An incidence angle modifier test was performed on December 9, 2006. The desired incidence angles are achieved by adjusting the azimuth angle of the collector. Table 1 summarizes the sequences of testing conditions and the corresponding measured efficiencies. The efficiency as a function of incidence angle is plotted in Figure 1. Figure 2 shows the incidence angle modifier with respect to the incidence angle and Figure 3 shows the incidence angle modifier as a linear function of the term [ -1 + 1 / cos(incidence angle) ]. The incidence angle modifier coefficient, b0, is estimated to be 0.179 based on the measurements. The test results are not in accordance with ASHRAE 93-2003, as the test conditions were not maintained within the allowed range over the required time period of 20 minutes. The test should be repeated if possible.