Circular water strategies in solar cells manufacturing

A specific material flow model and a TCO for a PERC (Passivated Emitter and Rear Cell) solar cell factory with a production capacity of 5 GWp/a was set up. The first step was to collect and validate data for the cell factory. In a second step a material flow analysis for all processes involving water and for the treatment of the wastewater streams was applied. With these analysis two potential circular water strategies, (i) the reuse of low contaminated wastewater (LCR) and (ii) a Minimal Liquid Discharge (MLD) approach are proposed. The economic and environmental performance of both strategies was assessed by a Cost-Benefit analysis and a LCA. The results show that for the investigated scenarios 38% and 79% of the water consumption and 40% and 84% of the wastewater indirect discharge at the cell factory can be saved by the LCR and MLD approaches, respectively. The environmental impact single score of the cells production decreased 0.4% when applying the LCR strategy and 3.2% with the MLD one. Important reductions on freshwater ecotoxicity, freshwater and marine eutrophication are achieved, mainly driven by the wastewater discharge reduction in the LCR case, and the recycling of a KOH and potassium silicates concentrate as alkali activator for cement substitutes production for the MLD case. CaF2 sludge is also recycled as fluorspar source. Cost reductions of 0.5% and 0.7% from cell production (without ingoing wafer) has been derived for the LCR and MLD strategies, respectively. Wide application of the results of this work is foreseeable, both in PERC factories and in higher efficiency cells like TOPCon (tunnel oxide passivated contact) and HJT (heterojunction) since many of the wastewater streams analysed are similar.