Evaluation and assessment of gravity load on mirror shape and focusing quality of parabolic trough solar mirrors using finite-element analysis

Constructional design and stiffness of the support structure significantly determine characteristic and magnitude of deformation. Resulting rms values of the sagged mirror panels are as high as SDx = 1.7 mrad and FDx = 6.3 mm (inner mirror, elastic case) and SDx = 1.1 mrad and FDx = 5.6 mm (outer mirror, cantilever case). Depending on the type of support structure, minimum and maximum values occur at different collector angles. Rms slope and focus deviation values are closer to the 0° (zenith) collector angle case than to the non-deformed (ideal) mirror shape. This leads to optimizing the mirror shape for 0° (zenith) collector angle. Different support structures in design and stiffness for shape accuracy assessment in laboratory and those used in the collector make it difficult to find one optimum shape for all types of mirror and collector.