Scientists of the Technical University of Berlin, Rena Technologies GmbHhe Fraunhofer Institute for Construction Physics IBP and the Fraunhofer Institute for Solar Energy Systems ISE have created for the first time a comprehensive model of water flows in a 5-gigawatt solar cell factory. On this basis, they examined the introduction of two different strategies for circular water use.
The result: With current production technologies, water savings of up to 79 percent and wastewater reduction of up to 84 percent would already be technically possible. This allows the construction of new solar cell factories even in places with lower water availability. The study is available free of charge in the latest issue of Solar Energy.
The research team analyzed the flows of water, wastewater and materials for the production of PERC solar cells with a maximum annual capacity of 5 gigawatts. The results are also of interest to factories producing or converting TOPCon or heterojunction solar cells, as the wastewater flows for these cell types are very similar.
Minimal liquid discharge
“Based on the model of this production, we analyzed different options for saving and recycling water,” explained Peter Brailovsky, one of the two main authors of the study and a scientist at Fraunhofer ISE. “We can recommend two approaches: the reuse of slightly contaminated wastewater (LCR) and the so-called ‘Minimum Liquid Discharge’ (MLD), in which certain waste is recycled elsewhere, for example, etching solutions left from the production of solar cells”. It can then be recycled and used in cement production.
“The results show that the MLD scenario can save up to 80 percent of freshwater and wastewater needs in the solar cell factory,” says Jascha Reich, second lead author and scientist at the Technical University of Berlin. “If the LCR approach is used, savings of up to 40 percent can be achieved. At the same time, the application of saving measures would not entail additional costs for production, but, on the contrary, would even entail slight cost savings.”
Closed water cycle
Furthermore, a closed water cycle greatly reduces the risk of a factory closing with weekly costs of around €1.9 million due to water shortages, for example during summer heat waves.
Solar cells are in themselves a very sustainable product. Integrated into a photovoltaic module, the energy needed to produce it pays for itself in a very short time, typically within 1.3 years for photovoltaic systems in Central Europe. “But we don’t have to rest on our laurels,” said Jochen Rentsch, head of the technology transfer department in the photovoltaics area at Fraunhofer ISE. “As everywhere in the manufacturing economy, photovoltaics should also be part of a circular economy.”
