IGPN - International Green Purchasing Network

February 10, 2026

Sourcing outside China essential for transparency and sustainability in the solar supply chain

WACKER is one of the few producers outside China manufacturing high-purity polysilicon – a key material for solar cell production. The company can demonstrate that all its materials are responsibly sourced. At the same time, solar modules using cells made from WACKER’s polysilicon are only marginally more expensive than modules based on supply chains fully located in China.

The Big Buyers Working Together (BBWT) Community of Practice (CoP) on Sustainable Solar visited WACKER’s Burghausen site to gain insights into how risks such as forced labor in the global solar supply chain can be minimized and what cost implications this entails.

While it is technically impossible to link every batch of silicon metal to a specific batch of polysilicon, WACKER has full control and transparency of every material which enters its processes. This is ensured through strict supplier controls, Ecovadis-based requirements, and full disclosure of quartz sources. Furthermore, each pallet of polysilicon is traceable to the customer who received it, enabling module manufacturers and ultimately buyers to confirm that the polysilicon used in their modules comes from WACKER.

Suppliers of silicon metal must provide a formal self-declaration confirming the origin of quartz used in their production. This decla ration includes disclosure of the quartz source, confirmation of its origin, and responses to WACKER’s sustainability and compliance questionnaires. Only suppliers meeting these requirements, together with Ecovadis documentation, are approved. Since silicon metal is typically produced near quartz mines, sourcing outside China is essential for a sustainable and responsible supply chain.

WACKER’s sustainable approach results in only a minimal cost increase: approximately €0.022 per watt-peak, translating to less than €0.001 per kWh. The price difference between a regular module and one using WACKER’s polysilicon is therefore negligible, making it easier for public buyers to justify choosing ethical and sustainable solutions.

For Europe’s solar industry to grow, clear signals of demand for sustainable solar panels are needed – through public procurement requirements or subsidies. The CoP emphasizes that carbon footprint criteria alone are insufficient, as some manufacturers can report low-carbon values or offset emissions through certificates. Berlin’s experience with traceability criteria and supplier declarations could serve as best-practice examples for other public buyers.

Learn more at ICLEI Sustainable procurement platform webpage.

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