"Besides the increasing market share of monocrystalline cells with their higher efficiencies, the rapid spread of diamond wire saws will considerably drive down the specific silicon consumption per watt," says Johannes Bernreuter, head of Bernreuter Research and author of the Polysilicon Market Outlook 2020.

Compared with traditional wire saws, which work with a slurry of silicon carbide particles wetting the wire, diamond wire saws allow not only a higher throughput and lower costs in wafer production, but also the use of a thinner wire. While the technical limit of slurry-based wire saws lies at a wire thickness of 100 micrometers (µm), diamond wire can be as thin as 60 µm and thus reduce the kerf loss significantly.

Diamond wire saws have already gained a large market share in the production of monocrystalline wafers, which have consequently become more competitive against the multicrystalline variant. In addition, LONGi Green Energy Technology, the largest manufacturer of monocrystalline wafers, is pushing monocrystalline technology with a massive expansion of its production capacity. Hence, Bernreuter Research assumes that the market share of monocrystalline wafers will rise from 27% in 2016 to 47% in 2020.

The increasing competition has forced the multicrystalline sector to solve the technical problem that has so far prevented the use of diamond wire for sawing multicrystalline wafers: Their surface becomes so smooth that it cannot be textured with the standard acidic etching solution. Meanwhile, the equipment manufacturers Schmid, RENA and RCT Solutions offer adapted etching processes using a metal catalyst or other additives, which are able to texture diamond-wire-cut multicrystalline wafers. GCL-Poly, the world’s largest manufacturer of multicrystalline wafers, as well as the big integrated solar module producers, such as Jinko and Canadian Solar, have already begun to switch from slurry-based to diamond wire saws. "Experts estimate that the transition will take four or five years for the whole industry," says Bernreuter. "Therefore, we expect that more than 90% of multicrystalline wafers will be sawn by diamond wire in 2020."

Even when using far more conservative assumptions, Bernreuter Research calculates an average silicon consumption of 4 g/W for 2020. Analyst Bernreuter warns that "the polysilicon industry has to prepare for the fact that demand is slowing down on two fronts: The annual growth rate of global photovoltaic installations is decreasing, and the polysilicon consumption for each new gigawatt installed in 2020 will be only half as much as it was in 2010."