Selective delamination by milling as a first step in the recycling of photovoltaic modules.

The recycling of photovoltaic modules has been a topic of increasing interest over the last years. At industrial scale, delamination of the module structure, which represents the first step in the recycling process, is currently achieved by multi-stage crushing. However, the quality of the outputs obtained through subsequent processing is low and offers room for improvement. Milling was investigated as an alternative physical delamination method. Lab-scale experiments were conducted to evaluate the applicability of the technology in general, as well as comparing a process by which all non-glass layers are removed at the same time (one-step) with one where the backsheet is removed as a separate fraction (two-step). Furthermore, a qualitative and quantitative analysis of the resulting outputs in each case was performed. Results show effective delamination by the milling process. Advantages in comparison to the currently used delamination techniques are identified in regard to the quality of the recovered glass, which is separated directly during delamination as well as the fact that the subsequent processing can therefore be focused on the polymers, metals and silicon contained within the removed materials. Some possibly problematic aspects in regard to upscaling have also been identified and discussed. While the two-step process enables the recovery of more homogenous outputs, it is also associated with a higher effort regarding input characterization and the milling process itself. In order to reach a conclusion about which process option is more feasible, additional investigations concerning the milling process, the input material and the output fractions are needed.

Thermal delamination of end-of-life crystalline silicon photovoltaic modules.

Thermal delamination - meaning the removal of polymers from the module structure by a thermal process - as a first step in the recycling of crystalline silicon (c-Si) photovoltaic (PV) modules in order to enable the subsequent recovery of secondary raw materials was investigated. A correlation between treatment temperature and duration was established by an iterative process. Furthermore, chemical characterization of the resulting solid outputs (glass, cell, ribbons and residues) was performed in order to assess their further processing options. Additionally, the effect of removing the backsheet as a pre-treatment before the actual delamination process was investigated in relation to the aforementioned aspects of treatment duration and output quality. Results show that increased temperatures reduce the necessary treatment duration (65 minutes at 500°C, 33 minutes at 600°C) while generating the same output quality. The backsheet removal leads to an additional duration decrease of more than 45% at each considered temperature, while also having positive effects relating to fewer solid residues and easier flue gas handling. In regard to the main output specifications no significant influence of the pre-treatment is observed. Overall thermal delamination can be seen as a feasible method in order to obtain high value secondary raw materials from c-Si PV modules, while backsheet removal as pre-treatment should be considered as advantageous from multiple standpoints.