Increasing electricity production by solar and wind energy is projected to impact the stability of electricity grids and consequently may limit the growth of renewable electricity generation. This issue can be ameliorated in part by increasing the flexibility of baseload power plants. A thermodynamic analysis of thermal energy storage (TES) coupled with a nuclear-powered Rankine cycle as one approach of increasing baseload flexibility is presented. During periods of excess capacity, the high-pressure steam supply is used to charge the TES. When electricity generation above the baseload capacity is required, the TES is discharged to generate steam for expansion in the low-pressure turbine. Pressure, temperature, and enthalpy state points within the cycle are presented over a range of charge and discharge rates. The capacity factor over a charge/discharge cycle is up to 9.8% higher than that of the same plant operated with steam bypass. This benefit increases with increasing charge and discharge power. With TES, the thermal-to-electrical efficiency is stable over a wide range of discharge rates. The results support future development of TES systems for baseload thermal power plants in a power grid in which renewable energy is prioritized.
- Capacity factor