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1. Material Use and Life Cycle Impact of Crystalline Silicon PV Modules Over Time

   https://doi.org/10.1109/PVSC48317.2022.9938923  

   Yuan, Luyao; Anctil, Annick (January 2022, 2022 IEEE 49th Photovoltaics Specialists Conference (PVSC))

   Most life cycle assessment (LCA) of crystalline silicon photovoltaics (c-Si PV) modules are based on public life cycle inventory (LCI) datasets with limited use of actual manufacturing data. We collect and calculate the amount of material used for production of different PV modules installed in the U.S. to analyze the trend in material intensity over and compare the numbers among various tier manufacturers and module reliability. Furthermore, results of LCA models using the public LCI data and the actual manufacturing material (specifically aluminum) data are compared to investigate the impact of material use on the life-cycle impact assessment of c-Si PV modules. Results show a trend of material use decrease over time and indicate a potential connection between material usage and the manufacturer tier – better manufacturers tend to use more materials for modules production which may lead to higher quality performance. Additional work will complete the life cycle assessment, explore more materials, and fill the data gap of PV modules produced by different manufacturer tiers in different years. 

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2. Material Requirement and Resource Availability for Silicon Photovoltaic Laminate Manufacturing in the Next 10 Years

   https://doi.org/10.1109/PVSC43889.2021.9518663  

   Heidari, Seyed M; Anctil, Annick (June 2021, 2021 IEEE 48th Photovoltaic Specialists Conference (PVSC))

   Material scarcity is a considerable threat to energy transition towards renewables. Photovoltaics (PV) installations are expected to increase rapidly in the next decade, which may increase the amount of material needed. This study created three scenarios (S 1 , S 2 , & S 3 ) to evaluate the impacts of potential technology improvements on the quantity of materials necessary for manufacturing silicon PV (Si PV) laminate in the next ten years. Our baseline was similar to previous studies, which applied theoretical models on PV historical data and ignored PV technology improvements that can influence future material projections. S 1 considered only market share and module efficiency, while S 2 covered wafer thickness improvements as well. S 3 was the scenario that more likely will occur in the next decade, which included module efficiency, market share, wafer thickness, glass thickness, and potential replacements such as using perovskite/silicon tandem. The material requirement for Si PV laminate manufacturing in S 3 was 22% to 78% lower than the baseline, S 1 , and S 2 . The highest material demand is expected to be for solar glass (74 million metric tons) and Metallurgical grade silicon (3 million metric tons) in the next decade. This study showed the importance of considering technology improvements to project the PV material requirement. 

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3. Evaluating the Environmental Benefit of Residential Photovoltaic Modules Early Retirement in California

   https://doi.org/10.1109/PVSC48317.2022.9938865  

   Kothari, Mallika; Anctil, Annick (January 2022, 2022 IEEE 49th Photovoltaics Specialists Conference (PVSC))

   The state of California is the foremost leader in solar photovoltaics (PV) installations in the United States. With 1,390,240 installations and 24.76% of the state's energy coming from solar, the demand for PV modules is steadily increasing. Most PV modules have an expected lifetime of 25-30 years. However, due to repowering or early module failure, module lifetime can often be shorter than anticipated. Current studies calculate the environmental impact of PV systems based on ideal installation conditions and a full 25-year module lifetime. This study considers the impact on the life cycle of PV systems from early PV module retirement and actual system installation in California. Using the life cycle cumulative energy demand, electricity data from the Energy Information Administration (EIA), and greenhouse gases, carbon payback time (CPBT) was evaluated. Data from various PV module rooftop residential installations in 2019 were collected from the California NEM database. Information on the system design (tilt, azimuth, module model) and module specification sheets were used to calculate the cumulative electricity generated in kilowatt-hours (kWh) over the system' lifetime. The calculated average CPBT was 2.8 years, shorter than most of the system lifetimes, and the mean number of zero carbon years experienced by earlier retired systems was about 5 years. Although the rapid movement towards solar energy is promising and essential as reliance on greener energy increases, attention must be paid to the diverse lifespans of PV modules, system design, and performance to substantiate or reject the assumption that PV always have a positive impact on the environment. 

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4. The greenhouse gas cost of agricultural intensification with groundwater irrigation in a Midwest U.S. row cropping system

   https://doi.org/10.1111/gcb.14472  

   McGill, Bonnie M.; Hamilton, Stephen K.; Millar, Neville; Robertson, G. Philip (October 2018, Global Change Biology)

   Abstract Groundwater irrigation of cropland is expanding worldwide with poorly known implications for climate change. This study compares experimental measurements of the net global warming impact of a rainfed versus a groundwater‐irrigated corn (maize)–soybean–wheat, no‐till cropping system in the Midwest US, the region that produces the majority of U.S. corn and soybean. Irrigation significantly increased soil organic carbon (C) storage in the upper 25 cm, but not by enough to make up for the CO₂‐equivalent (CO₂e) costs of fossil fuel power, soil emissions of nitrous oxide (N₂O), and degassing of supersaturated CO₂and N₂O from the groundwater. A rainfed reference system had a net mitigating effect of −13.9 (±31) g CO₂e m⁻² year⁻¹, but with irrigation at an average rate for the region, the irrigated system contributed to global warming with net greenhouse gas (GHG) emissions of 27.1 (±32) g CO₂e m⁻² year⁻¹. Compared to the rainfed system, the irrigated system had 45% more GHG emissions and 7% more C sequestration. The irrigation‐associated increase in soil N₂O and fossil fuel emissions contributed 18% and 9%, respectively, to the system's total emissions in an average irrigation year. Groundwater degassing of CO₂and N₂O are missing components of previous assessments of the GHG cost of groundwater irrigation; together they were 4% of the irrigated system's total emissions. The irrigated system's net impact normalized by crop yield (GHG intensity) was +0.04 (±0.006) kg CO₂e kg⁻¹yield, close to that of the rainfed system, which was −0.03 (±0.002) kg CO₂e kg⁻¹yield. Thus, the increased crop yield resulting from irrigation can ameliorate overall GHG emissions if intensification by irrigation prevents land conversion emissions elsewhere, although the expansion of irrigation risks depletion of local water resources. 

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5. The magnitude and pace of photosynthetic recovery after wildfire in California ecosystems

   https://doi.org/10.1073/pnas.2201954120  

   Hemes, Kyle S.; Norlen, Carl A.; Wang, Jonathan A.; Goulden, Michael L.; Field, Christopher B. (April 2023, Proceedings of the National Academy of Sciences)

   Wildfire modifies the short- and long-term exchange of carbon between terrestrial ecosystems and the atmosphere, with impacts on ecosystem services such as carbon uptake. Dry western US forests historically experienced low-intensity, frequent fires, with patches across the landscape occupying different points in the fire-recovery trajectory. Contemporary perturbations, such as recent severe fires in California, could shift the historic stand-age distribution and impact the legacy of carbon uptake on the landscape. Here, we combine flux measurements of gross primary production (GPP) and chronosequence analysis using satellite remote sensing to investigate how the last century of fires in California impacted the dynamics of ecosystem carbon uptake on the fire-affected landscape. A GPP recovery trajectory curve of more than five thousand fires in forest ecosystems since 1919 indicated that fire reduced GPP by 157.4 ± 7.3 g C m − 2 y − 1 ( mean ± SE,   n = 1926 ) in the first year after fire, with average recovery to prefire conditions after ∼ 12 y. The largest fires in forested ecosystems reduced GPP by 393.8 ± 15.7 g C m − 2 y − 1 ( n = 401) and took more than two decades to recover. Recent increases in fire severity and recovery time have led to nearly 9.9 ± 3.5 MMT CO 2 (3-y rolling mean) in cumulative forgone carbon uptake due to the legacy of fires on the landscape, complicating the challenge of maintaining California’s natural and working lands as a net carbon sink. Understanding these changes is paramount to weighing the costs and benefits associated with fuels management and ecosystem management for climate change mitigation. 

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