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Type Literature review
Authors Natalie Wieber
Published 2021
License CC-BY-SA-4.0
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Background of Recycling Solar PV[edit | edit source]

Overall Evaluations of Current State-of-the-art[edit | edit source]

P. Dias et al., "Comprehensive recycling of silicon photovoltaic modules incorporating organic solvent delamination – technical, environmental and economic analyses," Resources, Conservation and Recycling, vol. 165, p. 105241, Feb. 2021, doi: 10.1016/j.resconrec.2020.105241.

Abstract: 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.

  • Aluminum frame and junction box most profitable
  • "Positive net environmental impact"
  • 60 to 78 million tonnes of waste by 2050
  • Thin film modules have toxic waste, c-Si has lead and silver toxic
  • Limited resources... Si is now on the critical raw material list for EU
  • Would be good to use what we already have
  • Backsheet made of polyvinyl flouride (PVF)
  • Encapsulant typically EVA
  • Lead-tin coated Cu is tabbing
  • Soda-lime low-iron tempered glass
  • Si doped with phosphorous or boron
  • Anti-reflective coating... made of what?
  • Metal contacts are silver
  • Bottom is coated with Al
  • Thermal followed by chemical etching
  • FRELP has automated system for breaking down frame and cables, then heat and cut with high-frequency knife
  • PV in laminate is incinerated, ash is sieved then leached
  • Or stuff is just ground up with electronic waste
  • Electro-hydraulic fragmentation with sieving also used
  • Blade rotor crushing, thermal treatment or hammer crushing, shredding, electrostatic separation
  • Careful about solvent emissions
  • Recover undamaged cells with organic solvent ***
  • EVA is partially cross-linked and not, so in some solvents cross-linked fraction swells, the rest dissolves
  • Bad gases from this process?
  • Toluene seems to be best solvent but volatile - go to Kang paper for details on HOW - also could be reused
  • Downstream process involved thermal treatment, manually removing tabs (use XRF on tabs), leaching in nitric acid at room T for 2 hrs "under magnetic agitation"
  • Their total immersion in toluene time averaged 99 hrs, glass still intact but EVA decomposed, Si is not undamaged
  • Recycling done at large scale is better than landfilling

Md. S. Chowdhury et al., "An overview of solar photovoltaic panels' end-of-life material recycling," Energy Strategy Reviews, vol. 27, p. 100431, Jan. 2020, doi: 10.1016/j.esr.2019.100431.

Abstract: End-of-life (EOL) solar panels may become a source of hazardous waste although there are enormous benefits globally from the growth in solar power generation. Global installed PV capacity reached around 400 GW at the end of 2017 and is expected to rise further to 4500 GW by 2050. Considering an average panel lifetime of 25 years, the worldwide solar PV waste is anticipated to reach between 4%-14% of total generation capacity by 2030 and rise to over 80% (around 78 million tonnes) by 2050. Therefore, the disposal of PV panels will become a pertinent environmental issue in the next decades. Eventually, there will be great scopes to carefully investigate on the disposal and recycling of PV panels EOL. The EU has pioneered PV electronic waste regulations including PV-specific collection, recovery and recycling targets. The EU Waste of Electrical and Electronic Equipment (WEEE) Directive entails all producers supplying PV panels to the EU market to finance the costs of collecting and recycling EOL PV panels in Europe. Lessons can be learned from the involvement of the EU in forming its regulatory framework to assist other countries develop locally apposite approaches. This review focused on the current status of solar panel waste recycling, recycling technology, environmental protection, waste management, recycling policies and the economic aspects of recycling. It also provided recommendations for future improvements in technology and policy making. At present, PV recycling management in many countries envisages to extend the duties of the manufacturers of PV materials to encompass their eventual disposal or reuse. However, further improvements in the economic viability, practicality, high recovery rate and environmental performance of the PV industry with respect to recycling its products are indispensable.

  • CO2 emissions from Si PV negligable
  • 99.1 GWh solar PV was grid connected in 2017, Germany was first to connect to grid in 2007
  • Europe is actually working on a plan for waste
  • c-Si has 80% market shares as of 2020
  • Japan, China, and CA have no plans
  • Toxic waste in landfill could contaminate drinking water
  • Causes of module failure: poor design and defect in manufacturing, issues with electrical equipment and grounding, degradation of AR and EVA, incoherency with cracked cells, repeated load cycles, temp change affect contact in junction boxes, glass breakage, frames, cell interconnections, 40% failure from microscopic cracks and failures
  • Frame can go through secondary metallurgy
  • What is in the waste? Off gas?
  • High temp tube furnace, gas at 2L/h, heat to 500 C at 450 C/h, held for 1 hr
  • 4.3 and Table 1 summarizes most of the current methods tried
  • Policy not developed for encouraging recycling bc not enough EOL modules to make it worth it

R. Deng, N. L. Chang, Z. Ouyang, and C. M. Chong, "A techno-economic review of silicon photovoltaic module recycling," Renewable and Sustainable Energy Reviews, vol. 109, pp. 532–550, Jul. 2019, doi: 10.1016/j.rser.2019.04.020.

Abstract: 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.

  • Most recycling processes mix materials so it is hard to separate, lowering their value after recycling
  • Offers 3 main solutions: policy to increase the cost to landfill waste PV, recycling aims for value recovery instead of just mass recovery, have manufacturers design PV modules to ease recycling at EOL
  • Precious/scarce materials include Ag, Ga, In, Ge, Cd, Te
  • Other materials include Al, Cu, glass, Si
  • Pay back time could be as low as 1.6 years
  • Boron or phosphorous doped Si, current electrodes are Ag, Al, or Cu, Ar coating is Si3N4
  • Cells connected with Cu ribbon, encapsulated with EVA, front is glass, back is polymer
  • Dowcycling is extracting contaminated material
  • Upcycling is extracting pure/valuable material
  • Modules are shredded by glass recyclers since 75 weight % is glass
  • Al frame, junction box, and Cu cables manually removed, the rest is shredded
  • Al and glass recycled via manual/mechanical separation
  • Glass was recovered at 91 weight % after a tripe shredding
  • Cyrogenic process has been attempted for delamination - interfacial bonds are weakened by this - still yields powders
  • High-frequency knife cutting at higher temp yielded 98 weight % glass recovered - I think the rest of the module was preserved - potential for organic solvent
  • Thermal decomp of EVA in inert atmosphere at 500 C (backfoil peeled off beforehand)
  • When pyrolyzed, EVA becomes acetic acid, propane, propene, ethane, methane..... not ideal....apparently can be bruned off under oxygen environment - this combustion can balance out the energy used to heat the furnace
  • Wafers are much thinner than they used to be - difficult to recover without cracking
  • For chemical delamination, glass separated by soaking in HNO3 for a day (Bruton source)
  • Swelling of EVA may require additional pyrolysis
  • Flourine backfoil peeled off at elevated temp, scraped off, or combusted in specific incinerator (toxic byproducts)
  • Leaching is used for contaminated Si powder, typically HNO3 - powder cannot be used because of its purity
  • Etching uses more chemicals than leaching
  • AR and emitter grinded after leaching reduces chemicals even more
  • Table 2 for etching processes
  • Thermal recycling of Si wafers provides 70% energy reduction in Si wafer production
  • Environmental impact of downcycling or upcycling is better than landfill
  • Focus must be on flourine backfoils
  • Not enough waste to make it economically viable - once we're at 19000 tonne/year
  • Revenue factors are material market price, material weight, material purity, generated and collected waste (being generalized in a lot of LCA)
  • Al frames are across the board worth recycling but any other material is costs more than it is worth
  • Must recover high purity Si (probably thermal recycling is best) and Ag
  • If recycling could be faster it'd be cheaper

E. Klugmann-Radziemska and A. Kuczyńska-Łażewska, "The use of recycled semiconductor material in crystalline silicon photovoltaic modules production - A life cycle assessment of environmental impacts," Solar Energy Materials and Solar Cells, vol. 205, p. 110259, Feb. 2020, doi: 10.1016/j.solmat.2019.110259.

Abstract: To offset the negative impact of photovoltaic modules on the environment, it is necessary to introduce a long-term strategy that includes a complete lifecycle assessment of all system components from the production phase through installation and operation to disposal. Recycling of waste products and worn-out systems is an important element of this strategy. As the conclusions from the previous studies have shown, thermal treatment provides an efficient first step in the recycling process, while chemical treatment was more advantageous in the second step. This study aims to assess the environmental impact of recovering and recycling the valuable semiconductor silicon wafer material from photovoltaic solar cells. A comparison was made between producing new solar cells with or without recycled silicon material. The analysis of the photovoltaic cell life cycle scenario including material recycling presented in this article was performed using SimaPro software and data combined and extended from different LCI databases. The idea is that the use of recycled materials, which were energy-consuming in the primary production stage, allows to meaningly reduce the energy input in the secondary life cycle. All stages of the silicon cell life cycle contribute to the Global Warming Potential (GWP) and greenhouse gas emissions reductions through the use of recycled silicon material represented 42%. The total environmental impact of photovoltaic production can be reduced by as much as 58%, mainly through reduced energy consumption in the production process of high purity crystalline silicon.

  • Reusing materials that were expensive in first life cycle can decrease energy usage in second life cycle
  • Energy payback time for crystalline Si modules is 3.5-5 yrs, or 2.5 yrs for in desert
  • Reasons to recycle: landfill space for other waste, energy conservation, avoiding more raw material extraction, less emissions
  • Lots of energy to purify Si, Cl could be emitted which is toxic
  • Removal must occur in this order: front metal coating, bottom metal coating, AR coating, and n-p junction
  • How a wafer becomes a cell: texturization, emitter formation, parasitic junction removal, AR coating, front and back contacts
  • Claims monocrystalline Si cells are easier for second life cycle
  • EVA delamination takes a lot of energy, but recovering a whole cell can reduce new cell production energ consumption by 70%
  • If wafer isn't thick enough after process still viable as powder
  • Cells in this study were 270-300 um thick
  • Table 2 outlines production of a module in 2006
  • Ag recovered by electrolysis - ideal to reduce amount of Ag used in general
  • Figure 5 is a great diagram of recycling routes
  • LCA shows the environmental impact of reusing cells for production of new modules is two times better than making new ones

L. Frisson et al., "Recent improvements in industrial PV module recycling," Proceedings of the 16th European Photovoltaic Solar Energy Conference, vol. 1, Apr. 2000.

  • Pyrolysis with microwave heating causes cell cracks
  • Tri-ethylene glycol dissolution at 220-290 C also failed
  • Hot nitric acid may be worth trying but lots of acid required
  • Do I need to do my own TGA for EVA?
  • EVA decomp in air 450 C, decomp in N2 480 C - heating in N2 avoids exothermic reaction of EVA decomp, no swelling?
  • They heated modules in SiO2, sort of like the compressive force, with even T, mixing, and constant contact
  • Is this an expensive process?
  • Heating at an angle/in a "netting envelope" may provide better recovery
  • In this study, cells heated to 450 C for 20 min
  • Lifetime mapping with MFCA to verify quality maintained
  • HF, H2SO4, nitric acid process used
  • IV characteristics preserved
  • Etching in 20% NaOH is bad for interruptions at grain boundaries

Y. R. Smith and P. Bogust, "Review of Solar Silicon Recycling," in Energy Technology 2018, Cham, 2018, pp. 463–470, doi: 10.1007/978-3-319-72362-4_42.

Abstract: Photovoltaic (PV) modules are becoming an ever increasingly larger part of our energy portfolio. As more and more PV modules are installed and come on-line, management of end-of-life (EOL) modules becomes an important issue. Currently, management of overburden EOL PV modules is not an issue, but is anticipated to be by 2030. Recovery and recycling of valuable metals in PV modules presents several environmental and economic advantages. In this brief review, we will describe processes for refurbishing and recycling of PV silicon. These processes involve some combination of mechanical, thermal, and chemical processing, all of which all have their oPV) modules have become wn respective challenges. Also, projections of PV module material streams are also highlighted.

  • Amorphous Si not really used any more, but it still will need to be recycled!!
  • 40% of Si ingot gets cut away when sliced - this loss as well as energy necessary to produce new wafers makes reusing already wafered Si appealing (Sources 16, 20, 23)
  • Can we used PVF backing for anything?

What's in a Solar PV Module?[edit | edit source]

https://static.trinasolar.com/sites/default/files/PS-M-0532%20TALLMAX%20HalfCut_PE14H_NA_2019_A.pdf

  • Modules I will be working with
  • Multicrystalline Si
  • Glass is 3.2 mm thick, high transmission, tempered, does contain a ARC
  • EVA encapsulant
  • Backsheet described as "white"

R. D. McConnell and A. Hansen, "NCPV FY 1998 Annual Report," Annual Report, p. 572, 1999.

  • Naugard P is a typical antioxidant, Lupersol 101 and Cyasorb UV-531 are typical luminecents used in encapsulant
  • Other materials commonly used include cerium oxide-containing glass, Tefzel
  • They acheived 83% gel content (cross linking) as opposed to the typical 80% - good or bad?

Encapsulant (EVA)[edit | edit source]

E. Klampaftis and B.S. Richards, "Improvement in multi-crystalline silicon solar cell efficiency via addition of luminescent material to EVA encapsulation layer," Progress in Photovoltaics: Research and Applications, vol. 19, April 2011, doi: 10.1002/pip.1019. Abstract: This paper shows that an enhancement in the performance of commercial screen‐printed multi‐crystalline silicon photovoltaic modules can be achieved via luminescent down‐shifting of the incident light. Using fluorescent organic dyes dissolved in the pre‐existing poly‐ethylene vinyl acetate (EVA) encapsulation layer, an increase in the short‐wavelength external quantum efficiency of over 10% absolute, which results in 0.18% absolute higher efficiency, is reported. This approach offers the opportunity for prompt application at production scale, since it neither requires any modification to the module manufacturing process nor does it add to the cost of power generation. Copyright © 2010 John Wiley & Sons, Ltd.

  • Luminescent down-shifting(LDS) of incident light by having some species in the encapsulant
  • Generally all module EQE suffer in shorter wavelength range
  • 300-400 nm have high energy content so interact a lot with front layers of module
  • Reasons for EQE suffering at short wavelength: "parasitic absorption and reflection" from SiNx ARC, high doping means fast recomb rates, front glass reflects, encapsulant absorbs
  • LDS can help with above reasons besides the front glass reflection
  • So the species absorbs short wavelength then emits at a longer length so it can reach the PV
  • Used Lumogen-F Violet 570 dye as species to increase EVA absorption
  • PLQY and transmission confirm homogeneity of EVA
  • Used already made PV, sandwich of borosilicate glass and EVA on both sides of PV, vac laminated
  • High dye concentration emitted photons at 400-570 nm
  • Species didn't affect IQE, no affect on electronic properties
  • Species did increase EQE in 300-400 nm range

J. Pern, "Module Encapsulation Materials, Processing and Testing," p. 33., Dec. 2008.

  • Encapsulation contributes to 20-30 year life of PV module
  • Typical encapsulants: EVA, TPU, PVB, Silicones, Silicone/PU hybrid, Ionomer, UV-curable resin
  • Typical edge sealants: Polybutyl and Silicones for Al framed crystalline Si, Desiccant-type for thin film CdTe and CIGS, PIB-type
  • Typical superstrate: Glass (low-iron, tempered, plain or textured, UV-filtering/Ce, SiO2 ARC) or Flouropolymer (Tefzel, Tedlar, THV220)
  • Typical substrate/backfoil: Polymer Multi-laminates (Tedlar based, PET or PEN based - Protekt, Teijin Teonex, BaSO4 filled PET) or Glass
  • Will I need to dissolve backfoil?
  • Find out what kind of sealing I'm working with
  • Contains more details about encapsulation degradation

US Granted Patent No. 6093757

  • May be necessary to know how old module is - cross linking in EVA is dependent on time/degree of photo-oxidative degradation, and amount of cross linking present is the "gel" that can't easily be dissolved
  • Chromophores often produced in curing process, they (with UV) are an intitiant of the degradation of EVA via hydroproxidation
  • Aim for a fast cure, often causes bubbling which affects absorption
  • What makes a good encapsulant: photothermal and photochemical stability, not many chromophores made in curing, fast cure rate, ideal amount of cross linking, little bubbling, protection for antioxidant against moisture and thermal decomp

N. S. Allen, M. Edge, M. Rodriguez, C. M. Liauw, and E. Fontan, "Aspects of the thermal oxidation, yellowing and stabilisation of ethylene vinyl acetate copolymer," Polymer Degradation and Stability, vol. 71, no. 1, pp. 1–14, Jan. 2000, doi: 10.1016/S0141-3910(00)00111-7.Abstract: The thermal oxidation of ethylene-vinyl acetate copolymer [EVA-17 and 28% w/w VA (vinyl acetate) units] has been examined by thermo-gravimetric and hydroperoxide analysis, FTIR (Fourier transform infra-red), fluorescence spectroscopy and yellowness index. Thermal analysis indicates the initial loss of acetic acid followed by oxidation and breakdown of the main chain. The degradation rate is greater in an oxygen atmosphere as is the formation of coloured products. FTIR spectroscopic analysis of the oxidised EVA shows evidence for de-acetylation followed by the concurrent formation of hydroxyl/hydroperoxide species, ketone groups, α, β-unsaturated carbonyl groups, conjugated dienes, lactones and various substituted vinyl types. Hydroperoxide evolution follows typical auto-oxidation kinetics forming ketonic species. In severely oxidised EVA, evidence is given for the subsequent formation of anhydride groups. The initial fluorescence excitation and emission spectra of EVA is not unlike that reported for polyolefins confirming the presence of low levels of unsaturated carbonyl species. There are, however, significant differences in a long wavelength component in the fluorescence emission indicating the presence of other active chromophores. These long wavelength emitting components grow in intensity and shift to longer wavelengths with ageing time. However, unlike studies on PVC these emission spectra are limited due to the vinyl polyconjugation lengths and tend to be consistent with the formation of specific degraded units, possibly polyunsaturated carbonyl species of a limited length confined to the EVA blocks. During oxidation of EVA the original unsaturated carbonyl species remain as distinct emitting chromophores. This suggests that the growth and decay of these chromphores is virtually constant indicating that they could be an integral part of the EVA polymer that are responsible for inducing degradation. Degradation is limited to the vinyl acetate moieties where hydroperoxides can lead to the formation of polyconjugated carbonyl groups. The EVA degradation is therefore, different from that of PVC where in the latter case polyconjugated vinyl groups are evident through conjugated absorption bands in the UV spectrum. In the case of degraded EVA no such bands are observed. Also, degraded coloured EVA is not bleached by treatment with bromine, maleic anhydride or peracetic acid. Primary phenolic antioxidants exhibit variable activity in inhibiting the yellowing of EVA while combinations with phosphites and hindered piperidine stabilisers display powerful synergism confirming the importance of hydroperoxides as precursors. Thermal oxidation was also was displayed through the inhibition of lactone, carboxylic acid and alkene groups illustrating the fact that oxidation and yellowing are synonymous reactions.

  • EVA degrades because acetic acid forms then main chains break, so ethylene and vinyl acetate don't interact - does acetic acid form because of UV?
  • EVA hydroperoxidates so ketone and unsaturated ketone groups form

Chitra, D. Sah, K. Lodhi, C. Kant, P. Saini, and S. Kumar, "Structural composition and thermal stability of extracted EVA from silicon solar modules waste," Solar Energy, vol. 211, pp. 74–81, Nov. 2020, doi: 10.1016/j.solener.2020.09.039.Abstract: Ethylene-vinyl acetate (EVA), a copolymer of ethylene and vinyl acetate, is widely used as an encapsulant in the silicon solar module to bind the different layers together and protecting the solar cells from over stressing, cracking, and environmental effects. In this work, EVA has been recovered successfully from the used silicon solar module by thermal treatment at 170 °C temperature and the application of mechanical force. The established process is completely environment-friendly, as the EVA layer was recovered without any degradation and emission of any gas. The presence of extracted EVA and its chemical composition was confirmed from FTIR and EDAX measurements. It was observed from Thermogravimetry (TGA) and Differential thermogravimetry (DTG) that thermal degradation of EVA was a two-step process, and also the rate of reaction was fast in an air environment as compared to nitrogen environment. The extracted EVA is thermally stable until 215 °C in the air environment. From Differential scanning calorimetry (DSC) analysis, two endothermic peaks were observed at temperature 37 °C and 55 °C, which may be due to beginning of melting of vinyl acetate and ethylene crystallites respectively in air and nitrogen environment. From UV–visible spectroscopy, it was found that above 500 nm, the extracted EVA is transparent. After examined through the various characterization, it has been observed that extracted EVA shows quite similar properties as that of commercially available EVA. Therefore, the recovered EVA may be used in the encapsulation of solar modules and other applications in packaging and textile industries.

  • They mechanically removed Al frame, the rest was sheared with diamond wheel cutter rotating
  • Tedlar removed from module at 130 C
  • The rest was heated to 170 C, then EVA could be scraped off - no yellowing or residual gas - what about swelling or cracking of SI?
  • Concluded the EVA has same properties as before used as encapsulant, so can be reused for solar modules if processed at 170 C

K. V. den Broeck, N. V. Hoornick, J. V. Hoeymissen, R. de Boer, A. Giesen, and D. Wilms, "Sustainable treatment of HF wastewaters from semiconductor industry with a fluidized bed reactor," IEEE Transactions on Semiconductor Manufacturing, vol. 16, no. 3, pp. 423–428, Aug. 2003, doi: 10.1109/TSM.2003.815624.

Abstract: Within the semiconductor industry, large volumes of hydrogen fluoride (HF) containing wastewaters need to be treated. This paper describes a technique that makes it possible to treat HF wastewater with virtually no waste production. A method based on crystallization of CaF/sub 2/ on sand particles in a fluidized bed reactor, with trade name Crystalactor, was assessed for the first time with real wastewater originating from a semiconductor prototyping line. Several process parameters were investigated such as influent fluoride concentration, calcium reagent excess, pH, single versus multiple calcium reagent dosing, etc. It can be concluded that the performance of the reactor is greatly dependent on the initial concentrations of calcium and fluoride at the bottom of the reactor (referred to as local saturation). The original hardware design was changed from a single reagent dosing to a multiple reagent dosing to prevent too high local supersaturation values of fluoride and calcium and thus obtain higher CaF/sub 2/ crystallization efficiencies. Fluoride loads up to 7 kg/m/sup 2//spl middot/h were still possible with multiple reagent dosing, compared to a maximum treatable load of 3.5 kg/m/sup 2//spl middot/h for single reagent dose. Additionally, an alternative post-treatment process based on replacement of calcite by fluorite in a granular calcite column is demonstrated.

  • What to do with HF throughout solar PV process
  • Lots of HF used in production and recycling of semiconductor PV
  • Most of the time Ca is added in some way to form CaF2, Al is also good absorbent because bonds to F are higher but it is more costly
  • So they use reactor to grow CaF2 crystals on surface of sand grains

Backsheet (PVF)[edit | edit source]

C. Farrell et al., "Assessment of the energy recovery potential of waste Photovoltaic (PV) modules," Scientific Reports, vol. 9, no. 1, Art. no. 1, Mar. 2019, doi: 10.1038/s41598-019-41762-5.

Abstract: Global exponential increase in levels of Photovoltaic (PV) module waste is an increasing concern. The purpose of this study is to investigate if there is energy value in the polymers contained within first-generation crystalline silicon (c-Si) PV modules to help contribute positively to recycling rates and the circular economy. One such thermochemical conversion method that appeals to this application is pyrolysis. As c-Si PV modules are made up of glass, metal, semiconductor and polymer layers; pyrolysis has potential not to promote chemical oxidation of any of these layers to help aid delamination and subsequently, recovery. Herein, we analysed both used polymers taken from a deconstructed used PV module and virgin-grade polymers prior to manufacture to determine if any properties or thermal behaviours had changed. The calorific values of the used and virgin-grade Ethylene vinyl acetate (EVA) encapsulant were found to be high, unchanged and comparable to that of biodiesel at 39.51 and 39.87 MJ.Kg−1, respectively. This result signifies that there is energy value within used modules. As such, this study has assessed the pyrolysis behaviour of PV cells and has indicated the energy recovery potential within the used polymers found in c-Si PV modules.

  • Refer to for polymer ID
  • In order of mass, glass, anodized Al frame, two layers EVA, junction box, backsheet (usually either TPT or TPE)
  • Alternatives to Tedlar (flourine based polymer) are polyester, e-layers of ethylene copolymers, polyamides, or blends with PMMA
  • International Energy Agency claims chemical/thermal methods superior to mechanical methods of delamination
  • This study goes into how by-products of EVA decomp could be used for energy
  • Figure 1 is good reference for FT-IR
  • EVA decomp between 310-390 C, second decomp step between 410-510 C
  • Higher decomp T with lower ramp rate
  • Want to extract heat/energy from polymers
  • Page 7 breaks down EVA decomp process
  • Cut samples with water jet cutting
  • Samples heated for 10 min at 190 C, little cuts on the side to make peeling the backsheet off (watch for cooling) - some came off well, some left white residue on EVA
  • Page 10 might come in handy for FPV

K. J. Geretschläger, G. M. Wallner, and J. Fischer, "Structure and basic properties of photovoltaic module backsheet films," Solar Energy Materials and Solar Cells, vol. 144, pp. 451–456, Jan. 2016, doi: 10.1016/j.solmat.2015.09.060. Abstract: In this paper commercially relevant backsheets are characterized as to their material and laminate structure and basic optical and mechanical properties. Various multilayer backsheet materials were selected and analysed by optical microscopy, Raman spectroscopy, infrared spectroscopy (FTIR-ATR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), ultra violet visible near infrared spectroscopy (UV/VIS/NIR) and monotonic tensile testing. By Raman and infrared spectroscopy and DSC the polymeric materials of the various layers were identified. Furthermore it was shown for the thermoplastic ethylene vinylacetate copolymer (EVA) layers that three different vinylacetate (VA) contents were used. By TGA a content of inorganic fillers and pigments from about 6%m to approximately 20%m was detected. The hemispherical solar reflectance of the white pigmented backsheets was ranging from 0.695 to 0.838. The highest Young׳s modulus was found in polyvinylfluoride based multilayers while the lowest values were detected for polyamide based structures.

  • EVA substitutes inner layer of PVF, other outer layers include PVDF, ECTFE and THV
  • ID polymers with Raman confocal microscope and FTIR spectrometer with ATR (attenuated total reflexion)
  • Raman and infrared detected flouropolymers, and only Raman detected TiO2 and short glass fibers
  • Figure 5 and 6 for FT-IR expectations
  • Other engineering thermoplastics used in solar PV are PET, EVA, PA, and PP

Anti-reflective Coating[edit | edit source]

R. Li, J. Di, Z. Yong, B. Sun, and Q. Li, "Polymethylmethacrylate coating on aligned carbon nanotube–silicon solar cells for performance improvement," J. Mater. Chem. A, vol. 2, no. 12, pp. 4140–4143, Feb. 2014, doi: 10.1039/C3TA14625A.

Abstract: Polymethylmethacrylate (PMMA) coating has been spin-coated onto aligned carbon nanotube–silicon (CNT–Si) solar cells and the efficiency increased from 7.1% to 11.5%, and was further increased to 13.1% when doped with nitric acid (HNO3) under air mass (AM 1.5) conditions. The antireflection of PMMA coating and the decreased resistance at the CNT–Si interface during PMMA drying process together contributed to the performance improvement.

  • PMMA is antireflective
  • Carbon nanotube(CNT) -Si interface has lower resistance
  • Surface texturing with pyramid, nanocone, nanowire, and random for trapping light
  • Deposition of TiO2, Si3N4, Ta2O5 thin films for trapping light
  • Ag paste and liquid state GaIn eutectic used on Si substrate
  • PMMA thickness increase, wavelength of lowest reflectance increases
  • CNT-Si interface increases when CNT pushed into film by "shrink force" from PMMA coating and solvent evap