Performance of a rectangular secondary concentrator with an asymmetric heliostat field

Secondary concentrators with non-regular cross section have been proposed to permit additional degrees of freedom in heliostat field design, free of the limitations imposed by conventional rotationally symmetric concentrators. A new class of concentrators with a rectangular cross section was found by numerical optimization for heliostat fields having an elliptic contour with high eccentricity. An example of such a rectangular concentrator was constructed and tested at the Weizmann Institute, where the heliostat field has a strong asymmetry and is poorly suited for symmetric (having regular cross section) concentrators. The performance of the new concentrator has been tested using calorimetric and radiometric measurements. The tests were carried out for several heliostats, located in representative positions relative to the predicted acceptance contours of the concentrator. The results of the tests show an agreement with the prediction, and validate the new design for use with highly eccentric fields. A more general conclusion is the validation of the approach of optimizing faceted secondary concentrators with flexible geometry to match heliostat fields having a wide range of possible contours.