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Commissioning a 5 kW PV Array for Electrical Engineering University Curriculum

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Conference

2011 ASEE Annual Conference & Exposition

Location

Vancouver, BC

Publication Date

June 26, 2011

Start Date

June 26, 2011

End Date

June 29, 2011

ISSN

2153-5965

Conference Session

ECCD Poster Session

Tagged Division

Energy Conversion and Conservation

Page Count

14

Page Numbers

22.341.1 - 22.341.14

Permanent URL

https://peer.asee.org/17622

Download Count

20

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Paper Authors

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Jaime Ramos University of Texas, Pan American

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Dr. Ramos has been at The University of Texas Pan American since 2005, in the Department of Electrical Engineering. His research activities are directed towards the integration of renewable energy sources to the electric grid. Dr. Ramos is a Registered Professional Engineer in the state of Texas, and the Chair of the Rio Grande Valley Chapter of IEEE Power & Energy Society. Before coming to Texas, he accumulated significant experience in manufacturing, consulting, and teaching Electrical Engineering. He obtained a Ph.D. in Electrical Engineering in 1976 from Stanford University.

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Leonel Aguilera University of Texas, Pan American

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Leonel Aguilera earned his his B.S. degree in Electrical Engineering from The Technology Institute of Saltillo, Coahuila, Mexico in 2006. He expects to earn his M.S.E. degree in Electrical Engineering at the University of Texas, Pan American in Edinburg, TX on December 2011. His research interests are: Networking and Renewable Energy.

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Elizardo Garcia Universidad TecMilenio

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Sanjeev Kumar University of Texas, Pan American, Electrical and Computer Engineering

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Dr. Sanjeev Kumar is active in research & teaching in the area of Computer Security, Smart Grid Security, High-Speed Internet Switching/Routing, Wireless Ad Hoc Networks, Computer Architecture, and Digital Logic Systems. Before joining UTPA, Dr. Kumar worked with the leading networking companies in the US. In the networking industry, Dr. Kumar played a leading role in planning, research & development of new communications equipment and networks.

Dr. Kumar has authored over 50 technical papers. Dr. Kumar’s research findings have been cited by other researchers in the field. Dr. Kumar has served as Associate Editor for networking Journals, and as a member of technical program committee for international conferences. He has been awarded US and International patents for his inventions in the area of broadband networks. Dr. Kumar received the Ph.D. degree in Computer Engineering from North Carolina State University, Raleigh, North Carolina. He is the founder of NSF funded Network Research Lab (NRL) in Electrical Engineering Dept. at UTPA, and an elected Senior member of IEEE..

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Roman Garcia IEEE

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Roman Garcia earned his degree as an Electronic Technician in 2007. He is coursing his B.S, degree in Electrical Engineering at The University of Texas, Pan American. He is looking for a cleaner way to provide energy and illumination at lowest prices. His goals and vision on renewable energy and LED lightning had brought him to work as a research assistance on the project described in the paper.

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Jose Sanchez University of Texas, Pan American

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Jose Sanchez, The University of Texas, Pan American.
Jose Sanchez received his B.S.E.E. degree from The University of Texas, Pan American in May 2008. He expects to earn his M.S.E. degree in Electrical Engineering at the University of Texas, Pan American in May 2011. His primary interests lie
in the development of Energy Efficiency and Renewable Energy Systems and Technologies,
Power Electronics, and Smart Grid Design.

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Abstract

Commissioning a 5 kW PV array for Electrical Engineering University curriculumUniversities around the world 1,2,3 are developing new curricula on renewable energy, to preventthe shortage of qualified electrical engineers in power systems. This paper describes thecommissioning of a 5kW DC photovoltaic generation system (PVS), which is being used at TheUniversity of Texas Pan-American (UTPA) as an educational tool, to let students learn thefundamental principles and to get hands-on experience with power and renewable energysystems. The system topology is shown in Figure 1.The PVS is called a hybrid system because it has been designed to supply energy in threedifferent configurations: (a) for stand-alone and battery applications, (b) for grid-tiedapplications, and (c) as a back-up (emergency) system that supplies power to smart-gridlaboratory at UTPA.During the first stage of the commissioning process, our efforts have been focused onunderstanding the behavior of the system and on operating it in a reliable way, in the stand-aloneconfiguration. So far, (i) an energy balance of the PVS has been made, (ii) the correlation factorbetween its energy input and output has been computed, (iii) the efficiency has been calculated,(iv) the actual operating point has been analyzed, and (v) the maximum power and total energyproduction is being reported daily.Results show that the system is working with an efficiency close to 90%, with respect to thephotovoltaic generated power, but that it operates far away from its maximum power point. Thisis due, largely, to a second harmonic current introduced by the charge controller. The next step,in the commissioning process, will be to filter out a second harmonic current generated by thecharge controller (a Sunny Island unit) and to drive the PVS to its maximum power point.1- IntroductionAs State legislatures approve guidelines for the composition of renewable energy in the totalgeneration portfolios of electric utilities, several actors in the private as well as the public sectorshave increased year by year the amount of electric energy generated by wind, solar and othergreen technologies.In the past two years the federal government, through its Department of Energy has increased theamount of capital to stimulate the development of solar technologies, as well as the formation ofwell trained human resources to support this national effort.Solar photo voltaic technologies have been increasing its participation because they rely on themature and powerful semiconductor industry, and also because they offer unique operationalcharacteristics which the residential and commercial sectors can use for distributedgeneration.This environment has created within Universities a strong interest from students forthe acquisition of knowledge on Renewable Energy. Correspondingly, Faculty has madesignificant number of proposals to develop on-site low power photovoltaic generation resources,as a response to the student´s interest.This paper describes the work done during 2010 at the Electrical Engineering Department of TheUniversity of Texas Pan American- UTPA- to install photovoltaic systems to develop andconstruct learning materials. Basic experiments are described in detail. Topics includecommissioning a 5.18 kWDC fixed PV array; monitoring the energy and power produced by a5.52 kWDC two-axis sun tracking PV array; and obtaining current voltage characteristics ofsingle modules, by manual and automatic methods.The experiments are being evaluated with the assistance of undergraduate students who haveenrolled in one of the courses offered the Energy and Power systems course concentration.2- Resources and FacilitiesThe learning materials have been designed to use software and hardware available at UTPA. TheENGR fixed array uses software developed by Sunny Portal4 www.sunnyportal.com; studentsoperating this array will use LabVIEW programs to monitor electric variables. The TXU SunTracking Arrays use software developed by Insight View/Fat Spaniel5 to monitor itsperformance. These computational resources monitor the operation and state of the electronicinverters. Additionally, students use software developed by the authors to calculate the suntrajectory and incidence angles on the fixed modules.The hardware based experiments will be determined by the photovoltaic systems alreadyavailable at the University. Two systems are shown in Figures 1 and 2. Each experimentincludes a collection of modules, inverters, meters, and loads. A list of the PV systems is shownin Table 1. Table 2 includes a list of basic, intermediate and advanced experiments.Figure 1 - Schematic view of ENGR PV Solar Power System Figure 2 - North Half of the TXU Sun Tracking Arrays Table 1- Main photovoltaic components System Ratings Use Initial cost 1- ENGR PV fixed 5.18 kWDC VOC =438 DC grid battery storage. $ 57,000 array V, ISC = 8.1 A AC grid tied2- TXU Sun Tracking 5.52 kWDC VOC =443 AC grid tied $ 70,000 Arrays V, ISC = 8.3 A 3- Single module 155 Watts, VOC =43 I – V characteristic $ 1,000 V, ISC = 4.8 A 4- Sun Radiation Watts / m² Hand held, inexpensive $ 150 Power Meter Table 2- List of basic, Intermediate and Advanced Experiments Topic Activity Systems 1- Length of day Calculation & Monitoring 1- ENGR PV fixed array 2A- I V characteristic Manual measurements 3- Single module 2B- I V characteristic Oscillographic measurements. 3- Single module Maximum Power Point 3- Battery Storage Ampere-Hours calculations 1- ENGR PV fixed array 4- Battery Storage System kWh energy balance 1- ENGR PV fixed array 5- Capacity Factor Compare PV systems 1,2 6- Commissioning of the Upgrade instrumentation. 1- ENGR PV fixed array ENGR PV Array Networking3- Overview of available Renewable Energy TechnologiesDuring the planning phase of this work we addressed the question: Which renewable energysource would be best suited to the general physical conditions of the UTPA campus? Our naturalinterest within a Department of Electrical Engineering would be to operate a distributedgeneration resource able to evolve naturally as a micro/smart grid6,7 with a certain degree offlexibility to cover different utilization or integration schemes (DC /AC grids).We then examined the possibility of using wind turbines located on campus, with a limitedbudget. From the wind speed data at Edinburg, TX provided by the Texas Environmental QualityCommission8 we constructed yearly histograms. Our calculation showed the average wind speedto be less than 9 mph, making the UTPA campus a wind power class 1 site. Furthermore, westudied the market of small (micro) wind turbines, searching for one which mounted on a not toohigh tower could be operated reliably many days of the year. When we focused on their cut inwindspeed characteristics we did not find a proper solution.After reaching this conclusion our attention turned to solar photovoltaic systems. A nearby city(Brownsville) was listed in Tables of Solar Insolation by City9 with a yearly average of 5.0kWh/m²/day. This flux would guarantee the daily operation of the PV system, with the advantageof ease of installation on the rooftop of the Engineering building, with a small maintenanceburden.As we know solar PV technologies have evolved from silicon to flexible thin film, and tomultiple band gap semiconductor third generation cells. Facing the need to choose from thesetechnologies, we valued most to find a local provider which could deliver a turn-in-key system.Our choice was to start with a simple PV system, the ENGR fixed PV array.4- Experiments / Learning Materials4.1- Day length calculation and monitoringStandard texts on Solar Energy10 include a Chapter on how much sunshine is available. In thisexercise the students will learn how to calculate the solar position at any time of day, andconsequently sunrise and sunset times.The ENGR PV array main inverter (Sunny Boy 5000) outputs a daily file thru the Internet-www.sunnyportal.com condensing the activity of the device starting with the morning call andending with the good night call. For every day of the academic semester students will log intheir calculation and the Sunny Boy reports in Figure 3.4.2- Current Voltage Characteristic curve of low power modulesThis experiment is performed using System 3 of Table 1. Rooftop placed modules can be wiredto a two-pole disconnect in the Energy & Power System Lab, with a 120-ft feeder made of 2-6,1-10 AWG copper conductors in conduit tube. The curve can be obtained with two differentmethods:A) Manual- Using two 150 Watts rheostats, 0-10 Ω and 0-100 Ω, as well as voltmeter andammeter. Several points of the characteristic are plotted, including the open circuit voltage andshort circuit current. Since this procedure takes several minutes, no attempt is made to correlatethe plot with the insolation.B) Automatic curve tracing. At least two students participate in this experiment, using their cellphones. Student A on the rooftop is measuring normal solar radiation to the module, withinstrument 4 of Table 1. Student B at the workbench of the E&PS Lab is running the Figure 3- Day Length according to the SMA inverter reportoscilloscope and recording I V signals in channels 2 and 1, Figure 4. The module positiveterminal is connected to the collector of a 115 W npn bipolar transistor. From the emitter, a smallresistor- 0.25 Ω- is used as a current voltage converter. The base of this transistor is driven by ina Darlington configuration by a ramp voltage, driving the solar module from open circuit to nearshort circuit. Digital oscilloscope can plot the characteristic curve, and also produce CSV files,which on further analysis, will yield Excel graphs, such as the one shown in Figure 5. Figure 4- Schematic of transistor circuit to scan the solar module characteristicThis experiment has several important outcomes: A) correlate the I V graph with insolation B) correlate the curve with the solar trajectory and the module orientation. C) Obtain maximum power point; introduce the concept of MPP tracker D) Obtain an estimate of the module´s efficiency. E) Discuss alternative method to measure short circuit current. F) Train students on the installation and operation of series/parallel combination of modules. Figure 5- Single Panel Characteristic graph obtained with electronic sweep4.3- Battery Storage Amp-hours calculationsThis experiment and the next one are performed on the fixed ENGR PV array. A schematic ofthe components which integrate this system is shown in Figure 5. This system is endowed with 3sets of current and voltage sensors, located in three buses: # 1, at the array, # 2, at the battery, and # 3, atthe load. A data acquisition was put into use, with 6 analog to digital differential channels to monitor andstore these electrical variables. Usually, samples are taken every second, and their averages are storedevery 5 minutes (300 seconds).Further calculation of power, energy and charge can be done and displayed using usual software.Figure below shows the charge and discharge cycles for several days. Additional outcomes of theexperimetn are: A) observe the various types of charging modes. B) Discuss instrumentation or measuring problems. C) Observe charge controller set pointsFigure 6- ENGR fixed PV Array schematic showing major subsystems Figure 7- Battery nine-day charge and discharge cycle (December 2010)4.4- Battery Energy Balance kWh CalculationThe basic equation is the time derivative of the energy dw/dt = p(t), which can be integrated to∫ + ∫ = ∫ p(t) being the electric power = v(t) i(t). These integrals can be numerically performed usingtime intervals of 5 min. In such manner the graphs of Figure 8 can be produced. They show theamount of PV energy generated, and energy consumed at the battery and load. The student willbe able to estimate the efficiency of the electronic inverters.4.5- Capacity FactorsThe presence on campus of two PV arrays of similar power, but different tracking characteristicsis a good opportunity for the student grasp the concept of capacity factor, C. A usual definitionfor C = kWh produced / (kW Nominal * Hours). The relevant data can be obtained from the webservices embedded on the fixed array [3] and tracking [4] inverters. Figure 8 - Energy balance in the ENGR fixed PV array Table 3- Capacity factor for two arrays, during November 30th, 2010 Array Production kWh Max Power kW Capacity Factor 1- ENGR PV fixed array 10.24 2.73 8.23 % 2- TXU Sun tracking array 30.54 4.53 23.0 %4.6- Commissioning the ENGR fixed PV arrayA data acquisition system was put into use, with 6 analog to digital differential channels tomonitor the voltage and current of those points 1 (array), 2 (battery) and 3 (load), according toFigure (1). Currents were measured with Hall effect sensors, and voltages with simple resistivedivider circuits.As we developed trust in our instrumentation a good test is to verify the compliance withKirchhoff current law. Icharge controller + Ibatt = Iload . (1)Equation (1) was tested in two cases: Iload = 0 and Iload > 0. The oscillograms in Figures 9 and 10are evidence that our methods are devoid of fundamental errors. Figure 9. Battery and controller's currents showing 180 phase difference when Iload = 0. Figure 10. Battery and controller currents make up to Iload =19 A.As Iload is fairly constant, or slowly varying, the variation of battery current will be determinedby the variation of the controller current. Figures 9 and 10 show a strong second harmoniccomponent. Presently there is no element in the system to eliminate that harmonic content,therefore to monitor the current during daily periods 5-minutes averaging methods were adopted,in particular mean and rms values.Other main measurements at the selected points in Figure 6 are their voltages. We have usedsimple resistive dividers, designed with outputs in the range of 5 Volts, which are suitablyhandled by the data acquisition system.Students will design voltage divider circuits and make experiments for their calibration, as wellas Hall effect current sensors.5- Integration to curriculumThe Energy studies option at the EE Dept in UTPA is formed with the following set of courses:a. ELEE 4333 Renewable Energyb. ELEE 4372 Electric Machinery & Power Systems Fundamentals.c. ELEE 3371 Electric Power Systems Design & Applications (Buildings)d. ELEE 3370 Power ElectronicsThe equipment and systems developed in this project will enable UTPA to support this string ofcourses, and make a better course curriculum for ELEE 3370 Power Electronics. The DC powersource from the ENGR PV array will enable a variety of lab tests and experiments for thestudents.All experiments described in Section 4 require a basic knowledge of electric power topics.Students will benefit from previous work with basic instruments for voltage, current, power anddiagrams. Experiment 2B about I V characteristics requires knowledge of electronics circuits,and it would be possible to introduce the concept of transistor as switch to compensate for a lackof study. UTPA is now offering ELEE 4333 Renewable Energy as an elective course for juniorsand seniors. All the learning tools described in this work will be useful, in particular for powergeneration and system integration of solar technologies.6- Collaborative Research, Technology Transfer and Student EvaluationThe equipment and systems developed in this project is enabling joint collaborative researchactivities in the area of smart grid and security, involving researchers from the data networkingfield. Research proposals for joint collaborative research, in the area of smart grid, have beensubmitted to funding agencies at the state and national level, such as National ScienceFoundation.There are two campuses of The University of Texas in the Lower Rio Grande Valley: atBrownsville and at Edinburg, with similar sunshine characteristics. These two campuses of UTare active in writing joint educational proposals11 with the objective of developing and sharinglearning tools in the Renewable Energy field.The general educational outcomes of the EE program in UTPA are, concisely written: 1- usemath, 2- make experiments, 3- design equipments, 4- do team work, 5- communicate ideas, 6- beresponsible, 7- lifelong learning, and 8- computer literacy. Student's working on theseexperiments can develop further these abilities. Assessment of these outcomes will be done bythe inclusion of pertinent questions in Lab handouts.7- ConclusionGiven the current interest in the integration of solar technologies to the electric utilities, and thelack of teaching materials in this area, UTPA has developed six laboratory experiments on PVsolar technology topics. The experiments use software and hardware tools available by two PVarrays constructed on campus. The experiments are designed to be conducted by triplets ofstudents in two hour laboratory sessions.8- AcknowledgementsThis work has been possible in part by the generous gift of TXU Energy, Dallas Texas, whohave funded the TXU Sun Tracking Arrays.This material is based upon work supported by the Department of Energy under award numberDE-EE0004007.References1- R. W. Wies, R. A. Johnson, John Aspnes, "Design of an Energy-Efficient Standalone Distributed GenerationSystem Employing Renewable Energy Sources and Smart Grid Technology as a Student Design Project." POWERENERGY SYSTEMS GENERAL MEETING 2010- GM 14502- Gregory F. Reed, William E. Stanchina, "Smart Grid Education Models for Modern Electric Power SystemEngineering Curriculum." POWER ENERGY SYSTEMS GENERAL MEETING 2010- GM 07753- Marija Il'ic. "Teaching Smart Grids: Yet Another Challenge and Opportunity for Transforming Power SystemsCurriculum." POWER ENERGY SYSTEMS GENERAL MEETING 2010- GM 13764- Sunny WebBox Web Enabled Data logger & Controller for Alternative Energy Systems. 2005 SMA America Inc.http://129.113.130.242 (not public).5- http://siteapp.fatspaniel.net/siteapp/simpleView.jsf?eid=553237.6- B Prokoski, et al. "Making microgrids work" IEEE power & energy magazine, May/June 2008, p417- J. Driesenm F. Katiraci. "Design for Distributed Energy Resources". IEEE power & energy magazine, May/June2008, p30.8- http://www.tceq.state.tx.us9- Gilbert M. Masters- Renewable and Efficient Electric Power Systems. Wiley Interscience, 2004.10- M Iqbal. An Introduction to Solar Radiation. Academic Press 1983.11- University of Texas at Brownsville and University of Texas Pan American. South Texas Initiative. Energy &Environment Subcommittee. Report, June, 2010

Ramos, J., & Aguilera, L., & Garcia, E., & Kumar, S., & Garcia, R., & Sanchez, J. (2011, June), Commissioning a 5 kW PV Array for Electrical Engineering University Curriculum Paper presented at 2011 ASEE Annual Conference & Exposition, Vancouver, BC. https://peer.asee.org/17622

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