Matching Items (18)
Filtering by
- All Subjects: photovoltaics
- Creators: Tamizhmani, Govindasamy
- Creators: Goryll, Michael
- Status: Published
Description
Potential induced degradation (PID) due to high system voltages is one of the major degradation mechanisms in photovoltaic (PV) modules, adversely affecting their performance due to the combined effects of the following factors: system voltage, superstrate/glass surface conductivity, encapsulant conductivity, silicon nitride anti-reflection coating property and interface property (glass/encapsulant; encapsulant/cell; encapsulant/backsheet). Previous studies carried out at ASU's Photovoltaic Reliability Laboratory (ASU-PRL) showed that only negative voltage bias (positive grounded systems) adversely affects the performance of commonly available crystalline silicon modules. In previous studies, the surface conductivity of the glass surface was obtained using either conductive carbon layer extending from the glass surface to the frame or humidity inside an environmental chamber. This thesis investigates the influence of glass surface conductivity disruption on PV modules. In this study, conductive carbon was applied only on the module's glass surface without extending to the frame and the surface conductivity was disrupted (no carbon layer) at 2cm distance from the periphery of frame inner edges. This study was carried out under dry heat at two different temperatures (60 °C and 85 °C) and three different negative bias voltages (-300V, -400V, and -600V). To replicate closeness to the field conditions, half of the selected modules were pre-stressed under damp heat for 1000 hours (DH 1000) and the remaining half under 200 hours of thermal cycling (TC 200). When the surface continuity was disrupted by maintaining a 2 cm gap from the frame to the edge of the conductive layer, as demonstrated in this study, the degradation was found to be absent or negligibly small even after 35 hours of negative bias at elevated temperatures. This preliminary study appears to indicate that the modules could become immune to PID losses if the continuity of the glass surface conductivity is disrupted at the inside boundary of the frame. The surface conductivity of the glass, due to water layer formation in a humid condition, close to the frame could be disrupted just by applying a water repelling (hydrophobic) but high transmittance surface coating (such as Teflon) or modifying the frame/glass edges with water repellent properties.
ContributorsTatapudi, Sai Ravi Vasista (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Srinivasan, Devarajan (Committee member) / Rogers, Bradley (Committee member) / Arizona State University (Publisher)
Created2012
Description
Photovoltaic (PV) modules are typically rated at three test conditions: STC (standard test conditions), NOCT (nominal operating cell temperature) and Low E (low irradiance). The current thesis deals with the power rating of PV modules at twenty-three test conditions as per the recent International Electrotechnical Commission (IEC) standard of IEC 61853 – 1. In the current research, an automation software tool developed by a previous researcher of ASU – PRL (ASU Photovoltaic Reliability Laboratory) is validated at various stages. Also in the current research, the power rating of PV modules for four different manufacturers is carried out according to IEC 61853 – 1 standard using a new outdoor test method. The new outdoor method described in this thesis is very different from the one reported by a previous researcher of ASU – PRL. The new method was designed to reduce the labor hours in collecting the current-voltage ( I – V) curves at various temperatures and irradiance levels. The power matrices for all the four manufacturers were generated using the I – V data generated at different temperatures and irradiance levels and the translation procedures described in IEC 60891 standard. All the measurements were carried out on both clear and cloudy days using an automated 2 – axis tracker located at ASU – PRL, Mesa, Arizona. The modules were left on the 2 – axis tracker for 12 continuous days and the data was continuously and automatically collected for every two minutes from 6 am to 6 pm. In order to obtain the I – V data at wide range of temperatures and irradiance levels, four identical (or nearly identical) modules were simultaneously installed on the 2 – axis tracker with and without thermal insulators on the back of the modules and with and without mesh screens on the front of the modules. Several issues related to the automation software were uncovered and the required improvement in the software has been suggested. The power matrices for four manufacturers have been successfully generated using the new outdoor test method developed in this work. The data generated in this work has been extensively analyzed for accuracy and for performance efficiency comparison at various temperatures and irradiance levels.
ContributorsVemula, Meena Gupta (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Macia, Narcio F. (Committee member) / Rogers, Bradley (Committee member) / Arizona State University (Publisher)
Created2012
Description
With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane.
This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.
The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.
This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.
The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.
ContributorsHan, Bingru (Author) / Westerhoff, Paul (Thesis advisor) / Perreault, Francois (Committee member) / Sinha, Shahnawaz (Committee member) / Arizona State University (Publisher)
Created2017
Description
The volume of end-of-life photovoltaic (PV) modules is increasing as the global PV market increases, and the global PV waste streams are expected to reach 250,000 metric tons by the end of 2020. If the recycling processes are not in place, there would be 60 million tons of end-of-life PV modules lying in the landfills by 2050, that may not become a not-so-sustainable way of sourcing energy since all PV modules could contain certain amount of toxic substances. Currently in the United States, PV modules are categorized as general waste and can be disposed in landfills. However, potential leaching of toxic chemicals and materials, if any, from broken end-of-life modules may pose health or environmental risks. There is no standard procedure to remove samples from PV modules for chemical toxicity testing in the Toxicity Characteristic Leaching Procedure (TCLP) laboratories as per EPA 1311 standard. The main objective of this thesis is to develop an unbiased sampling approach for the TCLP testing of PV modules. The TCLP testing was concentrated only for the laminate part of the modules, as they are already existing recycling technologies for the frame and junction box components of PV modules. Four different sample removal methods have been applied to the laminates of five different module manufacturers: coring approach, cell-cut approach, strip-cut approach, and hybrid approach. These removed samples were sent to two different TCLP laboratories, and TCLP results were tested for repeatability within a lab and reproducibility between the labs. The pros and cons of each sample removal method have been explored and the influence of sample removal methods on the variability of TCLP results has been discussed. To reduce the variability of TCLP results to an acceptable level, additional improvements in the coring approach, the best of the four tested options, are still needed.
ContributorsLeslie, Joswin (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Srinivasan, Devarajan (Committee member) / Kuitche, Joseph (Committee member) / Arizona State University (Publisher)
Created2018
Fill Factor Loss Mechanisms: Analysis and Basic Understanding in Silicon Hetero-junction Solar Cells
Description
The objective of this thesis is to achieve a detailed understanding of the loss mechanisms in SHJ solar cells. The working principles of these cells and what affects the cell operation, e.g. the IV characteristics at the maximum power point (MPP) and the correspondingly ll factor (FF) are investigated. Dierent loss sources are analyzed separately, and the weight of each in the total loss at the MPP are evaluated. The total series resistance is measured and then compared with the value obtained through summation over each of its components. In other words, series resistance losses due to recombination, vertical and lateral carrier transport, metalization, etc, are individually evaluated, and then by adding all these components together, the total loss is calculated. The concept of ll factor and its direct dependence on the loss mechanisms at the MPP of the device is explained, and its sensitivity to nearly every processing step of the cell fabrication is investigated. This analysis provides a focus lens to identify the main source of losses in SHJ solar cells and pave the path for further improvements in cell efficiency.
In this thesis, we provide a detailed understanding of the FF concept; we explain how it can be directly measured; how it can be calculated and what expressions can better approximate its value and under what operating conditions. The relation between FF and cell operating condition at the MPP is investigated. We separately analyzed the main FF sources of losses including recombination, sheet resistance, contact resistance and metalization. We study FF loss due to recombination and its separate components which include the Augur, radiative and SRH recombination is investigated. We study FF loss due to contact resistance and its separate components which include the contact resistance of dierent interfaces, e.g. between the intrinsic and doped a-Si layers, TCO and a-Si layers. We also study FF loss due to lateral transport and its components that including the TCO sheet resistance, the nger and the busbars resistances.
In this thesis, we provide a detailed understanding of the FF concept; we explain how it can be directly measured; how it can be calculated and what expressions can better approximate its value and under what operating conditions. The relation between FF and cell operating condition at the MPP is investigated. We separately analyzed the main FF sources of losses including recombination, sheet resistance, contact resistance and metalization. We study FF loss due to recombination and its separate components which include the Augur, radiative and SRH recombination is investigated. We study FF loss due to contact resistance and its separate components which include the contact resistance of dierent interfaces, e.g. between the intrinsic and doped a-Si layers, TCO and a-Si layers. We also study FF loss due to lateral transport and its components that including the TCO sheet resistance, the nger and the busbars resistances.
ContributorsLeilaeioun, Mohammadmehdi (Ashling) (Author) / Goodnick, Stephen (Thesis advisor) / Goryll, Michael (Thesis advisor) / Bertoni, Mariana (Committee member) / Bowden, Stuart (Committee member) / Stuckelberger, Michael (Committee member) / Arizona State University (Publisher)
Created2018
Description
Ethylene vinyl acetate (EVA) is the most commonly used encapsulant in photovoltaic modules. However, EVA degrades over time and causes performance losses in PV system. Therefore, EVA degradation is a matter of concern from a durability point of view.
This work compares EVA encapsulant degradation in glass/backsheet and glass/glass field-aged PV modules. EVA was extracted from three field-aged modules (two glass/backsheet and one glass/glass modules) from three different manufacturers from various regions (cell edges, cell centers, and non-cell region) from each module based on their visual and UV Fluorescence images. Characterization techniques such as I-V measurements, Colorimetry, Different Scanning Calorimetry, Thermogravimetric Analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy were performed on EVA samples.
The intensity of EVA discoloration was quantified using colorimetric measurements. Module performance parameters like Isc and Pmax degradation rates were calculated from I-V measurements. Properties such as degree of crystallinity, vinyl acetate content and degree of crosslinking were calculated from DSC, TGA, and Raman measurements, respectively. Polyenes responsible for EVA browning were identified in FTIR spectra.
The results from the characterization techniques confirmed that when EVA undergoes degradation, crosslinking in EVA increases beyond 90% causing a decrease in the degree of crystallinity and an increase in vinyl acetate content of EVA. Presence of polyenes in FTIR spectra of degraded EVA confirmed the occurrence of Norrish II reaction. However, photobleaching occurred in glass/backsheet modules due to the breathable backsheet whereas no photobleaching occurred in glass/glass modules because they were hermetically sealed. Hence, the yellowness index along with the Isc and Pmax degradation rates of EVA in glass/glass module is higher than that in glass/backsheet modules.
The results implied that more acetic acid was produced in the non-cell region due to its double layer of EVA compared to the front EVA from cell region. But, since glass/glass module is hermetically sealed, acetic acid gets entrapped inside the module further accelerating EVA degradation whereas it diffuses out through backsheet in glass/backsheet modules. Hence, it can be said that EVA might be a good encapsulant for glass/backsheet modules, but the same cannot be said for glass/glass modules.
This work compares EVA encapsulant degradation in glass/backsheet and glass/glass field-aged PV modules. EVA was extracted from three field-aged modules (two glass/backsheet and one glass/glass modules) from three different manufacturers from various regions (cell edges, cell centers, and non-cell region) from each module based on their visual and UV Fluorescence images. Characterization techniques such as I-V measurements, Colorimetry, Different Scanning Calorimetry, Thermogravimetric Analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy were performed on EVA samples.
The intensity of EVA discoloration was quantified using colorimetric measurements. Module performance parameters like Isc and Pmax degradation rates were calculated from I-V measurements. Properties such as degree of crystallinity, vinyl acetate content and degree of crosslinking were calculated from DSC, TGA, and Raman measurements, respectively. Polyenes responsible for EVA browning were identified in FTIR spectra.
The results from the characterization techniques confirmed that when EVA undergoes degradation, crosslinking in EVA increases beyond 90% causing a decrease in the degree of crystallinity and an increase in vinyl acetate content of EVA. Presence of polyenes in FTIR spectra of degraded EVA confirmed the occurrence of Norrish II reaction. However, photobleaching occurred in glass/backsheet modules due to the breathable backsheet whereas no photobleaching occurred in glass/glass modules because they were hermetically sealed. Hence, the yellowness index along with the Isc and Pmax degradation rates of EVA in glass/glass module is higher than that in glass/backsheet modules.
The results implied that more acetic acid was produced in the non-cell region due to its double layer of EVA compared to the front EVA from cell region. But, since glass/glass module is hermetically sealed, acetic acid gets entrapped inside the module further accelerating EVA degradation whereas it diffuses out through backsheet in glass/backsheet modules. Hence, it can be said that EVA might be a good encapsulant for glass/backsheet modules, but the same cannot be said for glass/glass modules.
ContributorsPatel, Aesha Parimalbhai (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Green, Matthew (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2018
Description
This is a lectures series on photovoltaics. As the need for electrical energy rises, mankind has struggled to meet its need in a reliable lasting way. Throughout this struggle, solar energy has come to the foreground as a complete solution. However, it has many drawbacks and needs a lot of development. In addition, the general public is unaware of how solar energy works, how it is made, and how it stands economically. This series of lectures answering those three questions. After two years doing photovoltaic research, and an undergraduate degree in Electrical Engineering, enough expertise has been acquired present on at a late high-school to early college level. Education is key to improving the popularity of using solar energy and the popularity of investing in photovoltaic research. Solar energy is a viable option to satisfy our energy crisis because the materials it requires can quickly be acquired, and there is enough of material to provide a global solution. In addition, the amount of solar energy that hits the surface of the earth in a day is orders of magnitude more than the amount of energy we require. The main goal of this project is to have an effective accessible tool to teach people about solar. Thus, the lectured will be posted on pveducation.com, YouTube, the Barrett repository, and the QUSST website. The content was acquired in four ways. The first way is reading up on the current papers and journals describing the new developments in photovoltaics. The second part is getting in contact with Stuart Bowden and Bill Daukser at Arizona State University's Solar Power Lab as well as the other faculty associated with the Solar Power Lab. There is quite a bit of novel research going on at their lab, as well as a student run pilot line that is actively building solar cells. The third way is reading about solar device physics using device physics textbooks and the PVEducation website made by Stuart Bowden. The forth way is going into ASU's solar power lab.
ContributorsLeBeau, Edward (Author) / Goryll, Michael (Thesis director) / Bowden, Stuart (Committee member) / Dauksher, William (Committee member) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Bifacial photovoltaic modules are a relatively new development in the photovoltaic industry which allows for the collection and conversion of light on both sides of photovoltaic modules to usable electricity. Additional energy yield from bifacial photovoltaic modules, despite a slight increase in cost due to manufacturing processes of the bifacial cells, has the potential to significantly decrease the LCOE of photovoltaic installation. The performance of bifacial modules is dependent on three major factors: incident irradiation on the front side of the module, reflected irradiation on the back side of the module, and the module's bifaciality. Bifaciality is an inherent property of the photovoltaic cells and is determined by the performance of the front and rear side of the module when tested at STC. The reflected light on the back side of the module, however, is determined by several different factors including the incident ground irradiance, shading from the modules and racking system, height of the module installation, and ground albedo. Typical ground surfaces have a low albedo, which means that the magnitude of reflected light is a low percentage of the incident irradiance. Non-uniformity of back-side irradiance can also reduce the power generation due to cell-to-cell mismatch losses. This study investigates the use of controlled back-side reflectors to improve the irradiance on the back side of loosely packed 48-cell bifacial modules and compares this performance to the performance of 48 and 60-cell bifacial modules which rely on the uncontrolled reflection off nearby ground surfaces. Different construction geometries and reflective coating materials were tested to determine optimal construction to improve the reflectivity and uniformity of reflection. Results of this study show a significant improvement of 10-14% total energy production from modules with reflectors when compared to the 48-cell module with an uncontrolled ground reflection.
ContributorsBowersox, David Andrew (Author) / Tamizhmani, Govindasamy (Thesis director) / Srinivasan, Devarajan (Committee member) / School for Engineering of Matter, Transport and Energy (Contributor) / Engineering Programs (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
This is a lectures series on photovoltaics. As the need for electrical energy rises, mankind has struggled to meet its need in a reliable lasting way. Throughout this struggle, solar energy has come to the foreground as a complete solution. However, it has many drawbacks and needs a lot of development. In addition, the general public is unaware of how solar energy works, how it is made, and how it stands economically. This series of lectures answering those three questions.
ContributorsLeBeau, Edward Sanroma (Author) / Goryll, Michael (Thesis director) / Bowden, Stuart (Committee member) / Dauksher, Bill (Committee member) / Electrical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Potential-Induced Degradation (PID) is an extremely serious photovoltaic (PV) durability issue significantly observed in crystalline silicon PV modules due to its rapid power degradation, particularly when compared to other PV degradation modes. The focus of this dissertation is to understand PID mechanisms and to develop PID-free cells and modules. PID-affected modules have been claimed to be fully recovered by high temperature and reverse potential treatments. However, the results obtained in this work indicate that the near-full recovery of efficiency can be achieved only at high irradiance conditions, but the full recovery of efficiency at low irradiance levels, of shunt resistance, and of quantum efficiency (QE) at short wavelengths could not be achieved. The QE loss observed at short wavelengths was modeled by changing the front surface recombination velocity. The QE scaling error due to a measurement on a PID shunted cell was addressed by developing a very low input impedance accessory applicable to an existing QE system. The impacts of silicon nitride (SiNx) anti-reflection coating (ARC) refractive index (RI) and emitter sheet resistance on PID are presented. Low RI ARC cells (1.87) were observed to be PID-susceptible whereas high RI ARC cells (2.05) were determined to be PID-resistant using a method employing high dose corona charging followed by time-resolved measurement of surface voltage. It has been demonstrated that the PID could be prevented by deploying an emitter having a low sheet resistance (~ 60 /sq) even if a PID-susceptible ARC is used in a cell. Secondary ion mass spectroscopy (SIMS) results suggest that a high phosphorous emitter layer hinders sodium transport, which is responsible for the PID. Cells can be screened for PID susceptibility by illuminated lock-in thermography (ILIT) during the cell fabrication process, and the sample structure for this can advantageously be simplified as long as the sample has the SiNx ARC and an aluminum back surface field. Finally, this dissertation presents a prospective method for eliminating or minimizing the PID issue either in the factory during manufacturing or in the field after system installation. The method uses commercially available, thin, and flexible Corning® Willow® Glass sheets or strips on the PV module glass superstrates, disrupting the current leakage path from the cells to the grounded frame.
ContributorsOh, Jaewon (Author) / Bowden, Stuart (Thesis advisor) / Tamizhmani, Govindasamy (Thesis advisor) / Honsberg, Christiana (Committee member) / Hacke, Peter (Committee member) / Schroder, Dieter (Committee member) / Arizona State University (Publisher)
Created2016