A transient global model was used to obtain the solution of a thermal field within the entire furnace during a unidirectional solidification process for photovoltaics. The melt-solid interface shape was obtained by a dynamic interface tracking method. The thermal stress distribution in the silicon ingot was solved using the displacement-based thermo-elastic stress model. Furthermore, several different melt-solid interface shapes were obtained by using different growth velocities, and then the thermal stresses for different solidification times were compared. The simulation results suggested that the crucible constraint should be reduced and a longer solidification time should be used for growing a silicon ingot with low thermal stress and low dislocation density. (C) 2008 Elsevier B.V. All rights reserved.