The results of a simulation are the effective transmittance-absorptance products under the specified angles of incidence and directions. Every particular IAM value of each measuring point of the hemisphere equals the relation of absorbed power under the corresponding incidence angle and direction to the one in case of perpendicular incident radiation.

It should be mentioned that the definition of the IAM as described in EN 12975 is used. This is different to the way as the IAM of concentrating collectors such as parabolic trough collectors is defined, where the IAM is based on the direct normal irradiation (DNI).

Figure 4 shows the simulation results for an evacuated tube collector with ten tubes, each with an outer diameter of 58 mm. The diagram indicates the values of the simulated collector for a quarter of the hemisphere. The values were calculated for incidence directions defined in polar coordinates (0 — theta, ф — phi). The determined 3D-IAM-values then were reassigned to the projected longitudinal and transversal components (0t — theta_t, 0l — theta_l), respectively, in order to depict them more clearly.

There was build a mesh over the simulated points (red globes) seen in Figure 4 to display the 3D — IAM-values. The accuracy of the generated mesh depends on the distance of the simulated points to each other. It is advantageous to use the second possibility to simulate the 3D-IAM, using the projected longitudinal and transversal components (0t — theta_t, 0l — theta_l). It leads to a better resolution and the IAM-values are determined directly in the way as they are needed in TRNSYS. The result of this kind of 3D-simulation is shown in Figure 5.