Re-using Si kerff during cutting and wafering of Si ingots

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After crystallisation, side-, top- and bottom-parts are removed before the ingot is cut into blocks and then wafered. A considerable amount of silicon is lost in form submicron powders (kerf-loss) during the cutting processing of silicon ingots to obtain wafers: up to 50% of starting silicon goes into the coolant used during the sawing of silicon wafers. The ability to recycle the kerf-loss for solar ingot production will have beneficial effect in terms of savings of precious poly-silicon consumption and of waste reduction. Therefore, Garbo has patented and implemented a silicon recycling process which removes contaminations and brings silicon to “five nines” (or 5N), i.e. 99,999% purity. Purified silicon is then dried, compacted and packed under vacuum in order to obtain a stable silicon powder, that however needs to undergo a high temperature oxygen degassing process before being used as feed material in the standard production of solar ingots and cells.

Within Eco-Solar, the consortium will look at 3 factors that will give both environmental and monetary gain: Garbo will look at reducing chemicals consumption in Si kerf cleaning step and improving compact density of powders, while Norsun will carry out sawing tests with increased kerf-loss saturation level in sawing coolant, for Garbo to study if (how) the saturation level in the coolant affects the coolant recycling process and the recycled coolant quality, even if no variations are expected in this respect.

In total, the impact from the innovations could be saving more than 70% of the silicon kerf-loss, which will be assessed by bifa.

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