Fig. 10: System boundary of the photovoltaic module, TOPCon, is shown as an example.

Cradle-to-gate scope of the life cycle assessment modelling, including the key manufacturing stages of silicon wafer production, solar cell fabrication and module components such as glass, copper and ethylene-vinyl acetate used to produce a TOPCon photovoltaic module. Manufacturing is modelled as being done in China, with transportation of the photovoltaic modules to the European market. The environmental impact associated with the production of the manufacturing equipment, the use phase of the photovoltaic modules and their end-of-life are not included in the modelling and are shown as outside of the system boundary. Background data obtained from the Ecoinvent v3.10 database provides for raw material extraction and energy consumption inventories required for the foreground data for each component of the life cycle assessment modelling. Secondary data is used for wafer production, module components and transport processes, while primary data obtained from the industry is instead used to provide the TOPCon cell fabrication. Wafer production accounts for the production of the silicon ingot, which is sliced into ultra-thin wafers and passed to the cell fabrication stage. This includes the addition of dopants, passivation layers, texturing and the addition of metal electrical contacts. Wafers are then arranged in an appropriate configuration to create a photovoltaic module and connected electrically, including a junction box with a bypass diode. All waste from each manufacturing stage is considered in the life-cycle assessment modelling. Coloured arrows are used to simply clarify the flows.