Latitude- and temperature-based optimization of beam-down solar central receiver systems

Optical and energetic characteristics are studied for beam-down solar central receiver (SCR) systems. The geometrical configuration of the beam-down SCR system is optimized for maximum solar-to-thermal conversion efficiency, taking into account the effects of latitude and receiver temperature. System characterization and optimization are undertaken with a numerical model combining an in-house developed Monte-Carlo ray tracing optical model and a simplified receiver heat transfer model. A differential evolution (DE) algorithm is applied to automate the optimization process. Parallel computing using OpenMP is employed to reduce the computational time. From the simulations, the optimized optical configurations of the beam-down SCR systems under the specified conditions of receiver temperature and latitude are discovered. Under the assumptions made in this study, it is found that the acquired radiative power at the receiver aperture from the optimized systems ranges from about 35 MW to 45  MW, and the eccentricity of the hyperboloidal tower reflector is between 1.6 and 1.7. The maximum achievable solar-to-thermal conversion efficiency decreases from 0.43 to 0.36 when an SCR system operated at 1,800 K is moved from latitude 0° to 50°, mainly due to the increased cosine and shading losses with higher latitudes. In addition to reduced efficiencies, the heliostat field gets larger for higher latitudes, worsening its techno-economic performance when considering the cost per unit of useful energy output. A clear trend of efficiency decrease with the higher receiver temperature is demonstrated, resulting from the significant increase of receiver radiative emission losses with the temperature.