Renewable Energy Global Innovations features: Discrete cogeneration optimization with storage capacity decision support for dynamic hybrid solar combined heat and power systems in isolated rural villages

Significance Statement

Smart technology, deployed in rural village energy systems, has emerged as a prominent concept to relieve global energy poverty. It promotes the integration of renewable distributed energy resources by allowing improved data capture, energy management, and control automation. The development of new technologies and control processes, in order to bring clean energy to people living in rural off-grid areas, is needed as an alternative to paraffin and wood-fuel.

Solar cogeneration systems have the ability to attain considerably high levels of energy efficiency. These systems are designed to produce heat and electricity from the same device by recovering energy that would otherwise have been wasted making them suitable for district energy systems in off-grid areas. Solar cogeneration systems are inspiring a large number of developers to come up with packaged cogeneration systems, their emphasis being on functional controller design and scheduling optimization.

Unfortunately, control optimization for systems operating as stand-alone power packs in eco-villages often lack access to wideband wireless and cellular linkage infrastructure. Online control and optimization, therefore, becomes a challenge. Gerro Prinsloo and Robert Dobson from Stellenbosch University, South Africa, in collaboration with Andrea Mammoli from University of New Mexico, USA, focused on an integrated on-board control and optimization technique in a bid to realize load demand balancing with specific communication and cost restraints. Their work is published in Energy.

A storage optimization solution was proposed in the study and evaluated within the confines of an energy storage scenario for a rural solar microgrid. They used predicted generation and energy consumption profiles. Using this information along with other economical, physical and environmental restraints, the researchers were able to come up with a day-ahead control plan using an integrated integer linear programming technique.

The authors overlaid the discrete rural village electrical demand per hour onto the main supply contribution. Doing so, they highlighted the mismatch between peak load demand and the solar supply. It was possible to schedule the supply from a consumer point of view, but it wasn’t possible to shift produced loads to a period when excess energy was generated. Load shifting carefully took into consideration daily schedules of the villagers as not to be disruptive. Optimizing the generation schedule allowed the self-consumption and self-generation microgrid controller to reduce the effect on the consumer budget.

It was clear that a significant amount of solar energy was lost during the peak sunlight hours. This was mainly due to a limited microgrid storage capacity. The researchers, therefore, developed a storage optimization decision support system in a bid to curtail the added cost effect on the user. The system could now compare and track operating costs and storage extension capital cost. This would alert the user of billing cost versus operating cost savings that could be obtained by increasing the battery and hot water storage capacity.

Experimental results obtained by the authors indicate that incremental storage optimization can provide energy management efficiency and reduced customer bills. The developed hybrid decision support system ensured that less energy was dumped due to automated microgrid storage capacity specifications. The storage cost optimization gave approximately 66% reduction in daily microgrid liquefied petroleum gas (LPG) costs while the storage optimization posted an approximate annual financial gain of $130, as a result of reduced waste of energy.

About The Author

Andrea Mammoli is Professor of Mechanical Engineering at the University of New Mexico, and Director of the Center for Emerging Energy Technologies, an organization within the School of Engineering dedicated to research on the integration of distributed energy resources on the electricity grid through system architecture and controls. Mammoli has been active in the field of distributed energy systems since 2005, with projects including solar-assisted HVAC in commercial buildings, building-scale energy storage, distribution-level PV and battery systems, and microgrids, in the context of optimization and controls leading to better economics and enhanced resilience.

He conducts research in collaboration with the Electric Power Research Institute, Sandia National Laboratories and Lawrence Berkeley National Laboratory, among others. Mammoli obtained a Ph.D. in mechanical and materials engineering in 1995 from the university of Western Australia, and was Director’s Fellow at Los Alamos National Laboratory between 1995 and 1997 in the Energy and Process Engineering group, prior to joining UNM.

About The Author

Gerro Prinsloo is a Mechatronic Engineer and PhD Engineering student at the Department of Mechanical & Mechatronic Engineering at Stellenbosch University in South Africa and the Department of Mechanical Engineering at the University of New Mexico in the USA. He specializes in the mechanical and electronic design aspects of solar thermal systems and solar electrical power generation. He received his Bachelor’s degree in Mechatronic Engineering from Stellenbosch University in 2011 and a Master’s degree in Mechatronic Engineering from Stellenbosch University in 2014. His PhD research is being conducted at the Centre for Emerging Energy Technologies (CEET) at the University of New Mexico in Albuquerque and aims to solve challenges faced by rural African villages in terms of solar cogeneration systems with smart Microgrid distribution.

This research aims to implement novel energy management principles to support the use of renewable energy technologies in rural applications. He is a member of the Solar Thermal Energy Research Group (STERG) and a Candidate Professional Engineer with the Engineering Council of South Africa (ECSA) and he continues with Smartgrid research at the CEET Mesa Del Sol Research Labs in Albuquerque.

About The Author

Robert Dobson received his degree in Mechanical Engineering in 1969 and his postgraduate degree in Nuclear Engineering in 1970. He then registered as a Professional Engineer in 1973. He worked at the then Atomic Energy Board until 1980 and gained experience in the design, manufacture and testing of reactor components and systems. He then joined Kwikot LTD and gained experience in the design, manufacture and marketing of electric and solar water heaters and heat pumps. From 1985 and 1987 he was Engineering Services Manager at Kentron Pty LTD, a missile systems manufacturing company. Since 1988 he has been a Lecturer at the University of Stellenbosch. He now gives undergraduate courses in Food Engineering and Heat Transfer. He also gives postgraduate and specialist courses in Twophase Flow and Heat Transfer, and Nuclear Reactor Safety-Systems Engineering.

His research interests are in heat transfer using closed and closed-loop single and two-phase natural circulation thermosyphon-type heat pipes, and thermal management and control using heat pipes and other two-phase flow and heat transfer devices. The research focus on heat to electrical power conversion system safety and reliability enhancement using passive natural circulation systems. Over the past 15 years he has published 56 peer reviewed papers, presented 71 papers at international conferences, supervised 21 thesis projects and is at present supervising and co-supervising 6 Masters and PhD thesis projects.

Reference

Gerro Prinsloo², Andrea Mammoli¹, and Robert Dobson¹. Discrete cogeneration optimization with storage capacity decision support for dynamic hybrid solar combined heat and power systems in isolated rural villages. Energy, volume 116 (2016), pages 1051-1064

Show Affiliations

1. Centre for Renewable and Sustainable Energy Studies, Thermodynamic Research Group, Stellenbosch University, Stellenbosch, South Africa
2. Centre for Emerging Energy Technologies, University of New Mexico, Albuquerque, USA

 

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Renewable Energy Global Innovations features: An electrochemical approach to measuring oxidative stability of solid polymer electrolytes for lithium batteries

Significance Statement

For any type of commercially rechargeable battery, lithium batteries possess the highest energy density. For this reason, they find vast applications in electric vehicles. However, these batteries contain lithium salts dissolved in flammable solvents. If the battery is damaged, there is a high risk of explosion. Moreover, battery misuse can lead to rise in temperatures leading to dangerous exothermic reactions.

A solution to all these concerns can be found in the production of solid-state batteries. Polymer-lithium salt electrolytes have been analyzed for lithium battery applications. It has been found that polymer electrolytes are safe in the sense that they are nonvolatile, less reactive, less flammable and do not leak. Poly(ethylene oxide) displays higher conductivity when combined with lithium salts than other polymer electrolytes. This polymer can solvate well a good number of salts. Particularly, poly(ethylene oxide) doped with lithium bis-(trifluoromethanesulfonyl)imide salt exhibits enhanced ionic conductivity. Poly(ethylene oxide) can also be combined with strong polymers like polystyrene to form a robust block copolymer electrolyte.

Unfortunately, little is known about solid electrolyte electrochemical stability. Solid polymer electrolyte degradation may occur in the course of charging and discharging. By-products from side reactions may consume active materials leading to low energy density and reduced battery lifespan. For this reason, Professor Daniel Hallinan Jr. and colleagues developed an electrochemical method to lessen the effects of mass transport, enabling them to determine equilibrium reaction potentials and degradation of the solid electrolyte. Their work is published in Chemical Engineering Science.

The authors prepared two and three-electrode cells in an argon glove box. The cells comprised lithium metal counter electrode, and aluminum, copper, gold or carbon electrodes. They used poly(ethylene oxide) doped with lithium bis-(trifluoromethanesulfonyl)imide electrolyte. For the three-electrode cell, the authors placed a small lithium metal strip between two electrolyte spacers. They assembled the cell with the prepared polymer electrolyte (and a reference electrode) placed between the counter and working electrodes. These cells were then sealed and taken for electrochemical analysis.

They observed that aluminum corrosion in the poly(ethylene oxide) based electrolyte with bis-(trifluoromethanesulfonyl)imide was passivated. However, this was not the case with liquid electrolyte containing bis-(trifluoromethanesulfonyl)imide and ethylene carbonate. The team also noticed no effect of salt concentration in the voltammetry analysis of copper-polystyrene–b–poly(ethylene oxide)-lithium cell. However, current was a function of temperature. The open circuit voltage of the prepared cells corresponded to Cu/Cu²⁺ stripping, but current passage in both the linear sweep voltammetry and the variable reversed linear voltammetry analyses detected Cu/Cu⁺ reaction.

The study also found that gold was not an inert electrode for anodic reaction analyses in lithium cells. Actually, gold electrode posted an anodic reaction lower that the theoretical potential. The oxidative degradation of the solid polymer electrolyte was quantified using glassy carbon electrodes and Butler–Volmer kinetics. The study concluded that oxidative degradation of the polymer electrolytes is a slow reaction with high-activation energy, making them promising candidates for use with high voltage cathodes.

“We are excited about our approach to measuring electrochemical reaction kinetics in solid electrolytes, because such measurements have not been previously performed. Our highlighted work indicates that PEO-based electrolytes should be compatible with advanced (high voltage) cathodes for lithium batteries. We are currently applying our approach to reversible reactions on lithium battery electrodes. We anticipate these results to yield insight into limitations of lithium polymer batteries and enable more accurate modeling of battery performance.” Said Professor Daniel Hallinan Jr.

About The Author

Daniel T. Hallinan Jr. received degrees in Chemical Engineering and Philosophy from Lafayette College. His doctoral research, concerning transport in polymer electrolyte membranes for fuel cells, was conducted at Drexel University under Professor Joe Elabd. As part of a collaboration during his Ph.D., he also studied transport in polymers under Professor Giulio Sarti at the University of Bologna, Italy. He did postdoctoral research in the labs of Professor Nitash Balsara at the University of California, Berkeley and Lawrence Berkeley National Lab. There he established a laboratory to make lithium batteries using block copolymers and studied lithium dendrite formation in those batteries. He is now an assistant professor of Chemical and Biomedical Engineering at the FAMU-FSU College of Engineering.

His current research at Florida State University focuses on studying structure and dynamics of nanostructured polymer materials such as block copolymers and polymer-grafted nanoparticles. His projects are focused on increasing the transport rates and the stability of polymer electrolytes for lithium battery and water purification applications.

Reference

Daniel T. Hallinan Jr.^1,2, Alexander Rausch^1,2, and Brandon McGill^1,2. An electrochemical approach to measuring oxidative stability of solid polymer electrolytes for lithium batteries. Chemical Engineering Science, volume 154 (2016), pages 34–41.

Show Affiliations

1. Florida A & M University – Florida State University College of Engineering, Chemical and Biomedical Engineering, 2525 Pottsdamer Street, Tallahassee, FL 32310, United States
2. Florida State University, Aero-propulsion, Mechatronics and Energy Center, 2003 Levy Avenue, Tallahassee, FL 32310, United States

 

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Renewable Energy Global Innovations features: Coupled electrochemical thermal modelling of a novel Lithium-ion battery pack thermal management system

Significance Statement

Thermal management systems are crucial for a lithium ion battery pack. High performance, safe operation and longer battery life can be achieved when the battery is operated within a small temperature variation around the room temperature. This demands the application of a thermal management system so as to maintain a safe temperature operation range. Air cooling is among the simplest cooling systems but drawbacks such as low thermal conductivity and low heat capacity discourages its use. This has therefore motivated the development of new liquid coolant thermal management systems for the lithium ion battery pack used mainly for vehicular propulsion.

In a recent paper published in Applied Energy, Suman Basu and colleagues presented a new coupled electrochemical thermal modelling of Lithium-ion battery pack thermal management system. Their aim was to develop an economically feasible, safe, compact and high performance thermal management system for the lithium ion battery pack mainly used in the electric vehicles.

First, the research team designed the novel liquid cooling based thermal management system for the lithium ion pack which comprised of commercially available cells in 6S5P formation (Fig. 1). The design ensured safety and compactness by thermally connecting the cells with conduction elements made of aluminum which are used to conduct the heat away. They then developed a coupled electrochemical thermal model for the battery pack and simulated it. A three-dimensional computational fluid dynamics was then developed and validated based on numerical model for the electrochemical thermal modeling of the battery pack at high accuracies. The performance of the battery pack under various arrangements and operating conditions was then investigated and reported.

Fig1: Geometry of the Li-ion battery pack and thermal management system.

They observed that the heat generation from the cells is the function of local temperature and reaction rate which had to be resolved so as to predict the thermal performance correctly. The three-dimensional electrochemical model was used to obtain a complete description of the heat generation from the battery pack system. The system also helped in validation against experimental results used to evaluate the performance of the thermal management system under various operating conditions. Thermal contact resistances at the conduction element-channel and cell-conduction element interfaces were observed to be the main hindrance to the operation of this thermal management system (Fig. 2).

Excellent agreement has been achieved between the experimental measurements and simulation predictions from the tests conducted. Application of the thermal interface material at the interfaces is seen to reduce the contact resistances and improve the heat transfer. The thermal management system is seen to cool the pack effectively even at minimal coolant flow rates. At high discharge rate and low coolant flow rate, the maximum temperature rise is kept at a small range. Therefore, this novel and compact thermal management system can work effectively under stringent conditions and is a suitable candidate for electric vehicle battery pack.

Fig 2: Temperature contours of the first set of parallel cells in the pack as a function of contact resistance at the solid-solid interfaces at 0.9 C discharge rate and 0.2 ms-1 flow velocity.

About the author

Suman Basu received his PhD from the Pennsylvania State University working in Electrochemical Engine Center with Prof. C. Y. Wang. He is working in Li-ion battery modelling and simulation project in Samsung R&D India – Bangalore. His main interests are in electrochemical energy storage system, Li-ion battery management system including thermal management and capacity fade, two-phase flow modeling and heat transfer in PEMFC. He received his bachelors and masters degree in Mechanical Engineering from Jadavpur University, Kolkata and Indian Institute of Technology, Kanpur respectively.

Reference

Suman Basu¹, Krishnan S. Hariharan¹, Subramanya Mayya Kolake¹, Taewon Song², Dong Kee Sohn², Taejung Yeo². Coupled electrochemical thermal modelling of a novel Li-ion battery pack thermal management system. Applied Energy volume 181 (2016) pages 1–13

Show Affiliations

1. Next Generation Research (SAIT-India), Samsung R&D Institute India-Bangalore, #2870 Phoenix Building, Bagmane Constellation Business Park, Outer Ring Road, Doddanekundi Circle, Marathahalli Post, Bangalore 560 037, India
2. Energy Material Lab, SAIT, Samsung Electronics, Republic of Korea

 

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Renewable Energy Global Innovations features: Assessment of the Pointing Error of Heliostats with a Single Not Polar Rotation Axis for Urban Applications

Significance Statement

In view of increasing energy efficiency with the use of renewable energy, natural daylighting incorporated into buildings has been frequently highlighted due to an achievable reduction in economic cost and greenhouse gas emissions.

Various concentration systems are needed for natural lighting devices for the provision of increased collection of light energy for buildings and urban applications. One of such natural lighting devices is heliostats, which are commonly utilized in small urban applications.

An University of Cordoba researcher team led by Professors Manuel Torres Roldan, Rafael López Luque and Marta Varo Martínez published a research paper in journal, Solar Energy, which analyzes a previously designed heliostat system on its behavior and pointing errors when it’s rotation axis is not oriented along the direction of the Earth’s polar axis.

The authors’ objective was to improve the previous designed polar heliostat system, based on Fahrenheit mechanism, which needs to be oriented towards the Earth’s rotation axis. The improvement deals with the transformation of the polar heliostat mechanism to a generic one with the aid of an automatic control of its rotational speed, thereby eliminating any form of potential architectural restrictions of buildings as a result of the need of redirection in the polar heliostats.

The developed generic heliostat was capable of reflecting the sunbeams with high precision in the desired direction when its rotational speed was controlled automatically.

Considering a fixed focus F located at a height H in the zenithal direction of a terrestrial reference system and a horizontal square plane of side 6H, an average pointing error of 0.01 rad was discovered when the generic heliostat proposed is located at any point of the 36% of the horizontal surface while the average pointing error is below 0.02 rad when the heliostat is located at the 62% of the surface.

When analyzing the behavior of the proposed generic heliostat, it was discovered from graphs of different values of mapping coefficients and angular components that as the mechanism approaches that of the polar heliostat, a better performance was achieved.

The proposed generic heliostat system with Fahrenheit mechanisms and non-polar rotational axis directions can be optimally applied in urban environments due to the achieved admissible pointing errors for smaller urban applications.

Reference

Torres-Roldán, M., López-Luque, R., Varo-Martínez, M.  Assessment of the Pointing Error of Heliostats with a Single Not Polar Rotation Axis for Urban Applications, Solar Energy 137 (2016) 281–289.

Research Group of Physics for Renewable Energies and Resources, University of Córdoba, Albert Einstein Building, Campus de Rabanales, 14071 Córdoba, Spain.

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Renewable Energy Global Innovations features: On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves

Significance Statement

Battery management systems face usually different challenging tasks. One of the most important concerns the on-board evaluation of the total battery capacity in electric and hybrid electric vehicles. This is due to the fact that the battery capacity has to be computed without necessarily discharging the battery entirely starting from a fully charged state. In fact, during the vehicle operations, the discharge process is mainly carried out in a dynamic condition under variable current rates and temperature. Selecting a method to be used in this process has poised a challenge mainly for lithium iron phosphate cells.

In a recent paper published in Journal of Power Sources, Andrea Marongiu and colleagues estimated lithium iron phosphate batteries capacity by means of half-cell curves. Their research mainly focused on developing a new approach that is based on the detection of the actual degradation mechanisms by collecting plateau information.

First, a model was developed and introduced which described the characteristics of the electrode voltage curves of the lithium iron phosphate cells and the impact of aging on the full cell voltage. A description of the main degradation mechanisms that can occur during the lifetime of the lithium iron phosphate cell and a model capable of describing the effects of degradation on the electrode and on the full cell voltage curves were presented. The research team then introduced a new battery management system structure with an implemented algorithm for on-board capacity estimation.

The results reported in the work show that not all the information from the voltage plateaus has to be collected at the same time although the collection phases have to be over short duration intervals. The new introduced algorithm is simple to parametrize, since only the characteristics of the cell in a fresh state are needed, in terms of stoichiometry and half-cell voltage curves. Eventually, both during charge and discharge the algorithm is able to correctly track the actual battery capacity with an error of approximately 1%. Also, the new proposed BMS structure is designed in a way that part of the novel methodology can run offline (not-real time). This means that the approach can be implemented in cheap microcontrollers, as it does not need to be executed in real time.

The method presented in this paper is valid for lithium iron phosphate /G cells, primarily due to the need of collecting data of plateaus, which is one of the main features of this type of cells. Nevertheless, the proposed model and the approach shown in the literature have a general formulation, which demonstrate the benefit of the tracked aging information for different lithium-ion technologies and additional application scopes.

About The Author

Andrea Marongiu received his master degree in Electrical Engineering from the Cagliari University, Italy, in 2010. In March 2011 he joined the Institute for Power Electronics and Electrical Drives (ISEA) at the RWTH Aachen University, Germany, as a research associate and PhD student.

His areas of interest were lithium-ion batteries with special focus on lithium iron phosphate-based cells, EV batteries and the related on board Battery Management System. From August 2016 to February 2017 he worked as Lead Engineer Battery Algorithm at National Electric Vehicle Sweden AB in Sweden. Since March 2017 he works as battery expert at IK4-CIDETEC in Spain, in the field of hybrid system for automotive applications.

About The Author

Dirk Uwe Sauer currently holds the title of professor for electrochemical energy conversion and storage systems at the Institute for Power Electronics and Electrical Drives (ISEA) & Institute for Power Generation and Storage Systems (PGS) at E.ON ERC RWTH Aachen University as well as Principle Investigator at Helmholtz Institute Münster Ionics in Energy Storage.

Originally, professor Sauer studied physics at University of Darmstadt, Germany, and upon graduating in 1994 became a scientist, project coordinator and head of group at Fraunhofer Institute for Solar Energy Systems ISE in Freiburg until 2003. While at the Fraunhofer Institute for Solar Energy Systems ISE, Professor Sauer headed the groups for storage systems, the interdisciplinary team for off-grid and remote power supply-systems, and was the managing director of the club for rural electrification. In 2003, he was appointed as junior professor at RWTH Aachen University, in 2009 he was appointed as professor, and in 2012 he was appointed as full professor for electrochemical energy conversion and storage systems at RWTH Aachen University. In 2010, he became a founding partner of P3 Energy & Storage, and in 2015 he became a founding partner of both BatterieIngenieure GmbH as well as eBusplan GmbH. Together with Prof. Martin Winter he is chairman of the conference “Kraftwerk Batterie / Advanced Battery Power”.

About The Author

Nsombo Nlandi has studied computer science at the RWTH Aachen University in Germany and received his master degree in 2009. In 2013 he got his second master degree in electrical engineering at the University of Hagen, Germany. From 2009 to 2016 he worked as researcher associate at the Institute for Power Electronics and Electrical Drives (ISEA), where he pursued his PhD. His research interests were mainly focused on software for battery diagnostic, namely the development of intelligent Battery Management Systems (BMS). Since August 2016 he has joined National Electric Vehicle Sweden AB (Sweden) as Lead Engineer for Embedded Systems.

About The Author

Yao RONG was born in Nanjing, China. He received his bachelor degree in Electrical Power Engineering and Automation from the Shanghai Jiao Tong University in 2007. Afterwards he studied at the RWTH Aachen University the master course of Electrical Power Engineering. During this period he wrote his master thesis at the Institute for Power Electronics and Electrical Drives (ISEA), working meanwhile a student assistant. He obtained his master degree in 2014. In 2015 he joined Jiangsu Marathon Investment Management Co., Ltd In China, where he works currently as chief research officer.

References

Andrea Marongiu^1,3, Nsombo Nlandi^1,3, Yao Rong^1,3, Dirk Uwe Sauer^1,2,3. On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves.  Journal of Power Sources volume 324 (2016) pages 158-169.

Show Affiliations

1. Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, Jägerstrasse 17/19, D-52066 Aachen, Germany
2. Institute for Power Generation and Storage Systems (PGS), E.ON ERC, RWTH Aachen University, Mathieustrasse, D-52074 Aachen, Germany
3. Jülich Aachen Research Alliance, JARA-Energy, Germany

 

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