Low-Cost Clean Solar Silicon from Natural Quartzite

Solar farm, credit: LoveSilhouette/iStock via https://interestingengineering.com/the-future-of-solar-energy-as-an-alternative-energy-source

Project Introduction

Silicon is the dominant photovoltaic material for solar power due to its bandgap match to the solar spectrum, abundance, and relatively low cost. However, its production using the dominant Siemens process (trichlorosilane synthesis, distillation and chemical vapor deposition) is expensive, energy-intensive, and unsafe. EMRG is developing a process to produce solar silicon by molten salt electrolysis directly from natural quartzite with zero direct greenhouse gas (GHG) emissions, with energy use and economics similar to aluminum production (i.e. >90% less energy and 80-90% lower cost than current solar silicon processes), and with much better scalability and process safety.

Objectives

This project aims to: (1) develop a set of validated models of chemistry, phase transformations and transport to create understanding and inform scale-up engineering, and (2) lay the foundation for scale-up and commercialization by customer discovery, commercially-focused experiments, and first-cut design and physics and cost modeling of a cell and plant. The schematics at the right show the rough electrochemical process (though Si exists not as bare 4+ ions but in oxide/oxyfluoride complexes) and a switching system designed to dissolve incipient roughness and prevent dendrite formation.

Approach

This project establishes four integrated mathematical models of the process based on new experimental data which help in the understanding of silicon molten salt electrolysis and its scale-up.

The molten salt structure (MSS) model involves spectroscopic analysis coupled with atomistic models to understand the molecular structure of complex ions in the five-component molten salt.
The CALculation of PHAse Diagrams (CALPHAD) model to understand and predict thermodynamic and thermophysical properties of the molten salt including silica solubility, silicon compound volatility and ion mobility.
The transport model will study the reaction and diffusion kinetics of silicon electrodeposition at the cathode-electrolyte interface to predict deposit structure and composition.
A phase field model uses these molten salt properties to study the transport of silicon to the cathode and oxygen to the anode to understand boundary layer structure and improve the deposition rate.

Using these models, a new current waveform switching system is developed to maintain stable dendrite-free silicon growth at high current density. The new low-cost single operation silicon molten salt electrolysis replaces multiple energy-intensive unit operations of carbothermic silicon production, acid digestion, trichlorosilane synthesis, distillation, and chemical vapor deposition used in the current Siemens process.

Researchers: Aditya Moudgal, Mohammad Asadikiya, Ariana Ly, Vicky Luu, Jacob Hazerjian, Douglas Moore, Adam Powell

Sponsors: National Science Foundation Awards 1937818 and 1937829, US Department of Energy Solar Energy Technologies Office Office Contract DE-EE0008988

Publication: Moudgal, Buasai, Wu, McMahon, Hazerjian, Luu, Ly, Asadikiya, Powell, Pal, Zhong, "Finite Element Analysis and Techno-Economic Modeling of Solar Silicon Molten Salt Electrolysis," JOM, January 2021.

Collaborators: Yu Zhong, Uday Pal Research Group at Boston University

Google Sites

Report abuse