Design, construction, and qualification of a lightweight, modular heliostat made from high-performance concrete

With regard to climate change and the importance of utilization of solar energy, the development of a modular concrete heliostat is presented. The focus thereby lies on the design and the construction of the concentrator structure, demonstrating the technical proof of concept for a small-scale collector. The idea of using concrete as a structural material is its free shapeability, and its worldwide availability. With respect to accuracy demands, a high-performance concrete (HPC) is used that possesses a high compressive and also tensile strength. The collector is designed as a strut-like structure with main radial beams and a central mount to ensure high stiffness. A circular design minimizes shading effects in the solar field. By employing symmetry reduction methods, the concentrator is dissolved into equal segments making it a modular construction. To demonstrate the feasibility, a prototype with diameter 3.2 m and a weight of just about 340 kg consisting of four modules was developed. The production is achieved using a modular formwork made from polystyrene at the RPTU Kaiserslautern. The concrete heliostat is built-up and qualified at the solar tower Jülich (Germany) by means of photogrammetric measurement of the mirror surface. In addition, the concrete structure was measured in the lab of the Ruhr University Bochum. The deformations of the concrete structure vary mainly in the range of $\pm 1$  mm only indicating remarkable stiffness. In contrast, the mirror deformations reveal an optical efficiency of $SDrms=7.8$  mrad. However, these deformations are primarily attributed to the simple mirroring concept by means of clamping, which was not the central subject of the development. However, deviations between varying collector positions are less than 2 mm and only occur in local areas of single mirror facets, which additionally underlines the stiffness of the concrete structure.