Process information
| Key Data Set Information | |
| Location | CN |
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| Use advice for data set | When utilizing the provided LCA data for this industrial process, users should account for the possibility of variance in efficiency and yield due to alterations in module design and material composition over time. Special attention should be given to the separation processes, ensuring all toxic materials such as fluorinated backsheets are properly managed according to environmental regulations. The use of secondary processes such as pyrolysis may be necessary where solvent-based methods fail to remove residual EVA. Lastly, recognizing the fragility of newer, thinner Si wafers during processing is vital, as breakage can significantly impact recovery rates. |
| Technical purpose of product or process | The described industrial process relates to the recovery of valuable materials from decommissioned photovoltaic (PV) modules. The high-purity silicon wafers and other components are recovered through a multi-step approach that includes thermal and chemical delamination treatments. These recovered materials, particularly silicon wafers and glass, are then potentially recyclable into new solar modules for a second life cycle, contributing to the sustainable use of resources in the solar energy sector. |
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| General comment on data set | Thermal upcycling that aims to fully recover componentsincluding high-purity Si wafers. Additional thermal and chemical processes are involved, referred as “thermal recycling”. Thermal delamination separates the module by thermally decomposing the encapsulation layer between glass and solar cells. The polymeric encapsulation layer, mostly EVA, can be either pyrolyzedinto acetic acid, propane, propene, ethane, methane, and other combustible oils and gases under an inert gas environment (T1) or burned off under an oxygen environment (T2). In method T1, SolarCells Inc. first proposed recovery of Si wafers and functioning solar cells from old modules by pyrolytically decomposing EVA in an inert atmosphere in a tube furnace at about 500 °C. Prior to EVA vaporisation, the backsheet was manually peeled off. This pyrolytic delamination was also demonstrated using a fluidised bed reactor and a mufflefurnace with combustible gases recovered as heat or electricity. A peak temperature of 450–600 °C with a holding time of30 minutes to 1 hour was enough for full decomposition.Deutsche Solar and Solarworld demonstrated the thermal delaminationrecycling process for decommissioned modules in a 300 kW PV plants in Germany and Belgium. The delaminated solar cells were remanufactured into new modules and served a second life. Since 2005,the thickness of Si solar cells has been reduced to less than 200µm,making wafers more likely to break or crack during the thermal process. Cracking has been attributed to the mechanical stress caused bydecomposing gas behind the glass and the thermal deformation of the EVA at the rear. The breakage issue can be overcome either by toolmodification (e.g. additional fixed jig with grooves apart) orsimple pre-treatments (e.g. front glass cracking and rear EVA patterning) to quickly release stress generated from the decomposed gas. An optimised process could recover nearly 100%w of the tempered glass and high-purity solar grade Si. In method T2, instead of pyrolysis, EVA was combusted in an oxygen environment to provideenergy for the heating furnace. |
| Copyright | No |
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| Technology description including background system | Chemical delamination. The adhesive encapsulation layer can also be dissolved in either inorganic (C1) or organic (C2) solvents to delaminate the module. In method C1, solar glass was firstly separated fromsolar cells by immersing the module in nitric acid (HNO3) for 24 hours. In method C2, Doi et al. reported successfully dissolution of EVAin trichloroethylene at 80 °C for 10 days. The chemical process canbe accelerated with ultrasonic radiation. For example, Kim and Leereported the most effective organic dissolution of EVA in O-dichlorobenzene within 30 minutes to recover damage-free solar cells. Azeumo et al. reported complete dissolution of EVA in less than60 minutes in toluene with the presence of ultrasonic radiation. Insome occasions, the organic solvents could not remove the swollen EVAremaining on the surface, hence a secondary treatment such as pyrolysis is required. This unavoidably adds complexity.In addition to the front glass, fluorine-contained backsheets must beremoved before recycling solar cells because of its toxicity. The backsheet can be peeledoff from the module at elevated temperatures, mechanically removed during scrapping, grinding or milling operations, or thermally combusted in a licensed incinerator. For glass-glass modulesand those with fluorine-free backsheet, this step is unnecessary. |
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