On Analyzing the Optical Performance of Solar Central Tower Systems on Hillsides Using Biomimetic Spiral Distribution

The optical performance of solar central tower (CT) systems on hillsides of mountain areas is investigated based on the biomimetic spiral heliostat field distribution algorithm. The optical efficiencies and the field characteristics of different hillside solar field configurations are examined. The effect of various geometric parameters such as hillside tilt angle and the location of the receiver on the optical efficiency of the field are investigated and documented. The study is based on generating a 25 MW_th power plant at the location of Sierra Sun Tower in California, USA, using Planta Solar 10 (PS10) heliostats' parameters. This study is performed numerically using a specially developed code using matlab software. The biomimetic spiral distribution pattern and the particle swarm optimization (PSO) method were used to obtain optimum solar fields. The spiral distribution shape factors were optimized for pursuing maximum annual weighted field efficiency. It is found that the annual optical weighted field efficiency for hillside solar fields is always lower than that for a flat field for same receiver height. On the other hand, the field land area for small hillside-slopes is smaller than that of a flat field area. It is found that there is an optimum field tilt angle where the land area is minimum. The minimum field area for the system studied in this paper was associated with (15 deg) field tilt angle. Furthermore, it was found that as the tower height increases the annual optical field weighted efficiency increases until it reaches a peak value. It was also found that, the closer the tower to the beginning of the heliostat field, the higher the field efficiency with less number of heliostats and less land area.