The selected manufacturing process is based on obtaining gaseous halides from metallurgical silicon and the impurities it contains. The gases are fractionally distilled, and the halides from the impurities are removed. From the silicon halide, is obtained Polycrystalline silicon with a purity of up to 11N is obtained using a vapor deposition reactor (CVD/Siemens Reactor).

The Siemens process was first used to produce high-purity silicon in the 1950s in so-called CVD or bell reactors at temperatures of ~1100°C. Even today, it is the only process that guarantees 100% production of SG-Si with a purity of 11N.

Its main drawback is the high energy consumption required by the process.

This is the main reason why only nine factories are operating worldwide capable of achieving this level of purity. On the contrary, an undeniable advantage is that the CVD/Siemens process does not introduce any type of pollution into the environment beyond the waste heat from the process, which, moreover, is intended to be used in a cogeneration cycle.

The abundance of silicon in nature, on the one hand, and the complexity and cost of the reuse process, on the other, are the reasons why solar cells from solar panels that have either reached the end of their useful life or have not passed quality controls during manufacturing are not process for silicon reuse.

There is no doubt that processing for reuse would increase costs, either for the solar cell itself, if it were included in its cost of sale, or for the recovered element, if the cost of reuse were included in the element to reuse. However, this lack of reuse of solar silicon means that, in reality, the energy obtained through solar cells not from reuse or not programmed for reuse cannot be considered renewable energy since it violates Circular Economy Guidelines.

SONAGRE is committed to introducing a new format of polycrystalline primary silicon (PP-Si) to the market, traceable in origin as a Circular Economy product certified in accordance with UNECE principles. This “new” material can be used to manufacture new solar cells, whose energy production, in that case, could be considered renewable energy.

The production of PP-Si from solar cells will use a variant of the argon-gas-controlled atmosphere induction furnaces used at Silicios Onubensis complex for the production of solar-grade silicon rods. The processing furnaces will be larger and are designed considering that the raw material, in this case, contains copper, silver, and polymers (the other components of the solar cell). The different densities of the metals and other components allow separation by decantation and flotation, using three shafts on three different levels. Primary polycrystalline silicon will be extracted from the central shaft. Different silicon amalgams with two different types of mixtures will be extracted from the other two shafts. These amalgams are removed from the production cycle to be reprocessed in the silicon metallurgical plant at the same complex. The resulting primary polycrystalline silicon (PP-Si) is solidified directly into bars, which are ground to standard measurements of 156 x 156 mm x 180 µm. These bars are used to obtain wafers, which are used to manufacture new solar cells that will ultimately be installed in photovoltaic panels that comply with UNECE guidelines.