Solar Silicon and Savings

The photovoltaics industry continues to show healthy growth, fueled by demand for this form of energy generation and government funding programs available in a growing number of countries. But to sustain this growth the solar industry needs silicon—more accurately, polycrystalline silicon. This substance is in great demand because more than 80 percent of all solar modules are based on thin wafers of solar silicon.

Novel production plant for ultrapure silicon

In collaboration with SolarWorld AG and Joint Solar Silicon (JSSi), the joint venture established by the two partners, Evonik started up a novel production plant with an annual capacity of 850 metric tons at the Rheinfelden site in the Upper Rhine region in 2008. In this way Evonik is contributing toward further increasing the share of alternative energies in power generation—as well as securing a reliable supply of raw material for its partner SolarWorld.

Ultrapure polycrystalline silicon is then transported from Rheinfelden to Freiberg, in Saxony, where SolarWorld employees melt it down and allow it to resolidify into ingots. These are then processed to rods and cut into wafers from which SolarWorld fabricates solar cells and modules.

A new route to solar silicon

But it’s the method, not just quantity, that is of interest. Evonik’s researchers have discovered a new route to solar silicon that consumes significantly less energy than conventional processes. Raw silicon, which is actually abundantly available, must first be converted to ultrapure form before it can be further processed by the solar industry.

In the JSSi process, gaseous monosilane is decomposed at high temperatures into its elements, silicon and hydro- gen. This requires up to 90 percent less energy than the hitherto commonly used Siemens process. Undoubtedly, the conversion of trichlorosilane into monosilane also requires energy, but the overall energy saving is still an impressive 60 to 80 percent: a perfect example of energy efficiency that pays off.