6 Incidence angle modifier IAM
The Incidence angle modifier IAM is a correction factor representing how
the angel of radiation affects the performance of a collector. The IAM is
described by a longitudinal and a transversal component.
IAM longitudinal:
The tilt angle of the collector in combination with the zenith angle of the sun
results in the incident angle theta (=Θ) in longtitudinal direction.

IAM transversal:
The orientation angle of the collector in combination with the azimuth angle
of the sun results in the incident angle theta (=Θ) in transversal direction.
The transversal measurement was performed dynamically, what means
that the orientation of the tracker was fixed, just the tilt angle was tracked.
So the sun is turning around the collector and there is no longitudinal
influence (transversal at the present collector means transversal to the
ligament of the cover). The incident angle is changing during the day. The
resulting values for the incident angle Θ are the mean values between the
east and the west measurement.
For the measurement of the IAM longitudinal the orientation and the tilt
angle of the tracker were tracked, which means a steady state
measurement.
　　　　 Test method: 　　　　outdoor
　　　　 transversal:　　　　　 dynamic
　　　　 longitudinal:　　　　 steady state
　　　　 Latitude: 　　　　　　48.0o
　　　　 Longitude: 　　　　　7.8o
　　　　 Collector tilt: 　　　　tracked
　　　　 Collector azimuth:　　 tracked
IAM at 　:　　　 0o 　　10o 　　20o 　30o　　 40o　　 50o　　 60o　 　70o　 73o　 80o　 90o
transversal: 　1.00 　　1.00 　1.02 　1.10　 1.22 　　1.37　 1.42 　1.27 　1.42 　0.93 　0.05
longitudinal: 　1.00 　　1.00 　1.00 　1.00 　1.00　　0.96　 0.91 　0.79 　0.94 　0.53 　0.00
Table 2: Measured (bold) and calculated IAM data for SPA-58-1800-18-C