(a) Collection probabilities p_c for photons derived with a Monte-Carlo simulation for a side- and a bottom-mounted system in the statistical limit and with applied PBS. (b) Symbol-lines are the values for the concentration c_p derived from p_c in (a). Solid lines show the analytically calculated c_p(f) from equation (22). Side-mounted system shows less agreement between the analytically and the numerically derived concentration because photons entering the system close to a solar cell are absorbed with a higher probability. This leads to an inhomogeneous chemical potential μ for the incoming photons which violates the assumptions for the calculation. But, the approach μ =  const. is a good approximation in the statistical limit for the bottom-mounted solar cells [27].