Initial metal contents and leaching rate constants of metals leached from end-of-life solar photovoltaic waste: An integrative literature review and analysis

The photovoltaic (PV) technology is one of the fastest growing renewable and environmental friendly sources of electricity. However, this huge deployment rate is associated with generation of end-of-life (EoL) PV waste containing particularly, carcinogenic metals, once their operation phase ends. This study attempted to address this upcoming waste issue by systematically reviewing about 300 review/theoretical/case/research papers/books/patents published between 2000 and 2018. The information was compiled and synthesized on: (i) initial metal concentration/content (IMC) for silicon-PV, amorphous-PV, CIGS and CdTe PVs; ii) statistical characterisation and distribution of compiled IMCs; iii) leached metal concentrations (mg/l) from various PVs in water-based leaching solutions, as per standard waste characterisation methods, in acid leaching and landfill matrix; iv) metal leaching rate constants (LRC) by fitting exponential model on reported plots of leached metal concentration values versus time using the GetData software; v) feasible application of compiled IMC and LRC data for: a) Leachate Pollution Index (LPI) determination of an MSW landfill dumped with solar-PV waste, b) human health risk assessment (HHRA) for exposure to lead leached from solar PV waste in an MSW landfill; vi) data/knowledge gaps from literature review and highlight the required future research actions. The range of IMC values for top three solar PV-associated carcinogens, arsenic, cadmium and lead (% weight) were obtained to be: 0.00–0.001, 0.0001–19.84, and 0.003–5.09, respectively. Further, the range of LRC of solar PV-associated leached arsenic, cadmium and lead were obtained to be (per day): 0.00–0.129, 0.001–0.031, and 0.003–0.041, respectively. Leaching of Cd, Pb and Se from PVs have been mostly studied in acidic conditions (pH 3.0–6.5), whereas, fate of solar PVs in landfill conditions was not observed to be studied much. The estimation of contribution of solar PV in leachate pollution potential of an existing MSW landfill at T90 values (i.e., time required for 90% leaching of metals) showed an increase of 5.15% in pollution potential of landfill if landfill were to be dumped with EoL PV waste as well. HHRA for exposure to groundwater contaminated with leachate from a landfill dumped with lead containing solar PV waste did not pose any significant risk, however, the carcinogenic effects due to other metals under this scenario cannot be neglected. Out of 85 studies selected for content analysis, only 2.39% of them investigated the fate of PVs in landfill stimulating conditions. To address the fate of EoL solar waste and reduce uncertainty in present work, following future research actions need to be initiated: (i) conduct experimental studies to obtain data on metal leaching under realistic dumping scenarios and landfill conditions (intact solar panels with bigger size in MSW landfill); (ii) revise the expression of LPI for including solar PV-based LPI with critical parameters, like carcinogenic metals (cadmium); (iii) investigate suitability of existing standard hazardous waste characterizing methods (TCLP or WET) for PV waste.