of CO2 emissions (47.51 tons) can be reduced and 164.94 MWh of excess renewable power can be accommodated. Moreover, integrating lower-pressure steam has a slight advantage in accommodating renewable power; however, the carbon reduction benefit is not significant due to the lower round-trip efficiency.