Cast multicrystalline silicon ingots are widely used in photovoltaic manufacturing. A key issue to achieving high solar cell efficiencies is attaining an optimized temperature profile during ingot fabrication in order to control the formation of extended defects such as grain boundaries, sub-grain boundaries and dislocations. Numerical simulation is a powerful tool to help understand and depict the temperature distribution inside the growth furnace and to allow tailoring of the growth conditions to achieve high quality with a minimum of defects. Two major types of casting furnaces, direct solidification system and heat exchange method system, will be compared from the aspects of thermal field, crystal quality and related numerical simulations. (C) 2007 Elsevier B.V. All rights reserved.