Matching Items (36)
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.
Gas diffusion layers (GDLs) are a critical and essential part of proton exchange membrane fuel cells (PEMFCs). They carry out various important functions such as transportation of reactants to and from the reaction sites. The material properties and structural characteristics of the substrate and the microporous layer strongly influence fuel cell performance. The microporous layer of the GDLs was fabricated with the carbon slurry dispersed in water containing ammonium lauryl sulfate (ALS) using the wire rod coating method. GDLs were fabricated with different materials to compose the microporous layer and evaluated the effects on PEMFC power output performance. The consistency of the carbon slurry was achieved by adding 25 wt. % of PTFE, a binding agent with a 75:25 ratio of carbon (Pureblack and vapor grown carbon fiber). The GDLs were investigated in PEMFC under various relative humidity (RH) conditions using H2/O2 and H2/Air. GDLs were also fabricated with the carbon slurry dispersed in water containing sodium dodecyl sulfate (SDS) and multiwalled carbon nanotubes (MWCNTs) with isopropyl alcohol (IPA) based for fuel cell performance comparison. MWCNTs and SDS exhibits the highest performance at 60% and 70% RH with a peak power density of 1100 mW.cm-2 and 850 mW.cm-2 using air and oxygen as an oxidant. This means that the gas diffusion characteristics of these two samples were optimum at 60 and 70 % RH with high limiting current density range. It was also found that the composition of the carbon slurry, specifically ALS concentration has the highest peak power density of 1300 and 500mW.cm-2 for both H2/O2 and H2/Air at 100% RH. However, SDS and MWCNTs demonstrates the lowest power density using air and oxygen as an oxidants at 100% RH.
Low temperature fuel cells are very attractive energy conversion technology for automotive applications due to their qualities of being clean, quiet, efficient and good peak power densities. However, due to high cost and limited durability and reliability, commercialization of this technology has not been possible as yet. The high fuel cell cost is mostly due to the expensive noble catalyst Pt. Alkaline fuel cell (AFC) systems, have potential to make use of non-noble catalysts and thus, provides with a solution of overall lower cost. Therefore, this issue has been addressed in this thesis work. Hydrogen-oxygen fuel cells using an alkaline anion exchange membrane were prepared and evaluated. Various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts. Co and Fe phthalocyanine catalyst materials were synthesized using multi-walled carbon nanotubes (MWCNTs) as support materials. X-ray photoelectron spectroscopic study was conducted in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT and commercial Pt/C catalysts. The oxygen reduction reaction kinetics on these catalyst materials were evaluated using rotating disk electrodes in 0.1 M KOH solution and the current density values were consistently higher for Co phthalocyanine based electrodes compared to Fe phthalocyanine. The fuel cell performance of the MEAs with Co and Fe phthalocyanines and Tanaka Kikinzoku Kogyo Pt/C cathode catalysts were 100, 60 and 120 mW cm-2 using H22 and O2 gases. This thesis also includes work on synthesizing nitrogen doped MWCNTs using post-doping and In-Situ methods. Post-doped N-MWNCTs were prepared through heat treatment with NH4OH as nitrogen source. Characterization was done through fuel cell testing, which gave peak power density ~40mW.cm-2. For In-Situ N-MWCT, pyridine was used as nitrogen source. The sample characterization was done using Raman spectroscopy and RBS, which showed the presence ~3 at.% of nitrogen on the carbon surface.
With a recent shift to a more environmentally conscious society, low-carbon and non-carbon producing energy production methods are being investigated and applied all over the world. Of these methods, fuel cells show great potential for clean energy production. A fuel cell is an electrochemical energy conversion device which directly converts chemical energy into electrical energy. Proton exchange membrane fuel cells (PEMFCs) are a highly researched energy source for automotive and stationary power applications. In order to produce the power required to meet Department of Energy requirements, platinum (Pt) must be used as a catalyst material in PEMFCs. Platinum, however, is very expensive and extensive research is being conducted to develop ways to reduce the amount of platinum used in PEMFCs. In the current study, three catalyst synthesis techniques were investigated and evaluated on their effectiveness to produce platinum-on copper (Pt@Cu) core-shell nanocatalyst on multi-walled carbon nanotube (MWCNT) support material. These three methods were direct deposition method, two-phase surfactant method, and single-phase surfactant method, in which direct deposition did not use a surfactant for particle size control and the surfactant methods did. The catalyst materials synthesized were evaluated by visual inspection and fuel cell performance. Samples which produced high fuel cell power output were evaluated using transmission electron microscopy (TEM) imaging. After evaluation, it was concluded that the direct deposition technique was effective in synthesizing Pt@Cu core-shell nanocatalyst on MWCNTs support when a rinsing process was used before adding platinum. The peak power density achieved by the rinsed core-shell catalyst was 618 mW.cm-2 , 13 percent greater than that of commercial platinum-carbon (Pt/C) catalyst. Transmission electron microscopy imaging revealed the core-shell catalyst contained Pt shells and platinum-copper alloy cores. Rinsing with deionized (DI) water was shown to be a crucial step in core-shell catalyst deposition as it reduced the number of platinum colloids on the carbon nanotube surface. After evaluation, it was concluded that the two-phase surfactant and single-phase surfactant synthesis methods were not effective at producing core-shell nanocatalyst with the parameters investigated.
This is a two-part thesis:
Part 1 characterizes soiling losses using various techniques to understand the effect of soiling on photovoltaic modules. The higher the angle of incidence (AOI), the lower will be the photovoltaic (PV) module performance. Our research group has already reported the AOI investigation for cleaned modules of five different technologies with air/glass interface. However, the modules that are installed in the field would invariably develop a soil layer with varying thickness depending on the site condition, rainfall and tilt angle. The soiled module will have the air/soil/glass interface rather than air/glass interface. This study investigates the AOI variations on soiled modules of five different PV technologies. It is demonstrated that AOI effect is inversely proportional to the soil density. In other words, the power or current loss between clean and soiled modules would be much higher at a higher AOI than at a lower AOI leading to excessive energy production loss of soiled modules on cloudy days, early morning hours and late afternoon hours. Similarly, the spectral influence of soil on the performance of the module was investigated through reflectance and transmittance measurements. It was observed that the reflectance and transmittances losses vary linearly with soil density variation and the 600-700 nm band was identified as an ideal band for soil density measurements.
Part 2 of this thesis performs statistical risk analysis for a power plant through FMECA (Failure Mode, Effect, and Criticality Analysis) based on non-destructive field techniques and count data of the failure modes. Risk Priority Number is used for the grading guideline for criticality analysis. The analysis was done on a 19-year-old power plant in cold-dry climate to identify the most dominant failure and degradation modes. In addition, a comparison study was done on the current power plant (framed) along with another 18-year-old (frameless) from the same climate zone to understand the failure modes for cold-dry climatic condition.
To increase the deployment of photovoltaic (PV) systems, a higher level of performance for PV modules should be sought. Soiling, or dust accumulation on the PV modules, is one of the conditions that negatively affect the performance of the PV modules by reducing the light incident onto the surface of the PV module. This thesis presents two studies that focus on investigating the soiling effect on the performance of the PV modules installed in Metro Phoenix area.
The first study was conducted to investigate the optimum cleaning frequency for cleaning PV modules installed in Mesa, AZ. By monitoring the soiling loss of PV modules mounted on a mock rooftop at ASU-PRL, a detailed soiling modeling was obtained. Same setup was also used for other soiling-related investigations like studying the effect of soiling density on angle of incidence (AOI) dependence, the climatological relevance (CR) to soiling, and spatial variation of the soiling loss. During the first dry season (May to June), the daily soiling rate was found as -0.061% for 20o tilted modules. Based on the obtained soiling rate, cleaning PV modules, when the soiling is just due to dust on 20o tilted residential arrays, was found economically not justifiable.
The second study focuses on evaluating the soiling loss in different locations of Metro Phoenix area of Arizona. The main goal behind the second study was to validate the daily soiling rate obtained from the mock rooftop setup in the first part of this thesis. By collaborating with local solar panel cleaning companies, soiling data for six residential systems in 5 different cities in and around Phoenix was collected, processed, and analyzed. The range of daily soiling rate in the Phoenix area was found as -0.057% to -0.085% for 13-28o tilted arrays. The soiling rate found in the first part of the thesis (-0.061%) for 20o tilted array, was validated since it falls within the range obtained from the second part of the thesis.
The main objective of this research is to develop an approach to PV module lifetime prediction. In doing so, the aim is to move from empirical generalizations to a formal predictive science based on data-driven case studies of the crystalline silicon PV systems. The evaluation of PV systems aged 5 to 30 years old that results in systematic predictive capability that is absent today. The warranty period provided by the manufacturers typically range from 20 to 25 years for crystalline silicon modules. The end of lifetime (for example, the time-to-degrade by 20% from rated power) of PV modules is usually calculated using a simple linear extrapolation based on the annual field degradation rate (say, 0.8% drop in power output per year). It has been 26 years since systematic studies on solar PV module lifetime prediction were undertaken as part of the 11-year flat-plate solar array (FSA) project of the Jet Propulsion Laboratory (JPL) funded by DOE. Since then, PV modules have gone through significant changes in construction materials and design; making most of the field data obsolete, though the effect field stressors on the old designs/materials is valuable to be understood. Efforts have been made to adapt some of the techniques developed to the current technologies, but they are too often limited in scope and too reliant on empirical generalizations of previous results. Some systematic approaches have been proposed based on accelerated testing, but no or little experimental studies have followed. Consequently, the industry does not exactly know today how to test modules for a 20 - 30 years lifetime.
This research study focuses on the behavior of crystalline silicon PV module technology in the dry and hot climatic condition of Tempe/Phoenix, Arizona. A three-phase approach was developed: (1) A quantitative failure modes, effects, and criticality analysis (FMECA) was developed for prioritizing failure modes or mechanisms in a given environment; (2) A time-series approach was used to model environmental stress variables involved and prioritize their effect on the power output drop; and (3) A procedure for developing a prediction model was proposed for the climatic specific condition based on accelerated degradation testing
This is a two-part thesis.
Part 1 of this thesis investigates the influence of spatial temperature distribution on the accuracy of performance data of photovoltaic (PV) modules in outdoor conditions and provides physical approaches to improve the spatial temperature distribution of the test modules so an accurate performance data can be obtained in the field. Conventionally, during outdoor performance testing, a single thermocouple location is used on the backsheet or back glass of a test module. This study clearly indicates that there is a large spatial temperature difference between various thermocouple locations within a module. Two physical approaches or configurations were experimented to improve the spatial temperature uniformity: thermally insulating the inner and outer surface of the frame; backsheet and inner surface of the frame. All the data were compared with un-insulated conventional configuration. This study was performed in an array setup of six modules under two different preconditioning electrical configurations, Voc and MPPT over several clear sunny days. This investigation concludes that the best temperature uniformity and the most accurate I-V data can be obtained only by thermally insulating the inner and outer frame surfaces or by using the average of four thermocouple temperatures, as specified in IEC 61853-2, without any thermal insulation.
Part 2 of this thesis analyzes the field data obtained from old PV power plants using various statistical techniques to identify the most influential degradation modes on fielded PV modules in two different climates: hot-dry (Arizona); cold-dry (New York). Performance data and visual inspection data of 647 modules fielded in five different power plants were analyzed. Statistical tests including hypothesis testing were carried out to identify the I-V parameter(s) that are affected the most. The affected performance parameters (Isc, Voc, FF and Pmax) were then correlated with the defects to determine the most dominant defect affecting power degradation. Analysis indicates that the cell interconnect discoloration (or solder bond deterioration) is the dominant defect in hot-dry climate leading to series resistance increase and power loss, while encapsulant delamination is being the most dominant defect in cold-dry climate leading to cell mismatch and power loss.
The deposition of airborne dust, especially in desert conditions, is very problematic as it leads to significant loss of power of photovoltaic (PV) modules on a daily basis during the dry period. As such, PV testing laboratories around the world have been trying to set up soil deposition stations to artificially deposit soil layers and to simulate outdoor soiling conditions in an accelerated manner. This thesis is a part of a twin thesis. The first thesis, authored by Shanmukha Mantha, is associated with the designing of an artificial soiling station. The second thesis (this thesis), authored by Darshan Choudhary, is associated with the characterization of the deposited soil layers. The soil layers deposited on glass coupons and one-cell laminates are characterized and presented in this thesis. This thesis focuses on the characterizations of the soil layers obtained in several soiling cycles using various techniques including current-voltage (I-V), quantum efficiency (QE), compositional analysis and optical profilometry. The I-V characterization was carried out to determine the impact of soil layer on current and other performance parameters of PV devices. The QE characterization was carried out to determine the impact of wavelength dependent influence of soil type and thickness on the QE curves. The soil type was determined using the compositional analysis. The compositional data of the soil is critical to determine the adhesion properties of the soil layers on the surface of PV modules. The optical profilometry was obtained to determine the particle size and distribution. The soil layers deposited using two different deposition techniques were characterized. The two deposition techniques are designated as “dew” technique and “humidity” technique. For the same deposition time, the humidity method was determined to deposit the soil layer at lower rates as compared to the dew method. Two types of deposited soil layers were characterized. The first type layer was deposited using a reference soil called Arizona (AZ) dust. The second type layer was deposited using the soil which was collected from the surface of the modules installed outdoor in Arizona. The density of the layers deposited using the surface collected soil was determined to be lower than AZ dust based layers for the same number of deposition cycles.
Soiling is one of the major environmental factors causing the negative performance of photovoltaic (PV) modules. Dust particles, air pollution particles, pollen, bird droppings and other industrial airborne particles are some natural sources that cause soiling. The thickness of soiling layer has a direct impact on the performance of PV modules. This phenomenon occurs over a period of time with many unpredictable environmental variables indicated above. This situation makes it difficult to calculate or predict the soiling effect on performance. The dust particles vary from one location to the other in terms of particle size, color and chemical composition. These properties influence the extent of performance (current) loss, spectral loss and adhesion of soil particles on the surface of the PV modules. To address this uncontrolled environmental issues, research institutes around the world have started designing indoor artificial soiling stations to deposit soil layers in various controlled environments using reference soil samples and/or soil samples collected from the surface of PV modules installed in the locations of interest. This thesis is part of a twin thesis. The first thesis (this thesis) authored by Shanmukha Mantha is related to the development of soiling stations and the second thesis authored by Darshan Choudhary is associated with the characterization of the soiled samples (glass coupons, one-cell PV coupons and multi-cell PV coupons). This thesis is associated with the development of three types of indoor artificial soiling deposition techniques replicating the outside environmental conditions to achieve required soil density, uniformity and other required properties. The three types of techniques are: gravity deposition method, dew deposition method, and humid deposition method. All the three techniques were applied on glass coupons, single-cell PV laminates containing monocrystalline silicon cells and multi-cell PV laminates containing polycrystalline silicon cells. The density and uniformity for each technique on all targets are determined. In this investigation, both reference soil sample (Arizona road dust, ISO 12103-1) and the soil samples collected from the surface of installed PV modules were used. All the three techniques are compared with each other to determine the best method for uniform deposition at varying thickness levels. The advantages, limitations and improvements made in each technique are discussed.