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The major part of dissolved iron (DFe) in seawater is bound to organic matter, which prevents iron from adsorptive removal by sinking particles and essentially regulates the residence time of DFe and its availability for marine biota. Characteristics of iron-binding ligands highly depend on their biological origin and physico-chemical properties of seawater which may intensely alter under ongoing climate change. To understand environmental controls on the iron binding, we applied a function of pH and dissolved organic carbon (DOC) to describe changes in the binding strength of organic ligands in a global biogeochemical model (REcoM). This function was derived based on calculations using a thermodynamic chemical speciation model NICA. This parameterization considerably improved the modeled DFe distribution, particularly in the surface Pacific and the global mesopelagic and deep waters, compared to our previous model simulations with a constant ligand or one prognostic ligand. This indicates that the organic binding of iron is apparently controlled by seawater pH in addition to its link to organic matter. We tested further the response of this control to environmental changes in a simulation with future pH of a high emission scenario. The response of the binding potential shows a complex pattern in different regions and is regulated by factors that have opposite effects on the binding potential. The relative contributions of these factors can change over time by a continual change of environmental conditions. A dynamic feedback system therefore needs to be considered to predict the marine iron cycle under ongoing climate change.

The oceans currently take up around a quarter of the carbon dioxide (CO2) emitted by human activity. While stored in the ocean, this CO2 is not influencing Earth's radiation budget; the ocean CO2 sink therefore plays an important role in mitigating global warming. CO2 uptake by the oceans is heterogeneous, with the subpolar North Atlantic being the strongest CO2 sink region. Observations over the last 2 decades have indicated that CO2 uptake by the subpolar North Atlantic sink can vary rapidly. Given the importance of this sink and its apparent variability, it is critical that we understand the mechanisms behind its operation. Here we explore the combined natural and anthropogenic subpolar North Atlantic CO2 uptake across a large ensemble of Earth System Model simulations, and find that models show a peak in sink strength around the middle of the century after which CO2 uptake begins to decline. We identify different drivers of change on interannual and multidecadal timescales. Short-term variability appears to be driven by fluctuations in regional seawater temperature and alkalinity, whereas the longer-term evolution throughout the coming century is largely occurring through a counterintuitive response to rising atmospheric CO2 concentrations. At high atmospheric CO2 concentrations the contrasting Revelle factors between the low latitude water and the subpolar gyre, combined with the transport of surface waters from the low latitudes to the subpolar gyre, means that the subpolar CO2 uptake capacity is largely satisfied from its southern boundary rather than through air–sea CO2 flux. Our findings indicate that: (i) we can explain the mechanisms of subpolar North Atlantic CO2 uptake variability across a broad range of Earth System Models; (ii) a focus on understanding the mechanisms behind contemporary variability may not directly tell us about how the sink will change in the future; (iii) to identify long-term change in the North Atlantic CO2 sink we should focus observational resources on monitoring lower latitude as well as the subpolar seawater CO2; (iv) recent observations of a weakening subpolar North Atlantic CO2 sink may suggest that the sink strength has peaked and is in long-term decline.

Transdisciplinary research is intriguing and challenging. Early-career researchers in particular, who lack experience and are still working on their disciplinary standing, struggle with difficulties and uncertainties. We offer insights into the challenges faced and solutions found by seven transdisciplinary junior research groups. While transdisciplinarity offers a way to tackle complex social-ecological challenges, transdisciplinary research is a challenging task in itself. The integration of research methods across academic disciplines, the collaboration between researchers and practitioners, and the need to balance societal and disciplinary academic impacts pose many difficulties even to experienced applied scientists and even more so to early-career researchers. Young scholars face particular problems, given their lack of longer-term experience and their still fragile position within academia. Drawing on existing literature, an early-career researcher workshop, and our own experience as junior research group leaders, we discuss specific challenges and respective solution strategies of transdisciplinary research within the context of sustainability.

International audience; In the vast Low Nutrient Low-Chlorophyll (LNLC) Ocean, the vertical nutrient supply from the sub-surface to the sunlit surface waters is low, and atmospheric contribution of nutrients may be one order of magnitude greater over short timescales. The short turnover time of atmospheric Fe and N supply (

29th European Photovoltaic Solar Energy Conference and Exhibition; 3142-3146, Currently, there is no appropriate, standardized, accelerated test method to investigate the abrasion resistance of components of solar energy systems under sand storm conditions. Therefore, this paper deals with the development of a test method for the investigation of the sand abrasion mechanism on selected solar technical components. For this purpose, first, the mechanisms of surface damage induced by trickling sand are experimentally investigated. The designed method based on ASTM D968-05 enables to describe the sand abrasion mechanisms on aluminum reflectors and solar glasses. Also, differences in the abrasion resistance of the samples are revealed. In addition to changes in their optical properties, an increased surface roughness can be determined. Depending on the impact angle, hardness of the exposed material, sand trickling mass and sand concentration, different surface changes are caused. The concentrated particle stream led to strong abrasive damage on the reflector surfaces, whereas glasses show a better abrasion resistance to trickling sand because of their higher hardness. The second, horizontal test method designed according to the sandblasting principle allows a more realistic investigation of the sand abrasion process on samples under strong wind conditions. The low, sand-laden air flow causes less abrasive damage on the reflector surfaces.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1272-1276, Replacing Ag paste contacts in silicon solar cells by plated Ni/Cu contacts seems a logical next step in the evolution of industrial Si solar cell manufacturing. Ag paste contacts cause a significant share of the solar cell cost today and limit the efficiency of advanced Si solar cells. However, replacing a proven technology by another requires reliability of this technology. Cost and efficiency advantages alone are a high motivation for adopting a new metallization technology in mass production. Reliability of the contacts is a must. In this contribution we show that laser ablation followed by light induced plating of Ni and Cu and plating of a thin capping layer results in good and reliable contacts on industrial solar cell precursors. After plating of the complete metal stack a thermal annealing step is used to increase mechanical adhesion and to reduce resistive losses of the plated contacts (contact resistance and grid resistance). Excellent solar cell efficiencies can be combined with reliable contacts. Adhesion data and data after 60 cell module testing (as part of IEC61215) are reported next to the most influencing factors.

26th European Photovoltaic Solar Energy Conference and Exhibition; 3476-3479, Evaluating the performance of photovoltaic (PV) modules at oblique angle of incidence (AOI) is important for accurate energy yield prediction. The AOI effect has been investigated based on outdoor measurement and the following optical model simulation. The advantage of indoor over outdoor conditions is that irradiance, AOI, and module temperature can be well defined, while a major challenge is the spatial non-uniformity of irradiance when the module is tilted. The work presented herein concerns a multi-step approach that enables the prediction of module performance in the field at varying AOI using an indoor solar simulator. A class AAA solar simulator and a custom-designed module holder with bearings for tilting have been used for this study. The first step involves mapping out the spatial non-uniformities of irradiance at different AOI by collecting measurements for a reference cell at multiple points across the inclined plane. The I-V characteristics of the module were then measured in tilted configurations. The resulting I-V curve for a standard module with six rows of cells exhibited three platforms corresponding to the three different short-circuit currents generated each of the three strings. It was also found that AOI measurements could be used to determine which contains the current-limiting cell. This was accomplished through flipping the module left to right and repeating the I-V measurement at oblique AOI. Since the uppermost row receives less light than the lower row in a given string, the Isc of the individual string is always determined by the worst cell in the top row. Finally, the position of the monitor cell was adjusted to regulate the total amount of illumination to ensure 1000 W/m2 on one single string at different AOI for I-V measurement. Assuming that the quantum efficiency is uniform across the cell, such I-V characteristics are representative of the module performance in the field.

26th European Photovoltaic Solar Energy Conference and Exhibition; 3157-3161, The crystalline silicon photovoltaic (PV) module is a laminate assembly composed of materials with widely varying mechanical and thermal properties. The properties of these materials are important factors influencing the performance and reliability of modules following exposure to external mechanical stress. In particular, a key role of encapsulation is to protect the solar cells from external stresses, yet some encapsulant mechanical properties can vary with temperature. Since current mechanical loading tests for certification of PV modules are performed at room temperature, these tests may not adequately simulate or accelerate in-field mechanical stresses and failures. This work examines the impact on module performance and cell integrity of dynamic and static load testing at both high and low temperature using a custom-built mechanical testing rig capable of operating inside a climate chamber. Two different encapsulation materials were compared: a standard EVA thermosetting film and a silicone. The loading conditions were based on relevant qualification test standards and test modules were characterized for performance and damage using a solar simulator and electroluminescence imaging. Testing revealed significant differences in the ability of the encapsulant to protect the solar cells from damage due to mechanical loading at various temperatures, with the encapsulant modulus being a critical factor.

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