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About Solar Power

One of the main costs solar cells production, in terms of both economics and environment, is the silicon feedstock.

Rice hulls conversion to Solar Silicon. In a three-step process, rice hulls were purified and then converted into upgraded metallurgical silicon suitable for ingot production using directional solidification and solar-grade wafers. Pilot production of this new solar cell feedstock has successfully demonstrated solar cell efficiencies comparable to high purity polysilicon produced by conventional means.

  • The rice hulls contains about 20% amorphous silica (SiO2) with the balance being lignin, a structural organic polymer. Some twenty years ago, early efforts were first made to examine rice hulls as a high purity feedstock for producing improved metallurgical-grade silicon in a modified carbon-arc furnace.
  • In recent work, rice hulls were pulverized and leached in a proprietary mixture specifically designed to both convert and sequester heavy metals and other contaminants before the rice hulls were subjected to reaction in an advanced carbon-arc furnace. The furnace was designed with certain advanced pyrometallurgical features, such as gas blowing to assist in the successful reaction to upgraded metallurgical silicon (UMG-Si).

In the first case of particle reduction, the pulverized hulls were reduced to 5-20 microns. In the second case, the particles were reduced further to a sub-micron particle size in a similar but more vigorous process typically using similar ball mills along with and extended vortex-aided pulverization. The two sets of different particle size groups were then leached and sequestered to help eliminate the hard-to-remove contaminants such as phosphorous and boron. From the results of these different groups, it is clear from these data that the particle size does have a significant effect on the ability of the sequestering solution to remove contaminants.

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