In the experimental setup, 11W PL lamp [28] was used as a light source. The choice of this kind of lamp depends on the fact that the light it gives off resembles sunlight and the radiated heat amount is fairly low; thus it almost does not increase the cell temperature. This PL lamp was placed in the focus of a parabolic reflector which was located at the bottom of an opaque case. The stainless steel reflector was curved so as to reflect the light from the light source to the solar module in parallel (Figure 2). The opal glass used for diffusing the parallel reflected light was mounted on top of the case, just beneath the cover, whereas the solar module was placed on the inner cover.The areas to bemeasured were located on the glass so as that they would be in between this glass and the solar module when the cover was closed (Figure 3).