The light flux distribution at the focus of the primary parabolic mirror was mainly determined by its focal distance and by its rim angle. The accurate alignment of the primary parabolic mirror was considered essential for achieving the minimum focus spot. Since the focused on-axis and the defocused performances of a concentrator gave different flux distributions9, the primary mirror was accurately aligned in order to obtain minimum light spot at the focus. Under these conditions, a detailed map of the light distribution was generated by a small aperture (1.0mm) radiometer scanned across the focal plane. Detailed results on and off the focus were obtained. A typical flux distribution at the focal plane of the primary concentrator is given in Fig.2.

The average solar insolation at the scan time was 800W/m2. A near-Gaussian type distribution was obtained, with the maximum solar flux being 25.6W/mm2. Based on the flux distribution at the focal plane, the total solar power of 1258W was calculated which matched well with experimental measurement.