Eco-Solar organised this workshop in cooperation with the H2020 project CABRISS.
During the workshop, 35 participants from industry and institutes lively discussed the valorisation potential of 8 different kinds of waste selected from the value chain of photovoltaic production. Several creative solutions were identified and collected on canvas. Some groups already agreed on follow up meetings to elaborate deeper on cooperation potential to market the wastes.
The topics, their major outcomes and market prerequisites are:
Topic 1: Kerff Recycling in Metallurgical Applications
Si-kerff can be purified to 5N quality and utilized as feedstock blended with other solar grade silicon. Impurities are water, glycol, oil, SiC, Diamonds Fe, Ni, glass, oxidation products etc. Poorer qualities can be used e.g. in metallurgical applications. The major market for selling this technology is in Asia as the amount of kerf available in Europe is moderate.
Topic 2: Kerff Recycling for hydrogen fuels and sodium silicate
Si kerff can be purified and used for hydrogen fuels by oxidation of the Si particles in water with chemical additions. The material is converted to sodium silicates by reaction with sodium hydroxide. Storage and transportation of kerf is difficult for its high reactivity with oxygen and moisture generating hydrogen, therefore it is preferable to have the conversion process implemented at the same location where the wafer cutting is performed.
Topic 3: Quartz Reuse or Recycling (In Horticulture, Additives, Construction Materials etc.)
Crucibles that are used for melting and crystallization of silicon ingots are manufactured from high purity quartz or silica. After use, the crucibles break during cooling due to a partial phase transition of the glassy phase to b-cristobalite. The fragments may contain silicon, SiC, Si3N4 or SiOx on their surface. The material can be used in horticulture, milled quartz for additives (polymers, construction materials).
Other material can be used as SiO2 source for cement, concrete, inorganic fillers etc. Horticultural applications or decorative tile manufacturing will require more time for market development. The market size in Europe for silica and quartz crucibles is small.
Topic 4: Graphite Reuse
Graphite is used for heaters, crucibles and heat insulation, in silicon crystallization furnaces and Czochralski pullers. It may react with Si and SiOx vapour to SiC and CO. Si may also be deposited on the surface and in the pores of the graphite together with SiOx. The mechanical properties may change. Potential applications of the graphite would be SiC, activated carbon, soot, electrodes, additives etc. Time to market could be 1 year for abrasives and around 4 years for more complex products.
Topic 5: Recycling/ Reuse of Defect and Broken Cells
The solar cells may be cut to smaller pieces and used in solar powered gadgets. Another option is to remove the metal layers, antireflective coatings and dopant layers with selective etching, so that the silicon can be used as solar grade silicon again. The application of recovered solar grade silicon has to be seen on long term, and strongly correlates with the poly silicon price and avalaibility on the world market.
Alternatively, the metals can be recovered for use as Ag or aluminum compounds (e.g. for use as water chemicals). Poorer silicon qualities can be used in metallurgical applications.
Topic 6: Polymer Materials for PV
Most polymers are used energetically after recycling. Thermoplastics can in principle be melted and recycled, chemical recycling is under investigation as well. Development of recycling solutions for PVF, PVDF and other will require at least 1 year of R&D.
Topic 7: Reuse of Glass
Glass recycling is well established but due to the level of contamination, the glass from solar modules is mainly used as fiber or foam glass. Reuse in the flat glass or container glass industry is desired but requires high purity of the fractions. Implementation of new technologies can increase output quality within the next ten years.
Separate treatment of the polymer fraction during module recycling e.g. by thermal treatment allows high purity and yield of Si, Ag, Cu outputs.
Topic 8: Metal Recycling
During the recycling process the metals are separated with metal separators after crushing and/or milling of the modules. Al from the frames can be reused for remelting, Cu with Sn/Pb coatings can be recycled at Cu smelters, Ag from the solar cells can be removed via etching or melting of the solar cells. Cables go to cable recyclers. The existing metal recycling technology seems to be sufficient.
Presentation Eco-Solar by Martin Bellmann:
Presentation CABRISS by Terje Halvorsen: