Upgraded metallurgical grade silicon and polysilicon for solar electricity production: A comparative life cycle assessment

Abstract

Solar grade silicon (SoGSi) is a key material for the development of crystalline silicon photovoltaics (PV), which is expected to reach the tera-watt level in the next years and around 50TW in 2050. Upgraded metallurgical grade silicon (UMGSi) has already demonstrated to be a viable alternative to standard polysilicon in terms of cost and quality. This study presents the life cycle assessment (LCA) of UMG obtained by the FerroSolar process. Moreover, it shows the environmental impacts of PV modules and electricity generation based on this material. For this, an exhaustive review of the life cycle inventory (LCI) of PV value chain, from metallurgical grade silicon (MG-Si) down to electricity generation, has been carried out updating inputs for all processes. The Balance of System (BoS) has also been updated with current state of the art data for a fixed open ground large PV site (100 MWpk). Two different electricity mixes, with low and high carbon intensities, have been considered. The results reveal that for PV electricity generation using UMG-Si instead of polysilicon leads to an overall reduction of Climate change (CC) emissions of over 20%, along with an improvement of the Energy Payback Time (EPBT) of 25%, achieving significantly low values, 12 gCO2eq/kWhe and 0.52 years, respectively. Moreover, it is shown that UMG silicon feedstock is not the main contributor to the carbon and energy footprint of the produced electricity, leaving the first place to PV module manufacturing.