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Special Issue "Solar Cells and Modules: Fabrication, Characterization, and Environmental Issues"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A2: Solar Energy and Photovoltaic Systems".

Deadline for manuscript submissions: closed (20 March 2021) | Viewed by 8723

Special Issue Editor

Prof. Dr. Jürgen Heinz Werner
E-Mail Website
Guest Editor
Institute for Photovoltaics and Research Center SCoPE, University of Stuttgart, 70569 Stuttgart, Germany
Interests: solar cells; photovoltaics; renewable energy; energy storage; energy conversion; solid state electronics

Special Issue Information

Dear Colleagues,

At present, almost 600 GW of solar modules are installed worldwide. This power corresponds to an area of around 4000 km². The installed area is increasing daily by about three soccer fields, a number which, in terms of the total power and area, increases exponentially. The production cost of photovoltaic electricity ranges around a few ct/kWh and is lower than the cost of electricity from coal or nuclear power plants. Thus, the road to an environmentally friendly supply with electricity has been paved. Nevertheless, this success is accompanied by dynamic growth and creates certain problems. For example, some of the cell and module technologies contain toxic materials, such as lead and cadmium. These materials could leach out of the modules. Additionally, some modules degrade in electrical power. This Special Issue of Energies calls for papers in the following fields:

  • Stability and degradation of solar modules;
  • Reduction of material consumption (glass, Pb, Ag, Si, etc.);
  • Potential induced degradation;
  • Toxic materials and leaching experiments;
  • Recycling and waste management of photovoltaic modules;
  • Lowering of electricity cost;
  • Novel methods for the characterization of large area photovoltaic fields;
  • Energy yield improvements by bifaciality, temperature management, etc.

Prof. Dr. Jürgen Heinz Werner
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • solar modules
  • degradation
  • stability
  • toxic materials
  • waste
  • recycling
  • measurement techniques

Published Papers (8 papers)

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Research

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Article
Image Preprocessing for Outdoor Luminescence Inspection of Large Photovoltaic Parks
Energies 2021, 14(9), 2508; https://doi.org/10.3390/en14092508 - 27 Apr 2021
Viewed by 609
Abstract
Electroluminescence (EL) measurements allow one to detect damages and/or defective parts in photovoltaic systems. In principle, it seems possible to predict the complete current/voltage curve from such pictures even automatically. However, such a precise analysis requires image corrections and calibrations, because vignetting and [...] Read more.
Electroluminescence (EL) measurements allow one to detect damages and/or defective parts in photovoltaic systems. In principle, it seems possible to predict the complete current/voltage curve from such pictures even automatically. However, such a precise analysis requires image corrections and calibrations, because vignetting and lens distortion cause signal and spatial distortions. Earlier works on crystalline silicon modules used the cell gap joints (CGJ) as calibration pattern. Unfortunately, this procedure fails if the detection of the gaps is not accurate or if the contrast in the images is low. Here, we enhance the automated camera calibration algorithm with a reliable pattern detection and analyze quantitatively the quality of the process. Our method uses an iterative Hough transform to detect line structures and uses three key figures (KF) to separate detected busbars from cell gaps. This method allows a reliable identification of all cell gaps, even in noisy images or if disconnected edges in PV cells exist or potential induced degradation leads to a low contrast between active cell area and background. In our dataset, a subset of 30 EL images (72 cell each) forming grid (5×11) lead to consistent calibration results. We apply the calibration process to 997 single module EL images of PV modules and evaluate our results with a random subset of 40 images. After lens distortion correction and perspective correction, we analyze the residual deviation between ideal target grid points and the previously detected CGJ after applied distortion and perspective correction. For all of the 2200 control points in the 40 evaluation images, we achieve a deviation of less than or equal to 3 pixels. For 50% of the control points, a deviation of of less than or equal to 1 pixel is reached. Full article
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Article
Leaching via Weak Spots in Photovoltaic Modules
Energies 2021, 14(3), 692; https://doi.org/10.3390/en14030692 - 29 Jan 2021
Cited by 3 | Viewed by 929
Abstract
This study identifies unstable and soluble layers in commercial photovoltaic modules during 1.5 year long-term leaching. Our experiments cover modules from all major photovoltaic technologies containing solar cells from crystalline silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide [...] Read more.
This study identifies unstable and soluble layers in commercial photovoltaic modules during 1.5 year long-term leaching. Our experiments cover modules from all major photovoltaic technologies containing solar cells from crystalline silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). These technologies cover more than 99.9% of the world market. We cut out module pieces of 5 × 5 cm2 in size from these modules and leached them in water-based solutions with pH 4, pH 7, and pH 11, in order to simulate different environmental conditions. Unstable layers open penetration paths for water-based solutions; finally, the leaching results in delamination. In CdTe containing module pieces, the CdTe itself and the back contact are unstable and highly soluble. In CIGS containing module pieces, all of the module layers are more or less soluble. In the case of c-Si module pieces, the cells’ aluminum back contact is unstable. Module pieces from a-Si technology also show a soluble back contact. Long-term leaching leads to delamination in all kinds of module pieces; delamination depends strongly on the pH value of the solutions. For low pH-values, the time dependent leaching is well described by an exponential saturation behavior and a leaching time constant. The time constant depends on the pH, as well as on accelerating conditions such as increased temperature and/or agitation. Our long-term experiments clearly demonstrate that it is possible to leach out all, or at least a large amount, of the (toxic) elements from the photovoltaic modules. It is therefore not sufficient to carry out experiments just over 24 h and to conclude on the stability and environmental impact of photovoltaic modules. Full article
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Article
Size- and Surface-Dependent Solubility of Cadmium Telluride in Aqueous Solutions
Energies 2021, 14(2), 398; https://doi.org/10.3390/en14020398 - 12 Jan 2021
Cited by 2 | Viewed by 931
Abstract
Due to the toxicity of cadmium (Cd) and the scarcity of telluride (Te), CdTe-based photovoltaic modules have been under discussion during the last few years. In particular, the stability of CdTe in aqueous solutions is under debate. Here we show that the stability [...] Read more.
Due to the toxicity of cadmium (Cd) and the scarcity of telluride (Te), CdTe-based photovoltaic modules have been under discussion during the last few years. In particular, the stability of CdTe in aqueous solutions is under debate. Here we show that the stability of CdTe depends not only on the pH of water-based solutions but also on size and surface treatment of CdTe particles. We compare milled module pieces with CdTe powders of different particle size. The leaching of CdTe is conditioned by the outdiffusion of Cd and Te at the interface between CdTe particles and the aqueous solution. The smaller the particle size, the faster the leaching. Therefore, milled module pieces decompose faster than CdTe powders with relatively large grains. We observe a dependence on time t according to t0.43. The room temperature diffusion coefficients are calculated as DCd ≈ 3 × 10−17 cm2/s for Cd, and DTe ≈ 1.5 × 10−17 cm2/s for Te in pH4. The chemical instability in aqueous solutions follows thermodynamic considerations. The solution behavior of Cd and Te depends on the pH value and the redox potential of the aqueous solutions. Chemical treatments such as those used in solar cell production modify the surface of the CdTe particles and their leaching behavior. Full article
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Article
A Study of the Electrical Output and Reliability Characteristics of the Crystalline Photovoltaic Module According to the Front Materials
Energies 2021, 14(1), 163; https://doi.org/10.3390/en14010163 - 30 Dec 2020
Cited by 2 | Viewed by 738
Abstract
In recent years, various types of installations such as floating photovoltaic (PV) and agri-voltaic systems, and BIPV (building integrated photovoltaic system) have been implemented in PV systems and, accordingly, there is a growing demand for new PV designs and materials. In particular, in [...] Read more.
In recent years, various types of installations such as floating photovoltaic (PV) and agri-voltaic systems, and BIPV (building integrated photovoltaic system) have been implemented in PV systems and, accordingly, there is a growing demand for new PV designs and materials. In particular, in order to install a PV module in a building, it is important to reduce the weight of the module. The PV module in which low-iron, tempered glass is applied to the front surface, which is generally used, has excellent electrical output and reliability characteristics; however, it is heavy. In order to reduce the weight of the PV module, it is necessary to use a film or plastic-based material, as opposed to low-iron, tempered glass, on the front surface. However, if a material other than glass is used on the front of the PV module, various problems such as reduced electrical output and reduced reliability may occur. Therefore, in this paper, a PV module using a film instead of glass as the front surface was fabricated, and a characteristic analysis and reliability test were conducted. First, the transmittance and UV characteristics of each material were tested, and one-cell and 24-cell PV modules were fabricated and tested for electrical output and reliability. From the results, it was found that the transmittance and UV characteristics of the front material were excellent. In addition, the electrical output and reliability test results confirmed that the front-surface film was appropriate for use in a PV module. Full article
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Article
Degradation Rate Location Dependency of Photovoltaic Systems
Energies 2020, 13(24), 6751; https://doi.org/10.3390/en13246751 - 21 Dec 2020
Cited by 8 | Viewed by 872
Abstract
A main challenge towards ensuring improved lifetime performance and reduction of financial risks of photovoltaic (PV) technologies remains the accurate degradation quantification of field systems and the dependency of this performance loss rate to climatic conditions. The purpose of this study is to [...] Read more.
A main challenge towards ensuring improved lifetime performance and reduction of financial risks of photovoltaic (PV) technologies remains the accurate degradation quantification of field systems and the dependency of this performance loss rate to climatic conditions. The purpose of this study is to address these technological issues by presenting a unified methodology for accurately calculating the degradation rate (RD) of PV systems and provide evidence that degradation mechanisms are location dependent. The method followed included the application of data inference and time series analytics, in the scope of comparing the long-term RD of different crystalline Silicon (c-Si) PV systems, installed at different climatic locations. The application of data quality and filtering steps ensured data fidelity for the RD analysis. The yearly RD results demonstrated that the adopted time series analytical techniques converged after 7 years and were in close agreement to the degradation results obtained from indoor standardized procedures. Finally, the initial hypothesis that the RD is location dependent was verified, since the multicrystalline silicon (multi-c-Si) systems at the warm climatic region exhibited higher degradation compared to the respective systems at the moderate climate. For the investigated monocrystalline silicon (mono-c-Si) systems the location-dependency is also affected by the manufacturing technology. Full article
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Article
Clarification of Catalytic Effect on Large Stretchable and Compressible Rubber Dye-Sensitized Solar Cells
Energies 2020, 13(24), 6658; https://doi.org/10.3390/en13246658 - 17 Dec 2020
Viewed by 672
Abstract
Rubber involving magnetic compound fluid (MCF) and TiO2 is effective in dye-sensitized solar cells (DSSCs) to create large efficacy. Wearable and portable solar cells made of MCF rubber are the most desirable as soft materials in robots or flexible devices, and they [...] Read more.
Rubber involving magnetic compound fluid (MCF) and TiO2 is effective in dye-sensitized solar cells (DSSCs) to create large efficacy. Wearable and portable solar cells made of MCF rubber are the most desirable as soft materials in robots or flexible devices, and they are further desirable because they have self-generated power and power supply with sensing. Therefore, we investigated the effect of TiO2 catalysts on the photovoltaic effect of MCF rubber DSSCs under large tension and compression. The characteristics of the built-in electricity and photoelectricity were clarified experimentally. The experimental results were explained by a chemical–photovoltaic mechanism involving the behavior of dye, electrolytes, water, and rubber molecules, as well as a catalytic effect of the metal component of the MCF on Ni, Fe3O4, and TiO2. Once we are able to produce solar cells that have large tension and compression, the present experimental results and the model of the chemical–photovoltaic mechanism will be of great interest. Full article
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Review

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Review
Review of State of the Art Recycling Methods in the Context of Dye Sensitized Solar Cells
Energies 2021, 14(13), 3741; https://doi.org/10.3390/en14133741 - 22 Jun 2021
Cited by 8 | Viewed by 1096
Abstract
In times of climate change and dwindling fossil resources, the need for sustainable renewable energy technologies gains importance, increasingly fast. However, the state of the art technologies are energy intensive in their production, like monocrystalline photovoltaic, or even consist of not recyclable composite [...] Read more.
In times of climate change and dwindling fossil resources, the need for sustainable renewable energy technologies gains importance, increasingly fast. However, the state of the art technologies are energy intensive in their production, like monocrystalline photovoltaic, or even consist of not recyclable composite material, in the case of wind turbine blades. Despite a lack in efficiency and stability, dye sensitized solar cells (DSSC) have a high potential to supplement the state of the art green energy technology in future. With low production costs and no necessity for toxic compounds DSSCs are a potential product, which could circulate in the loops of a circular economy. Therefore, with this paper, we provide the status of research on DSSC recycling and an outlook on how recycling streams could be realized in the future for glass-based DSSCs without toxic components. The overview includes work on using recycled material to build DSSCs and extending the life of a DSSC, e.g., through rehydration. We also illustrate the state of sustainability research for DSSCs using the VOSviewer tool. To date, the term sustainability appears in 35 of 24,441 publications on DSSCs. In view of the global challenges, sustainability should be researched more seriously because it is as important as the efficiency and stability of DSSCs. Full article
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Review
Bifacial Photovoltaics 2021: Status, Opportunities and Challenges
Energies 2021, 14(8), 2076; https://doi.org/10.3390/en14082076 - 08 Apr 2021
Cited by 25 | Viewed by 2206
Abstract
In this paper we summarize the status of bifacial photovoltaics (PV) and explain why the move to bifaciality is unavoidable when it comes to e.g., lowest electricity generation costs or agricultural PV (AgriPV). Bifacial modules—those that are sensitive to light incident from both [...] Read more.
In this paper we summarize the status of bifacial photovoltaics (PV) and explain why the move to bifaciality is unavoidable when it comes to e.g., lowest electricity generation costs or agricultural PV (AgriPV). Bifacial modules—those that are sensitive to light incident from both sides—are finally available at the same price per watt peak as their standard monofacial equivalents. The reason for this is that bifacial solar cells are the result of an evolution of crystalline Si PV cell technology and, at the same time, module producers are increasingly switching to double glass modules anyway due to the improved module lifetimes, which allows them to offer longer product warrantees. We describe the general properties of the state-of-the-art bifacial module, review the different bifacial solar cells and module technologies available on the market, and summarize their average costs. Adding complexity to a module comes with the increase of possible degradation mechanisms, requiring more thorough testing, e.g., for rear side PID (Potential Induced Degradation). We show that with the use of bifacial modules in fixed tilt systems, gains in annual energy yield of up to 30% can be expected compared to the monofacial equivalent. With the combination of bifacial modules in simple single axis tracking systems, energy yield increases of more than 40% can be expected compared to fixed tilt monofacial installations. Rudimentary simulations of bifacial systems can be performed with commercially available programs. However, when more detailed and precise simulations are required, it is necessary to use more advanced programs such as those developed at several institutes. All in all, as bifacial PV—being the most cost-effective PV solution—is now becoming also bankable, it is becoming the overall best technology for electricity generation. Full article
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