Effect of Aspect Ratio of Heliostat on Cost of Energy from Solar Power Tower Plants

The solar power tower plant consists of thousands of heliostats, and heliostat field cost contributes nearly 40-50% of the total plant cost. This makes the cost of heliostat an important parameter while designing solar power tower plant, and it varies considerably with its size and wind loads. Furthermore, the size and aspect ratio of heliostat have a significant influence on the wind loads impacting its load-bearing components. While the importance of optimum size of reflector area has been studied by several researchers, its aspect ratio (width/height) has not been examined in detail. In this view, the main objective of this study is to identify the appropriate aspect ratio of a heliostat's reflector area. An analysis of heliostat cost using its reflector area and the aspect ratio as variable parameters illustrates that heliostat cost per unit area can be minimized by distributing costs into various categories having different cost dependencies on area as well as aspect ratio. Using the component-wise cost break-up of 148 m(2) Advanced Thermal Systems' heliostat as a reference, optimum area and aspect ratio of heliostat are determined parametrically. Further, a hypothetical power tower plant with 50 MW capacity and 6 h of thermal energy storage is simulated with heliostat fields comprising heliostats built with various aspect ratios and corresponding optimum reflector area. The results indicate that it is not only more economical to build heliostats with aspect ratio of around 2, but also such heliostat fields deliver higher optical efficiency on an annualized basis.