Life cycle assessment (LCA) of end-of-life photovoltaic panels

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Journal ISSN

Volume Title

Kemian tekniikan korkeakoulu | Master's thesis

Date

2024-08-29

Department

Major/Subject

Chemistry

Mcode

CHEM3023

Degree programme

Master's Programme in Chemical, Biochemical and Materials Engineering

Language

en

Pages

88

Series

Abstract

With the transition to clean and renewable energy worldwide, photovoltaic (PV) technologies have been increasingly utilized, and crystalline silicon (c-Si) PV panels are expected to remain dominant for a long time. The amount of EOL PV panels is predicted to reach millions of tons by 2050 globally. It has been proved that the recycling of PV panels has lower environmental burdens than other EOL disposal methods, and the recovery of secondary raw materials such as high-purity silicon and metals from them provides additional environmental and economic benefits. It is therefore essential to find the most efficient and environmentally friendly recycling methodologies. In this thesis, two recycling scenarios are designed to recover metallurgical grade silicon, copper and silver from EOL c-Si PVs based on a literature review on the state-of-art recycling technologies. In the first recycling scenario (SCE1), a combination of thermal and mechanical treatment is applied, and in the second scenario (SCE2), the pretreatment only involves a mechanical processing based on electro-hydraulic fragmentation (EHF) technology. The material recovery after pretreatment in both scenarios is achieved by hydrometallurgical processing. A unit-level life cycle inventory (LCI) has been complied for both recycling scenarios with the mass and energy data obtained from process simulation using HSC Sim software and data collected from literature. The environmental impacts of two recycling scenarios were then subjected to a gate-to-gate life cycle assessment (LCA) in openLCA software. Six impact indicators are evaluated: freshwater eutrophication (EP), global warming (GWP), photochemical ozone creation potential (POCP), ozone depletion potential (ODP), terrestrial acidification potential (AP), freshwater consumption (FC). The LCA results indicate that SCE2 overall performs better than SCE1. SCE2 shows lower impacts than SCE1 in all the evaluated impact categories except GWP, though the GWP of SCE2 is still lower than that of the primary production of equivalent amounts of products by 36%. For EP, POCP, AP and FC, the avoided environmental burdens in SCE2 range from 88% to 99% of the equivalent primary production. The subdivided impacts of SCE2 allocated to MG-Si either by mass or by value are lower than the impacts of the equivalent primary production by 30% - 96% for all the evaluated impact indicators. Sensitivity and uncertainty analyses were also conducted for each recycling scenario, which showed that both scenarios are most sensitive to nitric acid consumption. Further LCA uncertainty analysis was performed via Monte Carlo simulation that indicated relative standard deviations of 21% to 32% (SCE1) and 23% to 26% (SCE2), respectively. According to the results of this work, both designed recycling scenarios have scope for improvement. For SCE1, efforts should be made to manage the thermal treatment emissions of organic compounds and nitrogen dioxide and to decrease acid/alkali consumption. For SCE2, further research is required to scale up the application of EHF technology on EOL PVs and to develop effective methods for recovering and purifying silicon afterward.

Description

Supervisor

Lundström, Mari

Thesis advisor

Aromaa-Stubb, Riina

Keywords

life cycle assessment, end-of-life photovoltaic panels, process simulation, metallurgical grade silicon, silver, copper

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