Renewable Energy Global Innovations features: Micromorphological changes and mechanism associated with wet ball milling of Pinus radiata substrate and consequences for saccharification at low enzyme loading

Significance Statement

In the recent article of Dr. Alankar Vaidya and colleagues from Scion which is a Crown Research Institute dedicated to improving the international competitiveness of the New Zealand forest industry. The authors describe an investigation of wet vibratory ball milling as an effective pretreatment, before the enzymatic saccharification of the most recalcitrant lignocellulosic substrates such as Pinus radiata softwood using relatively low enzyme inputs. In this study, wet ball milling mechanism is proposed (see the Figure), based on the observed micromorphological changes and changes in the cellulose crystallinity with different ball milling time. A mathematical model validates the proposed ball milling mechanism. This research work is now published in the journal, Bioresource Technology. According to the team, radiata pine wood chips obtained from a sawmill were treated with steam under pressure and then refined to produce substrate that was diluted with water prior to the ball milling.

One third of the glucan was converted to glucose at enzyme loadings as low as 2 FPU/g of dry substrate, after 60 minutes of ball milling. They attributed this rapid enzymatic conversion of cellulose exposed in fibrils torn from cell walls. They use scanning electron microscopy to characterize micromorphological changes in the substrates that were ball milled for different times. Based on the observed micromorphological changes, the cellulose present in the substrate is assigned to different categories. Carbon-13 NMR spectroscopy was also used in their study to investigate whether exposure of cellulose in the crystallites changed during the ball milling process.

Alankar A. Vaidya the first author in the paper said, ball milling performed for less than 120 min showed extensive fiber breakage and defibrillation of the broken fibers exposing more and more cellulose to enzymatic hydrolysis. However, over-milling caused compression of the porous fragments to compact globular particles with a granular texture, decreasing accessibility of enzymes to cellulose. From the carbon-13 NMR spectroscopy investigations, partial loss of interior cellulose in crystallites occur when the fiber breakage was completed. The authors found that wet ball milling performed for optimum time can provide highly digestible softwood substrate at low enzyme loadings. At a low enzyme loading of 2 FPU/g of substrate and milling time of 120 min a total monomeric sugar yield of 306 g/kg of substrate was obtained which is higher than conventional pretreatment method such as steam exploded wood.

About The Author

Dr Alankar Vaidya completed Masters in Biochemistry in 1993 and then Masters in Biotechnology from Indian Institute of Technology, Kharagpur in 1996.  His doctoral work was on Design, synthesis and evaluation of affinity polymers for separation of enzymes under the guidance of Dr R. A. Mashelkar (FRS, FNAS) in the year 2000. His entire doctoral work was protected under 4 US patents.  He went to AIST Tsukuba, Japan in 2000 on ITIT fellowship where he worked on synthesis and evaluation of stimuli sensitive polymers for nucleotide separation. Thereafter, he was awarded two separate postdoctoral fellowships first in 2002 to work on Crosslinked Imprinted Proteins (CLIP’s) in the Lab. of Prof. Lutz Fischer at University of Hohenheim, Stuttgart, Germany and thereafter he secured DARPA postdoctoral fellowship award in 2004 from DOE to work with Prof. Richard Gross at Polytechnic University of New York, Brooklyn, USA where he worked on immobilized enzyme mediated polymer synthesis.

In 2009 he joined Scion (formerly Forest Research Institute) as a Scientist working on interdisciplinary fields such as biochemical route to biofuels, forest biorefinery, microbial biopolymers and production, isolation and application of enzymes in biomass hydrolysis or biomass valorisation.  He is author of 40 + scientific international publications including 3 book chapters. He was also granted 6 US patents to his credit.   

About The Author

 

Ian Suckling received his PhD in Chemistry from the University of British Columbia in 1983. He is presently the Research Leader, Biofuels and Bioenergy at Scion and prior to this has held a number of leadership and managerial roles within Scion.

Dr. Suckling is currently the New Zealand representative on IEA Bioenergy Task 39 – Commercializing Liquid Biofuels. His research interests focus on wood and wood processing chemistry in both the biofuels and pulp and paper industries, with a particular interest in lignin. He is author of 100 + scientific publications.  

About The Author

Dr Lloyd Donaldson, senior scientist, received his Master’s degree with honours in Plant Science in 1986 from the University of Canterbury and his doctorate in Wood Science in 2002 also from the University of Canterbury, New Zealand. 

He has worked at Scion (previously the New Zealand Forest Research Institute) since 1980 as scientist on wood anatomy and wood quality. In 2003 he was elected a fellow of the International Academy of Wood Science and since 2004 has served as associate editor for the International Association of Wood Anatomists Journal. From 2007 to 2012 he was president of the New Zealand Microscopy Society, and from 2013 has been the president of the Rotorua Branch of the Royal Society of New Zealand. In 2011 he received the Charles Fleming senior scientist award, and at various times has been visiting scientist at Swedish University of Agricultural Sciences, Beijing Forestry University, Institute of Multidisciplinary Research, University of Belgrade, and INRA, Reims, France.

His main research interests include wood structure/quality/properties relationships with emphasis on lignin topo-chemistry and microfibril angle, wood formation especially lignification, developing new techniques for quantifying wood structure and properties using confocal and electron microscopy, microscopy of genetically modified tissue/plants for phenotype evaluation, microscopy of biomaterials, fluorescence & electron microscopy, molecular microscopy, digital image processing & analysis, and wood identification. He is author of 111 scientific publications including 89 journal articles and 13 book chapters. 

About The Author

John Lloyd, a scientist at Scion, received his master’s degree with honours in chemistry from the University of Auckland, New Zealand in 1971.  He has worked as a scientist in the fields of wood chemistry and wood and fibre processing since that time. His contribution to the present paper was in attrition, thermochemical pretreatment and analytical chemistry.

Wood extractives and their impact on fibre processing was his initial research interest before concentrating on research into the preparation of chemical wood pulp fibres and their processing.  During his career he has led or contributed to a large number of projects requiring both fundamental and applied research and industrial troubleshooting.  He has worked closely with pulp and paper companies in helping them understand their processes better and to improve product quality.

He is the author of more than 30 peer reviewed scientific publications as well as numerous conference papers and presentations. In recent years his research interests include exploring opportunities for wood as a source of chemicals, bio-based products and biofuels.

About The Author

Sylke Campion received her MS in Chemistry and Environmental Protection in Neustadt / Weinstrasse in Germany in 1982 and worked at the University of Munich at the Institute for Water Research for 5 years.

She joined Scion (formally known Forest Research Institute) in Rotorua, New Zealand in 1993 as a technical assistant. She started in the paper and pulp division, PAPRO, and was intensively involved with the application of enzymes in the bleaching and strengthening of wood fibre pulp. Later, as a Senior Technician, she was involved in the manufacturing and testing of fibre cement boards for five years and from 2009 she is actively participated in lignocellulosic bioethanol initiative programme where she is involved in the production of ball milled pulp samples for subsequent enzymatic hydrolysis and testing of their digestibility into simple sugars for further ethanol production.

She is author of 19 scientific peer-reviewed publications and 194 technical papers.

Journal Reference

Alankar A. Vaidya, Lloyd A. Donaldson, Roger H. Newman, Ian D. Suckling, Sylke H. Campion, John A. Lloyd, Karl D. Murton, Micromorphological Changes and Mechanism Associated with Wet Ball Milling of Pinus Radiata Substrate and Consequences for Saccharification at Low Enzyme Loading, Bioresource Technology 214 (2016) 132–137.

Scion, Te Papa Tipu Innovation Park, 49 Sala Street, Rotorua 3046, New Zealand.

 

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Renewable Energy Global Innovations features: Polymeric Ionic Liquid Gel Electrolyte for Room Temperature Lithium Battery Applications

Significance Statement

Professor Bilal El-Zahab and doctoral students, Meer Safa, Amir Chamaani, and Neha Chawla from Florida International University (FIU) developed a free-standing gel polymer electrolyte (GPE) and evaluated its thermal and electrochemical properties in order to ascertain the overall performance of their synthesis in lithium battery applications. The new findings appeared in peer-reviewed journal, Electrochimica Acta.

The gel polymer electrolyte comprised of a pyrrolidinium-based polymeric ionic liquid (PIL), an imidazolium based ionic liquid [EMIM][TFSI], and the lithium salt [LiTFSI]. They compared two electrolytes: the gel polymer electrolyte and ionic liquid electrolyte to investigate stability and compatibility with lithium metal electrode using various electrochemical characterization techniques, including electrochemical impedance spectroscopy with further determination of their rate performance in a cell with LiFePO₄ cathode at room temperature.

Thermogravimetric analyses showed the prepared gel polymer electrolyte had a high thermal stability. The pair of polymeric ionic liquid and ionic liquid inside the gel polymeric electrolyte which contains ionic liquid and lithium salt content (LiTFSI) of about 80wt.% led to an improved ionic conductivity of approximately 3.35 mS×cm^-1 when measured at 25°C using electrochemical impedance spectroscopy.

The most notable improvement using the FIU team’s new gel polymer electrolyte was its improved cathodic limit and widened electrochemical stability window. The improved cathodic limit to below the plating potential of lithium made this gel polymer electrolyte a preferred choice in Li/LiFePO₄ cells. Moreover, the gel polymer electrolyte also showed higher lithium-ion transference number compared to the ionic liquid electrolyte indicating higher chemical affinity. This affinity was demonstrated using in Li/Li symmetrical cell that immensely outperformed the ionic liquid electrolyte.

The cyclic charge-discharge rate when observed at 40 cycles and 22°C showed that the gel polymer electrolyte batteries had a higher discharge capacity at higher C-rates compared to ionic liquid cells. The authors attribute this improved performance to the improved electrochemical and interfacial stability, and the increased Lithium transference number. The gel polymer electrolyte developed by the authors is an exciting development that can serve effectively as an electrolytic conductor with other lithium-ion electrodes.

About The Author

Mr. Meer Safa is a PhD candidate in Materials Science and Engineering at Florida International University working under the supervision of Dr. El-Zahab. He received his M.S. Materials Science and Engineering from Kungliga Tekniska Högskolan (KTH) in Sweden and his B.S. degree in Materials and Metallurgical Engineering from Bangladesh University of Engineering and Technology (BUET) in Bangladesh. His research concentrates on the synthesis of ionic liquids for the development of polymer electrolyte for lithium batteries and their electrochemical investigations. 

About The Author

Mr. Amir Chamaani is a Ph.D. candidate in Materials Science and Engineering at Florida International University. He received his M.S. in Nanomaterials Engineering from the Materials and Energy Research Center (MERC) in Tehran, Iran in 2011. He served as Research at MERC working on thin film anodes for Li-ion micro-batteries. He is currently a Dissertation Year fellow working under the supervision of Dr. El-Zahab on the development of polymer electrolytes, electrochemical, and materials characterizations of Lithium battery applications, especially Li-O₂ batteries. 

About The Author

Ms. Neha Chawla is a Ph.D. candidate in Materials Science and Engineering at Florida International University. She has received her M.S. in Materials Science and Engineering from Florida International University and her B.Eng. in Production Engineering from Mumbai University in India. She is currently working towards her Ph.D. under the supervision of Dr. El-Zahab developing cathodes for improved performance of lithium-oxygen batteries. 

About The Author

Dr. Bilal El-Zahab is an Assistant Professor of Mechanical and Materials Engineering at Florida International University (2012-present). He received in Ph.D. in Chemical Engineering from the University of Akron in Ohio and was a Postdoctoral Research Associate in Analytical Chemistry at Louisiana State University (2008-2010) and a Postdoctoral Associate in Chemical Engineering at Massachusetts Institute of Technology (2010-2012). His research interests include the development of advanced materials for energy storage and bioanaylical applications.  

Journal Reference

Meer Safa, Amir Chamaani, Neha Chawla, Bilal El-Zahab. Polymeric Ionic Liquid Gel Electrolyte for Room Temperature Lithium Battery Applications, Electrochimica Acta 213 (2016) 587-593.

Mechanical and Materials Engineering Department, Florida International University, Miami, Florida 33174, USA

 

 

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Renewable Energy Global Innovations features: Lead–acid batteries coupled with photovoltaics for increased electricity self-sufficiency in households

Significance Statement

Today, the use of solar panels and energy storage in homes is a much discussed subject. As countries push for renewables and new technologies such as solar panels or electric cars become ever more accessible, it seems as if the house of the future is set to be self-sufficient, independent from the grid, feeding its inhabitants’ needs with green energy from the sun. At the Université Libre de Bruxelles, researchers have been focusing on the problematic of home energy self-sufficiency for a long time and have come up with interesting results, recently published on the Applied Energy journal under the title “Lead-acid batteries coupled with photovoltaics for increased electricity self-sufficiency in households”.

They started by crunching up-to date Belgian data from the Royal Meteorological Institute, energy suppliers and installers and then ran these numbers through their simulation models. The conclusion is that energy self-sufficiency in homes with solar panels and batteries may come with an expensive price tag and that there may be better solutions out there to go green. The problem starts with the bad timing of solar energy and energy consumption: while the sun shines at its maximum around midday, most homes consume the most in the morning and in the evening. Add to that the fact that in many countries most of the solar energy is available in the summer months and you’re set for dark times. No matter how many solar panels are added up, the maximum attainable self-sufficiency will be around 40%. The good news is that 40% self-sufficiency is achievable at prices close to the grid ones, given the recent strong reduction in the cost of solar panels and their long lifetime.

To go beyond 40% self-sufficiency, energy storage seems the natural answer. The researchers coupled the solar panels with lead-acid batteries and the results are striking: all of a sudden, the energy consumed becomes really expensive. Trying to reach a self-sufficiency of 60% can easily cost twice as much as using the grid. And the batteries’ short lifetime and high price are not the only ones to blame: installation costs and extra required electrical equipment also play an important role. The lack of a long term energy policy keeps homeowners and installers cautious, afraid to invest and bear all the risks, a problem that recently granted Belgium a public reprimand from the International Energy Agency.

The researchers also took a look at the impact on the power grid of solar panels and home energy storage and the results seem grim. Homes equipped with such systems place a greater strain on the power grid. Also, power plants will need to be able to answer to quicker variations in demand. All this will impact power grid prices, a field where research is still lacking.

Fortunately, all is not lost. The paper points out that a hybrid approach must be taken for a sustainable energy use. Using several energy sources helps to balance out each one’s disadvantages. Consumption can also be adapted through intelligent appliances that can adjust to the conditions available, as can the energy storage system work in a more intelligent way. Recent energy storage technologies, such as li-ion batteries, continue to enjoy strong price reductions while the share of electric vehicles continues to increase. The field is evolving fast and research continues but, in the meanwhile, there is no magic bullet, the best option is to keep some solar panels and continue to play along with the grid.

 

About The Author

Professor Patrick Hendrick is the Head of Aero-Thermo-Mechanics Department at ULB (Université libre de Bruxelles) in Belgium.

He is active in research fields related to renewable energy and more particularly to energy storage, with projects on battery energy storage, pumped hydro energy storage, CAES or “green” hydrogen for seasonal storage with PEMFCs

 

About The Author

Guilherme de Oliveira e Silva is a researcher at the Université Libre de Bruxelles in Belgium where he has been studying the electric power industry, namely the impact of market liberalisation and the increased share of renewable energy sources and storage. ResearchGate, LinkedIn, Google Scholar.  

Journal Reference

Guilherme de Oliveira e Silva^, , Patrick Hendrick. Lead-acid batteries coupled with photovoltaics for increased electricity self-sufficiency in households. Applied Energy, Volume 178,  2016, Pages 856–867.

Aero-Thermo-Mechanics Dept. (ATM), École Polytechnique, Université Libre de Bruxelles (ULB), Belgium.

 

 

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Renewable Energy Global Innovations features: Co-cultivation of microalgae and nitrifiers for higher biomass production and better carbon capture

Significance Statement

Dragoljub Bilanovic and colleagues investigated the co-cultivation of nitrifiers with microalgae as a non-intrusive technique for selective removal of oxygen generated by microalgae. The study is now published in peer-reviewed journal, Bioresource Technology.

According to the researchers, to tackle the challenge of climate change, processes and practices, elimination of all anthropogenic carbon emissions from CO₂ must be deployed.  Current biological, chemical and physical processes being developed for carbon capture and storage are expensive to operate even when capturing and storing carbon from concentrated CO₂ sources. Photosynthesis was found helpful in reducing CO₂ emissions and will not decrease the concentration of the atmospheric CO₂.

Microalgae will produce about 280 ton of biomass per hectare per year, which indicate that a hectare microalgal reactor will release > 500 ton CO₂ to the atmosphere per year. Microalgal photosynthesis, has been found to be an excellent-natural carbon capture and microalgae biomass.

The authors calculated the oxygen excreted by microalgae into growth medium intentionally to balance the amount of oxygen needed for full oxidation of both ammonia and nitrite to provide N-NO₃ for microalgal growth. The research team assumed composition of ammonia oxidizers and nitrite oxidizing to be the same. Nitrifying bacteria use large quantities of oxygen to convert ammonia to nitrate, to avoid unnecessary accumulation of extracellular products, generated by Chlorella and nitrifying bacteria the experiments were terminated at the end of exponential phase. The team immobilized nitrifying bacteria to know how immobilization affects growth and oxygen concentration in mixed culture of suspended C. vulgaris and immobilized nitrifiers.

They observed that a higher chlorophyll concentration, and higher microalgae biomass production in the mixed-culture, which was due to nitrifying bacteria decreasing the local concentration of photosynthetic oxygen at the surface of microalgae cells thereby improving C. vulgaris growth. The lowest chlorophyll concentration was measured in mixed-culture in which the initial [N]/[A B] ratio was 4.20 indicating that the concentration of nitrifiers was sufficient to affect the concentration of dissolved oxygen but not sufficiently high to eliminate oxygen inhibition.

A somewhat smaller chlorophyll concentration was found with immobilized nitrifiers, up to 30% smaller, than with nitrifiers grown in suspended mode. They found biomass and chlorophyll concentration to be significantly higher in cultures where the dissolved oxygen concentration was kept below 9.0μL L-1 this shows microalgae to be more sensitive to oxygen inhibition than currently thought.

The study concluded higher biomass production is the main way to reduce atmospheric CO₂. Nitrifiers was able eliminate oxygen inhibition, enabling high levels of CO₂ conversion to organic compounds via photosynthesis. The microalgae biomass production method developed in this study can be scaled up into building reactors for removal of CO₂ straight from the atmosphere.

 

Journal Reference

Dragoljub Bilanovic¹ ,Mark Holland², Jeanna Starosvetsky³, Robert Armon³, Co-Cultivation of Microalgae and Nitrifiers for Higher Biomass Production and Better Carbon Capture, Bioresource Technology 220 (2016) 282–288.

Show Affiliations

1. Center for Environmental, Earth, and Space Studies, Bemidji State University, Bemidji, MN, USA.
2. Department of Biological Sciences, Salisbury University, Salisbury, MD, USA.
3. Division of Environmental, Water, and Agriculture Engineering, Faculty of Civil and Environmental Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel.

 

 

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Renewable Energy Global Innovations features: Investigation on application and performance of emission reduction measures at a pellet boiler

Significance Statement

Several pollutants can be emitted due to the incomplete combustion of biomass fuels. Mirjam Matthes and colleagues from DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH in collaboration with Ulrich Riebel from Brandenburg University of Technology Cottbus in Germany proposed a method for the emission reduction measures at a pellet boiler. They stated that the pollutants released from biomass small-scale firing systems cause major problems. They demonstrated a two-stage emission reduction method at a multifuel pellet boiler with catalytic flue gas cleaning and an electrostatic precipitation process. The tests were carried out with wood, miscanthus and corn strip waste.

In the pellet boiler the combustion takes place in a water cooled combustion chamber out of fireclay with an automatic deashing system. The combustion is regulated by three main factors, namely fuel supply, air supply in the form of primary air and secondary air and two chimney fans, which ensure negative pressure in the combustion chamber. The emission reduction measures aim at two results, on one hand removal of particulate matter and on the other hand removal of gaseous pollutants. The measures have been integrated in a temperature zone between 420 and 670 K. The precipitation has been processed using four discharge electrodes having a wire or a band form. The electrostatic precipitator has been operated in the voltage range of 16-20 kV to ensure a steady operation and avoid flashovers. The integration of both the electrostatic precipitator and the catalyst were taking place in the heat exchange zone with a bypass construction to guarantee continuous operation even during failure of the measures. The electrostatic precipitator is connected with the heat exchanger by a flue gas pipeline. The catalyst has been a commercially available metal honeycomb with a noble metal active phase. The catalyst position has been either upstream or downstream of the precipitator.

The authors successfully demonstrated a reduction of carbon monoxide and a reduction of particulate pollutants. The catalytic reduction of carbon monoxide has been about 50 % at a process temperature of 250 °C. This temperature has been achieved during full-load operation or with a catalyst heating system. Providing a periodic maintenance, the catalyst activity has been observed for several weeks. The particle precipitation efficiency depended on the used fuel type. For wood and miscanthus an average reduction of 70-80 % has been achieved, for corn strip waste only about 60 %. The differences in the collection efficiency can be induced by different particle concentration or also different type of particles. Supplemental investigations to the effects on particle number distribution showed, that particles larger than 20-30 nm are precipitated with the used system.  

About The Author

Mirjam Matthes is a research associate at DBFZ (DBFZ Deutsches Biomasseforschungszentrum gGmbH) in Leipzig for the department Thermo-chemical Conversion since 2011. She is involved in several projects dealing with development and implementation of primary and secondary emission reduction measures for small-scale biomass combustion systems. Her graduation as engineer of energy and environmental technology took place in 2009.

Since 2013, she is a PhD student at the University of Leipzig in cooperation with the University of Applied Sciences in Leipzig working on the topic of catalyst integration in small-scale biomass combustion systems.  

About The Author

Dr. rer. nat. Ingo Hartmann studied Energy Engineering at Leipzig University of Applied Sciences (HTWK Leipzig, 1998-2002) and wrote his doctoral thesis on “Microwave-assisted catalytic oxidation“ at the University of Leipzig (2003-2007). Since 2008, he is the research group leader for Small Scale Furnace Systems in the department of Thermo-chemical Conversion at DBFZ in Leipzig. He is also the leader of the research focus area Catalytic emission control at DBFZ.  

Journal Reference

Mirjam Matthes¹, Ingo Hartmann¹ , Andreas Groll², Ulrich Riebel², Investigation on application and performance of emission reduction measures at a pellet boiler, Biomass conversion and Biorefinery, 2016, Volume 6, pages 301-313.

Show Affiliations

1. DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Thermo-chemical Conversion Department, Leipzig, Germany
2. 2.BTU Cottbus-Senftenberg, Chair of Mechanical Process Engineering, Cottbus, Germany

 

 

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Renewable Energy Global Innovations features: A novel heat exchanger concept for latent heat thermal energy storage in solar power towers: Modelling and performance comparison

Significance Statement

Solar radiation is a very important renewable resource and conversion technologies are broadly characterized as either line or point focus depending on how they convert it into solar power. Due to the cyclic nature of solar energy, there is a need for energy accumulation and efficient storage. Various research works have aimed at increasing the utilization of renewable energy options. A considerable hurdle to the successful implementation renewable technologies remains energy storage. Without storage renewable resources will never compete with other baseload technologies like coal and nuclear.

Doctor Heinrich Badenhorst from the University of Pretoria in South Africa created an innovative alternative energy storage concept for solar power towers. The research is now published in the peer-reviewed journal, Solar Energy. “The work may completely revolutionize the way thermal energy storage is done for industrial power generation” says Dr Badenhorst.

Recently latent heat storage technology is being pursued to acquire a high storage capacity. This technology is has not yet been implemented in plants, instead the salts are used in their molten form and energy is stored as sensible heat. The cost of these salts are high and they comprise a significant portion of overall plant cost. If the storage capacity of the salt can be increased by utilizing latent heat in addition to sensible, the costs can be significantly reduced for the same storage capacity.

However technical development of this approach is held back by the very low thermal conductivity of the salts, especially in solid form. This makes it very difficult to extract the stored energy using traditional heat exchanger designs. Instead a radical new concept is required which is free of the limits of conventional heat exchanger design when dealing with a solid-liquid phase transition. The study focused on the conceptual feasibility of recovering both latent and sensible heat from a liquid salt stream via granulation inside a solar power tower. Three important designs were considered: retrofitting the Gemasolar plant with the new technology, a Greenfield design and an idealized system. Tower height, steam conditions, salt composition and other operating parameters are considered in optimizing the design.

Phase change material and salt composition play significant role in the author’s suggested system. Salt choice can improve the enthalpy of fusion and sets the phase transition temperature. This in turn sets the maximum achievable steam generation temperature for turbine operation. To achieve a feasible design several operating parameters were adjusted. An energy balance approach was used to lower the amount of phase change material required.

This study combined the existing molten salt designs with the concept of a prilling tower to form solar power tower granulator. The design model explored the influence of many parameters like particle diameter and salt composition as these demonstrate operational feasibility and techno-economic viability. The introduced system in this study was found to be cost effective with 20% reduction in the overall cost of existing plants. Further optimization and implementation of Greenfields designs yield additional cost benefits, making this a very attractive option for large scale energy storage for baseload electricity generation using renewable and sustainable solar energy.

About The Author

Dr Heinrich Badenhorst: Research at the SARChI Chair for Carbon Materials is aimed at developing new functional materials for energy applications. In the Bulk Carbon research group, led by Dr Heinrich Badenhorst, the objective is to develop novel approaches to thermal energy storage.

The primary focus is on maturing graphite nano-platelet additives, derived from naturally mined graphite to improve thermal conductivity. The work includes the construction of tailor-made measuring equipment to characterise difficult substances such as phase change materials and their composites. In addition, the research aims to concurrently develop practical implementations of the new technology, for example the integration of prilling or granulation into the solar power tower design as a unique way of rapidly extracting the captured solar energy. Related efforts in the group have centred on the development of direct solar absorbers using carbon black nanospheres.

This work is currently being used to develop a solar thermal flash based sea and brackish water desalination technology. Dr Badenhorst completed his PhD at the University of Pretoria on nuclear graphite technology, where he currently teaches heat, mass and momentum transfer.

His work has been acclaimed through the international Green Talents competition, as well as the highly prestigious Meyring Naude Medal awarded by the Royal Society of South Africa.  

Journal Reference

Heinrich Badenhorst, A novel heat exchanger concept for latent heat thermal energy storage insolar power towers: Modelling and performance comparison, Solar Energy, Volume 137, 2016, Pages 90–100.

Department of Chemical Engineering, University of Pretoria, Lynnwood Road, Pretoria 0083, South Africa.

 

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Renewable Energy Global Innovations features: Pricing mechanisms design for guiding electric vehicle charging to fill load valley

Significance Statement

The increased gap between the peak load and valley load of power grids prevailing due to uncoordinated charging load of large-scale electric vehicles can be alleviated by employing proper charging pricing mechanism for electric vehicles. This helps to achieve load valley filling for the power grid. The two scenarios such as non-cooperative scenario and cooperative scenario for flattening the power load profiles are considered in the study.

Each electric vehicle in the non-cooperative scenario, possess its own charging power without any cooperation with other electric vehicles whereas in the cooperative scenario, there is an aggregator controlling all the electric vehicles together. Zechun Hu and colleagues from Tsinghua University in China proposed coordinated charging strategies by deriving appropriate conditions of the valley-filling pricing mechanisms for both the non-cooperative and cooperative scenarios.

If electric vehicles are properly controlled, they can highly reduce network losses, balance renewable energy fluctuation and bring frequency regulation. Application of load valley filling in the electric vehicle ensures low cost in power load servings. This makes electric charging load an ideal source by providing flexibilities in selecting the period of charging vehicles.

In the non-cooperative scenario, EV owners optimize their charging schedules to minimize their individual charging costs. Game theory is applied to reach Nash equilibrium in order to gain extra profits. Thus cost is minimized by changing the charging schedule unilaterally. It is proved that the price function is a strictly increasing function of the total load implies the price function is valley-filling.

Fig. 1  Load profiles (left) and valley-filling price curve (right) in the non-cooperative scenario

In the cooperative scenario, the charging processes of all electric vehicles are coordinated through an aggregator to minimize the total charging cost. The function of aggregator involves checking for newly arrived electric vehicles to be charged and updating their information such as state of charge, arrival time and expected departure time. The sufficient and necessary condition of valley-filling price is derived and proved.

Fig.2.  Load profiles (left) and three different price curves (right) in the cooperative scenario (2476 EVs).

With a proper guidance to price mechanism design, the cooperative and non-cooperative charging strategies are proposed to reduce communication burden and guarantees quick convergence. The valley-filling pricing mechanism was designed in such a way that it maximizes social benefit and minimizes load variance. It depends on the electric vehicle owners to charge their vehicles depending on the market electric price signal. A dynamic load pricing strategy is chosen to avoid heavy peak loads during high population of electric vehicles. The application of such optimization methods and strategies ensure effective load valley profile along with reduced cost.

 

Journal Reference

Zechun Hu¹, Kaiqiao Zhan², Hongcai Zhang¹, Yonghua Song¹, Pricing mechanisms design for guiding electric vehicle charging to fill load valley,  Applied Energy, Volume 178,  2016, Pages 155–163.

Show Affiliations

1. Department of Electrical Engineering, Tsinghua University, Beijing, People’s Republic of China.
2. Electric Power Research Institute, China Southern Grid, Guangzhou, People’s Republic of China.

 

 

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