Water and wastewater treatment for Solar industry

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Courtesy of EnviroChemie GmbH

Solar cells arc manufactured in a complex process thai requires enormous know-how. The objective is to produce panels with a high level of efficiency at low cost. To achieve this, different production processes are used. A fundamental distinction is made between solar cells on the basis of silicon wafers and thin-film cells, in which a special process is used to apply the photovoltaic layer onto a carrier medium. The manufacturers of solar cells are constantly developing and improving the production processes.

For all methods, large quantities of water arc required. The production process leads to polluted wastewater. Since water is becoming increasingly valuable as a raw material, efficient water management is necessary. The wastewater from the production process must be treated in such a way that as much water as possible can be recycled. The treated wastewater must reliably comply with the discharge parameters so that it can be discharged without polluting the environ ment. Besides optimisation of the production process, optimisation of the wastewater treatment is often necessary. This is why EnviroChemie is conducting intensive research to continuously develop the process and thus to significantly increase water recycling rates. For this reason, the entire production process has to be taken into account in order to achieve not only 'end of the pipe' solutions, but also to offer production-integrated solutions. In Germany, the standards for wastewater treatment are high. They are laid down in Appendix 54 of the Wastewater Ordinance (AbwV). This appendix applies for wastewater whose contaminant load originates pri-marily from the production of semi-conductor components and solar cells, including the related prelreatment. intermediate treatment and after-treatment. In addition, local statutes laid down by local authorities and towns must also be complied with. These frequently lay down further requirements depending on the capacity of the local municipal sewage treatment plant and the pre* vious pollution of the outfall (river) into which the sewage treatment plant discharges the treated wastewater. The concepts also require that safety engineering should meet special standards. An example here is the formation of hydrogen from alkaline wastewater when silicon from wafer production is dissolved. Coordinated measures are required here for explosion prevention and protection. Fluoride is created in the production process as hydrofluoric acid HF. The handling of hydrofluoric acid requires special precautions, since this substance is extremely toxic and aggressive, and contact with even small quantities can have fatal consequences. These basic requirements must be met in all projects worldwide.

In the following, three examples will be used to show the continuing innovative water and wastewater treatment in the solar industry. The examples arc not only current projects, but also processes from the field of research and development.

Solar cell production In India
In the past few years, the production of wafers and cells has increasingly been transferred abroad. In some cases, the requirements for the treated wastewater differ from those in Germany. One example of this is India.

In India, ground and surface water naturally have a high concentration of fluoride. In the state of Rajasthan, almost all districts have high fluoride concentrations (up to 18 ppm) in their drinking/ground water sources. In southern Rajasthan. the concentrations of fluoride are up to 11 ppm (for comparison, in Germany the fluoride concentration is only 0.3 ppm). These high concentrations.

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