For more than 15 years FerroAtlantica (now Ferroglobe) has been developing a method of silicon purification to obtain Upgraded Metallurgical Grade Silicon (UMG-Si) for PV solar application without blending. After many improvements and optimizations, the final process has clearly demonstrated its validity in terms of quality and costs. In this paper the authors present new results stemming from a first mass-production campaign and a detailed description of the purification process that results in the tested UMG-Si. The subsequent steps in the value chain for the wafer, cell and module manufacturing are also described. Two independent companies, among the Tier-1 solar cells producers, were selected for the industrial test, each using a different solar cell technology: Al-BSF and black silicon + PERC. Cells and modules were manufactured in conventional production lines and their performances compared to those obtained with standard polysilicon wafers produced in the same lines and periods. Thus, for Al-BSF technology, the average efficiency of solar cells obtained with UMG-Si was (18.4 ± 0.4)% compared to 18.49% obtained with polysilicon-made wafers. In the case of black silicon + PERC, the average efficiency obtained with UMG-Si was (20.1 ± 0.6)%, compared to 20.41% for polysilicon multicrystalline wafers.

Upgraded metallurgical grade silicon (UMG-Si) for photovoltaic (PV) solar applications has been manufactured through the metallurgical route by means of the process developed by Ferrosolar. In an ambitious mass production test, performed in commercial solar cells and modules production lines, the silicon was proven to be appropriate for photovoltaics applications (Fornies et al., 2019 Mass production test of solar cells and modules made of 100% umg silicon. 20.76% record efficiency. Energies 12), reaching, in a conventional production line, up to 20.76% of solar cell efficiency with multicrystalline cells made of 100% UMG silicon. In this paper we present more results from the mentioned massive test. Defect engineering is being applied to improve the bulk lifetime of the UMG wafers and to guide in the identification of the limiting defects in the material. Moreover, the modules produced with 100% UMG silicon solar cells were installed together with the modules produced in the same production line with polysilicon material to assess the degradation of the UMG silicon when compared to polysilicon. After 24 months of outdoor PV generation, the degradation, in terms of Performance Ratio at 25C (25PR) diminution, has been the same for both types of modules. Additionally, a Life Cycle Assessment (LCA) has been performed for this UMG silicon and state-of-the-art Siemens polysilicon to compare the environmental impact of both silicon feedstocks. The results presented in this paper; chemical analysis of wafers, defect engineering, low degradation, average efficiency and environmental assessment, lead to a complete study of UMG silicon, confirming its potential to be used as raw material for PV applications.