Ray-tracing and Variation of Parameters

In order to carry out investigations and to describe an established collector we developed an input mask in which all relevant geometrical and material data can be entered. A macro is generated from this information that completely describes the collector and that can be executed by OptiCAD.

For instance, different types of CPC-reflectors can be easily generated just by entering the designated half acceptance angle and the reflector arc length in such a parametrical model. Every other parameter of the reflector geometry such as angle of truncation, concentration ratio and height of the reflector are automatically determined. For more information on CPC-collectors, see [2] and [3].

The next step after fixing the geometrical and optical properties of the different collector components is to define the simulation mode. Simulations in the transversal or longitudinal plane are possible or also for all other angles (3D-IAM).

Two different alternatives exist for the determination of the IAM-values over the hemisphere (3D — IAM):

image312Either, the simulation can be carried out in polar coordinates (0 — theta, ф — phi) or in the projections of the incident angle (0t — theta_t, 0l — theta_l). The latter are used e. g. in different solar simulation programs such as TRNSYS. Figure 3 shows the angle conventions for the projected incidence angles theta_t and theta_l of solar radiation incident from an optional direction.

Transversal

Подпись: Fig. 3. Projected angles of incidence in the longitudinal and transversal plane [4]

Longitudinal

Direction

When OptiCAD is started, the macro which also contains the description of the ray-tracing calculation is imported and executed. The interpretation of results (e. g. plot of 3D-IAM) happens automatically within the file of the input mask. Thus, it is assured that simulation settings and the output of a simulation as well as the analysis of results are documented together in one file.