Description du sujet de thèse

Large-scale agrivoltaics: impact of fouling processes by atmospheric particles on energy yield, solar panel aging and crops contamination under various climatic conditions
As interest in renewable energy grows, the fouling of photovoltaic modules has emerged as a significant issue. Deposition of particulate matter reduces light transmittance to the photovoltaic (PV) panels, leading to energy output reductions of up to 25%, with peak losses reaching 75%. The cost of cleaning PV modules can amount to millions of dollars per year, underscoring the importance of studying the reversibility of the soiling process. There is considerable interest in preventative approaches, such as (super)hydrophobic or hydrophilic antireflective coatings. However, most hydrophilic or hydrophobic coatings do not take into account the fact that adhesion depends not only on the surface characteristics but also on particle properties. Adhesion force varies highly as a function of particle size, shape and chemical properties, necessitating a more thorough investigation into the influence of particle characteristics on soiling potential. This investigation should consider factors such as climate, soil nature, humidity, and industrial or agricultural activities.
This thesis aims to bridge the gap between particle characteristics and their soiling potential, with the goal of developing an effective soiling mitigation approach based on regional atmospheric particulate matter composition that is harmless to crops and soils beneath the panels.

Contexte de travail

The PhD student will be hosted at CEREGE, Technopole de l'Arbois, Aix en Provence (Center for Research and Teaching in Environmental Geosciences). CEREGE is a joint research center that brings together multi-disciplinary fields in environmental geoscience research. He/She will be part of the Sustainable Environment group, which conducts studies on the life-cycle (from production, use and end of life) of materials and contaminants to understand bio-physico-chemical processes driving their reactivity, emission, transfer and impacts in different ecosystems.
The PhD student will be supervised by Mélanie Auffan, Senior Scientist at the CNRS CEREGE and Alicja Babst-Kostecka, Associate Professor in the Department of Environmental Science and Director of Center for Environmentally Sustainable Mining, UArizona. He/she will have the opportunity to spend time at the university or Arizona.

Mission
The research will address the following questions:
(1) What mechanisms govern particle deposition on PV panels? Can this information be used to predict the soiling potential of specific pollutant particles on PV panels installed above agricultural crops?
(2) What environmental factors (e.g., radiation, precipitation, temperature, biofilm, use of fertilizers and pesticides) influence the aging of PV surfaces? Do these environmental factors have an impact on particle deposition on PV panels?
(3) When developing an effective soiling mitigation approach, what factors should be prioritized (for example regional dust composition, surface roughness etc.)? How does the chosen soiling mitigation approach affect the aging of the panels throughout their lifecycle above crops?
o (4) Does the aging of panels and the implementation of different soiling mitigation approaches potentially result in adverse effects on the soil and crops beneath PV panels in an agrivoltaics setup? Is there a measurable difference in pollution levels (e.g., accumulation of harmful elements in soil and/or crops) and soil biophysicochemical properties between benchmark agricultural soil and soils beneath PV panels, considering the deposition of pollutants from the PV panels?
o Activities
This project will benefit from the worldwide collaborative network of the IRC CNRS ARIZONA and of partners in order to have access to fouled PV used in Agrivoltaic from all around the world (Europe, Africa, Asia, North America) under specific climates. Sites will be selected to represent different lifecycle stages and various soiling mitigation approaches.
A thorough physico-chemical characterization of the particles that deposit in PV panels localized in sites with contrasted climates will be performed as contents in major and trace elements (using ICP-MS and ICP-OES, TOC), mineralogy (XRD), size and shape (AFM, SEM, TEM), surface charge, hydrophobicity, to inform about the soiling potential of these dust samples depending on their nature, texture, and surface properties. The sources of these particles will be traced using geochemical and isotope fingerprinting to identify regions where different types of soiling may occur on solar panels. The 2D and 3D X-ray imaging systems at CEREGE will be used to identify surface roughness and microstructures in the panel and to study particle deposition as a dynamic phenomenon. The spatial resolution and detection limit of the state-of-the-art microXRF and X-ray tomography available will be particularly useful to inform on deposition and adhesive potential of particulate matter over the lifecycle of the PV panels. Furthermore, these results may highlight the efficiency of various surface coatings currently employed to prevent soiling.
Climate chamber (as the Suntest XLS+, at CEREGE) will be used to simulate radiation and rain events, to determine how environmental conditions such as humidity or temperature modify the deposition event, the leaching of adsorbed particles, and how the deposited particles age over time (as dissolution, re-precipation and cementation on solar panel surfaces) as well as biofilm development. Furthermore, in these model environments it will be possible to identify what physico-chemical factors drive lichen, algae, or biofilm growth, to study how these organisms adhere to the surface of PV panels more or less weathered.
We will perform large-scale field surveys across the climatic gradient of numerous agrivoltaics sites to assess the elemental composition of crops and soils beneath the PV panels. Agrivoltaics locations will be paired with adjacent benchmark agricultural sites. We will employ a portable X-ray fluorescence (pXRF) analyzer for rapid, non-destructive, and accurate elemental analysis of plant tissues and soil samples (van der Ent et al., 2019). This data will inform and drive the follow-up fieldwork phases, during which soil samples will be collected from the locations identified as potentially negatively impacted and will undergo in-depth laboratory tests, including soil microbial diversity and chemical analysis (Kushwaha et al., 2022).
o The major outcome of this work will be the meta-analysis of data addressing key aspects such as: i) mechanisms of particle deposition on PV panels, ii) environmental factors influencing panel aging; iii) soiling mitigation factors, and iv) potential adverse effects on soil and crops, which will inform our understanding of interactions between agrivoltaics and environmental sustainability. Limited information exists about practical and sustainable strategies for mitigating soiling on PV panels. Thus, the potential to generate new information and discover and identify new approaches is high.
o Skils :
The applicant should have a background in chemistry, geosciences or environmental sciences (or related) and experience in the behaviour and fate of particles in the environment and/or nano-specific physical and chemical analysis.

We are looking for motivated, self-organized candidates who like to work on challenging research questions in an international team and in large collaborative projects with partners across France and the US. We expect the successful applicant to be willing to present results at international conferences and to travel for scientific collaboration with project partners as well as for project meetings.

Contraintes et risques

Our working language will be French and English.

Informations complémentaires

Master in chemistry, geosciences or environmental sciences (or related)