Optimum Small-Scale Open and Direct Solar Thermal Brayton Cycle for Pretoria, South Africa

The open and direct solar thermal Brayton cycle is exposed to various weather conditions like changing solar irradiation, wind and surrounding temperature. The geometries of the receiver and recuperator and the turbine operating point as parameter can be optimised in such a way that they accommodate these weather changes and allow for high net power output throughout a typical year. In this paper, a method of obtaining these parameters based on total entropy generation minimisation is presented. A parabolic dish concentrator with a diameter of 4.8 m is used as well as an off-the-shelf turbo-machine. Results show that the net absorbed power at the receiver and maximum allowed receiver surface temperature play important roles in determining the optimum operating point and maximum net power output.