Waste inventory for a circular solar cell production value chain

A carbon neutral energy supply will rely heavily on the use of solar energy in different forms. Photovoltaics (PV), i.e. the generation of electricity from solar cells will be a cornerstone, and the production and deployment of solar panels have soared during the past 20 years, and PV now accounts for 60% of the global increase in renewable energy, according to IEA1. The production of solar cells is both a mature and immature industry at the same time: It is mature since robust industrial techniques exist that supply energy in amounts already comparable to traditional energy sources: nuclear, hydropower and fossil energy. It is immature because the development has occurred so fast that optimized routes for efficient resource handling need to be developed. During the production of solar panels large resource flows are generated, which currently largely end up as waste. Here to the challenge in re-use is connected to the material properties: The composition, purity and morphology will determine how the current waste should be processed in order to realize the value potential. We have therefore performed a waste inventory for three important material flows occurring from silicon-ingot and wafer manufacturing in the PV production value chain: Si kerf from sawing of wafers, silica from crucibles used in crystal pulling and graphite from crystal growth furnaces. Utilising the circular potential of these waste products, 9.6 Mt of silicon, 1.2 Mt of silica and 0.6 Mt of graphite could be unlocked by 2050 as secondary raw materials.