Pin Fin Microgap Coolers for Concentrating Photovoltaic Arrays

May 11, 2015 09:00

Abstract: Concentrating photovoltaic (CPV) systems are among the most promising renewable power generation options and will require aggressive thermal management to prevent elevated solar cell temperatures and to achieve the conversion efficiency, reliability, and cost needed to compete with alternative techniques. Two-phase, evaporative cooling of CPV modules has been shown to provide significant advantages relative to single-phase cooling but, to date, the available two-phase data has been insufficient for the design and optimization of such CPV systems.

This Keynote lecture will begin with a brief review of CPV technology and the solar cell cooling techniques described in the literature. Energy modeling, relating the solar energy harvest to the "parasitic" work expended to provide the requisite cooling, will be used to support the efficacy of two-phase cooling for CPV applications. Attention will then turn to the available correlations for pin-finned microgap coolers and the gaps which must be addressed to enable such thermal management for CPV arrays. This will be followed by a detailed description of an experimental study of 3 pin-finned microgap coolers for CPV systems and the derived heat transfer and pressure drop correlations. The data spans a large parametric range, with heat fluxes of 1 - 170 W/cm^2, mass fluxes of 10.7 - 1300 kg/m^2-s, subcooled (single phase) flow as well as exit qualities up to 90%, and 3 heat transfer fluids (water, HFC-134a, HFE-7200). The lecture will close with a brief case study of two-phase CPV cooling, demonstrating that the application of this thermal management mode can lead to a more energy efficient CPV system.

Bio: Dr. Avram Bar-Cohen is an internationally recognized leader in the development and application of thermal science and engineering to microelectronic, optoelectronic, energy conversion, and RF systems. Through his professional service in IEEE and ASME, many decades of university research, and service to the US government, he has defined and guided the field of thermal packaging and facilitated the emergence of high reliability consumer electronics, computing platforms, and microwave communication and radar systems. His research and publications, as well as short courses, tutorials, and keynote lectures have helped to create the scientific foundation for the thermal management of micro- and nanoelectronic components and systems. He is an Honorary member of ASME and Fellow of IEEE, as well as Distinguished University Professor in the Department of Mechanical Engineering at the University of Maryland. From 2001 to 2010 he served as the Chair of Mechanical Engineering at Maryland. Bar-Cohen’s honors include the IEEE-CPMT Field Award for 2014 and the IEEE-CPMT Outstanding Sustained Technical Contributions Award (2002), the Luikov Medal from the International Center for Heat and Mass Transfer in Turkey (2008), and ASME’s Heat Transfer Memorial Award (1999), as well as the Edwin F. Church Medal (1994) and Worcester Reed Warner Medal (2000). Bar-Cohen serves on the IEEE-CPMT Board Of Governors (2011-2017) and has co-authored Design and Analysis of Heat Sinks (Wiley, 1995) and Thermal Analysis and Control of Electronic Equipment (McGraw-Hill, 1983), and has edited/co-edited 22 books in this field. He has authored/co-authored some 400 journal papers, refereed proceedings papers, and chapters in books; has delivered 70 keynote, plenary and invited lectures at major technical conferences and institutions, and he holds 8 US and 3 Japanese patents. He has advised to completion 64 PhD and master’s students at the University of Maryland, the University of Minnesota and the Ben Gurion University (Beer Sheva, Israel), where he began his academic career in 1972. From 1998-2001 he directed the University of Minnesota Center for the Development of Technological Leadership and held the Sweatt Chair in Technological Leadership.

Toward High-Efficiency Hybrid (Electricity and Heat) High-Concentration Photovoltaic Systems

May 11, 2015 09:00

Abstract: Photovoltaic power generation is a growing renewable primary energy source, expected to assume a major role as we strive toward fossil fuel free energy production. However, the rather low photovoltaic efficiencies limit the conversion of solar radiation into useful power output. Hybrid systems extend the functionality of concentrating photovoltaics (CPV) from simply generating electricity, to providing simultaneously electricity and heat. The utilization of otherwise wasted heat significantly enhances the overall system efficiency and boosts the economic value of the generated power output. The system presented in this lecture is the outcome of collaborative research in my research group, with the IBM research lab in Zurich and the Fraunhofer Institute for solar energy systems in Freiburg, Germany. It consists of a scalable hybrid photovoltaic-thermal receiver package, cooled with an integrated high performance microchannel heat sink we initially developed and optimized for the efficient cooling of electronics. The package can be operated at elevated temperatures due to its overall low thermal resistance between solar cell and coolant. The effect of the harvested elevated coolant temperature on the photovoltaic efficiency is investigated. The higher-level available heat can be suitable for sophisticated thermal applications such as space heating, desalination or cooling (polygeneration approaches). A total hybrid conversion efficiency of solar radiation into useful power of 60% has been realized. The exergy content of the overall output power was increased by 50% through the exergy content of the extracted heat.

Bio: Professor Dimos Poulikakos holds the Chair of Thermodynamics at ETH Zurich, where in 1996 he founded the Laboratory of Thermodynamics in Emerging Technologies in the Institute of Energy Technology. He is also the Head of the Institute of Energy Technology at ETH. He was a Member of the Research Commission of ETH (2001-2005) and the Vice Chair and then Chair of the Leonard Euler Center in Switzerland (2002-2005). He served as the Vice President of Research of ETH Zurich in the period 2005-2007. Professor Poulikakos was the ETH director of the IBM-ETH Binnig-Rohrer Nanotechnology center, a unique private-public partnership in nanotechnology at the interface of basic research and future oriented applications (2008-2011). He was the Head of the Mechanical and Process Engineering Department at ETH Zurich (2011-2014). His research is in the area of interfacial transport phenomena and thermodynamics with a host of related applications, and on the development of transformative energy technologies. The focus is on understanding the related physics, in particular at the micro- and nanoscales and employing this knowledge to the development of novel technologies. Specific current examples of application areas are the direct 3D printing of colloids with nanoscale resolution, the science-based design of supericephobic and omniphobic surfaces, the chip/transistor-level 3D integrated cooling of electronics, the development of facile methods for the fabrication of plasmonic sunlight absorbers and the development of surface textures for biological applications under realistic fluidic environments (accelerated and guided cell adhesion and re-endothelialization).
Professor Poulikakos has supervised to completion over 60 Doctoral dissertations to date. He has published ca. 400 research articles in top peer reviewed journals in areas such as heat transfer, fluid dynamics, energy, nanotechnology, materials, chemistry and chemical engineering, applied physics, and bioengineering/biophysics, as well as numerous articles in proceedings of professional conferences and a graduate level textbook on Conduction Heat Transfer (Prentice Hall, 1994). He has also edited and co-authored a special volume of Advances in Heat Transfer (1996), dedicated to transport phenomena in materials processing. In Thomson Reuters Web of Sciences he has over 7700 citations and an h-factor of 45. In Google scientific citations he has ca. 15700 citations and an h-factor of 54. Among the awards and recognitions he has received for his contributions are the White House/NSF Presidential Young Investigator Award in 1985, the Pi Tau Sigma Gold Medal in 1986, the Society of Automotive Engineers Ralph R. Teetor Award in 1986, the University of Illinois Scholar Award in 1986 and the Reviewer of the Year Award for the ASME Journal of Heat Transfer in 1995. He is the recipient of the 2000 James Harry Potter Gold Medal of the American Society of Mechanical Engineers. He was a Russell S. Springer Professor of the Mechanical Engineering Department of the University of California at Berkeley (2003) and the Hawkins Memorial Lecturer of Purdue University in 2004. He received the Heat Transfer Memorial Award for Science in 2003 from ASME. In 2008 he was a visiting Fellow at Oxford University and a distinguished visitor at the University of Tokyo. He is the recipient of the 2009 Nusselt-Reynolds Prize of the World Assembly of Heat Transfer and Thermodynamics conferences (awarded every four years), for his scientific contributions. He is the 2012 recipient of the Max Jacob Award, for eminent scholarly achievement and distinguished leadership in the field of fluidics and heat transfer. Awarded annually to a scholar jointly by (ASME) and (AIChE), the Max Jacob Award is the highest honor in the field of heat transfer these professional organizations bestow. He was presented with the Outstanding Engineering Alumnus Award of the University of Colorado in Boulder in 2012. He received the Dr.h.c. of the National Technical University of Athens in 2006. In 2008 he was elected to the Swiss National Academy of Engineering (SATW), where since 2012 he serves as president of its science board. Professor Poulikakos has been a frequent keynote speaker in many conferences worldwide. He is the Editor in Chief or member of the editorial board of several top tier international journals. He is a Fellow of the American Society of Mechanical Engineering (ASME). He represents Switzerland in the world assembly of heat transfer conferences.

SUNgas: Opportunities and Challenges for Solar Thermochemical Fuels

May 12, 2015 08:40

Abstract: Displacing fuels derived from petroleum with synthetic solar fuels offers the opportunity to harness and store the earth's most abundant energy resource, to reduce anthropogenic emissions of greenhouse gases, and to meet an expanding global demand for fuel. This presentation will present a review of the state-of-the art developments and the technological challenges of realizing the thermodynamic potential of solar thermochemical approaches to convert water and carbon dioxide to fuel. First, solar gasification will be presented as an important stepping stone to the more compelling goal of splitting water and carbon dioxide A new process developed at the University of Minnesota in which biomass, or carbonaeous waste, is gasified in a molten carbonate salt will be presented. The talk will cover the kinetics of gasification in a ternary blend of molten carbonate salt, design and characterization of a prototype solar reactor, and approaches to interface the process with a downstream fuel production plant. Second, production of synthesis gas via solar thermochemical metal-oxide redox cycles will be presented. Here the focus will be on cerium dioxide based cycles and the development of approaches to effective heat recovery. Advances in the thermal sciences required to meet the challenge of achieving solar-to-chemical efficiencies exceeding 10% will be highlighted.

Bio: Professor Jane Davidson received her B.S. and M.S. in Engineering Mechanics from the University of Tennessee and a PhD in Mechanical Engineering from Duke University. At the University of Minnesota, she is Professor of Mechanical Engineering and Director of the Solar Energy Laboratory. She holds the College of Science and Engineering Ronald L. and Janet A. Christenson Chair in Renewable Energy. Her current research is in the areas of absorption-based energy storage for buildings, and thermochemical processes to produce solar fuels. Her efforts in research and engineering education have been recognized with the 2004 ASME John I. Yellott Award, the 2007 American Solar Energy Society Charles Greeley Abbot Award, the 2009 Ada Comstock Award for excellence in Science and Engineering, and the 2012 ASME Frank Kreith Award. She is a Fellow of ASME and ASES.

Grid Operations with High Penetration of Photovoltaic Systems

May 12, 2015 08:40

Abstract: The solar energy market has been growing rapidly during the last decade, especially in the grid-tied photovoltaic (PV) market sector. Over the past few years, solar PV has moved light years ahead of where it stood in the first half of 2012. Between 2012 and 2014 in the United States, cumulative residential and non-residential installations have both doubled while cumulative utility PV installations have more than quadrupled. GTM Research and the Solar Energy Industries Association project that more than 18 GW of utility-scale solar to be online by the end of 2016.

Utility-scale PV production is economically competitive with natural gas and/or is well suited to hedge against natural gas price volatility. Besides, utilities enjoy better community reputations when they pursue clean, renewable power resources. The most straightforward way to reduce carbon footprints is to simply use less power. By its distributed nature, solar allows utilities to employ "smart grid" technologies more efficiently. Power may be switched and directed to where it's needed the most, and line losses and other usage factors may be minimized.

Although the U.S. solar market has more than doubled over the past two years, looking ahead, systemic challenges to growth loom both in the near term. If utility-scale PV penetration become significant fractions of the connected generation, it is no longer appropriate for the PV generators to be considered as a "negative load". They must take part in the operation of the power system. A major challenge in integrating high penetrations (>20%) of solar-energy rests in a grid's ability to handle the intrinsic variability of solar power. Real-time grid operators are therefore especially concerned about large-scale PV systems operating under cloudy conditions and large disturbances.

In this keynote talk, the development of innovative technologies to handle the intrinsic variability of photovoltaic plant generation and enable high penetration levels while maintaining secure real-time grid operations will be presented.

Bio: G. Kumar Venayagamoorthy received his Ph.D. degree in electrical engineering from the University of Natal, Durban, South Africa, in 2002. He is the Duke Energy Distinguished Professor of Power Engineering and a Professor of Electrical and Computer Engineering at Clemson University. Prior to that, he was a Professor of Electrical and Computer Engineering at the Missouri University of Science and Technology (Missouri S&T), Rolla, USA. Dr. Venayagamoorthy is the Founder and Director of the Real-Time Power and Intelligent Systems Laboratory (http://rtpis.org). He is currently an Honorary Professor of the School of Engineering at the University of Kwazulu-Natal, Durban, South Africa. Dr. Venayagamoorthy’s research interests are in the development and applications of advanced computational algorithms for smart grid applications, including power system stability and control, optimization, operations, intelligent sensing and monitoring and signal processing. He has published 2 edited books, 8 book chapters, and over 450 refereed journal and conference proceeding papers.

Dr. Venayagamoorthy is a recipient of several awards including a 2008 US National Science Foundation (NSF) Emerging Frontiers in Research and Innovation Award, a 2007 US Office of Naval Research Young Investigator Program Award, a 2004 NSF CAREER Award, the 2010 Innovation Award from St. Louis Academy of Science, the 2010 IEEE Region 5 Outstanding Member Award, and the 2006 IEEE PES Walter Fee Outstanding Young Engineer Award. He is the recipient of the 2012 Institution of Engineering and Technology (IET) Generation, Transmission and Distribution Premier Award for the best research paper published in 2010/2011 for the paper “Wide area control for improving stability of a power system with plug-in electric vehicles”. His work is cited over 8500 times and has an h-index of 48.

Dr. Venayagamoorthy is involved in the leadership and organization of many conferences including the General Chair of the 2015/2014/2013 Power System Conference (Clemson, SC, USA), and Chair/co-Chair of the 2015/2014/2013/2011 IEEE Symposium of Computational Intelligence Applications in Smart Grid (CIASG). He is currently the Chair of the IEEE PES Working Group on Intelligent Control Systems, and the Founder and Chair of IEEE Computational Intelligence Society (CIS) Task Force on Smart Grid. He is currently an Editor of the IEEE Transactions on Smart Grid. Dr. Venayagamoorthy is a Senior Member of the IEEE, and a Fellow of the IET, UK, and the SAIEE.

Optimal Design of Stationary Flat-Plate Solar Collectors: Deterministic and Probabilistic Approaches

May 13, 2015 08:40

Abstract: Because of the soaring energy prices, many countries have shown an increased interest in the utilization of solar energy. The optimization of the solar energy collector design plays a critical role in the efficient collection of solar energy. Flat-plate collectors can be designed in applications that require energy delivery at moderate temperatures (up to 100◦C above ambient temperature). These collectors use both beam and diffuse solar radiation, and do not need to track the sun. They are simple to manufacture and install with relatively low maintenance cost which make this kind of solar collectors more popular. The design of a flat-plate solar collector embraces many relationships among the collector parameters, field parameters and solar radiation data at any given location. The shading decreases the incident energy on collector plane of the field. The multi-objective optimum design of stationary flat-plate solar collectors is presented in this work. The clear day solar beam radiation and diffuse radiation at the location of the solar collector (Miami) are estimated. The maximization of the annual average incident solar energy, maximization of the lowest month incident solar energy and minimization of the cost are considered as objectives.. The game theory methodology is used for the solution of the three objective problems to find the best compromise solution. The sensitivity analysis with respect to the design variables and the solar constant are conducted to find the relative influence of the parameters on the design. The multi-objective optimum design of stationary flat-plate solar collectors under probabilistic uncertainty is also considered. The three objectives stated earlier are considered in the optimization problem. The solar constant, altitude, typical day of each month and most of the design variables have been treated as probabilistic variables following normal distribution. The game theory methodology is used for the solution of the three objective constrained optimization problems to find a balanced solution. A parametric study is conducted with respect to changes in the standard deviation of the mean values of design variables and probability of constraint satisfaction. This work represents a novel application of the multi-objective optimization strategy, including probabilistic approach, for the solution of the solar collector design problem. The present study is expected to help designers in creating optimized solar collectors based on any specified requirements.

Bio: Dr. Singiresu S. Rao is currently a Professor in the Department of Mechanical and Aerospace Engineering at University of Miami, Coral Gables, Florida. He served as the Chair of the Department of Mechanical and Aerospace Engineering during the period 1998-2011. Earlier, Dr. Rao served as a Professor in the School of Mechanical Engineering at Purdue University, West Lafayette, Indiana during 1985-1998 and Professor of Mechanical Engineering at Indian Institute of Technology, Kanpur, India during 1972-1984. He was a Visiting Research Scientist at NASA Langley Research Center, Hampton, Virginia during 1980-1981. Dr. Rao received his Ph.D. in Engineering Mechanics and Design from Case Western Reserve University, Cleveland, Ohio. He received the Vepa Krishna Murthy gold medal from Andhra University for securing university first rank among students of all branches of engineering in all five years, and Lazarus Prize from Andhra University for securing university first rank among students of mechanical engineering in B.E. Dr. Rao received the First Prize in James F. Lincoln Design Contest, as a graduate student, in 1971 for his paper on “Automated Optimization of Aircraft Wing Structures”.

Dr. Rao’s research interests include multiobjective optimization, uncertainty models in engineering analysis and design, structural control, structural dynamics, and renewable energy systems. He published 185 papers in refereed journals (mostly in ASME and AIAA journals) and 145 papers in conference proceedings in these areas. He made several pioneering contributions in the areas of multi-objective optimization and game theory, reliability-based design, and fuzzy, interval and evidence-based methods in engineering analysis and design. In 1999, the Society of Automotive Engineers (SAE) International awarded Dr. Rao the Distinguished Probabilistic Methods Educator Award with the citation “For demonstrated excellence in research contributions in the application of probabilistic methods to diversified fields, including aircraft structures, building structures, machine tools, air-conditioning and refrigeration systems and mechanisms.” Dr. Rao published the first papers on single and multiobjective optimization of fuzzy engineering systems in 1987. He introduced new fields of research known as “fuzzy finite element analysis”(1995), “fuzzy boundary element analysis”(2001) and fuzzy meshfree methods (2012) by publishing the first papers in these areas. He presented the first applications of interval methods to engineering analysis and optimization in 1997 and 2002, respectively. Since 1995, Dr. Rao has been demonstrating the application of evidence theory (Dempster-Shafer theory) to optimization and uncertainty analysis of engineering systems. In 2009, he presented an evidence-based approach for the safety analysis of uncertain systems. Dr Rao received Outstanding Researcher Award from Telugu Association of North America (TANA), Distinguished Award from American Telugu Association (ATA) and Eliahu L. Jury Award for Excellence in Research from University of Miami for his original research contributions. In 2012, the American Society of Mechanical Engineers awarded Dr. Rao the “ASME Design Automation Award” with the citation, “for pioneering contributions to Design Automation, particularly, in muliobjective optimization and uncertainty modeling, analysis and design using probability, fuzzy, interval and evidence theories”. In 2013, the American Society of Mechanical Engineers (ASME) presented Dr. Rao the Worcester Reed Warner Medal for outstanding contributions to the permanent literature of engineering through his highly popular books and numerous trendsetting research papers. Dr. Rao advised 31 Ph.D. students and 27 M.S. thesis students. Dr. Rao gave keynote lectures at numerous international conferences on engineering optimization, uncertainty models, renewable energy systems and computational methods.

Dr. Rao published eight books which are being used as text books at hundreds of universities throughout the world. These include Mechanical Vibrations, 5th Ed, Prentice-Hall, 2011; Applied Numerical Methods for Engineers and Scientists, Prentice-Hall, 2002; Reliability Engineering, Pearson Prentice Hall, 2015 (published in April 2014), Engineering Optimization: Theory and Practice , 4th Ed, John Wiley, 2009; Vibration of Continuous Systems, John Wiley, 2008; The Finite Element Method in Engineering, 5th Ed, Elsevier, 2011; Reliability-Based Design, McGraw-Hill, 1992; and Optimization: Theory and Applications, Wiley Eastern, 1979. Dr. Rao co-edited (with S. Braun and D. Ewins) the 3-volume Encyclopedia of Vibration, Academic Press, San Diego, 2002. He was very active in the Design Automation Committee activities during its early years. He served as the Papers Review Chairman and Chairman of the Design Automation Conferences held in Orlando (in 1987) and Boston (in 1988). He edited the Conference Proceedings under the titles “Advances in Design Automation-1987 (Volumes 1 and 2)” and “Advances in Design Automation -1988” (the title of “Advances in Design automation” for the Proceedings was introduced by Dr. Rao in 1987 and was used for the DAC proceedings subsequently for several years until the digital proceedings were introduced).

Inspecting PV-Plants Using Aerial, Drone-mounted Infrared Thermography System

May 13, 2015 08:40

Abstract: Worldwide more than 140 GW photovoltaic plants are installed. 2013 more than 104.000.000 US-Dollars were invested. Thus, PV plays an increasing role for the global supply with electricity. Therefore safety and reliability aspects gain in importance for operation and maintenance of PV-plants. Monitoring, especially imaging techniques, like infrared (IR) thermography are valuable tools for inspecting PV-plants. Measurement systems consisting of an IR-camera and an aerial, unmanned vehicle visualize malfunctioning modules due to recorded temperature irregularities. There are several benefits of this method: fast, reliable, non-destructive, contact-free and measuring during operating conditions. Furthermore, this technique is efficiently applicable to inaccessible roof mounted systems as well as to extended field plants. In this paper the fundamentals of infrared thermography are presented with regard to investigating PV-Plants and PV-modules. The impact of measurement parameters, e. g. observation angle, flight altitude, flight velocity, on the imaging, the measured temperature distribution, and the data evaluation will be discussed. Suitable weather conditions, as sunny and cloudless blue sky, no wind, are necessary to ensure analyzable IR-images. IF these requirements are fulfilled outstanding features indicate defect modules, which are localized easily using IR-imaging. IR-images of PV-plants and single modules will be shown. Depending on the temperature distribution evidence for specific failure modes are given. Thus, cell fracture, soldering failure, short-circuited cells, by-passed substrings, can be distinguished easily using IR-imaging. Extra analyses verify the negative impact of the identified defects on the module performance.

Bio: My name is Dr. Claudia Buerhop-Lutz. I studied material science at the Friedrich-Alexander University of Erlangen-Nürnberg in Germany. This knowledge about the treatment and behavior of the different materials is a valuable basis for my actual job characterizing photovoltaic modules, which compose out of many different materials. Since 2006 I work at the Bavarian Center for Applied Energy Research (ZAE Bayern) in Erlangen, Germany. Here, I was responsible for the thermography, infrared imaging, especially photovoltaics. 2008 we were the first who started to use IR-thermography for outdoor analysis of PF-modules. The results of the first experiments we documented in the so called “IR-handbook” which is available free of charge in the internet and frequently downloaded. During the last years I improved the measuring procedure and data evaluation with my colleagues. Since 2010 we work with aerial drone-mounted IR-imaging systems. We started with a model helicopter, nowadays we find the best solution is a multicopter. Actually, my scientific interest focuses on the contactless and non-destructive imaging of installed PV-modules and on the study of the aging behavior and degradation mechanisms of PV-modules under real operating conditions.