Design Of Compliant Heliostats For Solar Power Tower System

Solar energy is an important, renewable energy. Solar power tower technologyuses its heliostats to collect and concentrate solar thermal energy whose applicationsincluding electricity generation, chemical engineering, and fuel synthesis. Concentratorsystem is the key part which constitutes40-50%of the plant’s overall capital. Currentlyit has the problem with low-precision heliostats which introduces optical spillage andthermal loss, and limits the converting efficiency. Hence, this dissertation investigatesnew design methodology to achieve low-cost, high performance compliant heliostat.The ideal heliostat shape is solved analytically to be adaptive off-axis paraboloidsas a function of the sun incidence angle and mirror location. A compliant mechanismapproach is proposed to implement the shapes. This approach tailors the stiffness of theflat mirrors permitting simple concentrated moments to form the off-axis paraboloidshapes. This approach was tested through simulations and experiments.Location-based shape optimization is proposed for the heliostat system to improvethe performance at a low cost. The optimization comprises finite element analysis,optical ray-tracing, and Newton’s method for optimize annual average efficiency. Theresults show that the proposed method has the RMS slope error of0.453mrad for a100m×200m field. Simulation shows substantial efficiency improvement on asolar power tower system with a volumetric air receiver and a gas turbine.The deformation of the compliant heliostat by gravity and wind is modeledanalytically and numerically. The results indicate the relationship between thedeformation and the mirror thickness, thickness ratio, and material properties. Materialswith high Young’s modulus-density ratio and Young’s modulus could benefit themechanism to reduce the gravity and wind deflection respectively.A100mm heliostat prototype with a scale ratio of1:10is designed andmanufactured. Shape measurement experiment shows the improvement of the designover the flat mirror and uniform stiffness mirror. The solar concentrating experimentshows the proposed design could reduce spot area by45.5%compared to the flat mirror.