Circular production strategies and sustainable design criteria in PV manufacturing

Solar PV is a crucial technology for the transition to more sustainable economies. Multiple Life Cycle Assessments (LCA) have been made to assess PV environmental impacts. The core of these studies lies on the Life Cycle Inventories (LCI) used for the manufacturing of PV system components. This work identifies several research gaps in the existing LCI: 1) the LCI needed to be systematically updated to take account of technological developments, 2) the facilities and services supporting the main production processes were not covered in detail, and 3) the LCI aggregated at the factory level doesn’t allow the study of energy, material and resource flows. This dissertation presents a process-based bottom-up modelling approach to integrate LCI and circularity strategies for the polysilicon to PV module value chain. Circular production LCI for p- type Cz silicon wafers, Passivated Emitter and Rear Contact (PERC) solar cells and glassbacksheet PV modules with an aluminium frame are integrated and disclosed. The methodology includes a first step of data collection and validation for the reference products and production processes. In a second step, the required process and facilities equipment is determined and dimensioned. The third step is to dimension the civil, structural, and architectural infrastructure for a polysilicon to PV module industrial site with a production capacity of 5 GWp/a. With both the operational and the infrastructure requirements, integral reference products LCI are created. Finally, a number of circularity strategies are proposed and evaluated through comparative LCA and their Total Cost of Ownership., these analyses and results are published in three peer-reviewed publications that integrate this cumulative dissertation. A first publication examines material and solid waste flows and proposes the circular strategies Revalorized Waste (RW) and Vertical Integration (VI). With the RW and VI strategies, it is possible to avoid and revalorize 87% of the solid waste produced in a 5 GWp/a Poly-Si to PV module industrial site, this represents a circular flow of raw materials of 18,756 metric tons per year. In a second publication, the water, chemical, wet exhaust and wastewater flows of a PERC solar cell factory are scrutinized and the circular strategies Low Contaminated wastewater Reclaim (LCR) and Minimal Liquid Discharge (MLD) are envisioned. With the MLD strategy 79% of the water consumption and 84% of the wastewater indirect discharge of a PERC cell factory can be saved. In regions with limited water availability, the LCR and MLD strategies, as well as the reduction or elimination of silane consumption, can become enablers for new investments in PV manufacturing and reduce operational risks of existing production sites. Finally, a third publication calculates the environmental impact of the procurement and construction of the industrial site and proposes the use of a sustainable structural Timber Building System (Timber BS). A key outcome is the creation of updated and state-of-the-art LCI datasets for PV factories. Their adoption into the Ecoinvent database is recommended to replace outdated II datasets from the early 2000s. The LCI update resulted in factory environmental impact reductions ranging from 11.7% to 94.3% for 14 of the 15 environmental impact categories assessed. The updated factory environmental impacts contribute between 0.16% and 4.42% of the total PV module environmental impact for all impact categories assessed. These results show that most of the environmental impacts are due to the operation of the industrial site rather than from its procurement and construction. A sensitivity analysis shows that the most effective measure to reduce environmental impacts of all categories and the cost is to increase the PV module efficiency. A 10% efficiency increase translates into 9.1% reductions on all environmental impacts and Total cost of ownership. A 10% reduction in metallization paste consumption reduces the Resource use, mineral and metals impact by 6.6%. Silane consumption savings of 10% in the cell factory allow a reduction of Water use of 5.7%. Technical parameters with a significant environmental impact, so-called environmental hotspot parameters, and a strong cost driver, such as higher cell efficiency and thinner wafer pitch, are being continuously improved by the PV industry. However, to promote improvements in environmental hotspot parameters with a strong environmental driver and a weak cost driver, such as silane and water consumption and wastewater discharge reduction, environmental policy instruments may be required.