Validation of reverse Hartmann test for mirror shape measurement of parabolic trough concentrator

A method for the surface shape qualification of a parabolic trough solar concentrator, based on the reflection of sinusoidal fringes in the mirror surface and their distortions due to the surface deviations from ideal geometry, has been developed. Without complex calibration, accurate surface slope data were collected and reduced by using sixteen-step phase shifting methods. As the gradient data may not be ideally available for the entire surface, surface deviations and geometrical parameters were obtained through Zernike slope polynomials iterative fitting and the Southwell integration algorithm. Additionally, an absolute reference measurement for calibration of the measurement accuracy using three standard mirrors is presented. It is shown that the proposed method can easily test the surface shape and concentration efficiency of a solar concentrator with high slope measurement accuracy (less than 0.05 mrad in the x-direction) and high spatial resolution (more than 2.5 × 10⁶ points per mirror facet).