Operation strategy of the heliostat field and receiver based on categorization of DNI fluctuation types

Transient changes in receiver heat are due to Direct Normal Irradiance (DNI) fluctuations, requiring operational strategies for receiver safety in cloudy weather. The effects of different operational strategies on the outlet temperature of molten salt and the tube wall temperature change rate were conducted by a 3D model. A strategy with heliostat field defocusing is recommended during long-time high fluctuations and moderate fluctuations with high dispersion. Under conditions of long-time moderate fluctuations with moderate and low dispersion and long-time low fluctuations, the rated outlet temperature set at 565 °C can meet the need. However, it is necessary to increase the molten salt flow before and after DNI ≤ 300 W/m² to avoid too fast tube temperature change rate. According to the coefficient of variation (CV) during short-time DNI fluctuation, the strategy of heliostat defocusing (CV less than 50%) or rated outlet temperature (CV more than 50%) can be chosen. Combining the solar power tower (SPT) system model and cost model, the thermodynamic performance and economic analysis for systems with and without operational strategies were studied. With the operational strategy, the electricity generation was reduced by 3.39% compared to systems without any strategy. However, the lifetime of the receiver was increased, resulting in a 2.17% reduction in the Levelized Cost of Energy (LCOE).