Beside the collection efficiency, other optical characteristics have been monitored to evidence how much they are affected by geometrical deformations of the solar trough profile. The second study combines the consequences of mirror deformations with misalignment and tracking errors.

The crucial optical features to be considered in examining alignment and sun tracking are angular misalignment and acceptance angle of the solar trough collector.

The angular misalignment is simulated tilting the solar trough, with a rigid rotation of parabolic mirror and absorber around the axis of parabolic vertexes. Analogously to the previous study, the parameters defining the solar trough layout are: f=780mm, D=50mm, G=70mm, T=2mm. Figures 4-5 show parabolic mirror profile and circular absorber section, whose centre is located in the parabola focus. Figure 5 illustrates the rigid rotation of parabolic mirror and absorber, for a tilt angle of 1.1°. For rotation in the right direction, the collected light impinges on the left portion of the metal pipe, instead of being symmetrically distributed as shown in Fig. 4, corresponding to tilt angle 0°.

The effect of collector angular misalignment is assessed considering the collection efficiency E (ratio between focused and entering light). The behaviour of collection efficiency is reported in Fig. 6, for misalignment angles in the range (-1.5°; 1.5°). The absorber centre is located in the focal point of parabolic mirror. The curve evidences that the collection efficiency almost maintains its maximum value between -1.1° and 1.1° for the solar trough under test. This limit angle represents the acceptance angle of the solar trough collector: significant energy losses will appear for angular misalignments exceeding the acceptance angle 1.1° (in Fig. 5).

Since the consequences of angular misalignment depend on the geometrical parameters of solar collector, this second study proceeds combining the angular misalignment effects with the mirror deformations effects.