Solar photovoltaic (PV) installations must be properly dismantled and any waste treated and disposed at the end of project life. However, because most of the world’s nearly 400 GW of PV systems have been built in the past decade – each expected to operate for between 20 and 30 years – current PV module waste volumes do not yet justify widespread operation of PV recycling facilities.
The necessary policies and technologies for recycling PV systems are currently under rapid development. With modifications to the European waste electrical and electronic equipment directive (WEEE 2012/19/EU) in 2012, take back and recycling of PV modules is, in fact, already mandatory in Europe. There, take back and recycling is currently performed in small but annually-increasing quantities. Even though waste treatment is considered part of a module’s life cycle, only a few life cycle inventories (LCI) of energy and materials flows are available for the industrial recycling processes that are used today to recycle crystalline silicon-based (c-Si) PV modules.
LCI are the data inputs that inform lifecycle assessments which quantify the environmental impacts across the full life cycle of PV modules—from manufacturing and use to end of life. To help progress the industry forward, a survey of European recyclers was performed to characterize existing commercial recycling processes and share associated life cycle inventory data.
System Boundaries
The reference unit, or “functional unit” in the vocabulary of life cycle assessment, is defined as the processing of one metric ton of crystalline silicon PV modules in recycling lines for laminated glass, metals, and electronic wastes. Today, all modules are processed in discrete batches, yet not metered at that scale. Thus the process energy for a batch is estimated based on scaled annual production data as well as on input and output streams. All the recyclers that participated indicated that the recycled output materials were processed further downstream; these were not included in the study as they are outside of the control and knowledge of the respondents. Direct emissions (e.g., dust and water emissions) were also not accounted for in the recycling processes.
Results
Sixteen recyclers were contacted worldwide between 2015 and 2016, of which five European companies (one in Belgium, two in Italy, and two in Germany) provided LCI data. Survey responses indicate that the participating companies are fully compliant with the WEEE directive. The companies’ practices often even exceed the current demands set by the WEEE directive, though future WEEE requirements may become more stringent. In all cases, the batches of PV modules processed to date represent a small share of the total recycling capacity of the plants. Four of five recyclers incorporated the module recycling processes into their preexisting lines without any modifications except for some new parameter settings and optimizations.
Conclusions
Very little public information is available regarding the environmental effects of PV module recycling processes and, more generally, options for decommissioning and disposal of PV systems. This research is valuable for understanding current recycling processes employed in Europe where PV module recycling is already mandatory according to the WEEE Directive. As such systems for the collection of modules have been implemented and commercial recyclers have started to recycle waste modules in full compliance with the laws—mostly by using excess capacity in existing recycling facilities designed to treat laminated glass, metal, or e-waste.The current WEEE mandates do not require a high enough recovery fraction of the mass of input modules to necessitate specialized module recycling processes to recover more minor constituents. However, that seems likely to change in the near future.By contrast, there is currently no regulatory framework for PV recycling in the U.S., but state-level legislation and initiatives are under consideration.
This study also helps to inform the direction of future research. As indicated in the results reported by the five respondents of our survey, better recovery yields seem to require more process steps and greater energy consumption. To minimize the life cycle environmental impact of PV generated electricity (considering from the manufacture of the PV modules to their use and end-of-life management) and also to increase the value of module recycling, recovery of valuable but trace constituents like silver will be necessary. This will require both greater waste streams to justify dedicated recycling facilities and further research and development. Development of dedicated PV module recycling facilities that offer higher yields, recovery of valuable materials, and optimization of electricity consumption can offer environmental and economic benefits to all stakeholders involved.
