The use of the network simulation method (NSM) for the modeling of thin-film solar modules is discussed. It will be shown that for the accurate modeling of small defects using the NSM, a variable mesh is required to keep the computation time within reasonable limits. A simulation tool for thin-film solar modules is developed that implements the NSM with a variable, adaptive mesh. The results of this model will be compared with electroluminescence experiments on a Cu(In,Ga)Se2 solar module with a defect (shunt). Furthermore, it is demonstrated that the program can handle complex-shaped inhomogeneities such as local variations in solar cell properties, illumination, and contact layer resistance.