In this contribution, we analyze factors determining the magnitude of the persistent photoconductivity (PPC) effect, defined as a difference in the hole concentration after and before illumination. Based on the Lany-Zunger model, we derive the equation describing the magnitude of the PPC with only two parameters: the density of (V-se-V-cu) complexes and the relaxed hole concentration. We apply the derived equation to the experimental data measured on Cu(In,Ga)Se-2 solar cells with and without sodium. We demonstrate that significant differences in the PPC can be explained in some cases by differences in the relaxed hole concentration. Furthermore, we show that deep defect levels situated close to the Fermi level can also substantially influence the magnitude of the PPC. (C) 2016 Elsevier B.V. All rights reserved.