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Metal dissolution from end-of-life solar photovoltaics in real landfill leachate versus synthetic solutions: One-year study
Abstract
To investigate the after end-of-life (EoL) concerns of solar panels, four commercially available photovoltaics of 1515cm2 size in broken and unbroken conditions were exposed to three synthetic solutions of pH 4, 7, 10 and one real municipal solid waste (MSW) landfill leachate for one-year. Encapsulant degradation and release, probability of metals exceeding their surface water limit, and change in pollution index of leachate after dumping of solar panels were investigated. Rainwater stimulating solution was found to be predominant for metal leaching from silicon-based photovoltaics, with Ag, Pb and Cr being released to 683.26 mg/L (26.9%), 23.37 mg/L (17.6%), and 14.96 mg/L (13.05%) respectively. Copper indium gallium (de) selenide (CIGS) photovoltaic was found to be least vulnerable in various conditions with negligible release of In, Mo, Se and Ga with value ranging between 0.2 and 1 mg/L (0.30%-0.74%). In contrast, minimal metals were released to MSW leachate compared to other leaching solutions for all photovoltaics. Positive correlation was observed between encapsulant release and metal dissolution with a maximum encapsulant release in silicon-based photovoltaics in rainwater conditions. Probability of exceedance of leached metals to their respective surface water limits for Al (multi and mono crystalline-silicon (c-Si)), Ag (amorphous photovoltaic) and In (CIGS) has shown the maximum exceedance of 92.31%. The regression analysis indicated that conditions of the modules and pH of the leaching solution play significant roles in the leaching of metals. The increase in leachate contamination potential after one-year of photovoltaics dumping was found to be 12.02%, 10.90%, 15.26%, 54.19% for amorphous, CIGS, mono and multi c-Si photovoltaics, respectively. Overall, the maximum metal release observed in the present study is 30% of the initial amount under the most stressful conditions, which suggests that short-term leaching studies with millimeter sized sample pieces do not represent the realistic dumping scenarios.
Keywords: End-of-life, solar panel, photovoltaic, metal, leaching
... For other metals, a cationic leaching pattern was observed, which means decrease in leached concentrations with increase in pH. Similar leaching behaviour was observed by Nover et al. (2017) and Nain and Kumar (2020c), providing the significance of investigating long-term leaching behaviour. Maximum correlation between metal leachability and total metal content was observed for Cd, Ga and Se with Pearson's correlation coefficient value (r p ) ! 0.998 and pvalue < 0.05. ...
... The amount of metals release is also restricted by encapsulant, which is used to encapsulate various layers to provide stability and protection from environmental conditions. Earlier E-waste studies have shown the interference of encapsulant in metal release (Nain and Kumar, 2020c). Studies have shown that water penetration through the laminated edges and back sheet of module can result in encapsulant degradation and delamination (Jadhav et al., 2016). ...
... Due to this, moisture can get to the cells and interact with metals present in semiconductor layer. The corrleation between encapsulant release and metal leachability is discussed in a recent study by author (Nain and Kumar, 2020c) and possible schematic is shown in Fig. 5. High metal dissolution from CIGS PV in present study could be explained by the fact that thin-film PV modules are more prone to water penetration than silicon-based modules (Parida et al., 2011). ...
The upcoming end-of-life solar photovoltaics (PV) waste stream is a huge concern before solid waste professionals due to presence of hazardous metals like lead or cadmium. The objective of present study was to understand the metal dissolution from PVs under four standard waste characterization regulatory tests of U.S., Germany, and Japan and their representativeness with actual landfill leachate. Modules were exposed to real municipal solid waste landfill leachate for extended extraction duration, agitation and diluted leachate to investigate the effect of various parameters on metal dissolution. The results indicated that extractions using landfill leachates resulted in lower metal release than standard methods. The leached concentration was within the threshold limit except for cadmium, copper, lead and selenium, with maximum lead release from amorphous-PV of 8.68 mg/L and 6.91 mg/L with respect to TCLP and WET tests, respectively. Arsenic showed negligible release with maximum concentration of 0.046 mg/L from copper indium gallium de-selenide (CIGS) PV. Regardless of small size (1-2 cm pieces) and agitation, Germany and Japan’s standard tests resulted in minimal release except copper from CIGS PV. Leaching without agitation, showed negligible release from all photovoltaics whereas when agitation is applied to diluted leachate, significant release was observed with aluminum and copper leached up to 145.32 mg/L (multi-silicon) and 139.01 mg/L (amorphous-photovoltaic), respectively. CIGS was most hazardous with Metal Hazard Score (calculated on the basis of magnitude of leached metals with respect to their threshold limit and subsequent health effects) of 23.19, when exposed to standard tests. For all scenarios, increased metal release was observed with decrease in sample size and increase in dilution factor and thus, leaching in highly acidic conditions are by no means representative for modules dumping in realistic conditions.
... Module breakage is very rare during operational phase [12], however, disposal of broken modules could result in human health risk [13]. A recent study by Nain and Kumar,[89] reported the one-year leaching on four PV modules, and reported 17.6% of lead release form c-Si modules in acidic conditions. Another study by Ramos-Ruiz et al. [15] reported arsenic release from GaAs to be about 2.8-fold higher than the TCLP and WET regulatory limits. ...
... Various studies in past have shown metal leaching from dumped solar modules from environment, though, small modules pieces were used [1,14]. Also, there might be a possibility of material release from large module pieces [89], hence, FTA was applied to identify key factors responsible for dumping and material release from modules. The interrelation between various basic events gives the probability of occurrence of an undesired event, which is the top event, such as encapsulated material release from dumped broken module. ...
... Exposure of module partially covered with dust to high humidity can result in corrosion and long-term exposure can cause moisture ingression which results in encapsulant delamination [35]. The moisture ingress between layers can affect the encapsulant stability resulting in delamination [89]. Further, studies have shown that snow or hailstorms can cause severe damage to modules, such as glass cracking or solder joint failure [36]. ...
The present study addresses the aspect of upcoming stream of solar photovoltaics waste. The aim of this study was to understand the possibility of material release from end-of-life solar modules using an integrated approach of literature review and stakeholders survey. it involved (i) identification of failure events responsible for degradation of photovoltaic modules were identified from literature review , (ii) evaluation of these events by a survey of stakeholders of photovoltaic industry and (iii) investigation of their perceptions on events responsible for generation of end-of-life modules, present management and recycling practices, (iv) conducting of fault tree analysis and risk priority number analysis for finding severe failure events responsible for dumping and material leaching from solar modules. Assessment indicates that environmental factors, like high UV irradiation, humidity, temperature play significant role in module degradation. As per survey, more than 90% of manufacturers were involved in crystalline-silicon photovoltaic business. Only 20% manufacturers replied when asked on the aspect of end-of-life modules, showing that the photovoltaic waste is comparatively a new subject and not enough discussion have been devoted to it. Lack of recycling infrastructure, incentives, and environmental awareness significantly influence recycling and recuse practices. With worst-case scenarios, the maximum probability of the material release from dumped solar panels was found to 0.053. As per manufacturer’s opinion, the most critical factors resulting in modules failure are glass breakage and encapsulant degradation. Among various events, the module breakage during operation event have highest probability value (i.e., 0.313). Risk priority number analysis suggests that generation of end-of-life photovoltaic and environmental damage resulting to metal leaching as the most significant events. Damage during manufacturing and installation were least significant events resulting in degradation. At present, 76% producers do not recycle or reuse photovoltaic waste material, preferably sell them to informal waste recyclers or rag pickers. Findings from the present study highlight the urgency to develop a suitable system for collection and management of end-of-life photovoltaic modules.
... Toxicity associated with photovoltaic technologies are of concern because lead, tin, cadmium, silicon, and copper are known to be harmful to the ecosystem and human health (Kwak et al., 2020) and inappropriate disposal of this waste may cause the leaching of such toxic metals to soil or water (Li et al., 2019). However, recent toxicity studies have found metal concentrations from waste PV leachates to be within regulations, implying that their discard may be safe (Nain and Kumar, 2020a;Savvilotidou et al., 2017). The polymers associated with the panel are also of concern since they can release toxic gasses when incinerated (Liao et al., 2020). ...
Photovoltaic (PV) panel manufacturing is increasing worldwide, which subsequently increases the amount of waste PV. This study proposes to recycle waste PV using organic solvent delamination followed by downstream thermal and leaching procedures. Firstly, experimental data is obtained using small commercial modules by replicating a recycling route taken from the literature. Based on the experimental results, life cycle cost analysis (LCCA) and life cycle assessment (LCA) are applied to evaluate the experimental and optimized industry scale processes. Results show that the main profitable recycling avenues are for aluminum frame and junction box removal; and that downstream processes can separate and recover all the remaining materials, but not profitably. The laboratory and high-throughput-optimized processes, considering the median costs and revenues, have a net cost of 29.00 and 3.30 USD per module, respectively. The complete recovery of materials using the proposed method is unlikely to be profitable and this may only be achievable where labor is not expensive. Alternatively, the complete recycling of waste PV could be made economically viable by reducing process time, increasing automation and/or providing financial subsidies. The environmental analysis, however, shows that the optimized process modelled here has a positive net environmental impact. The results are also compared against the cost/environmental impact of landfilling such waste. In summary, the proposed recycling route is capable of completely recovering the main materials in waste PV (aluminum frames, junction box, silver, copper tabbing, silicon, backsheet and unbroken glass) and can have a positive environmental impact, but it is not economically profitable.
Silicon recovery from diamond wire saw silicon powder (DWSSP) waste is of great significance for increasing production profits and alleviating hazardous effects on the ecological environment. The purity of recovered silicon powder is determined by the purification efficiency during acid leaching pretreatment. Because the metallic impurities present in DWSSP are mostly physically mixed rather than chemically bound, the reaction rate is very fast in the initial stage of acid leaching, whereas it is difficult to dissolve the retained impurities in the later stage with the depletion of metal fragments adhered on the surface of the silicon matrix. Many prior studies have failed to consider the retained metallic impurities that reside in the inner silicon particle surfaces. Therefore, this study investigates the dissolution behavior of retained impurities via the dissolution of Al in HCl solution as an example. Thermodynamic results indicate that the Al dissolution process is dominated by entropic changes (ΔS0), rather than enthalpic changes (ΔH0). Furthermore, the dissolution behavior of Al is in accordance with the diffusion-controlled step in the Avrami mode, and the kinetic parameters were found to be A=5.85×107, Ea=49.27kJ·mol-1, and m<1. The determined dissolution behavior provides a clear understanding of the removal of retained metallic impurities from DWSSP via an acid leaching pretreatment. This study provides enlightenment for the further purification of silicon recovered from DWSSP waste.
Photovoltaic industry has shown tremendous growth among renewable energy sector. Though, this high installation rate will eventually result in generation of large volume of end-of-life photovoltaic waste with hazardous metals. In present study, reported leached metal contents from different photovoltaics in previous investigations were utilized for (i) potential fate and transport analysis to soil and groundwater and, (ii) estimating ecological and human health risks via dermal and ingestion pathways for child and adult sub-populations. The results indicate that the children are at highest risk, mainly due to lead (hazard quotient from 1.2 to 2.6). Metals, such as cadmium, lead, indium, molybdenum and tellurium pose maximum risks for child and adult sub-populations via soil-dermal pathway followed by soil-ingestion pathway. This is further proved by calculated high values of contamination factor and geo-accumulation index for cadmium (102.4), indium (238.9) and molybdenum (16.12). The estimated soil contamination is significant with respect to aluminium, silver, cadmium, iron, lead, however, groundwater contamination was insignificant. Exposure to polluted soils yields an aggregate hazard index (for non-cancer effects) > 1 for all four pathways, with soil dermal pathway as the major contributor. Lead poses significant cancer risk for all scenarios (average risk: 0.0098 to 0.047 (soil) and 2.1 × 10⁻⁵ to 3.5 × 10⁻⁵ (groundwater)), whereas acceptable non-cancer risk was observed for other metals from groundwater exposure. Further, variance contribution and spearman correlation coefficient analysis show that metal concentration, exposure frequency and ingestion rate are the main contributors towards overall uncertainty in risk estimates. More detailed assessment for environmentally-sensitive metals should be carried out by considering other field breakage scenarios also, although the assessment suggests low risk for majority of metals examined.
Ethylene vinyl acetate (EVA) has for decades been the material of choice for photovoltaic (PV) module encapsulation. However, while it is relatively inexpensive and initially adheres well to module components, EVA discolors with age and—as interfacial adhesion degrades—becomes susceptible to delamination, ultimately resulting in reduced module efficiency and shortened service lifetimes. As potential replacements for EVA, ionomer thermoplastic materials cure faster, are more resistant to discoloration and potential induced degradation, and do not evolve corrosive acetic acid, making them compatible with new device materials such as perovskites. Since there is limited information on ionomer durability for PV module applications, a series of field and accelerated laboratory aging studies were conducted to assess ionomer interface stability in the presence of terrestrial environmental stressors. It is shown that adhesion to the glass and cell interfaces of PV modules is inferior to EVA, both before and after aging, rendering ionomers particularly susceptible to delamination after short timeframes. Potential solutions to improve ionomer adhesion are discussed.
Thin-film solar panels (TFSPs) are widely used in integrated photovoltaic and solar power systems because of their perfect photovoltaic characteristics and ductility. These panels differ from the traditional silicon-based solar panels, in that the metal thin-film layers contain some potentially toxic metals such as zinc (Zn), copper (Cu), nickel (Ni), gallium (Ga), lead (Pb), indium (In) and chromium (Cr). In this study, we examined the environmental pollution that might be caused by disposing of TFSP as domestic trash at the end of their useful life. We used acid extract to simulate metal leaching toxicity and acidic corrosion, and then buried TFSPs in three types of soils to determine if metals might be released into the soil. Our results indicated that the amounts of dissolved metals increased as both the contact time with the acid and the acid concentration in the solution increased during nitric acid extraction. Heavy metals were released from TFSPs in the burial experiment, and the rates of metal release changed with variations in both the amounts of TFSPs in the soil and the soil properties. The increased concentrations of heavy metals such as Zn, Cu, Ni, Ga, Pb, In and Cr in soil samples were correlated to the amounts of TFSPs added. The results of this study confirmed that, when buried, TFSPs polluted the soil.
Solar photovoltaic trees (SPVT's) are chosen as an alternative option for electricity generation due to numerous benefits (especially in land utilization, urban infrastructure, and landscaping). Currently, SPVT's are available in many designs, and one among them is the novel phyllotaxy pattern. Technically, SPVT's seem to be more reliable and cost-effective. The expected average lifetime of the photovoltaic (PV) modules used in SPVT's is around 25 years. Once, the lifetime is over, these SPVT's must undergo a waste management process, and the scope for recycling is very high. Even though the scope for PV waste recycling is very high, many recyclers face the problems especially in estimating material recovery potential. In this paper, thermal and chemical treatments based end-of-life (EOL) method is used to estimate the material recovery potential from the phyllotaxy pattern-based SPVT. Initial estimations on the total embodied materials of the SPVT system is evaluated based on the components material fraction. Next, under the applied EOL management method, material recovery potential is estimated as per the material (aluminum, copper, glass, silver, and steel). Lastly, a few limitations with this EOL method are highlighted, and presented results aim to serve as useful data for the recyclers to have decisions.
Even with a long lifetime of 25-30 years of green energy production, end-of-life treatment of solar photovoltaic modules can negatively impact the environment if not handled properly. This is particularly urgent when the use of photovoltaics has grown at an unprecedented rate, generating clean energy all over the world. Therefore, it is essential to develop commercially viable end-of-life recycling technologies to guarantee a sustainable future for the photovoltaic technology. Silicon photovoltaic modules, the most popular photovoltaic technology, have been shown to be economically unattractive for recycling-the materials are mixed and difficult to separate, and have low value, so that the cost of recycling is hardly recovered. In this paper, we review the state-of-art recycling technology and associate it with a quantitative economic assessment to breakdown the cost structure and better understand the presented economic barrier. The techno-economic review allows us to identify essential framework and technology changes required to overcome the current barrier to implementing commercial-scale recycling. (i) The authority may impose price signal to impress direct landfill of end-of-life modules while proactively establish an effective collection network. (ii) The local recyclers may aim at value recovery as a step beyond mass recovery, especially targeting at recovery of intact silicon wafers and silver to guarantee the recycling revenue. Meanwhile, efforts should be put on reducing the recycling processing cost. (iii) Photovoltaic module manufacturers may take end-of-life responsibilities and up-design the product to facilitate end-of-life recycling, which includes features for simple disassembly, recycling, and reducing or eliminating the use of toxic components.
The goal of this study was to assess the sustainability of a modified cellulose nanofiber material for the recovery of precious gold from chloride solution, with a special focus on gold recovery from acidic solutions generated by cupric and ferric chloride leaching processes. TEMPO-oxidized cellulose nanofiber in hydrogel (TOCN), dry (H-TOCN, F-TOCN) and sheet form (S-TOCN) was examined for gold adsorptivity from chloride solution. Additionally, this work describes the optimum conditions and parameters for gold recovery. The data obtained in this investigation are also modeled using kinetic (pseudo first-order and pseudo second-order), isotherm best fit (Freundlich, Langmuir and Langmuir-Freundlich), and thermodynamic (endothermic process) parameters. Results demonstrate that high levels of gold removal can be achieved with TEMPO-oxidized cellulose nanofibers (98% by H-TOCNF) and the interaction characteristics of H-TOCN with gold suggests that other precious metals could also be efficiently recovered.
Reclamation of the dumps/landfills having huge quantities of decades-old garbage (aged waste or legacy waste) in an environmentally sound manner is one of the major challenges faced by the developing nations in general and in particular by urban local bodies in India. The article presents the feasibility of landfill mining operation specifically to recover soil-like material at old dumpsites of India for re-use in geotechnical applications. Aged municipal solid waste was collected from three dumpsites of India and initial tests were conducted on the soil-like material of the municipal solid waste. Initial tests results of grain size distribution, compositional analysis, organic content, total dissolved solids, elemental analysis, heavy metal analysis and colour of the leached water from finer fraction of aged municipal solid waste are presented. From the preliminary investigation, it was found that organic content in 15–20-year-old dumpsites varies between 5%–12%. The total dissolved solids ranges between 1.2%–1.5%. The dark coloured water leaching out from aged waste, with reference to local soil, is one of the objectionable parameters and depends on the organic content. The concentration of heavy metals of the finer fraction were compared with the standards. It was found that copper, chromium and cadmium are present at elevated levels in all the three dumpsites. The study concluded that the bulk of the soil-like material from aged municipal solid waste landfills can be used as cover material for landfills at the same site. However, some treatment in terms of washing, thermal treatment, blending with local soil, biological treatment, etc., is required before it can be re-used in other geotechnical applications.
The issue of recycling waste solar cells is critical with regard to the expanded use of these cells, which increases waste production. Technology establishment for this recycling process is essential with respect to the valuable and hazardous metals present therein. In the present study, the leaching potentials of Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, Penicillium chrysogenum, and Penicillium simplicissimum were assessed for the recovery of metals from spent solar cells, with a focus on retrieval of the valuable metal Te. Batch experiments were performed to explore and compare the metal removal efficiencies of the aforementioned microorganisms using spent media. P. chrysogenum spent medium was found to be most effective, recovering 100% of B, Mg, Si, V, Ni, Zn, and Sr along with 93% of Te at 30 °C, 150 rpm and 1% (w/v) pulp density. Further optimization of the process parameters increased the leaching efficiency, and 100% of Te was recovered at the optimum conditions of 20 °C, 200 rpm shaking speed and 1% (w/v) pulp density. In addition, the recovery of aluminum increased from 31 to 89% upon process optimization. Thus, the process has considerable potential for metal recovery and is environmentally beneficial.
Recent trends in the international photovoltaic (PV) sector indicate strong growth in terms of capacity and production, which is positively influencing the process of energy system decarbonisation. The aim of this review was to promote productive paradigms for a ‘closed cycle’ economy based on the enhancement of resource efficiency and the reduction of waste. To this end, the articulate framework for the management of end-of-life PV panels was analysed, highlighting strengths and weaknesses from the perspective of transitioning towards a circular economy. The conceptual framework is based on a comprehensive review and analysis of relevant literature to describe the main technological and environmental implications associated with PV energy production. Consequently, this paper highlights the most important critical elements, potential opportunities, and limitations deriving from the technological, managerial and organisational aspects of enhancing recovery and recycling rates. The review and the proposed framework might be useful for further research on this important yet complex topic.
The EVA, decomposition of single junction amorphous silicon solar module (a-Si:H) observed during outdoor deployment has been studied. The decay and thermal breakdown of EVA in the encapsulating material of PV module is a sign of low quality in thin film solar cell. The decomposition of EVA due to localized heating affects the reliability and efficiency of PV module. It also has negative influence on the conductive ZnO2 layer and the heat dissipating mechanisms of the PV module. The thermal susceptibility and stability of the encapsulating material was investigated using Thermogravometric (TGA), result shows low quantity of EVA substance in the affected region due to loss of volatile substance from the affected region after decomposition.
Cadmium telluride (CdTe) and cadmium selenide (CdSe) are increasingly being applied in photovoltaic solar cells and electronic components. A major concern is the public health and ecological risks associated with the potential release of toxic cadmium, tellurium, and/or selenium species. In this study, different tests were applied to investigate the leaching behavior of CdTe and CdSe in solutions simulating landfill leachate. CdTe showed a comparatively high leaching potential. In the Toxicity Characteristic Leaching Procedure (TCLP) and Waste Extraction Test (WET), the concentrations of cadmium released from CdTe were about 1500 and 260 times higher than the regulatory limit (1 mg/L). In contrast, CdSe was relatively stable and dissolved selenium in both leaching tests was below the regulatory limit (1 mg/L). Nonetheless, the regulatory limit for cadmium was exceeded by 5- to 6- fold in both tests. Experiments performed under different pH and redox conditions confirmed a marked enhancement in CdTe and CdSe dissolution both at acidic pH and under aerobic conditions. These findings are in agreement with thermodynamic predictions. Taken as a whole, the results indicate that recycling of decommissioned CdTe-containing devices is desirable to prevent the potential environmental release of toxic cadmium and tellurium in municipal landfills.
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Grid-connected solar photovoltaic (PV) power is currently one of the fastest growing power-generation technologies in the world. While PV technologies provide the environmental benefit of zero emissions during use, the use of heavy metals in thin-film PV cells raises important health and environmental concerns regarding the end-of-life disposal of PV panels. To date, there is no published quantitative assessment of the potential human health risk due to cadmium leaching from cadmium telluride (CdTe) PV panels disposed in a landfill. Thus, we used a screening-level risk assessment tool to estimate possible human health risk associated with disposal of CdTe panels into landfills. In addition, we conducted a literature review of potential cadmium release from the recycling process in order to contrast the potential health risks from PV panel disposal in landfills to those from PV panel recycling. Based on the results of our literature review, a meaningful risk comparison cannot be performed at this time. Based on the human health risk estimates generated for PV panel disposal, our assessment indicated that landfill disposal of CdTe panels does not pose a human health hazard at current production volumes, although our results pointed to the importance of CdTe PV panel end-of-life management.
The major potential environmental impacts related to landfill leachate are pollution of groundwater and surface waters. Landfill leachate contains pollutants that can be categorized into four groups (dissolved organic matter, inorganic macrocomponents, heavy metals, and xenobiotic organic compounds). Existing data show high leachate concentrations of all components in the early acid phase due to strong decomposition and leaching. In the long methanogenic phase a more stable leachate, with lower concentrations and a low BOD/COD-ratio, is observed. Generally, very low concentrations of heavy metals are observed. In contrast, the concentration of ammonia does not decrease, and often constitutes a major long-term pollutant in leachate. A broad range of xenobiotic organic compounds is observed in landfill leachate. The long-term behavior of landfills with respect to changes in oxidation-reduction status is discussed based on theory and model simulations. It seems that the somewhere postulated enhanced release of accumulated heavy metals would not take place within the time frames of thousands of years. This is supported by a few laboratory investigations. The existing data and model evaluations indicate that the xenobiotic organic compounds in most cases do not constitute a major long-term problem. This may suggest that ammonia will be of most concern in the long run.
The present study addresses the aspect of upcoming stream of solar photovoltaics waste. The aim of this study was to understand the possibility of material release from end-of-life solar modules using an integrated approach of literature review and stakeholders survey. it involved (i) identification of failure events responsible for degradation of photovoltaic modules were identified from literature review , (ii) evaluation of these events by a survey of stakeholders of photovoltaic industry and (iii) investigation of their perceptions on events responsible for generation of end-of-life modules, present management and recycling practices, (iv) conducting of fault tree analysis and risk priority number analysis for finding severe failure events responsible for dumping and material leaching from solar modules. Assessment indicates that environmental factors, like high UV irradiation, humidity, temperature play significant role in module degradation. As per survey, more than 90% of manufacturers were involved in crystalline-silicon photovoltaic business. Only 20% manufacturers replied when asked on the aspect of end-of-life modules, showing that the photovoltaic waste is comparatively a new subject and not enough discussion have been devoted to it. Lack of recycling infrastructure, incentives, and environmental awareness significantly influence recycling and recuse practices. With worst-case scenarios, the maximum probability of the material release from dumped solar panels was found to 0.053. As per manufacturer’s opinion, the most critical factors resulting in modules failure are glass breakage and encapsulant degradation. Among various events, the module breakage during operation event have highest probability value (i.e., 0.313). Risk priority number analysis suggests that generation of end-of-life photovoltaic and environmental damage resulting to metal leaching as the most significant events. Damage during manufacturing and installation were least significant events resulting in degradation. At present, 76% producers do not recycle or reuse photovoltaic waste material, preferably sell them to informal waste recyclers or rag pickers. Findings from the present study highlight the urgency to develop a suitable system for collection and management of end-of-life photovoltaic modules.
There has been a substantial growth in the deployment of solar photovoltaic (PV) panels in the past couple decades. Solar PVs have a life span of about 25 years and much of the deployed PVs will soon reach their end of life (EoL). It is now timely to plan for the EoL of PVs to recover valuable materials and recycle PV modules sustainably. The goal of this study was to analyze the environmental impacts of different recycling methods for crystalline silicon (c-Si) and CdTe panels. A life cycle assessment (LCA) was performed for delamination and material separation phases of recycling solar panels. The LCA results showed that the recycling of c-Si and CdTe PVs contribute 13–25% and 3–4%, respectively to the entire PV lifecycle impacts. Also, for both c-Si and CdTe PVs, the thermal-based recycling methods resulted in lower environmental impacts than chemical and mechanical methods, except for pyrolysis. Nitric acid dissolution used for c-Si PV recycling had the highest impacts among all methods since the material consumption for this method has not been optimized for industrial use. Results from this study suggested that current techniques used in recycling of PVs, produce higher impacts than extraction of Al, Si and glass for c-Si and extraction of glass for CdTe. Lastly, this study identified which materials to prioritize for highest economic and environmentals benefits from recycling. These will be Ag, Al, Si, and glass in c-Si modules, and Te, Cu, and glass in CdTe modules.
Ethylene-vinyl acetate (EVA) is the predominating material of choice for making the encapsulant film for photovoltaic (PV) modules. The easy accessibility, low cost, high transparency, long track record, widespread know-how on processability and performance, and to some extent, ignorance of the criticality of encapsulant film on the long-term performance of PV modules have made EVA, a dominant player in the PV industry. In parallel, due to economic reasons, the majority of encapsulant development has moved to a direction of compromising the quality to meet the cost target. In recent years, the PV industry has started recognizing, polyolefin-based encapsulants as technically superior when compared to EVA. Polyolefin-based encapsulant comes in either a crosslinked or thermo-plastic version. Thermoplastic polyolefin offers several advantages related to processability and performance over the crosslinked version. In the current study, we compare a newly developed thermoplastic polyolefin-based encapsulant and a state of the art EVA encapsulant from different aspects of fundamental material properties, like optical, thermal, mechanical, etc. and discuss their implication on the performance of a solar module.
The photovoltaic (PV) technology is one of the fastest growing renewable and environmental friendly sources of electricity. However, this huge deployment rate is associated with generation of end-of-life (EoL) PV waste containing particularly, carcinogenic metals, once their operation phase ends. This study attempted to address this upcoming waste issue by systematically reviewing about 300 review/theoretical/ case/research papers/books/patents published between 2000 and 2018. The information was compiled and synthesized on: (i) initial metal concentration/content (IMC) for silicon-PV, amorphous-PV, CIGS and CdTe PVs; ii) statistical characterization and distribution of compiled IMCs; iii) leached metal concentrations (mg/l) from various PVs in water-based leaching solutions, as per standard waste characterization methods, in acid leaching and landfill matrix; iv) metal leaching rate constants (LRC) by fitting exponential model on reported plots of leached metal concentration values versus time using the GetData software; v) feasible application of compiled IMC and LRC data for Leachate Pollution Index (LPI) determination of an MSW landfill dumped with solar-PV waste; vi) human health risk assessment (HHRA) for exposure to lead leached from solar PV waste in an MSW landfill; vii) data/knowledge gaps from literature review and highlight the required future research actions.
The ranges of IMC values for top three solar PV-associated carcinogens, arsenic, cadmium and lead (% weight) were obtained to be: 0.00-0.001, 0.0001-19.84, and 0.003-5.09, respectively. Further, the range of LRC of solar PV-associated leached arsenic, cadmium and lead were obtained to be (per day): 0.00-0.129, 0.001-0.031, and 0.003-0.041, respectively. Leaching of Cd, Pb and Se from PVs have been mostly studied in acidic conditions (pH 3.0-6.5), whereas, fate of solar PVs in landfill conditions was not observed to be studied much. The estimation of contribution of solar PV in leachate pollution potential of an existing MSW landfill at T90 values (i.e., time required for 90% leaching of metals) showed an increase of 5.15% in pollution potential of landfill if landfill were to be dumped with EoL PV waste as well. HHRA for exposure to groundwater contaminated with leachate from a landfill dumped with lead containing solar PV waste did not pose any significant risk, however, the carcinogenic effects due to other metals under this scenario cannot be neglected. Out of 85 studies selected for content analysis, only 2.39 % of them investigated the fate of PVs in landfill stimulating conditions. To address fate of EoL waste and reduce uncertainty in present work, following future research actions need to be initiated: (i) conduct experimental studies to obtain data on metal leaching under realistic dumping scenarios and landfill conditions (intact solar panels with bigger size in MSW landfill) ; (ii) revise the expression of LPI for including solar PV-based LPI with critical parameters, like carcinogenic metals (cadmium); (iii) investigate suitability of existing standard hazardous waste characterizing methods (TCLP or WET) for PV waste.
Solar cell industry produces high quantities of waste in form of broken, damaged, and rejected cells, whereas milling and filtering practices are typically used to recover the valuable materials (Al, Ag and Si) from such Waste Solar Cell Wafers (WSCWs). This recycling approach has its disadvantages, e.g. excessive energy consumption and dust emission causing loss of valuable metals. To fulfil the concept of Zero Waste for WSCWs, the authors present a sustainable technology for liberation of valuable metals from WSCWs and synthesis of added value products, in particular Ag nanoparticles and Al microparticles. The suggested technology consisted of three different approaches combined to liberate each material individually. The technology started with an Al layer disintegration process using Dimethyl Sulfoxide (as an eco-friendly and sustainable solvent) supported by ultrasonic treatment to break van der Waals’ bonding between spherical Al microparticles that compose the Al paste layer, thus liberating Al in microparticle suspension form with particle size ∼3 μm, recovery rate >98%. After that, leaching by nitric acid and other eco-friendly reagents (Sodium Chloride, Ammonia solution and glucose syrup) assisted by ultrasonic treatment was used to dissolve Ag and later precipitate it in form of nanoparticles with avg. size 30 nm, yield >92%. Finally, etching using paste containing phosphoric acid was done to remove anti-reflection coating and purify the Si substrate with final recovery rate >99%. SEM-EDS, XRD, FTIR, and TEM were used for analysis of extracted materials as well as changes in the solvent. Investigation was also concerned with determining economic/global warming impacts of the technology.
PV modules which are installed worldwide have a defined lifetime for useful service after which the panels become End-of-Life (EoL) products. An enormous amount of obsolete solar PV modules will be added to the waste stream in the near future. Hence, the EoL photovoltaic waste stream could cause an appalling problem in the future if a holistic management strategy is not considered. Despite the vast research on photovoltaic technology, little is known about the perspective of how the EoL PV modules will be handled. The current study systematically investigates global research on EoL PV modules to identify gaps for further exploration. The review reveals that most of the research concentrates on the recovery and recycling of PV panels. Also, the vast majority of the research is mostly carried out in laboratory-scale. The geographical distribution of the studies was concentrated on 15 countries including the USA, Italy, and Taiwan, the latter of which has produced the most publications. Life-cycle-assessment and reverse logistics (RL) are two critical aspects of PV waste management and have only recently received attention from researchers, with 11 and six papers respectively. There are still many countries which have not attempted to forecast their EoL solar-panel waste stream and develop recycling infrastructure. Based on review findings, the future research must be focused on forecasting the PV waste streams, development of recycling technologies, reverse logistics and the policies of individual PV consumer countries. Finally, this study develops a foundation for future research on Photovoltaic waste management to build upon.
Precious metals are widely applied in many industry fields due to their excellent corrosion resistance, good electrical conductivity and high catalytic activity. However, the reserves of precious metals falls short of the production globally. The rapid generation of end-of-life products has become the significant resources of precious metals. Among these products, electronic waste (e-waste) and spent catalysts are more concentrated since they account for over 90% of precious metals in industry. This article provides an overview of various technologies on the recovery of precious metals from e-waste and spent catalysts. It shows that recycling technologies have been significantly improved in recent years. The recycling processes have transferred from leaching by aqua regia, cyanide and chlorine in acid solution to less pollution agents leaching. Environment-oriented technologies have been raised great attention in precious metals recycling. The advantages and environmental impacts of these recycling technologies have been discussed in detail. However, there are still some challenges for future promotion. In order to achieve the environment-friendly and sustainable recycling for precious metals with high recovery rate, several considerations have been proposed.
Hazardous elements like lead, cadmium etc. are growingly being used in solar photovoltaics (PV). The major distress is the risk related to the potential release of these constituents in the environment. This paper reviews the leaching behaviour of various metallic constituents in soil & water and compiles the latest literature on PV. Analysis shows that there is substantial release of various metallic components in the environment and exist data gaps in (1) lack of information for solar PV disposal, (2) standardized leaching tests representing actual landfill conditions (e.g., studies with actual landfill waste and leachate) (3) Life Cycle Inventories from cradle to grave (4) kinetics data for metal leaching (5) PV wastewater characterization. These identified data gaps need to be filled by conducting more research in this direction so that exposure to toxic metals can be estimated with more confidence and efforts for protecting them can be made.
The influence of the ethylene-vinyl acetate (EVA) film quality on potential induced degradation was studied on in-house developed mini modules with p-type monocrystalline silicon solar cells. The modules were assembled with EVA films of equivalent qualities, but different ages and exposed to an accelerated test (relative humidity = 85%, T = 60 °C, V
$_{\text{bias}}$
= +1000 V). The age of the EVA film was determined from the time we received the EVA film, and opened the sealed enclosure and the time of lamination. After the EVA film was removed from the sealed enclosure, it was kept in a dark place at room temperature. The storage times of the “fresh,” “aged,” and “expired” films were: less than 14 d, around 5 mo, and more than 5 years, respectively. While modules with a “fresh” EVA film exhibit almost no degradation, the modules with the “aged” EVA film degrade very rapidly and severely. Their degradation rate was around 0.2%/d during the 2000 h of damp heat test. We also observed a strong silver line corrosion, which occurs because of the peroxide leftovers in the “aged” EVA films.
In this study, copper (Cu) and aluminum (Al) particles derived from waste crystalline silicon solar cell modules were etched with mixed acid containing HNO3 and HCl, and the optimal mixing conditions were examined for the purpose of recovering silicon with high yield. The crushed particles of waste silicon solar cells were used after sieving between 450 and 600 μm particle size. The Cu etching rate decreased with the increasing HCl concentration in the region of HNO3/HCl ≧ 3.36, whereas it increased at HNO3/HCl < 3.36. The Al etching rate increased when HCl was added, although it was almost independent of the amount of HNO3. 99.6% silicon purity was achieved at the treatment time of 30 min. The rate-determining step of Cu and Al etchings was represented by the volume reaction model instead of the surface reaction model. The CuCl coating was observed on the residuals of Cu. The increasing HCl blocked the Cu etching, but the excess Cl− promoted the dissolution of CuCl due to complex formation, corresponding to the regions of HNO3/HCl ≧ 3.36 and HNO3/HCl < 3.36, respectively. In the region of HNO3/HCl < 3.36, the spontaneous complete etching time of Cu and Al was achieved with higher HNO3 concentration of 8.5–10 mol/L.
Gallium arsenide (GaAs) is a material widely used in electronic devices. Disposal of electronic waste containing GaAs in municipal solid waste landfills raises concerns about the public health and ecological risks associated with the potential release of toxic arsenic (As) species. In this study, different tests were performed to investigate the leaching behavior of particulate GaAs in aqueous solutions. In the U.S. Toxicity Characteristic Leaching Procedure (TCLP) and California Waste Extraction Test (WET), the concentrations of As released from the GaAs particles were about 2.6-2.8-fold higher than the regulatory limit (5 mg/L). A much higher As concentration (72 mg/L), accounting for as much as 15.4% of the initial As in GaAs, was solubilized in a pH-7.6 synthetic landfill leachate under ambient atmosphere after 120 days. Additional tests performed to evaluate the dissolution of GaAs under a range of redox conditions, pH levels, ionic strength, and presence of organic constituents commonly found in landfills revealed that oxic environments and mildly alkaline conditions (pH 8.1-8.5) promote release of As (chiefly arsenite) and gallium species to the surrounding aqueous environment. The rate of As release in long-term exposure experiments was initially constant but later progressively diminished, likely due to the formation of a passivating layer on the surface of GaAs consisting of corrosion products rich in poorly soluble gallium oxides (Ga2O3 and Ga(OH)3). This hypothesis was confirmed by surface analysis of GaAs particles subjected to leaching using X-ray photoelectron spectroscopy (XPS). These findings suggest that further research is needed to assess the potential release of toxic As from electronic waste in municipal landfills.
To determine if there are potential concerns related to the environmental end-of-life impacts of photovoltaic (PV) or quantum-dot display (QD) technologies, the goal of this study was to assess the magnitude of heavy metal leaching using simulated landfill methodologies from devices in an attempt to forecast the lifecycle environmental impacts of subsequent generations QD-enabled PV technologies. The underlying hypotheses are (H1) existing PV and QD thin-film technologies do not release heavy metals at concentrations exceeding RCRA or State of California regulatory limits; and (H2) the disposal of PV and QD thin-film technologies does not exceed Land Disposal Restrictions (LDR). Three task-oriented objectives were completed: (O1) five representative PV panels and two representative thin-film displays with QD technology were obtained from commercial sources; (O2) RCRA Toxicity Characteristics Leaching Procedure (TCLP) tests and California Waste Extraction Tests (WET) were conducted in addition to microwave-assisted nitric acid digestion; and (O3) results were compared to the existing regulatory limits to examine the potential environmental end-of-life concerns. The heavy metal concentrations obtained from PV panels and QD thin-film displays when exposed to simulated landfill environments and extreme case leaching scenarios were generally several orders of magnitude lower than the promulgated standards and probably not of major concerns related to end-of-life safe disposal of these commercially available products. With exception to the findings for lead under the RCRA rules, the results confirmed that PV and QD thin-film technologies do not release heavy metals at concentrations exceeding RCRA or State of California characteristic hazardous waste regulatory limits. However, lead, mercury, and potentially other heavy metal releases have to be monitored to ensure that the disposal of this type of waste is in compliance with RCRA’s LDR requirements and universal treatment standards because the second underlying hypothesis could not be completely supported for the leaching of these heavy metals. It could be anticipated that newer and more sophisticated soldering materials and approaches in the next generation of PV panels would significantly reduce the use of RCRA heavy metals or nanomaterials. However, although the generated data is limited to these representative PV and QD technologies and as such should not be considered applicable to the entire gamete of present-day technologies, these findings suggest that their release from future PV QD technologies would likely be greater from non-end-of-life processes, than from traditional land disposal routes.
With the enormous growth in the development and utilization of solar-energy resources, the proliferation of waste solar panels has become problematic. While current research into solar panels has focused on how to improve the efficiency of the production capacity, the dismantling and recycling of end-of-life (EOL) panels are seldom considered, as can be seen, for instance, in the lack of dedicated solar-panel recycling plants. EOL solar-panel recycling can effectively save natural resources and reduce the cost of production. To address the environmental conservation and resource recycling issues posed by the huge amount of waste solar panels regarding environmental conservation and resource recycling, the status of the management and recycling technologies for waste solar panels are systemically reviewed and discussed in this article. This review can provide a quantitative basis to support the recycling of PV panels, and suggests future directions for public policy makers. At present, from the technical aspect, the research on solar panel recovery is facing many problems, and we need to further develop an economically feasible and non-toxic technology. The research on solar photovoltaic panels' management at the end of life is just beginning in many countries, and there is a need for further improvement and expansion of producer responsibility.
The Photovoltaic Engineering Handbook is the first book to look closely at the practical problems involved in evaluating and setting up a photovoltaic (PV) power system. The author’s comprehensive knowledge of the subject provides a wealth of theoretical and practical insight into the different procedures and decisions that designers need to make. Unique in its coverage, the book presents technical information in a concise and simple way to enable engineers from a wide range of backgrounds to initiate, assess, analyze, and design a PV system. It is beneficial for energy planners making decisions on the most appropriate system for specific needs, PV applications engineers, and anyone confronting the practical difficulties of setting up a PV power system.
Some photovoltaic module technologies use toxic materials. We report long-term leaching on photovoltaic module pieces of 5 × 5 cm² size. The pieces are cut out from modules of the four major commercial photovoltaic technologies: crystalline and amorphous silicon, cadmium telluride as well as from copper indium gallium diselenide. To simulate different environmental conditions, leaching occurs at room temperature in three different water-based solutions with pH 3, 7, and 11. No agitation is performed to simulate more representative field conditions. After 360 days, about 1.4% of lead from crystalline silicon module pieces and 62% of cadmium from cadmium telluride module pieces are leached out in acidic solutions. The leaching depends heavily on the pH and the redox potential of the aqueous solutions and it increases with time. The leaching behavior is predictable by thermodynamic stability considerations. These predictions are in good agreement with the experimental results.
China is the world’s largest PV market now. At the end of lifetime, large waste volumes of PV modules need to be recycled. In this paper, the expected PV waste volume is overviewed. By 2034, the EOL PV modules will reach 60 to 70GW. But there are currently no specific regulations for EOL PV modules and the technology research has just started. Technology status is illustrated for crystalline silicon and thin film PV modules. Policy suggestion and technology R&D tendency have been carried out for future.
Ethylene vinyl acetate (EVA) is the dominating material for the encapsulation of solar cells. A better understanding of the cross-linking reaction progress during PV module lamination could lead to promising approaches for shortening of PV module lamination times but also for optimization of the EVA formulation. Therefore, the main aim of this study is to investigate the cross-linking behavior of EVA but also for optimization potentials of the EVA formulation. Currently, a degree of cross-linking higher than 70% obtained from Soxhlet extraction, is used as quality control standard in PV industry. Thermomechanical properties of the investigated EVA films demonstrate a sufficient state of cross-linking already after 5 min, which corresponds to a Soxhlet value of around 50%. Nevertheless, the effect of the remaining, still reactive peroxide cross-linker under service relevant conditions cannot be neglected. Therefore, the behavior of mini-modules manufactured at different lamination times and stored under various aging conditions is investigated. EVA not fully cured during lamination are undergoing postlamination cross-linking. At the same time, remaining active cross-linker causes discoloration at soldering ribbons after accelerated aging. The cross-linking time in the lamination process may be reduced to ≥6 min, compromising between high throughput in production and the need of avoiding degradation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 133, 44912.
The effects of sulfide levels on arsenic leaching and speciation were investigated using leachate generated from laboratory-scale construction and demolition (C&D) debris landfills, which were simulated lysimeters containing various percentages of gypsum drywall. The drywall percentages in lysimeters were 0, 1, 6, and 12.4 wt% (weight percent) respectively. With the exception of a control lysimeter that contained 12.4 wt% of drywall, each lysimeter contained chromated copper arsenate (CCA) treated wood, which accounts for 10 wt% of the C&D waste. During the period of study, lysimeters were mostly under anaerobic conditions. Leachate analysis results showed that sulfide levels increased as the percentage of drywall increased in landfills, but arsenic concentrations in leachate were not linearly correlated with sulfide levels. Instead, the arsenic concentrations decreased as sulfide increased up to approximately 1000 μg/L, but had an increase with further increase in sulfide levels, forming a V-shape on the arsenic vs. sulfide plot. The analysis of arsenic speciation in leachate showed different species distribution as sulfide levels changed; the fraction of arsenite (As(III)) increased as the sulfide level increased, and thioarsenate anions (As(V)) were detected when the sulfide level further increased (>10⁴ μg/L). The formation of insoluble arsenic sulfide minerals at a lower range of sulfide and soluble thioarsenic anionic species at a higher range of sulfide likely contributed to the decreasing and increasing trend of arsenic leaching.
End-of-Life (EoL) photovoltaic (P/V) modules, which are recently included in the 2012/19/EU recast, require sound and sustainable treatment. Under this perspective, this paper deals with 2nd generation P/V waste modules, known as thin-film, via applying chemical treatment techniques. Two different types of modules are examined: (i) tandem a-Si:H/μc-Si:H panel and, (ii) Copper-Indium-Selenide (CIS) panel. Panels’ pretreatment includes collection, manual dismantling and shredding; pulverization and digestion are further conducted to identify their chemical composition. A variety of elements is determined in the samples leachates’ after both microwave-assisted total digestion and Toxicity Characteristic Leaching Procedure (TCLP test) using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) analysis. The analysis reveals that several elements are detected in the two of panels, with no sample exceeds the TCLP test. Concentrations of precious and critical metals are also measured, which generates great incentives for recovery. Then, further experiments, for P/V recycling investigation, are presented using different acids or acid mixtures under a variety of temperatures and a stable S/L ratio, with or without agitation, in order to determine the optimal recycling conditions. The results verify that chemical treatment in P/V shredded samples is efficient since driving to ethylene-vinyl acetate (EVA) resin’s dissolution, as well as valuable structural materials recovery (P/V glass, ribbons, cells, P/V intermediate layers). Among the solvents used, sulfuric acid and lactic acid demonstrate the most efficient and strongest performance on panels’ treatment at gentle temperatures providing favorably low energy requirements.
Leachate pollution index (LPI) is an environmental index which quantifies the pollution potential of leachate generated in landfill site. Calculation of Leachate pollution index (LPI) is based on concentration of 18 parameters present in leachate. However, in case of non-availability of all 18 parameters evaluation of actual values of LPI becomes difficult. In this study, a model has been developed to predict the actual values of LPI in case of partial availability of parameters. This model generates eleven equations that helps in determination of upper and lower limit of LPI. The geometric mean of these two values results in LPI value. Application of this model to three landfill site results in LPI value with an error of ±20% for ∑i(n)wi⩾0.6.
Recently the potential environmental hazard of photovoltaic modules together with their management as waste has attracted the attention of scientists. Particular concern is aroused by the several metals contained in photovoltaic panels whose potential release in the environment were scarcely investigated. Here, for the first time, the potential environmental hazard of panels produced in the last 30 years was investigated through the assessment of up to 18 releasable metals. Besides, the corresponding ecotoxicological effects were also evaluated. Experimental data were compared with the current European and Italian law limits for drinking water, discharge on soil and landfill inert disposal in order to understand the actual pollution load. Results showed that less than 3% of the samples respected all law limits and around 21% was not ecotoxic. By considering the technological evolutions in manufacturing, we have shown that during the years crystalline silicon panels have lower tendency to release hazardous metals with respect to thin film panels. In addition, a prediction of the amounts of lead, chromium, cadmium and nickel releasable from next photovoltaic waste was performed. The prevision up to 2050 showed high amounts of lead (30 t) and cadmium (2.9 t) releasable from crystalline and thin film panels respectively.
There is a global consensus on making full use of renewable energy because of human concern for energy security and environmental deterioration. Power generation with large-scale renewable energy such as solar and wind energy has become the trend of modern power systems, and the resulting impacts on power systems are more and more prominent. Therefore, there is great concern from academic and engineering areas of all countries. In China, as the fastest growing country in the photovoltaic (PV) industry in the world, these problems are particularly outstanding. This paper extensively reviews the present research and application status of large-scale PV (LSPV) power generation in China, discusses the modelling and simulation techniques of LSPV, explores impacts of LSPV integration on dynamic and static characteristics of power systems, and describes key technologies about LSPV power generation delivery and consumption from the perspective of power system planning, simulation, dispatching and control. Additionally, this paper also refines academic and engineering problems, and recommendations are proposed for future research and development of LSPV power generation in China.
The appropriateness of regulatory methods to characterise the toxicity of photovoltaic (PV) modules was investigated to quantify potential environmental impacts for modules disposed of in landfills. Because solar energy is perceived as a green technology, it is important to ensure that end-of-life issues will not be detrimental to solar energy's success. United States Environmental Protection Agency Method 1311, California waste extraction test, and modified versions of both were performed on a multi-crystalline silicon module and cells and a copper indium gallium diselenide (CIGS) module. Variations in metal leachate concentrations were found with changes in testing parameters. Lead concentrations from the multi-crystalline module ranged from 16.2 to 50.2 mg/L. Cadmium concentrations from the CIGS module ranged from 0.1 to 3.52 mg/L. This raises doubt that regulatory methods can adequately characterise PV modules. The results are useful for developing end-of-life procedures, which is a positive step towards avoiding an e-waste problem and continuing trends of increasing installation and cost reduction in the PV market.
The crude processing of electronic waste (e-waste) has led to serious contamination in soils. While microorganisms may play a key role in remediation of the contaminated soils, the ecological effects of combined pollution (heavy metals, polychlorinated biphenyls and polybrominated diphenyl ethers) on the composition and diversity of microbial communities remain unknown. In this study, a suite of e-waste contaminated soils were collected from Guiyu, China, and the indigenous microbial assemblages were profiled by 16S rRNA high-throughput sequencing and clone library analysis. Our data revealed significant differences in microbial taxonomic composition between the contaminated and the reference soils, with Proteobacteria, Acidobacteria, Bacteroidetes and Firmicutes dominating the e-waste-affected communities. Genera previously identified as organic pollutants-degrading bacteria, such as Acinetobacter, Pseudomonas and Alcanivorax, were frequently detected. Canonical correspondence analysis revealed that approximately 70% of the observed variation in microbial assemblages in the contaminated soils was explained by eight environmental variables (including soil physiochemical parameters and organic pollutants) together, among which moisture content, decabromodiphenyl ether (BDE-209) and copper were the major factors. These results provide the first detailed phylogenetic look at the microbial communities in e-waste contaminated soils, demonstrating that the complex combined pollution resulting from improper e-waste recycling may significantly alter soil microbiota.
It is important to understand photovoltaic (PV) module degradation for the design of PV systems. In the present study results of degradation in mono-crystalline-silicon PV generator of a solar water pump after 28 years of outdoor exposure at a western Himalayan location in the Indian state of Himachal Pradesh, are presented. The main objective is to study the impact of PV degradation on solar pump performance, reliability and life-expectancy under field conditions. Main defects observed in PV modules are encapsulant discolouration, delamination, oxidation of front grid fingers and anti-reflective coating, glass breakage and bubbles in back sheet. Hot spots are identified using thermal imaging and degradation is quantified by measuring PV parameters under indoor and outdoor conditions. Sun simulator is used to test degraded modules under standard testing conditions. Average power degradation of PV generator is found to increase 1.4% per year which is reasonable considering materials and technology used about three decades ago. The open circuit voltage is found to show an average increase of 2.8% requiring further experimental investigations. The study has relevance in improving the performance and life-expectancy of PV based systems beyond the warranty period of 25 years by replacing most degraded modules. Follow up research areas are also identified.
The photovoltaic effect of thin-film Copper Indium Gallium Selenide cells (CIGS) is conferred by the latter elements. Organic photovoltaic cells (OPV), relying on organic light-absorbing molecules, also contain a variety of metals (e.g. Zn, Al, In, Sn, Ag). The environmental impact of such technologies is largely unknown, in particular when the physical integrity deteriorates upon end-of-life, possibly facilitating cell constituent leaching. This study analyzed long-term inorganic leaching from damaged OPV and CIGS into different model waters. Leachate concentrations were put into perspective by calculating Predicted Environmental Concentrations (PEC) for several scenarios. Roof-top acidic rain run-off from CIGS was found to be the predominant emission source for metals and metalloids, with Cd released to such extents that PEC (173.4 µg Cd L-1) would considerably exceed acute toxicity concentrations for Daphnia magna. Other PEC for CIGS (9.9 mg Mo L-1, 9.4 µg Se L-1, resp.) were in the range of teratogenic effects. In contrast, OPV released little metals with calculated PEC being below even conservative drinking water guidelines. Time-resolved single-particle ICP-MS indicated that some metals (Zn, Mo, Ag) were in nanoparticulate form, raising nano-toxicity concerns. Leaching kinetics called for revision of existing standardized (accelerated) leaching protocols, since long-term release was most relevant.
Water vapor ingress significantly impacts the performance and the long-term reliability of copper indium gallium selenide photovoltaic modules. A cost effective packaging method that can protect photovoltaic modules from the operating environment is critical to their widespread commercialization. Due to the sensitivity of both the copper indium gallium selenide cells and the electrodes to water vapor, they need an encapsulant with low water vapor permeation as well as side sealing materials, resulting in a high cost of manufacturing. Hence, a packaging strategy without sealing materials is proposed with new encapsulant materials. In this study, the overall amount of permeated water vapor through ionomer and polyvinyl butyral encapsulants was investigated and compared with widely used encapsulants such as ethylene vinyl acetate. The diffusion and solubility coefficients were calculated from the experimentally determined water vapor transmission rate in both transient and steady state transport regimes. To understand the permeation mechanism of water vapor through the encapsulant, the temperature dependence of the diffusion and solubility coefficients was investigated. Based on experimentally determined permeation properties, the amount of water vapor absorption and the ingress speed into the PV module under a continuously varying environment were investigated. Ethylene vinyl acetate shows its excellence among encapsulants, when simply considering ingress speed of water vapor (slower permeation), while ionomer dominantly outperforms other materials, when focusing on the total amount of water absorption (less permeation).
The energetic and environmental life cycle assessment of a 4.2kWp stand-alone photovoltaic system (SAPV) at the University of Murcia (south-east of Spain) is presented. PV modules and batteries are the energetically and environmentally most expensive elements. The energy pay-back time was found to be 9.08years and the specific CO2 emissions was calculated as 131g/kWh. The SAPV system has been environmentally compared with other supply options (diesel generator and Spanish grid) showing lower impacts in both cases. The results show the CO2-emission reduction potential of SAPV systems in southern European countries and point out the critical environmental issues in these systems.
A technique to quantify the leachate pollution potential of landfills on a comparative scale using an index known as the Leachate Pollution Index (LPI) has been developed and reported elsewhere. The LPI is a quantitative tool by which the leachate pollution data of the landfill sites can be reported uniformly. It is an increasing scale index and has been formulated based on the Delphi technique. The formulation process involved selecting variables, deriving weights for the selected pollutant variables, formulating their subindices curves, and finally aggregating the pollutant variables to arrive at the LPI. The aggregation function is one of the most important steps in calculating any environmental index. If the aggregation function is ambiguous, the result will raise an unnecessary alarm, indicating a comparatively less polluted environmental situation as more contaminated. Similarly, if the aggregation function is eclipsed, a false sense of security may be created, indicating a highly polluted environmental situation as less polluted. In this paper, the concept of LPI is described in brief and the various possible aggregation functions are described and used to calculate LPI values for an actual landfill site to select the most appropriate aggregation function. Based on the results, it is concluded that the weighted linear sum aggregation function is the best possible aggregation function for calculating LPI. Sensitivity analysis of the six short-listed aggregation functions is performed to substantiate this conclusion.
This paper evaluates the performance parameters of five photovoltaic (PV) modules comprising crystalline silicon, multi-crystalline silicon and edge-defined film-fed growth (EFG) silicon technologies. This evaluation was accomplished by measuring and analysing the modules' performances during initial, intermediate and final stages of a 17-month test period. The effect of temperature and irradiance on the performance parameters was investigated. Results obtained indicate that some modules exhibited shunting behaviour and that the EFG silicon module experienced moisture ingress, which in part, resulted in 14% performance degradation. An analysis of the results revealed that the moisture ingress effectively reduced the active module area, resulting in reduced photon absorption, consequently reducing the electron-hole generation as indicated by the reduced short-circuit current. In addition, the EFG-Si module's shunt resistance appeared to decrease over the test period. The rest of the modules showed relatively stable performance, information that is crucial to the system designer and consumer.
Global environmental concerns and the escalating demand for energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till date. The power from sun intercepted by the earth is about 1.8 x 1011 MW, which is many times larger than the present rate of all the energy consumption. Photovoltaic technology is one of the finest ways to harness the solar power. This paper reviews the photovoltaic technology, its power generating capability, the different existing light absorbing materials used, its environmental aspect coupled with a variety of its applications. The different existing performance and reliability evaluation models, sizing and control, grid connection and distribution have also been discussed.
The dumping of solid waste in uncontrolled landfills can cause significant impacts on the environment and human health. The
principal concern is focussed on the pollution potential due to migration of the leachate generated from the landfill sites
into the groundwater, the surface water or the sea. In this paper, the concept of the leachate pollution index, a tool for
quantifying the leachate pollution potential of landfill sites, has been described and its practical application has been
demonstrated by comparing the leachate contamination potential of two active and two closed landfills sites in Hong Kong.
It has been found that the leachate generated from the closed landfills can have equal or more contamination potential in
comparison to the active landfill sites and hence, the remediation actions and post-closure monitoring should be ensured at
the closed landfills till the leachate generated is stabilized and poses no further threat to the environment.