Under 2011 började MacBat AB ta fram ett elenergilager kallat Macbat Energy Storage System (MESS), vilket är uppbyggt av 360 stycken tvåvolts bly-syrabatterier inhysta i ett 20 fots container. Då bly-syrabatterier är känsliga för värme är den här studien inriktad på att utreda hur stort kylbehovet blir under olika förutsättningar där kyldistribution, drifttemperatur på batterierna, klimat, isolering och termiska tröghet är varierande parameterar. Det ska även avgöras vilken konfiguration av kyldistribution och isolering som ger lägst kylbehov för de studerade klimaten, vilka är av varmtempererad, arid och tropisk karaktär. För att besvara studiens två mål togs fyra matematiska modeller fram i SIMULINK. Två luftkylda och två vattenkylda där en av varje var isolerad med 100 mm mineralull medan den andra var oisolerad. För samtliga modeller varierades drifttemperaturen mellan 25 – 35 °C och de studerade klimaten utgjordes av Phnom Phen, Kambodja, Djibouti, Djibouti, Bagdad, Irak samt London, England. För de vattenkylda modellerna varierades även MESS termiska tröghet i spannet 1,8058 – 9,0288 MJ/K genom att öka mängden kylvatten i systemet som användes för att kyla batterierna. Batteriernas drifttemperatur visade sig vara den parameter som i högst grad avgör kylbehovets storlek. Isoleringen gav en reducerande effekt på kylbehovet i de fall då omgivningstemperaturen under längre perioder överstiger batteriernas drifttemperatur. Varierande termisk tröghet, i de vattenkylda modellerna, hade liten eller ingen inverkan på kylbehovet. Det beror förmodligen på att den termiska massa som konstant finns i batterierna i form av elektrolyt var betydligt större. I fråga om vilken konfiguration av distributionssystem och isolering som ska användas för att erhålla ett lågt kylbehov visade sig detta bero på klimatet och drifttemperaturen på batterierna. Varmtemperade klimat som London behöver dock inget kylsystem överhuvudtaget. / In 2011 MacBat AB began to develop a electrical energy storage system called Macbat Energy Storage System (MESS), which is made up of 360 two volt lead acid batteries housed in a 20 foot container. However, while lead acid batteries are sensitive to heat this study is focused on investigating how great a cooling demand will be required under different conditions in which chilled distribution, operating temperature of the batteries, climate, insulation and thermal inertia are varied parameters. The study will also determine the configuration of chilled distribution and isolation that gives minimum cooling requirements for the studied climates, which is warm temperate, arid and tropical nature To answer the study's two goals four mathematical models were developed in SIMULINK. Two air-cooled and two water-cooled where one of each was insulated with 100 mm mineral wool while the other was bare. For all models the operating temperature varied between 25 - 35 ° C and the studied climates consisted of Phnom Penh, Cambodia, Djibouti, Djibouti, Baghdad, Iraq, and London, England. For the water cooled models thermal inertia was also varied in the range of 1.8058 to 9.0288 MJ/ K by increasing the amount of cooling water in the system used to cool the batteries. The battery operating temperature was proven to have the most significant impact on the cooling load. The isolation yielded a reducing effect on the cooling load in the case where the ambient temperature surpassed the battery operating temperature during longer periods. Varying thermal inertia of the water cooled models had little or no impact on the cooling load. It is probably due to the electrolyte in the batteries. It is a considerably larger source of thermal mass and is constant in all the models. Which configuration, regarding the distribution system and insulation, that obtains a low cooling requirement was found to depend on the ambient climate and the battery operating temperature. However, warm temperate climates such as London requires no cooling system at all.

Higher penetration of volatile renewable sources and increasing load demand are putting a strain on the current utility grid structure. Energy storage solutions are required to maintain grid stability and are vital components to future smart grid designs. Flywheel energy storage can be a strong part of the solution due to high cycle life capabilities and flexible design configurations that balance power and energy capacity. This dissertation focuses on developing design methodologies for advanced flywheel energy storage, with an emphasis on sizing flywheel energy storage and developing lumped parameter modeling techniques for low loss, high temperature superconducting. The first contribution of this dissertation presents a method for using an optimal control law to size flywheel energy storage and develops a design space for potential power and energy storage combinations. This method is a data driven technique, that utilizes power consumption and renewable generation data from a particular location where the storage may be placed. The model for this sizing technique includes the spinning losses, that are unique to flywheel energy storage systems and have limited this technology to short term storage applications, such as frequency and voltage regulation. For longer term storage solutions, the spinning losses for flywheels must be significantly reduced. One potential solution is to use high temperature superconducting bearings, that work by the stable levitation of permanent magnet materials over bulk superconductors. These advanced bearing systems can reduce losses to less than 0.1% stored energy per hour. In order to integrate high temperature superconducting bearings into flywheel system designs, accurate and reduced order models are needed, that include the losses and emulate the hysteretic, non-linear behavior of superconducting levitation. The next two contributions of this dissertation present a lumped parameter axissymmetric model and a 3-D lumped parameter transverse model, which can be used to evaluate bearing lifting capabilities and transverse stiffness for flywheel rotor designs. These models greatly reduce computational time, and were validated against high level finite element analysis, and dynamic experimental tests. The validation experiments are described in detail. / text

abstract: This thesis addresses the issue of making an economic case for energy storage in power systems. Bulk energy storage has often been suggested for large scale electric power systems in order to levelize load; store energy when it is inexpensive and discharge energy when it is expensive; potentially defer transmission and generation expansion; and provide for generation reserve margins. As renewable energy resource penetration increases, the uncertainty and variability of wind and solar may be alleviated by bulk energy storage technologies. The quadratic programming function in MATLAB is used to simulate an economic dispatch that includes energy storage. A program is created that utilizes quadratic programming to analyze various cases using a 2010 summer peak load from the Arizona transmission system, part of the Western Electricity Coordinating Council (WECC). The MATLAB program is used first to test the Arizona test bed with a low level of energy storage to study how the storage power limit effects several optimization out-puts such as the system wide operating costs. Very high levels of energy storage are then added to see how high level energy storage affects peak shaving, load factor, and other system applications. Finally, various constraint relaxations are made to analyze why the applications tested eventually approach a constant value. This research illustrates the use of energy storage which helps minimize the system wide generator operating cost by "shaving" energy off of the peak demand. / Dissertation/Thesis / M.S. Electrical Engineering 2013

The continuous escalation of intermittent energy added to the grid and forecasts of peaking power demand increments are rising the effort spent for evaluating the economic feasibility of energy storages. The aim of this research is the techno-economic analysis of Compressed Air Energy Storage (CAES) systems, capable of storing large quantities of off-peak electric energy in the form of high-pressure air, as an ―energy stock‖ which allows the production of high-profit on-peak electricity when required by the grid. Several studies of both conventional and innovative adiabatic concepts are carried out in order to identify and improve the parameters that mostly affect the plant performances. Technical models, that consider the effect of time, are developed to evaluate the parameters that reduce the electric energy spent for compressing the air and that maximize the electric energy produced. In the conventional plant, particular attention is put on the understanding of the effects of air storage pressure range, recuperator, reheating and Turbine Inlet Temperature. For the adiabatic instead, a thorough analysis of the challenging Thermal Energy Storage (TES) is performed for understanding the advantages and drawbacks of this novel efficient concept of CAES. In a further step the economic analyses are aimed at evaluating the different configurations proposed in the technical investigation and the effects that variations of generation train and storage characteristics have on the profitability. After an analysis of the TES impact on the profits, a final comparison is carried out against two existing technologies: Pumped Hydro Energy Storage and gas turbine. The results of these studies confirm, from a technical and economic point of view, the reasons of the growing interest toward CAES as a feasible solution to manage the intermittent energy production. In particular they underline the conventional CAES as promising technology to undertake.

In the last decade, the power generation mix and the energy markets have been affected by the growing development of distributed and renewable energy sources.Nevertheless, a significant drawback of solar and wind energy is their intermittent and weather-dependent production, which often leads to a mismatch between renewable energy production and its use. Thus, the need for energy storage is recently emerging and becoming more relevant in this era of the energy transition. Among several technologies, today, pumped hydro energy storage (PHES) represents the largest share of the energy storage systems in the world. However, possible new investors, who might be attracted by potential profit in PHES, are repelled bythe long payback period and the scarcity of adequate site topology for such power plants. Relevant design decisions can be taken to reduce the costs and improve the performance or to escape the PHES topographical requirements. For this reason, the first part of this PhD thesis reviews and provides potential assessments of some unconventional PHES systems, applied in synergy with existing infrastructures. Such is the standpoint of micro facilities near waterway locks, or underground cavities used as lower reservoirs (UPSH), or the use of pump-turbines at variable geometryto cope with fluctuating loads.Moreover, important information on PHES in micro-scale is largely missing and their potential in distributed energy systems still needs to be unveiled. In the attempt to fill this gap, this thesis provides a techno-economic overview of the design and characterization of a first-of-its-kind PHES micro facility. In micro-scales hydropower projects, the initial capital cost of a conventional hydroelectric unit is hard to be determined and often economically prohibitive. Interestingly, in order to cut the total capital investment, the micro-PHES prototype runs with a single centrifugal pump for both pumping and generating phases and exploits existing stormwater reservoirs. The variable speed regulation is also implemented and it allows the pump to constantly operate at the maximum hydraulic efficiency in order to deal with load variations. In the same way, the pump working in reverse, namely pump as turbine (PaT), runs at the most suitable speed and it keeps a high efficiency over a wide load range. In addition, the analysis of the techno-economic parameters for such a system provides an important dataset for micro-PHES feasibility breakdown.PaTs are a legitimate cost-effective option in micro hydropower but an universal performance prediction does not exist. Their hydraulic efficiency can possibly shift from the higher efficiency of traditional hydraulic turbines. Nowadays, these reasons restrict PaTs exploitation. In this thesis, a multivariate regression method is applied to the CFD results to build a surrogate model of the PaT hydraulic characteristics as a function of the cutwater geometrical modifications. Based on this model, an optimization problem is solved to identify the most advantageous geometrical assetof the PaT cutwater to maximize the hydraulic efficiency. The presented methodology and design optimization of the cutwater in PaTs, which are extremely suited to our current energy generation needs, provides a unique and much-sought guide to its performance, improvements, and adaptation to hydropower. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Shifting the load demand of a commercial office space to utilise off peak tariffs would lead to cost savings as power is cheaper at this time. To achieve this shift, chemical energy storage was considered using Lead Acid batteries, Lithium-ion batteries and Advance Lead Acid batteries. The output of these storage types is electricity. Current costs of storage do not support the option of reducing peak demand by adding chemical storage, as electricity from the grid is cheaper over the storage project life. A levelised cost analysis was completed and lithium-ion batteries proved to be the outright best choice for chemical storage in commercial office spaces. Town buildings were analysed and assessed for energy savings in order to reduce overall load demand. Incorporating chemical storage as a viable option was assessed based on cost. Heating, Cooling and lighting proved to be the highest load demands in the buildings. Cost savings in buildings can be better met by increasing the efficiency in buildings, rather than by reducing the cost by shifting the purchase of electricity from peak to off-peak tariffs. More suitable options to chemical energy storage would be to replace standard lights with energy efficient variations, installing an air heat pump to heat the space and ice thermal storage to cool the space. The use of a solar thermosyphon will meet the demand for heated water. Solar energy generation was assessed as an alternative as off-peak electricity stored using chemical storage proved to be too costly. A 50kW system would be suitably sized when peak sun hours were above the local areas average. Net metering could be used to offset costs during the winter months, when the peak sun hours fall below the average.

With the increase in the world energy demand and environmental incentives, renewable energy sources (RES) need to determine their place as some of the primary power sources in future power systems. However, due to uncertain energy production, renewable energy sources cause unbalance in the power system due to the unsynchronized supply and electricity demand. The intermittent power production causes undesired power fluctuation, affecting the power quality and reliability of the power source. Energy storage is one solution that is debated to increase the reliability of renewable energy production. This thesis aims to model and simulate hybrid energy storage system (HESS), constructed of hydrogen and ultracapacitor energy storage, to investigate different operation strategies for everyday use and crises. The two different energy storage technologies complement each other, where hydrogen fuel cells can produce power for long periods of time while the ultracapacitor can quickly maintain the balance of production and consumption of electricity for a short instance. The HESS showed promising results for emergency power supply and supported service operation strategies. In case of a power shortage, the HESS could cover for the disconnected production. The ultracapacitor proved to be a suitable component due to its ability to support the shortcomings of a hydrogen energy storage system. Moreover, the HESS could meet the requirements to deliver support services. However, further studies have to be done to investigate how the HESS can deliver multiple support services to increase profit and help maintain the power system's balance and security.

This study investigates Compressed Air Energy Storage (CAES) application in the electrical power and transportation industries. Information concerning current CAES projects is presented. A thorough thermodynamic analysis of the CAES process is completed; including theoretical efficiency determination for several variants of the compression and expansion processes. Industry claimed efficiencies ranging from 26% to 82% are presented and explained. Isothermal and Isentropic efficiency baselines are developed. Energy density of compressed air on both a mass and volume basis is compared to other energy storage methods. Best expected efficiency of a hypothetical CAES system is determined to be 34% using currently achievable efficiencies and 63% considering 100% efficient compression and expansion. A .5 kW CAES system, built from commercial off the shelf components (COTS) to demonstrate the CAES concept, is documented and discussed. This system includes a LabView data acquisition system which was used to record all test results. LabView was also used to develop a complete test bed program that determined real time thermodynamic state properties, component efficiencies, mass flow rates, power outputs and several other performance characteristics of the demonstration system. The LabView program allowed real time efficiency and power optimization of the demonstration system. Results of demonstration system testing are thoroughly discussed. Total system efficiency was very poor; 3.6% electrical conversion efficiency, .040 refrigeration coefficient of performance (COP) and a 5.0% overall efficiency which considers both cooling and electrical storage properties. Several paths for possible future projects involving the demonstration system and CAES are presented.

Thermal energy storage (TES) systems based on renewable energy sources (concentrated solar, wind, and photovoltaic etc.) are crucial to reducing dependence on conventional energy generation systems and reducing renewable energy’s intermittent nature. TES can be utilized in conjunction with concentrated solar power (CSP) in particle-based power cycles where the particles can be charged (heat addition) using solar energy and then discharged (heat extraction) using particle-based heat exchangers (HX). Efficient particle based HXs are vital in coupling heat transfer fluid (HTF) from thermal receivers to power cycle working fluid (WF). Heat transfer enhancement is essential for adopting particle-based moving packed-bed heat exchangers (MPBHXs) in next-generation TES systems, as MPBHXs usually exhibit low particle bed-to-wall heat transfer coefficients and total heat transfer rate. This dissertation focuses on addressing the limitations of MPBHXs by computationally studying the heat transfer performance enhancement due to granular flows in metal foam-based MPBHXs and reactive flow-based MPBHXs. Comprehensive multidimensional, multiscale, and multiphysics models are developed to predict the TES/TCES (Thermochemical energy storage) performance accurately. First, the flow properties through metal foams are determined, followed by granular flow through metal foam-based particle-to-sCO2 HXs to predict the heat transfer enhancement. Then, granular flows with reactive and sensible heat-only particles are studied in particle-to-sCO2 HXs to predict the heat transfer enhancement, followed by the development of discrete element models (DEM) in inclined moving bed granular flows to study particle-scale heat and mass transfer. Overall, this study provides valuable insights into effective modeling of granular flows from continuum to discrete scales and improved design and operation of particle-based heat exchangers and thermochemical reactors.

Continued emission of green house gases has energized research activity worldwide to develop efficient ways to harness renewal energy. The availability of large scale energy storage technologies is essential to make renewal energy a reliable source of energy. Redox flow batteries show potential in this direction. These batteries typically need expensive membranes which need replacement be-cause of fouling. The recently proposed soluble lead redox flow battery (SLRFB), in which lead ions deposit on electrodes in charge cycle and dissolve back in discharge cycle, can potentially cut down the cost of energy storage by eliminating membrane. A number of challenges need to be overcome though. Low cycleability, residue formation, and low efficiencies are foremost among these, all of which require an understanding of the underlying mechanisms. A model of laminar flow-through SLRFB is first developed to understand buildup of residue on electrodes with continued cycling. The model accounts for spatially and temporally growing concentration boundary layers on electrodes in a self consistent manner by permitting local deposition/dissolution rates to be controlled by local ion transport and reaction conditions. The model suggests controlling role for charge transfer reaction on electrodes (anode in particular) and movement of ions in the bulk and concentration boundary layers. The non-uniform current density on electrodes emerges as key to formation of bare patches, steep decrease in voltage marking the end of discharge cycle, and residue buildup with continuing cycles. The model captures the experimental observations very well, and points to improved operational efficiency and decreased residue build up with cylindrical electrodes and alternating flow direction of recirculation. The underlying mechanism for more than an order of magnitude increase in cycle life of a beaker cell battery with increase in stirrer speed is unraveled next. Our experiments show that charging with and without stirring occurs identically, which brings up the hitherto unknown but quite strong role of natural convection in SLRFB. The role of stirring is determined to be dislodgement/disintegration of residue building up on electrodes. The depletion of active material from electrolyte due to residue formation is offset by “internal regeneration mechanism”, unraveled in the present work. When the rate of residue formation, rate of dislodging/disintegration from electrode, and rate of regeneration of active material in bulk of the electrolyte becomes equal, perpetual operation of SLRFB is expected. The identification of strong role of free convection in battery is put to use to demonstrate a battery that requires stirring/mixing only intermittently, during open circuit stages between charge and discharge cycles when no current is drawn. Inspired by our experimental finding that the measured currents for apparently diffusion limited situations (no external flow) are far larger than the maxi-mum possible theoretical value, the earlier model is modified to account for natural convection driven by concentration gradient of lead ions in electrolyte. The model reveals the presence of strong natural convection in battery. The induced flow in the vicinity of the electrodes enhances mass transport rates substantially, to the extent that even in the absence of external flow, normal charge/discharge of battery is predicted. The model predicted electrochemical characteristics are verified quantitatively through voltage-time measurements. The formation of flow circulation loops driven by electrode processes is validated qualitatively through PIV measurements. Natural convection is predicted to play a significant role in the presence of external flow as well. The hitherto unexplained finding in the literature on insensitivity of charge-discharge characteristics to electrolyte flow rate is captured by the model when mixed mode of convection is invoked. Flow reversal and wavy flow are predicted when natural convection and forced convection act in opposite directions in the battery. The effect of the presence of non-conducting material (PbO on anode) on the performance of SLRFB is studied using a simplified approach in the model. The study reveals the presence of charge coup de fouet phenomenon in charge cycle. The phenomenon as well as the predicted effect of depth of discharge on the magnitude of charge coup de fouet are confirmed experimentally.