The German team created models to demonstrate the potential for saving water in the manufacturing of PERC silicon solar cells using a circular approach and existing technology.
For a 5 GW factory, it was found that water usage could be reduced by up to 79% and wastewater discharge could be decreased by up to 84%, representing a substantial improvement compared to a standard scenario.
The Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany has developed models to evaluate and compare two circular water strategies for a 5 GW passivated emitter and rear (PERC) solar cell factory.
This is the first comprehensive water model for a solar cell factory that has been published, according to the researchers.
The team examined two different scenarios for freshwater and wastewater flow in comparison to a conventional PERC cell manufacturing plant.
The first scenario, referred to as low contaminated wastewater (LCR), involves reclaiming rinsing waters for indirect discharge in compliance with regulations, and using certain wastewater streams as fresh water for downstream applications.
The second scenario, known as minimal liquid discharge (MLD), aims to minimize the amount of wastewater leaving the factory while identifying and recovering valuable materials from the wastewater.
Cost-benefit analysis and life cycle assessments (LCA) were conducted for each scenario using Umberto 11 software and the Ecoinvent database.
The analysis also included specific material flow models, environmental assessments, and total cost ownership (TCO) calculations.
“An overall environmental impact analysis is required to determine if the proposed solutions achieve a net environmental improvement for the solar cells production system,” stated the team.
“The results show that for the investigated scenarios 38% and 79% of the water consumption and 40% and 84% of the wastewater indirect discharge at the cell factory can be saved by the LCR and MLD approaches, respectively.”
Furthermore, cost reductions of 0.5% and 0.7% from cell production were identified for LCR and MLD strategies, respectively.
“Compared to the reference scenario, the proposed circular water strategies offer significant water and wastewater savings,” said the group.
We evaluated various water and wastewater treatment technologies, taking into account factors such as cost, energy requirements, operational risks, and complexity.
We specifically focused on water recycling technologies that are commercially available and suitable for treating the unique chemical composition of PV wastewater, including reverse osmosis, calcium fluoride precipitation, and ultrafiltration.
Additionally, our team collected comprehensive data for each step of PERC solar cell production.
We also considered specific constraints such as a throughput of 2819 m2 cells per hour, and product specifications including a thickness of 160 µm, area of 244.32 cm2, power output of 5.37 W, and a cell power conversion efficiency of 22%.
The team utilized various tools to develop the scenario models. Phreeqc software was employed for mixing streams, evaporation, precipitation, and neutralization reactions, as well as for utilizing chemicals.
Phreeqc is a computer program that specializes in speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations.
The SIT.dat database was used to model solutions for evaporation processes involving high-saline solutions.
Additionally, DuPont WAVE water treatment design software was used to simulate membrane processes.
The team also demonstrated water and wastewater stream models, including water reclamation processes.
The EU Environmental Footprint, Version 3.0 was utilized for the life cycle impact assessment (LCIA), resulting in a reduction of 0.4% for LCR and 3.2% for MLD in the environmental impact single score of cell production.
“The performed lifecycle costs analysis has shown that such technologies are economically viable for this application, but energy, water and wastewater discharge prices had to be carefully assessed,” said the academics, adding that net cell production cost reductions of €0.025/W and €0.035/W are achievable for the LCR and MDL strategies, respectively.
“Reductions in environmental impact on the cell factory are estimated from -1.4% to 34.3% for the different impact categories, with significant reductions in the freshwater ecotoxicity, freshwater and marine eutrophication for both circular water strategies,” explained the team.
In their examination of the MLD scenario, they observed that it necessitated a high amount of thermal energy and higher initial and operating costs for the necessary equipment.
However, they also pointed out that MLD allows for a 79% reduction in freshwater usage and an 84% reduction in wastewater production, leading to yearly savings in freshwater and wastewater expenses, as well as the potential to recover valuable by-products for use in other industries.
Looking to the future, the researchers anticipate adoption in tunnel oxide passivated contact (TOPCON) and heterojunction (HJT) factories, as many of the analyzed wastewater streams exhibit similar characteristics.
They suggest setting up a demonstrator to verify the projected savings, as numerous technical obstacles had to be addressed.
Source Researchers from Germany’s
