Environmental Sustainability of Emerging Solar Photovoltaic Technologies
Authors:   , Khalifa Sherif A. , Baxter Jason B. 
Published: August 2022

Decarbonizing today's electricity grid is a top priority to curb impending consequences of anthropogenic climate change. Solar photovoltaic (PV) technologies have grown into a low-cost, reliable, and sustainable power source, already becoming the cheapest source of electricity in some parts of the world. To transition into a clean grid, cumulative global PV deployment need to grow by at least 10 times from today's 1 TW PV capacity. This rapid growth in PV deployment presents emerging sustainability challenges including increased demand to specific material supply chains and emergence of large volume of waste stream as PV modules are retired several decades later. The overall objective of this thesis is to apply analytical sustainability tools embedded in life cycle thinking and industrial ecology to anticipate environmental and human health impacts of evolving incumbent crystalline silicon (c-Si) and emerging lead halide perovskite (LHP) PV technologies at industry-relevant scales. This thesis presents three novel contributions by answering the following research questions about PV sustainability. (1) How do the evolution of c-Si module design, performance, and end of life pathways impact cradle-to-cradle material circularity to support a circular, resource-conserving economy? (2) What is the projected environmental impact of novel chemical precursors used in pre-commercial LHP PVs at industrial scale? (3) What is the potential magnitude of human health risks associated with the accidental release of Pb leachate during a breakage event of LHP modules in a prospective utility-scale installation? These questions are addressed in the analyses presented in chapters 2,3 and 4, respectively. Chapter two presents an open-source dynamic material flow analysis model of PV systems (PV DMFA) spanning the period 2000-2100 to trace and quantify material flows throughout their cradle-to-cradle life cycles. A case study was carried out to study PV flat glass and aluminum, which comprise 80-90% of PV modules. Results indicate that improving initial deployment parameters, particularly those related to system performance and reliability (i.e., efficiency degradation and lifetimes), has the most impact in minimizing material life cycle waste and significantly alleviating raw material demand. We also found out that scaling a robust PV recycling infrastructure that emphasizes recovery of high-quality scrap is essential to closing material loops. Chapter three presents a detailed ex-ante supply chain modeling for perovskite cationic precursors including methylammonium iodide (MAI), formamidinium iodide (FAI) and cesium iodide (CsI) and their subsequent life cycle environmental and energy impacts. These precursors make perovskite alloys that create a high efficiency thin film in LHP PV module. Results from this work contradict those of prior literature that warned against deploying high-performing FA-rich LHP alloys, citing outsized environmental impacts. Our results indicate that the process-based climate change, cumulative energy demand, and human toxicity impacts of CsI, MAI, and FAI are similar to each other and to lead iodide (PbI2) salts on a molar basis.. Additionally, the impacts of the perovskite precursors are ~1000-fold smaller than those of glass when considering amounts needed per module area. Therefore, selection of perovskite composition can be based on PV efficiency and operational stability, without additional constraints of environmental impact. Finally, chapter four presents a screening-level, human health risk assessment for released Pb leachate in hypothetical breakage events of emerging LHP modules. Presence of Pb is essential to retain the high efficiency of LHP thin films, but also raises toxicity concerns and therefore a risk assessment is necessary. We applied and expanded upon fate and transport models for PV contaminants to estimate the Pb concentrations in soil, groundwater aquifer and air for large-scale conceptual PV sites under partial and full (i.e., site-wide) breakage events. Results indicate that Pb exposure point concentration in topsoil could exceed regulatory limits, but its concentration will be diluted to acceptable limits within the first centimeter of soil. Single point concentrations for Pb in air and groundwater stays within the acceptable limits. However, in extreme cases, Monte Carlo exposure concentrations in air exceeds permissible limits when topsoil becomes heavily contaminated. Results for groundwater risk stayed robust in Monte Carlo analysis. The study highlights the need for more accurate modeling methods for leachable contaminants and warrants further attention to active site management during catastrophic events. With hopes for more equitable and sustainable future