- Additional Posters
FESC May 2015 Workshop
ADDITIONAL POSTER LISTINGS
WEDNESDAY, May 20
ADDITIONAL POSTER SESSION: 5:20pm – Poster Set-up; 5:25-5:55pm – Additional Poster Session
|Track 1: Renewable/Alternative Power and Storage|| Track 2: Biomass
|Poster #||Title/ Presenter Name||Poster #||Title/ Presenter Name|
|1.||Sustainability in Rapid Prototyping – Joseph Prine, John McCormack, Jorge Vargas, Jaspreet Dhau, Sesha Srinivasan, Ryan Integlia, Florida Polytechnic University||2.||Dual Purpose Benefits of the Sweetpotato Crop: Biofuel and Animal Feed – Lara R. Nesralla, Wendy A. Mussoline, Ann C. Wilkie, University of Florida/IFAS|
|3.||Cultivation of Filamentous Algae for Bioenergy Production – Kimberly D. Hafner, Ann C. Wilkie, University of Florida|
|4.||Impact of Phytohormones on Microalgal Growth and Lipid Content – Brett S. Nelson, Ann C. Wilkie, University of Florida|
|5.||Techno-Economic Analysis of Bioethanol Production From Lignocellulosic Biomass: Process Integration with Energy Recovery From Wastes – Na Wu, Pratap Pullammanappallil, University of Florida|
|6.||Synthesis of Biodiesel via Supercritical Transesterification Route from Waste Cooking Oil – Z. Cerniga, Shriyash Deshpande, D. Townsend, K. Cogswell; A. Driscoll, A. Sunol, G. Philippidis, M. Pandey, University of South Florida|
|Track 3: Solar Energy||Track 4: Energy Efficiency|
|Poster #||Title/ Presenter Name|| Poster #
||Title/ Presenter Name|
|7.||Avian Mortality at Solar Energy Facilities in Southern California – Stephanie Meyers, Lee Walston, University of Illinois at Urbana–Champaign||14.||Anomaly Identification, Detection and Correction on Distribution Networks: a Non-technical Power Loss Study Case – Rodrigo D. Trevizan, Aquiles Rossoni, Arturo S. Bretas, University of Florida|
|8.||A Thermo-Mechanical Method for Fabrication of Porous Structure for Solar Thermo-Chemical Fuel Production – Kelvin Randhir, Like Li, Nick AuYeung, Amey Barde, Renwei Mei, David Hahn, James Klausner, University of Florida||15.||Integration of Technologies for Recovery of Energy and Nutrients from Dairy Wastes – Shunchang Yang, University of Florida|
|9.||Detailed Analysis of Spatially Mapping Solar Cell Parameters – Kortan Ogutman, Kris Davis, University of Central Florida||16.||An Experimental Investigation of Occupancy-Based Control of Commercial Building Climate – Jonathan Brooks, Siddharth Goyal, Rahul Subramany, Yashen Lin, Timothy Middelkoop, Prabir Barooah, University of Florida|
|10.||Modeling of Scroll Expanders for Decentralized Power Generation using Solar Energy as Heat Source – Arun Kumar Narasimhan, Rajeev Kamal, Yogi Goswami, Elias K. Stefanakos, University of South Florida|
|11.||Investigation of Long Term Reactive Stability of Ceria for Use in Solar Thermochemical Cycles – Nathan R. Rhodes, Michael M. Bobek, David W. Hahn, University of Florida|
|12.||High Throughput Processes for PV Module Manufacturing – Vasilios Palekis, S. Collins, V. Evani, M. Khan, C. S. Ferekides, University of South Florida|
|13.||Understanding the Impact of Point Defects on the Performance of Thin Film Solar Cells – Vamsi Evani, M. I. Khan, P. Bane, V. Palekis, S. Collins, C. Ferekides, University of South Florida|
|Track 5: Smart Grid and Energy Storage|
|Poster #||Title/ Presenter Name|
|17.||Distributed Optimization-based Load Control in a Power Grid for Primary Frequency Response while Minimizing Consumer Disutility – Jonathan Brooks, Prabir Barooah, University of Florida|
|18.||Smart And Flexible Resources to Harness Solar Power in Florida – D. Surya Chandan, A. S. Bretas, Sean Meyn, Prabir Barooah, University of Florida|
|19.||Solar-Driven Photo-Thermochemical Water-Splitting Cycle with Integrated Thermal Energy Storage – Nazim Muradov, Ali T-Raissi, Nan Qin, University of Central Florida/FSEC|
ADDITIONAL POSTER SESSION
Wednesday, May 20 – 5:25 pm – 5:55 pm
RENEWABLE/ALTERNATIVE [POWER AND STORAGE (POSTER SESSION)
Sustainability in Rapid Prototyping – Joseph Prine, John McCormack, Ryan Integlia, Jaspreet Dhau, Sesha Srinivasan, Jorge Vargas, Florida Polytechnic University
Rapid prototyping is a versatile technology, one form of which is 3D printing, which has the potential to become a viable manufacturing process. 3D-Printers utilize stock material thermoplastics like Polylactic Acid, a biodegradable plastic, or Acrylonitrile butadiene styrene, a common thermoplastic. This project proposes a smart manufacturing system with a focus on sustainability, utilizing 3D printing techniques with recyclable material. This system would be automated and easy to use. Pick-and-place robotic systems could introduce non-printed components, like circuit boards, into the product as it is being printed. The stock material could be sourced from 3D printer waste, or even recyclables like plastic bottles. Material additives could be mixed with this source material to create stock material that has additional properties, like magnetic properties, high electrical conductivity, elasticity, and/or toughness. The final design of this system will be able to be scaled from a single unit to an entire automated factory, depending on need.
BIOMASS (POSTER SESSION)
Dual Purpose Benefits of the Sweetpotato Crop: Biofuel and Animal Feed – Lara R. Nesralla, Wendy A. Mussoline, Ann C. Wilkie, University of Florida-IFAS Extension
Sweetpotato, Ipomoea batatas L., is a highly nutritive crop grown in many developing countries and it is commonly grown as a low-cost food resource. In Florida, however, sweetpotato is being considered as a viable biofuel crop to replace declining citrus groves. It is advantageous because of its rusticity, low maintenance and high adaptability to extreme conditions such as droughts and flooding. An industrial variety (CX-1) has roots with high dry matter and starch content, which results in high ethanol yields compared to other common feedstocks such as corn and wheat. The sweetpotato crop offers both a root yield and an above-ground leafy biomass (aerial vines) that can be used as a nutritious animal feed supplement. Although the fresh vine yield often exceeds the root yield on a per hectare basis, the potential value of the vines is often overlooked. The vines can be fed fresh or dried, or they can be ensiled and stored for use during the less productive periods of the year when pastures are not available. The ensiling process involves a fermentative process in which bacteria produce lactic acid by utilizing substrates such as soluble sugars and organic acids. During this process there is a decrease in pH and an increase in temperature and ammonia nitrogen. The fresh material is cut, compacted, stored in a silo, and sealed to protect it from yeast and mold growth. When ensiling is conducted properly, the nutritive value of the silage will be preserved and digestibility will be improved since the cell wall components are broken down during the fermentation process.
The objectives of this research were to determine the fermentative capacity (FC) index of sweetpotato vines and to evaluate the forage quality of both fresh and ensiled vines. FC is dependent upon moisture content, buffering capacity and soluble carbohydrate concentrations. The FC index was measured for seven varieties of sweetpotato vines and the averages for both the fresh (38) and wilted (37) vines exceeded the minimum capacity (35) required to promote lactic fermentation. Fresh and ensiled vine characteristics, including dry matter, crude protein (CP), and neutral detergent fiber (NDF), were assessed for five different sweetpotato varieties. The average CP of fresh and ensiled vines was 12% and 13% DM, respectively, which both exceed the minimum CP of 7% DM recommended for optimal digestibility. CP represents the nitrogen content of the feed, which is necessary for anaerobic bacteria to carry out fermentation in the rumen. The average NDF concentration for fresh (35% DM) and ensiled vines (44% DM) were both within the optimal range of 25-60% DM to supply ample nutrients without discouraging voluntary intake of the feed.
The results indicate that the ensiling process is ideal for sweetpotato vines based on their fermentative capacity and the conservation of nutrients. Sweetpotato vines can be a highly nutritious, low-cost alternative to grain-based feeds to support livestock year-round. Thus, the sweetpotato crop offers a dual purpose production for both biofuel (from roots) and animal feed (from vines).
Cultivation of Filamentous Algae for Bioenergy Production – Kimberly D. Hafner, Ann C. Wilkie, University of Florida-IFAS Extension
Algae are high-yielding plants and a potential alternative to conventional fossil fuels that can alleviate the greenhouse effect while simultaneously treating wastewater. Cultivating algae requires high nitrogen inputs to sustain growth and produce feedstock biomass, providing a possible bioremediation option for high-ammonia wastewaters such as stillage from cellulosic ethanol production. Utilization of stillage for algae growth can offset the energy consumed in the pretreatment and distillation operations of bioethanol production by providing algal biomass for conversion into biofuels. In addition, algal biomass can serve as a feedstock for anaerobic digestion to produce methane-rich biogas.
The objective of this study was to develop optimal cultivation methods for maximum biomass yield of Spirulina, a filamentous cyanobacterium. Spirulina is a robust algal species due to its ability to thrive in alkaline environments. Its size and filamentous morphology allows for manageable harvest, thus minimizing costs and energy consumption for biomass recovery. Spirulina was cultivated in Modified Zarrouk’s Medium with sodium bicarbonate as the carbon source. Subcultures were prepared with 10% inoculum in 1L vessels (500 mL active volume). Cultures were illuminated at 250 µmol photons/m2/s on a 12:12 photoperiod. Algal growth was monitored by spectrophotometry using absorbance at 680nm.
The effect of culture vessel geometry on biomass growth was evaluated. Using an orbital shaker as the mixing method, the results indicated that biomass growth rate was much higher using a Roux culture bottle (13.4 mg/L/h) compared to an Erlenmeyer flask (7.9 mg/L/h). The high biomass yields for the Roux bottle were likely due to better light penetration into the growing culture because of the greater surface area-to-volume ratio in the Roux bottle (98.7 m2/m3) versus the Erlenmeyer flask (41.3 m2/m3). The shape of the Roux bottle reduces self-shading of cells in the culture which results in higher growth rates in comparison to the Erlenmeyer flask. The Roux bottle culture also displayed more mass transfer and turbulence during rotational mixing.
The effect of mixing strategy was also evaluated. Using Roux bottles as the cultivation vessel, mechanical shaking (120 rpm) and aeration mixing (4.0 L/h) methods were compared and similar biomass growth rates (13.4 and 13.5 mg/L/h, respectively) were observed. In theory, mechanical shaking has the distinct advantage of reducing ammonia stripping which retains the nitrogen in solution for algal uptake, thus promoting biomass growth. Based on observation, the shaker promotes better mass transfer between the culture medium and algal cells, and increases frequency of cell exposure to light and dark zones. However, mixing speeds must be closely monitored since excessive mixing can create shear forces that lead to filament fracture. Also, aerators result in a loss of water by evaporation, which can potentially increase salinity levels if working with saline media such as stillage and wastewaters. Further research will be conducted with a focus on utilizing stillage as a cultivation medium and evaluating Spirulina’s potential as a phycoremediator and biofuel feedstock.
Impact of Phytohormones on Microalgal Growth and Lipid Content – Brett S. Nelson, Ann C. Wilkie, University of Florida-IFAS Extension
The confluence of increasing energy demand and uncertain fuel reserves has sparked a need for research in alternative energy, and specifically, biofuels. Microalgae are potential feedstocks for biofuels because of their fast growth rate and ability to produce lipids that can be extracted and converted into biodiesel. However, new methods of inducing high lipid contents and/or biomass growth are necessary for the production of algae biofuels to become economical. The objective of this research was to investigate the effect of exogenous plant hormones on microalgae biomass growth and lipid content. Plant hormones are signal molecules that regulate plant growth and development. Chlorella vulgaris, a locally isolated strain with demonstrated ability to produce lipids, was selected as the test organism. Chlorella vulgaris was grown in BG-11 standard growth medium. Plant hormones of the auxin (1-naphthaleneacetic acid (NAA)), cytokinin (trans-zeatin riboside (tZ)), and abscisic acid (ABA) hormone classes were added, individually and in combinations, to determine their impact on cell biomass and lipid content. All experimental trials were conducted in triplicate. Auxin and cytokinin plant hormones are known to aid in the stimulation of plant cell growth. ABA is known to improve stress tolerance and inhibit plant cell growth. Thus, the combination of these different plant hormones is expected to synergistically improve biomass yield and lipid production.
During the individual treatments of 1 ppm tZ, 5 ppm NAA, 5 ppm ABA, and 50 ppm ABA, there was no significant difference in biomass yield compared to the control. However, lipid yields for each individual treatment increased when compared to the control. The increase in lipid yields was correlated with increasing phytohormone concentrations rather than with the specific class of phytohormone evaluated. For example, the overall increase with the 1 ppm solution was 2.0 times higher than the control, while the 5 ppm and 50 ppm solutions were 2.8 and 3.4 times higher, respectively. There was no discernable difference in lipid yield between the treatments with 5 ppm NAA and 5 ppm ABA. Thus, increasing concentrations of phytohormones had the most significant impact on lipid yield during the singular treatments.
The three combination treatments of phytohormones were as follows: (A) 1ppm tZ + 5ppm NAA; (B) 1ppm tZ + 5ppm NAA + 5ppm ABA; and (C) 1ppm tZ + 5ppm NAA + 50ppm ABA. Each of the three combination treatments showed an increase in biomass yield over the control, with the most significant increase (47%) observed with combination (B). Combination (B) also had the highest increase in lipid yield (8.2 times the control) and was the only combination treatment that exhibited a synergetic interaction among the individual phytohormones. For example, combination (B) had a higher lipid yield when the three phytohormones were combined (11.5 mg) versus the additive improvement of all three phytohoromones applied singularly (10.6 mg). The other two combinations (A) and (C) showed diminishing effects when compared to the individual treatments. Based on the treatments evaluated, combination (B) is the optimal phytohormone applicaton for improving biomass and lipid yields in Chlorella vulgaris.
Techno-Economic Analysis of Bioethanol Production from Lignocellulosic Biomass: Process Integration with Energy Recovery from Wastes – Na Wu, Spyros Svoronos, Lonnie Ingram, Ismael Nieves, Pratap Pullammanappallil
Ethanol is the primary liquid biofuel produced on a large scale in US. Currently ethanol is produced from corn starch. However, concerns related to food security and prices, and environmental impact arising from cultivating and using a food and feed source for fuel production have prompted the utilization of more sustainable feedstocks for ethanol production. Non-food crops (mostly lingo-cellulosic in nature) and agricultural residues as feedstock for production of ethanol may alleviate these concerns. In this research an ASPEN (AspenTech, Cambridge MA) based process flowsheeting model was developed for a lignocellulosic ethanol biorefinery. All sections of a biorefinery including pretreatment, saccharification, fermentation and ethanol recovery were modeled. The flowsheet was validated using operating data from the pre-commercial scale Stan Mayfield Biorefinery Pilot Plant operated by the University of Florida. The Stan Mayfield Pilot Plant currently uses sugarcane bagasse as feedstock. The bagasse is subjected to a dilute phosphoric acid and steam explosion pretreatment to solubilize the hemicellulose and to free up the cellulose for subsequent saccharification using commercial cellulase enzymes. The saccharified bagasse is fermented to ethanol. Ethanol is recovered from fermentation broth by distillation followed by dehydration. An anaerobic digester was integrated to the process for treatment of stillage from the distillation units. Anaerobic digestion is a biochemical process that mineralizes organic matter to a gaseous biofuel called biogas containing 50-60% methane. Process operating data for simulation of anaerobic digester operation was obtained from laboratory scale experiments.
An energy analysis, using the validated flowsheet, was performed to evaluate energy consumption in various sections of the biorefinery. Possible process modifications to minimize energy consumption were also analyzed. The impact of introducing anaerobic digestion on the overall economics and energy balances were also investigated. Experimentally it was found that a liter of stillage contains sufficient organic matter to produce about 10 liters of methane (or about 17 liters of biogas). Through anaerobic digestion about 85 – 90% of the BOD of the stillage wastewater was also removed. It was found that biogas from anaerobic digestion can displace around 30% of fuel consumption in the plant.
Synthesis of Biodiesel via Supercritical Transesterification Route from Waste Cooking Oil – Z. Cerniga, Shriyash Deshpande, D. Townsend, K. Cogswell, A. Driscoll, A. Sunol, G. Philippidis, M. Pandey, University of South Florida
A continuous biodiesel production process is under development for powering the University bus system at the University of South Florida, by means of a portable production unit with a weekly capacity of 400 gallons of B100 grade biodiesel. Unlike conventional biodiesel production processes, the process is performed at supercritical conditions and does not require a catalyst. This eliminates the need to have a catalyst separation system and also saves on the large amounts of water required for the biodiesel wash. Along with the catalyst free operation, supercritical transesterification is capable of producing biodiesel with residence times of a few minutes, which makes the process novel in itself. The process is also tolerant to the presence of water in the waste oils. Heat integration between the hot products and cold reactants reduces the utility costs. The alcohols will be obtained from the university hospital wastes and laboratory wastes produced on campus. The process is designed to recycle the excess alcohol back to the system. Such provisions reduce the costs of raw materials, which makes the process sustainable. Glycerol, the byproduct generated from this process is relatively pure as compared to other conventional processes, and can be used for production of high quality soap or high-value pharmaceutical applications.
An orthogonal design is implemented to study the effects of various key process parameters on the biodiesel yield: temperature, pressure, residence time and molar ratio of alcohol to oil. The temperature of operation ranges from 250 C to 340 C and the pressure ranges from 1,500 to 2,000 psia. The alcohol is in excess, 2-8 times the stoichiometric amount. A response surface methodology approach is used to identify the optimum conditions for this process.
Gas chromatography-mass spectrometry (GC-MS) is used for determining the product composition. Methyl heptadecanoate (C17) is used as the internal standard to assist the quantification of methyl esters (biodiesel). The yield of esters is determined based on the peak area represented by each ester present, in comparison to the calibration of the internal standard. This method follows the EN14103 standard for biodiesel analysis. The poster presentation will report on the experimental progress, process scale up, analysis via gas chromatography and life cycle considerations.
SOLAR ENERGY (POSTER SESSION)
Avian Mortality at Solar Energy Facilities in Southern California – Stephanie Meyers, Lee Walston, University of Illinois at Urbana–Champaign
Renewable energy accounts for about 8 percent of the total energy consumption in the United States, and this percentage is expected to increase as we grow less dependent on non-renewable resources. Ecological impacts of these developments are emerging as a result of increased renewable energy development. Impacts of large-scale solar developments on avian communities have received recent attention. However, little is known about the population-level implications of solar avian fatalities and the context of these fatalities relative to other avian mortality sources. We studied solar avian fatalities in a region of Southern California to present the current state of knowledge about this new source of avian mortality. We also attempted to compare this information from what is known on avian impacts at solar facilities to fatalities at existing wind facilities. As systematic monitoring becomes more prevalent and data more available among solar energy facilities, we may be able to gain a better understanding of the impacts on avian communities. Once we obtain valuable knowledge in this area of research, we can begin to develop successful mitigation measures.
A Thermo-Mechanical Method for Fabrication of Porous Structure for Solar Thermo-Chemical Fuel Production. – Kelvin Randhir, Like Li, Nick AuYeung, Amey Barde, Renwei Mei, David Hahn, James Klausner, University of Florida
Production of synthetic fuels using solar energy is being investigated to improve energy sustainability. The most widely accepted approach is a thermo-chemical route using concentrated solar radiation for two-step water and/or carbon dioxide splitting for production of hydrogen and/or carbon monoxide. The first step is to thermally reduce a reactive oxide to its lower oxidation state followed by the second step in which the reduced oxide is oxidized back to its initial state using steam or carbon dioxide generating hydrogen or carbon monoxide.
A number of materials have been tested for applicability in this process and cerium dioxide has proven to be most effective till date. Some perovskite type materials have also shown promising potential. Regardless of the material that will be selected eventually for large scale implementation, an economical method to produce a stable porous form of the same needs to be developed.
The simplest method that was explored at the University of Florida for fabrication of a porous reactive bed of cerium dioxide was the thermo-mechanical method. Large samples that were compacted in water by sedimentation were sintered at very high temperatures and crushed to an optimum sized particles. Use of this method limits sintering at initial stage and forms a porous skeleton with a stable surface area. The principle behind this method is to form single grain particles which have effectively lower surface energy than the starting loose powders. The inhibition of sintering at initial stage is due to formation of curvatures equal to the final particle curvature at the point of contact.
Porous reactive beds formed using this method has been tested for several redox cycles and showed good stability. The optimum particle size for cerium dioxide heat treated at 1500 °C was found to be 125 µm to 150 µm. However large reactive beds made of such small particles increases the inlet pressure of the system. In order to tackle the large pressure drop and maintain decent reactivity the recommended particle size range is 355 to 1000 µm.
This method can be easily extended to reactive materials like perovskites and other non-stoichiometric compounds which do not undergo structural changes during oxidation-reduction reactions.
Detailed Analysis of Spatially Mapping Solar Cell Parameters – Kortan Ogutman, Kris Davis, University of Central Florida
Atmospheric pressure chemical vapor deposition (APCVD) is a versatile manufacturing process that offers much promise in enabling significant efficiency gains and cost reductions for crystalline silicon (c-Si) solar cells. In this presentation, recent results on the deposition and subsequent processing of functional oxide films using an in-line, high throughput APCVD system will be reported. The materials deposited in this work include aluminum oxide, titanium oxide, silicon oxide, and doped silicon oxide. These oxide films and film stacks can be utilized for doping (e.g., emitter and surface field formation), surface passivation, and photon management on the front and rear side of c-Si solar cells. Experimental data regarding the microstructure, optical properties, and electronic properties of the films will be presented, along with the impact of these films on cell efficiency and other relevant cell parameters. Implications of these results for standard and novel c-Si cell architectures will be covered.
Modeling of Scroll Expanders for Decentralized Power Generation using Solar Energy as Heat Source – Arun Kumar Narasimhan, Rajeev Kamal, Yogi Goswami, Elias K. Stefanakos, University of Florida
Scroll device was invented by a French engineer Léon Creux in 1905, but it was not commercialized until the arrival of CNC machining tools in 1970’s. Since then the scroll compressors have been used in commercial HVAC applications, automobiles and turbo superchargers. Recently, scroll compressors have been modified to run as scroll expanders for power generation. They are characterized by low rotational speeds that make them suitable for Organic Rankine Cycles for small-scale power generation. These modified expanders have a volume ratio of about 3, while ORC’s require 3-15. This introduces some losses in the expander. Hence, the study aims to develop high-volume-ratio (3-15) scroll expanders for micro-CSP ORC units (~1-25 kW) for decentralized power applications. A scroll device consists of two inter-fitting scrolls, one fixed and the other orbiting that are involutes of a common base circle. The scrolls start from the base circle at an involute initial angle and end at an involute ending angle. The two scrolls are then indexed at 180 from each other resulting in tangential contacts which are called the conjugate or mating points. These mating points form crescent shaped pockets between the two scrolls called chamber volumes. In operation, the superheated and high pressure fluid (from solar field) enters through the suction port at the center. As the orbiting angle increases, the fluid moves to the crescent shaped expansion chambers and with further increase in orbiting angle, opens up to the discharge angle and exits at lower pressure, thereby doing mechanical work which is then converted to electricity. In this work, the authors discuss the design methodology of scroll geometry and the chamber volumes as a function of orbiting angle. The symmetric scroll expander geometry shown below is generated from the following parameters: radius, Rb = 3.26 mm, inner involute initial angle, fi0 = 1.4 radians, outer involute initial angle, and fo0 = 0 radians and involute ending angle, Fe = 20 radians.
Investigation of Long Term Reactive Stability of Ceria for Use in Solar Thermochemical Cycles – Nathan R. Rhodes, Michael M. Bobek, David W. Hahn, University of Florida
The use of an intermediate reactive material composed of ceria is explored for solar fuel production through a CO2-splitting thermochemical redox cycle. To this end, powder and porous ceria samples are tested with thermogravimetric analysis (TGA) to ascertain their maximum fuel production potential from the CeO2 -> CeO(2-delta) cycle. A maximum value of the non-stoichiometric reduction factor delta of ceria powder was 0.383 at 1450 C. The reactive stability of a synthesized porous ceria sample is then observed with carbon dioxide splitting at 1100 C and thermal reduction at 1450 C. Approximately 86.4% of initial fuel production is retained after 2000 abbreviated cycles, and the mean value of delta is found to be 0.0197. Scanning electron microscopy (SEM) imaging suggests that the porous ceria structure is retained over 2000 cycles despite apparent loss of some surface area. Energy dispersive x-ray spectroscopy (EDS) line scans show that oxidation of porous ceria becomes increasingly homogenous throughout the bulk material over an increasing number of cycles. Significant retention of reactivity and porous structure demonstrates the potential of porous ceria for use in a commercial thermochemical reactor.
High Throughput Processes for PV Module Manufacturing – Vasilios Palekis, S. Collins, V. Evani, M. Khan, C. S. Ferekides, University of South Florida
Cadmium Telluride PV continues to be the lowest cost technology on a $/Watt basis for the manufacturing of PV modules. The highest efficiency reported to-date for a small area CdS/CdTe solar cell of the superstrate configuration is 21%, and for commercial-scale modules 17%. Further reductions in manufacturing costs can be realized through improvements in manufacturing such as increased throughput. This work describes efforts to develop laser-based processes to enable higher throughputs for the manufacture of CdTe PV modules. Localized surface and bulk film heating are being addressed.
The formation of stable, low resistance and non-rectifying contact to p-CdTe is a significant challenge in the fabrication of highly efficient solar cells. Surface preparation techniques including wet etches are typically used to produce a p+ surface through the formation of a Te-rich layer, followed by the deposition of the metallic contacting material. In this study laser annealing treatment is investigated in order to replace wet treatments for modifying the CdTe surface prior to contact formation. The laser anneals were carried out using a KrF excimer laser at 248nm with a 25ns pulse. CdTe films laser treated (LT) using different incident laser fluences and number pulses. Significant improvements in device performance,elimination of roll-over and increase in Voc and FF, were observed when solar cells were laser treated at 50mJ/cm2 fluence.
An essential processing step for fabricating high efficiency CdTe/CdS solar cells is the heat treatment (HT) in the presence of CdCl2. The CdCl2 treatment causes significant changes to the films’ photovoltaic and structural characteristics including recrystallization resulting in less grain boundary defects and the formation of a shallow acceptor complex, VCd-ClTe. This HT also facilitates interdiffusion of CdS and CdTe at the CdTe/CdS junction resulting in reduced interface recombination and therefore better performance. In this study a NIR diode laser operating at 808nm is used for the CdCl2 activation that can significantly reduce the treatment time from 20min (typical HT) to 1-2 minutes and therefore improve throughput in a manufacturing environment. Laser treated devices showed increased carrier collection in the blue and red regions of the spectrum from CdS thinning and S diffusion to CdTe lowering its bandgap. VOC, JSC and FF’s improved for laser treated devices when compared to non-treated ones. At higher laser power densities carrier concentration was higher than conventional treated devices. However, this did not result an increase in VOC. The best cell fabricated to-date using a laser-based CdCl2 treatment resulted in an efficiency of 13.25%.
Understanding the Impact of Point Defects on the Performance of Thin Film Solar Cells – Vamsi Evani, M. I. Khan, P. Bane, V. Palekis, S. Collins, C. Ferekides, University of South Florida
Extensive research on Cadmium Telluride (CdTe) based thin film photovoltaic technology over the past two decades has helped laboratory efficiencies reach the 20% mark. Current research is aimed at improving the efficiencies towards the theoretical efficiency limit. Most of the advancement in efficiencies have been brought about by improving the Short Circuit Current (JSC) and Fill Factor (FF) but no significant improvement in Open Circuit Voltage (VOC) was possible. High quality CdTe films with minority carrier lifetimes (beyond 5ns) are necessary to achieve higher VOC’s and therefore higher efficiencies. Native defect concentration which plays a vital role in determining the doping and hence the VOC of CdTe based solar cells, can be altered by controlling the stoichiometry during CdTe growth. Te-rich growth conditions, which favor the formation of point defects responsible for p-type conductivity, also favor formation of defects, which reduce minority carrier lifetime. Therefore, the stoichiometry needs to be precisely controlled in order to improve the doping and also achieve good carrier lifetimes. Conventional deposition techniques do not allow any control of stoichiometry during the growth process. This study investigates a novel deposition technique called Elemental Vapor Transport (EVT) that offers a control of stoichiometry (hence the intrinsic doping) during CdTe growth. CdTe films are deposited from elemental Cd and Te, and the stoichiometry is varied by changing the gas phase ratio of Cd and Te. Such in situ control over the concentration of the native defects enables control of intrinsic doping and provides an opportunity for incorporation of extrinsic dopants by creating suitable vacancies. The presentation will discuss the electronic properties of the deposited films and fabricated solar cells as a function of the gas phase Cd to Te ratio during the EVT process. The effect of the deposition process on the properties of films and solar cells is being investigated using techniques such as TRPL, SIMS and TEM.
ENERGY EFFICIENCY (POSTER SESSION)
Anomaly Identification, Detection and Correction on Distribution Networks: a Non-technical Power Loss Study Case – Rodrigo D. Trevizan, Aquiles Rossoni, Arturo S. Bretas, University of Florida
According to OECD statistics, the losses in electric transmission and distribution accounted for about 8% of the total produced energy worldwide in 2014. The great majority of these losses are in distribution networks. In some regions, this value can dramatically increase due to non-technical losses (NTL). The main causes of NTL are electricity theft, frauds in power meters and meter failure. The financial costs caused by these losses harm the entire society, as they are included in the electricity bill, paid by the regular consumers. In addition, the errors in energy meters can lead to imprecise technical losses estimation and gross errors in smart grids measurement systems. In order to mitigate NTL, utilities can perform inspections in clients’ electricity meters to detect and correct irregularities. However, performing on-site inspections is costly, therefore inspecting all consumers is not financially feasible. For this reason, methods to detect anomalous clients automatically were proposed in the literature. Some of the most promising techniques of this kind are based on pattern recognition of irregular consumers. In this work, a hybrid method based on the supervised classifier Optimum-Path Forest (OPF) and the Geometrical Approach State Estimator (GSE) is proposed for NTL identification. The GSE is applied to the distribution network using available power measurements and also consumption forecasts, called pseudo measurements. The errors of the GSE are interpreted as the amount of NTL in a given region. This error is then used as an input to the OPF classifier. This classifier uses the information of the errors in a given region along with the monthly consumption record of the customers to identify patterns of consumers where there may be NTL. The classifier is trained using information stored in the utility database, which contains patterns of both normal and irregular consumers where inspections were previously performed. At the end of this process, the classifier shortlists clients who are candidates for inspection. In order to assess the performance of the proposed method, tests are conducted on a database derived from residential consumer data found in the literature and in the IEEE 123-Bus Test Feeder. Two different test cases were analyzed. In the first one, the NTL are concentrated at some transformers in one region of the test feeder, while in the second one, the NTL are spread throughout the feeder. Those assumptions are based on some references which state that there is a high correlation between location and NTL. The results show that the mean performance of the OPF classifier can improve from 53.18% to 72.43% of customers correctly identified as having NTL for the first case when the hybrid method was used instead of standard OPF. For the second condition, the performance increased from 46.97% to 57.51%. The results show that a hybrid approach between heuristic methods, such as the OPF classifier, and state estimation can result in a more efficient method for NTL location. Therefore, implementing such a system can help electric utilities improve their economic performance by reducing NTL.
Integration of Technologies for Recovery of Energy and Nutrients from Dairy Wastes – Shunchang Yang, Pratap Pullammanappallil, University of Florida
Livestock operations are a major cause of pollution of water resources. Nitrogen (N) and Phosphorus (P) contamination of lakes and river systems in Florida have been attributed in some cases to run-offs from dairy operations. Currently manure from most dairies is land applied supplying the nutrient and water for crop growth. The extent to which manure can be applied is restricted through regulations based on N and P loadings per unit area of land. Consequently large farm areas are required to dispose dairy manure. Also there are concerns associated with pathogen and odors from manure. With the rising, global demand of fertilizers; technologies for recovering N and P nutrients from wastewater is gaining more attention.
Anaerobic digestion (AD) is a biochemical process that mineralizes organic compounds to a gaseous biofuel called biogas containing 60% methane. This process has been traditionally applied for waste management as it not only produces a fuel but also reduces the organic pollutant content of the waste stream. Anaerobic digestion can also mitigate the odor and pathogen problem associated with waste streams. Dairy manure (DM) is a good candidate for anaerobic digestion and several digesters have been set up to treat manure. Nitrogen and phosphorous compounds like ammonia and phosphate are conserved during anaerobic digestion if not mobilized from nitrogen and phosphorous containing organic compounds. The effluent from an anaerobic digester is an ideal stream to recover phosphate. Phosphorous can be recovered in the form of a mineral called struvite (MgNH4PO4•6H2O). Some amount of ammonium is also removed in this manner. Struvite precipitation and its recovery is affected by pH, molar ratios of magnesium, ammonium and phosphate, and mixing regimes.
In this paper we will present the performance of a pilot scale Induced Blanket Reactor (IBR) anaerobic digester treating manure from both flushed and scrapped dairies. The performance of the reactor was measured in terms of loading rate, hydraulic retention time, biogas production, biogas composition, pH, and volatile organic acid concentration. The effluent from IBR was then processed for struvite recovery. The struvite precipitation process was simulated by MinTeq software to optimize the pH and amount of magnesium loaded. The struvite recovery process was implemented in a lab scale apparatus. Experiments were conducted using both raw and anaerobically digested effluent to quantify the extent of phosphate and ammonia removal through struvite recovery. The integration of struvite recovery with anaerobic digestion results in an effluent that is lower not only in organic content but also phosphate coupled with energy recovery.
An Experimental Investigation of Occupancy-Based Control of Commercial Building Climate – Jonathan Brooks, Siddharth Goyal, Rahul Subramany, Yashen Lin, Timothy Middelkoop, Prabir Barooah, University of Florida
We present results from a week-long experimental evaluation of a scalable control algorithm for a commercial building heating, ventilation, and air-conditioning (HVAC) system that was proposed in our earlier work. Most commercial buildings’ HVAC systems are inefficient because they use daily operation schedules without knowledge of actual occupancy. This can adversely affect occupant comfort if, for example, an occupant is present in the building after-hours. Similarly, this can waste energy if a room is being fully conditioned when it is empty. The control algorithm tested here changes temperature set points based on real-time occupancy measurements to save energy. The experiments showed that the proposed controller resulted in 37% energy savings over baseline without sacrificing indoor climate. In contrast to prior work that reports energy savings without a careful measure of the effect on indoor climate, we verify that the controller indeed maintains indoor climate just as well as the building’s baseline controller from measurements of a host of environmental variables and analysis of before-after occupant survey results.
SMART-GRID & STORAGE (POSTER SESSION)
Distributed Optimization-based Load Control in a Power Grid for Primary Frequency Response while Minimizing Consumer Disutility – Jonathan Brooks, Prabir Barooah, University of Florida
A key aspect of the power grid is that power generated must equal power demanded. If this condition is not met, generators may be damaged, and blackouts may ensue. Traditionally, when generation and demand become unbalanced, different generators throughout the grid adjust their generation. This ramping is often less efficient for generators while also increasing emissions. Increased penetration of volatile renewable energy sources poses new challenges for maintaining the balance between generation and demand. If generators are used in the same traditional capacity, fleets of new fossil-fuel generators will be needed as backups to mitigate the renewable energies’ volatility, which may offset the benefits of renewable energies themselves. Controllable loads offer a great resource to maintain this balance. Instead of generators adjusting generation, loads can adjust demand, which does not affect emissions, but the impact on consumers must be minimized. One way for loads to provide this service to the grid is for loads to track a reference signal broadcast by a central balancing authority. In previous work, our group has shown through experiments conducted on the University of Florida campus that fans in a commercial building’s HVAC system can track such reference signals well. This requires communication between each load and the central balancing authority, however, which may not be practical for all loads. Another approach is for loads to use local information to make decisions. We have developed a distributed load-control algorithm in which every load varies its consumption based on local frequency measurements and communication with only nearby loads so that consumption and generation are equalized in the whole grid–thereby reducing system frequency deviations from the nominal operating point–while minimizing its own disutility that results from varying consumption. All loads collectively step to decrease total disutility at each iteration by adjusting consumption individually such that total consumption is unaffected. Simultaneously, each load additionally increases or decreases consumption to balance generation and total consumption. This is done in a distributed manner that preserves communication constraints among loads.
Smart and Flexible Resources to Harness Solar Power in Florida – D. Surya Chandan, A. S. Bretas, Sean Meyn, Prabir Barooah, University of Florida
Power Quality (PQ) is an important characteristic of electric power systems. The growing concern about climate changes and the perennial oil crisis has piqued the interest in Distributed Generation (DG), which in turn poses new challenges in power quality management. The index of PQ in this paper is “variation in voltage magnitude”.
Distributed generation (DG) is viewed as a potential threat to power quality, which is the likely motivation for the IEEE 1547 Standard: “DG shall not actively regulate the voltage and shall not cause the system voltage to go outside the requirements of ANSI C84-1, Range A (95% to 105%).” That is, this standard mandates that DG such as distributed solar operate with fixed power factor (unity PF). This policy ignores the potential value of power electronics connected to DG that could be harnessed to regulate voltage and reactive power. The thesis of this research is that there is a need to de-rate the inverters and make them “Smart” to provide reactive power control.
The intermittent nature of the DG can cause power fluctuation and voltage flicker. Voltage regulation under these conditions is an imperative technical challenge. We also advocate incentives for DG’s to de-rate their inverters to overcome this challenge.
We propose a control strategy in which there is communication between the distribution control center in a region and equipment on the distribution network to achieve a flat voltage profile with increased DG. The control of several resources is performed in unison: in addition to controllable inverters, power consumption from flexible loads can be modulated to regulate real power in conjunction with batteries. The control problem is formulated as an optimization problem, in which power quality is optimized, subject to constraints on quality of service to each load. The optimal solution determines the configuration of capacitor banks, batteries, power consumption of flexible loads, and the power injection from the DG’s.
In addition to power quality, the cost function in this optimization problem will take into account stress on equipment and systems technical power losses. For example, the control solution will reduce the number of automatic tap changes of an on-load distribution transformer and technical power losses in a line. This will reduce the payback period on the capital invested for infrastructure.
Simulations are performed using a statistical model based on observed solar generation profiles in the state of Florida. We use the appropriate load profile for various loads. We perform power flow analysis of the feeder by applying the Modified Ladder Iterative technique. The solution determines the voltage magnitudes at all nodes, active power of flexible load, total feeder input, line flow and power loss in each line section (KW). We simulate the extreme conditions by considering a highly volatile profile for solar radiation on a cloudy day and by turning a heavy load on and off.
Test results show that with appropriate design of control strategies and communication infrastructure, power quality and reliability can be maintained even with increased penetration of DG.
Solar-Driven Photo-Thermochemical Water-Splitting Cycle with Integrated Thermal Energy Storage – Nazim Muradov, Ali T-Raissi, Nan Qin, University of Central Florida – Florida Solar Energy Center
Solar water-splitting thermochemical cycles (WSC) constitute the ultimate option for hydrogen production since this pathway does not require any fossil fuels. WSC can achieve overall energy (solar-to-H2) conversion efficiencies of 40% and higher (compared to 28-32% for advanced electrolysis). There have been more than 300 WSCs conceived for water splitting of which, only less than a dozen or so are still being researched worldwide. The main limitations of the existing solar-powered WSC are that they (i) utilize only thermal (IR) component of the solar irradiation (neglecting quantum component), (ii) do not take into consideration the intermittent nature of the solar resource, and (iii) involve technically-challenging reagents transport and separation stages. FSEC researchers have developed a new family of hybrid sulfur–ammonia (S-A) photo-thermochemical WSC that circumvent the above shortcomings. S-A cycles through the means of solar beam-splitting utilize the quantum (UV-Vis) and the thermal (IR) portions of the solar spectrum for hydrogen and oxygen production, respectively, as represented by the following generic equations:
- SO2 + 2NH3 + H2O ? (NH4)2SO3 (chemical absorption) 25°C
- (NH4)2SO3 + H2O ? (NH4)2SO4 + H2 (solar UV-Vis photocatalytic) 20-80°C
- (NH4)2SO4 + MO ? 2NH3 + MSO4 + H2O (solar IR thermal) 400-500°C
- MSO4 ? MO + SO2 + 1/2O2 (solar IR thermocatalytic) 850-950°C
Where MO is alkali metal sulfate (e.g., Na2SO4, K2SO4, Rb2SO4). The step (1) is a simple chemical absorption process taking place at near ambient conditions. In the photocatalytic step (2) hydrogen production is accomplished using narrow band gap photocatalysts (e.g., CdS). Of particular interest are binary photocatalysts based on the combination of two semiconductors with suitable band gaps (e.g., CdS-ZnS, CdS-NiS, CdS-MoS2, and others). The reaction (3), in the case of MO=K2SO4, results in the production of K2S2O7 molten salt, which can be pumped through pipes as liquid, thus, simplifying materials transport and handling. Another advantage of the new cycle is that it provides integrated (or in situ) thermal storage and energy recovery by means of the molten salt K2S2O7-based system as integral part of WSC. The overall photon conversion efficiency was estimated at 25.3%.