Context and Project
At the global scale, photovoltaic industry is booming to match the demand for clean, renewable and ecocompatible energy sources for the forthcoming green transition. Together with this spreading comes concerns about actual circularity of this industry. In particular, the management of waste materials and energy coming from the production of solar panels has to be addressed to confirm the social, environmental and economic acceptability of solar energy.
As a matter of facts the current production chain for module manufacturing is far from being eco-friendly and economically sustainable: whilst producing PV grade silicon is highly intensive in terms of natural resources (6kg for 1kg EG-Silicon) and energy (80kWh/kg corresponding to 80kg of CO2 emitted per kilogram of Silicon with the Chinese electricity mix), 40% of the ultrapure Silicon is dramatically wasted during the wafering step (kerf powder). In addition, multicrystalline ingot casting and monocrystalline ingot pulling consumes large amounts of – currently – disposable purified silica crucibles and graphite parts from the thermal setups.
The H2020 EU ICARUS (Convention n° 958365) project is granted to address all the waste materials streams from the wafer manufacturing in order demonstrate modular processing solutions at industrial scale to retrieve 95% of high-value raw materials from silicon ingot and wafer manufacturing, through eco-efficient processing, refining, and transformation of industrial silicon, graphite and silica waste streams.
However, recycling Silicon kerfs raises scientific, technological and economic issues: diamond wire saw used for the wafering being water-cooled with lubricant additives (mostly PolyEthyleneGlycol), Silicon kerfs are consequently partly oxidized (silica layer) and contaminated with PEG residues. Efficiently reclaiming Silicon kerfs implies the ability to provide satisfactory raw materials back to the photovoltaic chain. Hence, recycled Silicon must comply with specifications of the ingot manufacturer regarding the shape (granules/chunks) and mostly purity (metallic and light impurities management).
Based upon a strong and well-established collaboration between Grenoble INP – through SIMaP laboratory – and ROSI Solar startup company, a pilot line will be developed in the framework of the ICARUS project to achieve kerf recycling. From previous lab-scale results and proprietary know-how, the main objective is to be able to achieve kerf purification and reconditioning matching PV specifications. A series of low and high temperature processes are implemented to demonstrate both the technological efficiency and economic performance.
Regarding kerf purification, a first set of low temperature treatments are lowering the initial light impurities (C,O) content from a few weight percent level below 1w%. High temperature treatment is then needed to further decrease the residual light impurities content to match the requested ppm level (5N Solar grade). Deoxidation and decarburization of the kerf powder will be considered through metallurgical treatment at high temperature, meaning above the melting point of Silicon, implementing a physico-chemical transfer from the condensed phase towards gas phase to evacuate by-products of reactions.
In this context, the recruited postdoc will be fully involved in the design of the purification pilot. Given the high interaction level needed to achieve the ambitious objectives of the ICARUS project between SIMAP laboratory and ROSI, a joint team will be developed to enhance and promote scientific and technical advancements between the partners.
In particular, the postdoc will focus on the scientific development of the deoxidation and decarburization process at high temperature mostly through an experimental approach, that will be completed by thermodynamic and kinetics calculations:
i. Based on the existing literature and in relation with his/her supervisor, the postdoc will mostly
consider on the ternary system Si-O-C (condense/gas) in order to
ii. The postdoc will design the experimental plan, conduct the experiments and analyze the results with
the support of dedicated characterizations. Experimental tests will be made with model compounds
and with industrial compounds in order to validate the proposed technological solutions.
iii. Thermodynamic and kinetics calculations will be employed to assess the performance of the
mechanisms, to aim at an optimized process.
iv. Reporting (oral presentations, reports) will be performed at the team and project levels
As part of the joint SIMAP/ROSI team, the postdoc will also benefit from industrial feedbacks about the scalability and cost breakdown of the approach.