Determination of key parameters for sizing the heliostat field and thermal energy storage in solar tower power plants

The optimal sizing of the solar tower power plant with thermal energy storage is critical for increasing the system reliability and reducing the investment cost. However, the combined effects of key design parameters for sizing the solar tower power plants, including design direct normal irradiance, solar multiple and thermal storage hours, on the thermo-economic system performance under different solar resources are still unclear. In this study, a thermo-economic model for a 50 MW solar tower power plant based on steam Rankine cycle with molten salt storage has been developed to explore the optimal combinations of these parameters at four sites in China. The coupled relationship between these parameters and their effects on the annual electricity generation, solar-to-electricity efficiency and levelized cost of energy have been identified. The results show that the optimal design direct normal irradiance for minimal levelized cost of energy depends on both the annual irradiation level and the distribution of solar irradiance, which differs from the recommended values obtained from the traditional methods. It is found that the irradiation received by heliostats at the optimal design condition accounts for a specific percentage (Le., 72-75%) of the annual irradiation for the cases in this study. The sensitive analysis by varying the main financial parameters indicates that the optimal design direct normal irradiance and the corresponding percentage slightly vary with the heliostat cost. The results can provide a theoretical reference for determining the optimal size of the heliostat field and thermal energy storage for solar tower power systems under different solar resources.