An overview of simulation models in use for optimizing the edge-defined film-fed growth (EFG) process of thin-walled hollow silicon tubes at WACKER SCHOTT Solar is presented. The simulations span the length scales from complete furnace models over growth simulations with a mesoscopic description of the crystalline character of silicon down to solidification simulations with atomic resolution. Results gained from one model are used as input parameters or boundary conditions on other levels. Examples for the application of these models and their impact on process design are given. These include the reduction of tube thickness variations, the control of tube deformations, residual stresses and dislocation densities and the identification of twin formation processes typical for EFG silicon. (C) 2009 Elsevier B.V. All rights reserved.