From pv magazine Global
A white paper published this week by UK analysts Exawatt and Germany’s Nexwafe analyses the current state of PV manufacturing. The study reveals opportunities and challenges for new technologies, particularly Nexwafe’s innovative “Epiwafer” process for the production of silicon wafers.
Nexwafe’s technology does away with the polysilicon production and ingot pulling stages of production, replacing them with a process that grows wafers direct from silicon tetrachloride gas, or the trichlorosilane gas that’s today used as the feedstock for polysilicon production. By cutting these heavy, industrial stages from the PV supply chain the process promises lower manufacturing costs, lower equipment capex and reduced environmental impacts, as well as potentially better quality, thinner wafers able to reach higher efficiencies once processed into cells.
The white paper, which is available for download from Nexwafe’s website, seeks to place this technology within the context of today’s PV manufacturing landscape and evaluate its potential. Nexwafe is currently developing a 500MW demonstration line for its technology in Germany, and last year picked up €39 million ($42.5 million) in an investment round led by India’s Reliance Industries. Despite these successes, the technology still has a way to go to prove itself at scale.
Exawatt finds significant opportunity for this new technology to play off of other developments in PV manufacturing. And it is able to produce wafers at any size, avoiding reported challenges in ingot pulling for the largest 210 mm format.
The process also allows for wafers to be made much thinner than the current ingot/diamond wire saw processing allows. Nexwafe CEO Davor Sutija recently told pv magazine that the company would most likely produce its first wafers at 120 microns, and that it could go much thinner than this later on, if manufacturers are able to improve handling of the thinner, more fragile products in other stages. Exawatt notes that this would offer an advantage or heterojunction cells in particular, where the optimal thickness is 100 microns or even less, while PERC and TOPCon structures work best on a cell between 150 and 200 microns, as can be achieved using the current processes.
Nexwafe’s process also promises lower oxygen content and even dopant distribution – adding up to as much as 1.1% absolute efficiency gain, as well as opening up further possibilities. “In the longer term, the high level of process control afforded by the EpiWafer process could allow for additional techniques to be employed to continue pushing cell efficiencies higher, for example though the incorporation of quantum wells,” states Exawatt.
The recent push for energy security and localised PV supply chains also creates an opportunity for regions outside of China to produce a differentiated production, rather than trying to compete on scale with established industry giants. Exawatt notes that Nexwafe has signed letters of intent with several of the key players looking to establish PV manufacturing outside of China, alongside the investment from Reliance in India.
The biggest remains the scale up from “lab to fab,” with Exawatt warning that the initial 500MW facility in Germany will not be cost competitive with current wafer prices, though this model begins to improve once Nexwafe reaches larger capacities of 3GW and then 6GW.
“From a financial perspective, the key challenge will be to successfully scale up and bridge the gap from lab-scale production to high volume. From a technical perspective, it will be key to demonstrate that the theoretical increases in cell efficiencies afforded by EpiWafers can be realised in practice in cell manufacturing,” the report concludes. If that potential can be realised, the PV industry may yet see another revolution in wafer manufacturing.”
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