<p> One of the main problems in using the photovoltaic system is the low energy conversion efficiency of photovoltaic cells and, furthermore, during the long operational period of solar cells, their energy conversion efficiency decreases even more due to increase in operating cell temperature over a certain limit. One way of improving the efficiency of photovoltaic system is to maintain a low operating temperature by cooling it down during its operation period. This study compares the effects of cooling on the performance of photovoltaic system. Experiments are performed on the solar panel inclined at fixed 45&deg; angle without active cooling initially to have a set of reference performance parameters for comparison. Afterwards, cooling of the solar panel is carried out using air and water, separately, as the cooling fluids. I-V tests and temperature tests, for all the cases, are performed for comparative analysis. The energy balance calculations showed that the experimental results are in conformity with the theoretical results. The results further showed that the cooling of photovoltaic system using water over the front surface enhances the performance even more as compared to air cooling of solar panel. </p>

<p> This dissertation describes the design, development, and field validation of a concentrator photovoltaic (CPV) solar energy system. The challenges of creating a highly efficient yet low-cost system architecture come from many sources. The solid-state physics of photovoltaic devices present fundamental limits to photoelectron conversion efficiency, while the electrical and thermal characteristics of widely available materials limit the design arena. Furthermore, the need for high solar spectral throughput, evenly concentrated sunlight, and tolerance to off-axis pointing places strict illumination requirements on the optical design. To be commercially viable, the cost associated with all components must be minimized so that when taken together, the absolute installed cost of the system in kWh is lower than any other solar energy method, and competitive with fossil fuel power generation. </p><p> The work detailed herein focuses specifically on unique optical design and illumination concepts discovered when developing a viable commercial CPV system. By designing from the ground up with the fundamental physics of photovoltaic devices and the required system tolerances in mind, a select range of optical designs are determined and modeled. Component cost analysis, assembly effort, and development time frame further influence design choices to arrive at a final optical system design. </p><p> When coupled with the collecting mirror, the final optical hardware unit placed at the focus generates more than 800W, yet is small and lightweight enough to hold in your hand. After fabrication and installation, the completed system's illumination, spectral, and thermal performance is validated with on-sun operational testing.</p>

<p> The output characteristic of a photovoltaic (PV) module varies as the environmental conditions of the module&rsquo;s operation change. Changes in operating temperature and incident sunlight dynamically change the maximum power available from a PV module, as well as the output voltage. The output voltage of the PV generating system must be regulated, in order to ensure proper power quality for connection to an electrical load, building electric power system, or the electric grid.</p><p> PV modules are typically connected in series strings and parallel arrays to create PV generating systems. Non-uniform environmental conditions create voltage mismatches throughout PV generating systems. A mismatch between module voltages can severely reduce the amount of power available from the overall generating system. These system losses can be eliminated by regulating the output voltage of each module.</p><p> This dissertation proposes a power electronic device that fulfills two objectives: extracting maximum power from the single PV module, and regulating the output voltage to ensure a constant value. This dissertation reviews the analytical design of such a system, and validates this design in simulation, utilizing MATLAB/SIMULINK and ANSYS Simplorer.</p>

<p> The percentage of electricity supplied by photovoltaic (PV) generators is steadily rising in power systems worldwide. This rise in PV penetration may lead to larger fluctuations in power system frequency due to variability in PV generator output at time scales that fall between the inertial damping and automatic generation control (AGC) responses of power systems. To reduce PV generator variability, active power controls can be implemented in the power electronic inverters that interface PV generators to the power system. Although various types of active power controls have been developed, no standard methodology exists for evaluating the effectiveness of these controls at improving power system frequency regulation. This dissertation presents a method for predicting the effects of short-term PV variability on power system frequency for a PV generator with active power control provided by integrated energy storage. A custom model of a PV generator with integrated energy storage is implemented in a power system dynamic simulator and validated through experiments with a grid emulator. The model is used to predict the effects of short-term PV variability on the frequency of the IEEE 9-bus test power system modified to include a PV generator with integrated energy storage. In addition, this dissertation utilizes linear analysis of power system frequency control to predict worst-case frequency deviations as a function of the amount of energy storage integrated into PV generators. Through simulation and emulation on a scaled experimental prototype, the maximum frequency deviation caused by the PV generator with a small amount of integrated energy storage is found to be approximately 33% lower than the maximum frequency deviation caused by the PV generator alone. Through linear analysis it is shown that by adding only 36.7 kWh of integrated energy storage to a 1.2 MW PV system, the worst-case frequency deviation on the IEEE 9-bus test system can be reduced 65% from 0.45 Hz to 0.16 Hz. The techniques presented enable estimation of the maximum PV penetration or minimum integrated energy storage requirement to meet a frequency regulation target for a particular power system. Integrated energy storage can then be compared to other active power controls in order to choose a method that meets frequency control requirements at minimum cost.</p>

abstract: Power rating photovoltaic modules at six irradiance and four temperature matrix levels of IEC 61853-1 draft standard is one of the most important requirements to accurately predict energy production of photovoltaic modules at different climatic conditions. Two studies were carried out in this investigation: a measurement repeatability study and a translation procedure validation study. The repeatability study was carried out to define a testing methodology that allows generating repeatable power rating results under outdoor conditions. The validation study was carried out to validate the accuracy of the four translation procedures: the first three procedures are from the IEC 60891 standard and the fourth procedure is reported by NREL. These translation procedures are needed to translate the measured data from the actual test conditions to the reporting rating conditions required by the IEC 61853-1 draft standard. All the measurements were carried out outdoors on clear days using a manual, 2-axis tracker, located in Mesa/Tempe, Arizona. Four module technologies were investigated: crystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide. The modules were cooled and then allowed to naturally warm up to obtain current-voltage data at different temperatures. Several black mesh screens with a wide range of transmittance were used for varying irradiance levels. From the measurements repeatability study, it was determined that: (i) a certain minimum distance (2 inches) should be maintained between module surface and the screen surface; (ii) the reference cell should be kept outside the screen (calibrated screen) as opposed to inside the screen (uncalibrated screen); and (iii) the air mass should not exceed 2.5. From the translation procedure validation study, it was determined that the accuracy of the translation procedure depends on the irradiance and temperature range of translation. The difference between measured and translatet power at maximum power point (Pmax) is determined to be less than 3% for all the technologies, all the irradiance/ temperature ranges investigated and all the procedures except Procedure 2 of IEC 60891 standard. For the Procedure 2, the difference was found to fall between 3% and 17% depending on the irradiance range used for the translation. The difference of 17% is very large and unacceptable. This work recommends reinvestigating the cause for this large difference for Procedure 2. Finally, a complete power rating matrix for each of the four module technologies has been successfully generated as per IEC 61853-1 draft standard. / Dissertation/Thesis / M.S.Tech Technology 2010

<p> Measurement of the vapor-liquid equilibrium (VLE) of fluid mixtures with many components presents a challenge. Data describing such mixtures, like fuels, are important for the development of alternative energy sources and to support forensic science, but there is a lack of suitable instrumentation to provide data with reasonable uncertainty for mixtures with many components. In this thesis, three different techniques for fluid characterization are explored: the advanced distillation curve (ADC), the advanced distillation curve with reflux (ADCR), and PLOT-cryoadsorption. Two pyrolysis fuels similar to gasoline and diesel fuel made from polypropylene were studied with respect to volatility, composition, and energy content using the advanced distillation curve. The diesel fuel demonstrated volatility very similar to previously measured diesel fuels. The gasoline was less volatile than petroleum-derived counterparts and did not meet specifications.</p><p> Two pyrolysis crude oils made from ponderosa pine and dairy manure were assessed using the ADC coupled to an approach for characterizing fluids with multiple, immiscible liquid phases. Both oils contained high water levels and would require further refinement before use. The organic phases of each oil contained components indicative of the feedstock used.</p><p> A modification of the ADC method, the advanced distillation curve with reflux, was introduced as an approach to measuring the VLE of fluids with many components. The ADCR additionally approximates the weathering of an ignitable liquid that occurs during an arson fire and measures VLE across a range of weathered conditions. The method was demonstrated using two simple mixtures. The measurements agreed well with models, indicating that ADCR is a suitable VLE metrology.</p><p> Vapor-liquid equilibrium data are crucial for interpreting the results of headspace characterization used often in forensic science. One headspace method, portable PLOT-cryoadsorption, was tested in a series of experiments in the laboratory and then deployed for the first time in a field environment that simulated a cargo container. The technology was found to be rapid and sensitive to a variety of compounds of interest to forensic science. Each of the three techniques described in this thesis contribute valuable property data for multicomponent mixtures, towards the development of high-quality predictive models.</p><p>

abstract: 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. / Dissertation/Thesis / M.S. Engineering 2012

<p> With improvements in power harvesting transducers' power density, and power reduction in communication transceiver systems, displays, sensors and energy-aware microprocessors, smart wireless network nodes are becoming ubiquitous throughout our daily life. Digital signage has gained popularity with the integration of smart wireless network nodes into the application space replacing traditional signage and badges. Primary battery sources traditionally supply energy for digital signage, however, that generates waste and maintenance costs that are counterproductive to using digital signage. Therefore, a digital signage prototype called the wireless display sensor node (WDSN) with a micro-power photovoltaic energy harvesting system was developed at UC Davis and is presented as an alternative in this work. The WDSN and node management system is comprised of an electrophoretic display, Wi-Fi radio, photovoltaic and vibration power transducers, internet connected management system, sensors and power harvesting power electronics. A holistic energy approach was used to drive the development of the proposed digital badge and signage. This approach encompasses the characterization of vibrational and photovoltaic energy sources, analyzing the energy requirement from typical digital signage and developing a power harvesting energy management system that will maximize the lifetime and allow for self sufficiency of the digital signage. To bridge the gap between the energy source and the required peripheral supplies, a multiple input and multiple outputs (MIMO) H-bridge DC to DC converter was designed to harvest and regulate photovoltaic energy, and deliver energy to the various continuously active, and charge-and-execute loads of the WDSN. The H-bridge DC to DC converter comprising of a single inductor, two input power FETs from both primary and secondary power sources, and five symmetric output power FETs to create the various supply rails, supply the regulated energy required for the radio, the display, the sensors and the microcontroller. For the charge-and-execute supplies, a constant current ramp charging was developed to transfer charge at the maximum power point current of the photovoltaic cell to the supply capacitors of the peripherals that support the charge-and-execute supply generation. The MIMO H-bridge DC to DC converter presented supports active regulation using pulse width modulation for high current loads, pulse frequency modulation for light current loads, and ramp charging for capacitive loads. The controller was designed using digital logic and the entire MIMO H-bridge DC to DC converter occupies an area of 0.36&nbsp;mm2 to 1.63&nbsp;mm2 depending on the power transistor size selection. The measured instantaneous peak power efficiency is 86% while driving a 63&nbsp;?A load with a transient energy efficiency delivered to the load is 81%. The prototype WDSN dissipates 933&nbsp;mJ to complete a server data synchronization and display refresh. The WDSN update energy when supplied with vibrational and photovoltaic power harvesting is equivalent to 7.52&nbsp;hours of casual continuous walking (34.44&nbsp;?W), 1,230 laboratory door toggles (open and close at 986&nbsp;?W) and 12&nbsp;hours of continuous office lighting (7&nbsp;am to 7&nbsp;pm with a daily total of 958&nbsp;mJ under an average of 538&nbsp;Lux of CFL lighting).</p><p>

abstract: ABSTRACT As the use of photovoltaic (PV) modules in large power plants continues to increase globally, more studies on degradation, reliability, failure modes, and mechanisms of field aged modules are needed to predict module life expectancy based on accelerated lifetime testing of PV modules. In this work, a 26+ year old PV power plant in Phoenix, Arizona has been evaluated for performance, reliability, and durability. The PV power plant, called Solar One, is owned and operated by John F. Long's homeowners association. It is a 200 kWdc, standard test conditions (STC) rated power plant comprised of 4000 PV modules or frameless laminates, in 100 panel groups (rated at 175 kWac). The power plant is made of two center-tapped bipolar arrays, the north array and the south array. Due to a limited time frame to execute this large project, this work was performed by two masters students (Jonathan Belmont and Kolapo Olakonu) and the test results are presented in two masters theses. This thesis presents the results obtained on the south array and the other thesis presents the results obtained on the north array. Each of these two arrays is made of four sub arrays, the east sub arrays (positive and negative polarities) and the west sub arrays (positive and negative polarities), making up eight sub arrays. The evaluation and analyses of the power plant included in this thesis consists of: visual inspection, electrical performance measurements, and infrared thermography. A possible presence of potential induced degradation (PID) due to potential difference between ground and strings was also investigated. Some installation practices were also studied and found to contribute to the power loss observed in this investigation. The power output measured in 2011 for all eight sub arrays at STC is approximately 76 kWdc and represents a power loss of 62% (from 200 kW to 76 kW) over 26+ years. The 2011 measured power output for the four south sub arrays at STC is 39 kWdc and represents a power loss of 61% (from 100 kW to 39 kW) over 26+ years. Encapsulation browning and non-cell interconnect ribbon breakages were determined to be the primary causes for the power loss. / Dissertation/Thesis / M.S.Tech Technology 2012

abstract: Organic optoelectronic devices have remained a research topic of great interest over the past two decades, particularly in the development of efficient organic photovoltaics (OPV) and organic light emitting diodes (OLED). In order to improve the efficiency, stability, and materials variety for organic optoelectronic devices a number of emitting materials, absorbing materials, and charge transport materials were developed and employed in a device setting. Optical, electrical, and photophysical studies of the organic materials and their corresponding devices were thoroughly carried out. Two major approaches were taken to enhance the efficiency of small molecule based OPVs: developing material with higher open circuit voltages or improved device structures which increased short circuit current. To explore the factors affecting the open circuit voltage (VOC) in OPVs, molecular structures were modified to bring VOC closer to the effective bandgap, &#8710;EDA, which allowed the achievement of 1V VOC for a heterojunction of a select Ir complex with estimated exciton energy of only 1.55eV. Furthermore, the development of anode interfacial layer for exciton blocking and molecular templating provide a general approach for enhancing the short circuit current. Ultimately, a 5.8% PCE was achieved in a single heterojunction of C60 and a ZnPc material prepared in a simple, one step, solvent free, synthesis. OLEDs employing newly developed deep blue emitters based on cyclometalated complexes were demonstrated. Ultimately, a peak EQE of 24.8% and nearly perfect blue emission of (0.148,0.079) was achieved from PtON7dtb, which approaches the maximum attainable performance from a blue OLED. Furthermore, utilizing the excimer formation properties of square-planar Pt complexes, highly efficient and stable white devices employing a single emissive material were demonstrated. A peak EQE of over 20% for pure white color (0.33,0.33) and 80 CRI was achieved with the tridentate Pt complex, Pt-16. Furthermore, the development of a series of tetradentate Pt complexes yielded highly efficient and stable single doped white devices due to their halogen free tetradentate design. In addition to these benchmark achievements, the systematic molecular modification of both emissive and absorbing materials provides valuable structure-property relationship information that should help guide further developments in the field. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2014