Recycling of Discarded Photovoltaic Solar Modules for Metal Recovery: A Review and Outlook for the Future

The extensive deployment of photovoltaic (PV) modules at an expeditious rate worldwide leads to a massive generation of solar waste (60–78 million tonnes by 2050). A stringent recycling effort to recover metal resources from end-of-life PVs is required for resource recovery, circular economy, and subsequent reduction of environmental impact. The recovery of metallic resources (silicon, silver, copper, lead, and tin) from the first-generation PVs and critical elements (tellurium, indium, selenium, and gallium) from second-generation PVs are mainly targeted. This review systematically discusses the recycling literature of both generations of solar cells, market value calculations, recycling preferences, global trends, and the Indian perspective. The status of PV module recycling on a commercial scale and academic research efforts are discussed. The review systematically discusses the various possible pretreatments and extraction/refining processes. The pretreatments (physical, chemical, thermal, and hybrid processes) play a decisive role in up-gradation, impurity removal, and metal recovery. The challenges include homogeneous collection, process efficiency, holistic resource recovery, and energy considerations. Toxicity characteristics of both generations, life cycle assessment studies, recycling challenges with proposed flowsheets, and a detailed future outlook are propounded to develop a holistic metal recovery approach. In comparison, crystalline Si PVs comprise the maximum economic value. One tonne of mixed PVs (first and second generation) can yield ∼9.32 kg of Cu, ∼0.30 kg of Ag, ∼33.48 kg of Si, ∼1.12 kg of Sn, ∼1.12 kg of Pb, ∼4.9 g of Cd, ∼2.5 g of Te, and ∼3.4 g of In.