Large multicrystalline silicon ingots, up to 69 cm square cross section weighing 240 kg have been produced using the Heat Exchanger Method (HEM). These ingots are produced by adaptation of a single-crystal growth process - HEM -so that controlled directional solidification can be carried out at low cost. Growth is achieved from the bottom of the crucible to the top, with a planar solid-liquid interface. Control is exercised up to the top corners of a square cross-section silicon ingot. During solidification the ambient is controlled to yield low oxygen and carbon concentrations. After solidification is complete, the ingot is in situ annealed to reduce residual stress and produce uniform properties. From loading to unloading, the cycle time is about 56 hours.

HEM multicrystalline silicon ingots can be used for many high technology applications. For solar cell applications, HEM silicon is characterized by long diffusion length, cm-size grains, vertical orientation of columnar grain boundaries, low oxygen concentrations and narrow resistivity range. The structural and electrical properties are uniform from top to bottom and center to edges of the ingot.

In research during investigation for potential of HEM silicon for photovoltaic applications, the world's highest efficiency multicrystalline silicon solar cells -18.6% (1 cm² area) - were fabricated by Georgia Institute of Technology. HEM silicon is compatible with various solar cell processing techniques. High efficiency solar cells have been fabricated worldwide.