Comparison of FC systems with solar cells at the sides or at the back as sketched in Figures 1b and 1c. (a) Systems at collector length l = 10d. Without PBS side-mounted solar cells provide slightly higher collection probabilities for 10^-3 < f < 4 × 10^-1. Applying PBS eliminates the difference in collection probability p_c for high coverage fractions. Both systems achieve approximately p_c = 1 for coverage fractions f ≈ 1. For coverage fractions f < 10^-2 mounting solar cells at the FC back side is of slight advantage. (b) Systems at collector length l = 100d. Mounting solar cells at collector sides leads to higher collection probabilities for all cases. Compared to Figure 7a, the side-mounted system obtains the same values. Therefore, this system works still in the small-scale limit, whereas for this collector length the bottom-mounted system is already in the transition regime to the large-scale limit which is also shown in Figure 5.