low-cost solar-grade silicon (SoG-Si) feedstock is demanded
MG-Si is commercially produced through the reduction of silicon oxide (quartz) with carbon in submerged arc furnaces
contains impurities such as Fe, Al, Ti, Mn, C, Ca, Mg, B, P and so on.
The minimum required purity of silicon for photovoltaic applications is 6N and for silicon wafers used in the semiconductor industry is 9N
The development of several alternative routes to the traditional Siemens chemical process of producing pure silicon, was accelerated the produced polysilicon by this method is still the most used type of silicon feedstock for solar cell manufacturing. In 2009, it had a market share of 97.5% of all the silicon feedstock used for solar cell production, while the rest (2.5%) was represented by upgraded metallurgical grade silicon materials and silicon scrap from the semiconductor industry[2]
The main advantage claimed by manufacturers that developed dedicated metallurgical refining routes concerns the low energy consumption rate
According to Norway, france and China, the produced SoG-Si through the combinations of metallurgical methods can provide the required impurity levels for PV applications such as 0.3 ppmw B, 0.6 ppmw P and 1-10 ppmw metals
silicon purification process >> slag treatment, acid leaching, directional solidification, segregation refining, plasma purification, post plasma segregation, gas blowing, vacuum refining, oxidation for B removal, vacuum treated for P removal[3][4][5][6][7]
Upgraded metallurgical grade silicon and polysilicon for solar electricity production: A comparative life cycle assessment[8] ** main
Solar grade silicon (SoG-Si) 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.
UMG >> in terms of cost and quality
life cycle assessment (LCA) of UMG obtained by the FerroSolar process
Two different electricity mixes, with low and high carbon intensities, have been considered.
PV electricity generation using UMG 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
The power sector is the main responsible of the world’s greenhouse gases (GHG) emissions, with approximately 70%, due to the predominant share of fossil fuels.[9]
the decarbonization of the power sector is mandatory to achieve the objective of limiting the global average temperature rise to 1.5 °C , as stablished in the Paris Agreement, back in 2016.[10]
Nowadays, crystalline silicon technology accounts for over 95% of the worldwide market and it can be safely assumed that will remain the same for the following years[13][14]
Nowadays the market demand of solar grade silicon is almost completely covered by polysilicon, produced by different configurations of the Siemens process.
Alternatives to Siemens polysilicon are Fluidized Bed Reactor (FBR) Solar Silicon and upgraded metallurgical grade silicon (UMGSi), and even direct carbothermic reduction of silica.
The UMG silicon assessed in this work has been manufactured through the metallurgical route by means of the process developed by Ferrosolar in Spain.[15]
In a previous mass production test, performed in commercial solar cells and modules production lines, this feedstock has proven to be appropriate for PV applications, reaching, in a conventional production line, up to 20.76% of solar cell efficiency with multicrystalline cells made of 100% UMG silicon.[16][15]
process-based LCA, according to the Methodology Guidelines on LCA of Photovoltaic Electricity published by the International Energy Agency (IEA)[17]
LCI
module eff: 18.43% (UMG), 18.55%(poly Si)
cradle to use
transport of the different materials between production steps has been not considered, with exception of PV modules transport to PV site location
it has been shown before that transportation only accounts for a minor part of the final impact in electricity[18]
the reference year used for both mixes is 2018, for which homogeneous data was available. Spanish mix has been selected because Ferrosolar process is meant to be carried out in the facilities located at Puertollano, Spain [15] and can be considered among lower carbon intensity mixes.
Inventory for mounting structure and electrical installation has been calculated from current real data gathered from TINOSA Project, comprised of several plants, with a total installed power of 180MWpk.[19]
End-of-life (EoL) management has been taken out of this study due to the lack of industrial scale data, as these PV systems have not still reached the minimum volume needed for economical reutilization and recycling processes that will be needed by the end of the next decade[20]
No difference should be found in recycling between polysilicon and UMG-Si as the recovery of silicon is expected to provide low grade silicon (similar to metallurgical grade)[21]
umg: Ferrosolar's UMG silicon for solar applications has a boron concentration bellow 0.2 ppmw and a phosphorous concentration that can be tailored between 0.1 and 0.3 ppmw. Metals concentration is below 0.5 ppmw (including Fe, Al, transition, alkaline and alkaline earth elements). These specifications are suited for multicrystalline silicon applications. inventory purposes the process has been divided in its main steps: slagging, vacuum refining and directional solidification. Two additional processes have been modelled: an inert melting step, whose purpose is to recycle non pure Si material from the final steps of the process to reduce material consumption, and a final step in which the final formulation of the product is obtained
Predictably, due to the higher carbon intensity of its energy mix, UMG-CN CC category result is 33% higher than UMG-ES
he differences between the pairs UMG-ES/poly-ES and UMG-CN/poly-CN are 24% and 15% for CC and 33% respectively.
CC calculated emissions vary between 12.1 and 21.4 gCO2eq/kWhe for UMG-ES and poly-CN scenarios.
Upgraded metallurgical-grade silicon solar cells with efficiency above 20%[22]
The independently measured results yield a peak efficiency of 20.9% for the best upgraded metallurgical-grade silicon cell and 21.9% for a control device made with electronic-grade float-zone silicon.
Performance Analysis of a Grid-Connected Upgraded Metallurgical Grade Silicon Photovoltaic System[23]
this study investigates the outdoor performance of a 1.26 kW grid-connected UMG-Si PV system over five years
a mono-Si PV system installed at the same place
The production of UMG-Si can be five times more energy efficiency than the conventional Siemens process to produce solar grade silicon; hence, the cost of UMG-Si is much lower[24][25]
PV modules made from UMG-Si manufactured by Canadian Solar and Silicor Materials are being tested at the National Renewable Energy Laboratory (NREL)[26]
In China, a UMG-Si PV plant with a capacity of 330 kW has been built[27]
The 1.26 kW UMG-Si PV array consists of 6 polycrystalline silicon based CS6P-210PE modules manufactured by Canadian Solar, and the 1 kW mono-Si PV array consists of 5 HIP-200BA3 modules manufactured by Sanyo (San Diego, CA, USA). The PV arrays are installed at a fixed direction with a tilt angle of 40° to receive maximal average solar irradiation. The PV arrays are connected to inverters manufactured by PV Powered for the UMG-Si PV system and by SMA for the mono-Si PV system.Long-term performance annual degradation rate, Rd, was 0.44% for the UMG-Si PV system and 0.71% for the mono-Si PV system with a data filtering threshold of 600 W/m2.
↑Safarian J, Tranell G, Tangstad M (2012) Processes for Upgrading Metallurgical Grade Silicon to Solar Grade Silicon. Energy Procedia 20:88–97. https://doi.org/10.1016/j.egypro.2012.03.011
↑Bernreuter J, Haugwitz F (2012) The Who’s Who of Solar Silicon Production. Executive Summary
↑Geerligs LJ, Wyers GP, Jensen R, et al (2002) solar-grade silicon by a direct route based on carbothermic reduction of silica: requirements and production technology. In: Proceedings of the 12th Workshop on Crystalline Silicon Solar Cell Materials and Processes. pp 215–218
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↑Einhaus R, Kraiem J, Cocco F, et al (2006) PHOTOSIL–Simplified production of solar silicon from metallurgical silicon. Proc of the 21st European PVSEC 6–9
↑Hopkins RH, Rohatgi A (1986) Impurity effects in silicon for high efficiency solar cells. Journal of Crystal Growth 75:67–79
↑Kondo J, Okazawa K, Hiyoshi M, et al (2011) Compensation Free SOG Silicon Feedstock by Metallurgical Refinement.
↑Méndez L, Forniés E, Garrain D, et al (2021) Upgraded metallurgical grade silicon and polysilicon for solar electricity production: A comparative life cycle assessment. Science of The Total Environment 789:147969. https://doi.org/10.1016/j.scitotenv.2021.147969
↑Breyer C, Bogdanov D, Aghahosseini A, et al (2018) Solar photovoltaics demand for the global energy transition in the power sector. Progress in Photovoltaics: Research and Applications 26:505–523
↑Jäger-Waldau A (2019) PV status report 2019. Publications Office of the European Union: Luxembourg 7–94
↑IEA N (2020) Projected costs of generating electricity 2020. IEA, Paris
↑IEA N (2010) Projected costs of generating electricity. International Energy Agency 10:618
↑Philipps S, Warmuth W (2018) Photovoltaics Report Fraunhofer ISE. Fraunhofer Institute for Solar Energy Systems ISE, Freiburg im Breisgau, Germany
↑Philipps S, Warmuth W (2019) Photovoltaics report fraunhofer institute for solar energy systems. ISE with Support of PSE GmbH November 14th; Fraunhofer ISE: Freiburg, Germany
↑ 15.015.115.2Forniés E, Ceccaroli B, Méndez L, et al (2019) Mass production test of solar cells and modules made of 100% UMG silicon. 20.76% record efficiency. Energies 12:1495
↑Forniés E, Del Cañizo C, Méndez L, et al (2021) UMG silicon for solar PV: from defects detection to PV module degradation. Solar Energy 220:354–362
↑Frischknecht R, Heath G, Raugei M, et al (2016) Methodology guidelines on life cycle assessment of photovoltaic electricity. National Renewable Energy Lab.(NREL), Golden, CO (United States)
↑Stamford L, Azapagic A (2018) Environmental impacts of photovoltaics: the effects of technological improvements and transfer of manufacturing from Europe to China. Energy technology 6:1148–1160
↑Bramberger M (2020) Aurinka Internacional escoge a SENS para desarrollar 180 MW en Almería. In: pv magazine España. https://www.pv-magazine.es/2020/05/08/aurinka-internacional-escoge-a-sens-para-desarrollar-180-mw-en-almeria/. Accessed 21 Jul 2025
↑Chowdhury MS, Rahman KS, Chowdhury T, et al (2020) An overview of solar photovoltaic panels’ end-of-life material recycling. Energy Strategy Reviews 27:100431
↑Latunussa CEL, Ardente F, Blengini GA, Mancini L (2016) Life Cycle Assessment of an innovative recycling process for crystalline silicon photovoltaic panels. Solar Energy Materials and Solar Cells 156:101–111. https://doi.org/10.1016/j.solmat.2016.03.020
↑Zheng P, Rougieux FE, Samundsett C, et al (2016) Upgraded metallurgical-grade silicon solar cells with efficiency above 20%. Applied Physics Letters 108:122103. https://doi.org/10.1063/1.4944788
↑Huang C, Edesess M, Bensoussan A, Tsui KL (2016) Performance Analysis of a Grid-Connected Upgraded Metallurgical Grade Silicon Photovoltaic System. Energies 9:342. https://doi.org/10.3390/en9050342
↑Modanese C, Di Sabatino M, Søiland A, et al (2011) Investigation of bulk and solar cell properties of ingots cast from compensated solar grade silicon. Progress in Photovoltaics 19:45–53. https://doi.org/10.1002/pip.986
↑Odden JO, Lommasson TC, Tayyib M, et al (2014) Results on performance and ageing of solar modules based on Elkem Solar Silicon (ESSTM) from installations at various locations. Solar Energy Materials and Solar Cells 130:673–678. https://doi.org/10.1016/j.solmat.2014.04.002
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