Joint Optimal Design and Operation of Hybrid Energy Storage Systems

The wide range of performance characteristics of storage technologies motivates the use of a hybrid energy storage systems (HESS) that combines the best features of multiple technologies. However, HESS design is complex, in that it involves the choice of storage technologies, the sizing of each storage element, and deciding when to charge and discharge each underlying storage element (the operating strategy.We formulate the problem of jointly optimizing the sizing and the operating strategy of an HESS that can be used for a large class of applications and storage technologies. Instead of a single set of storage element sizes, our approach determines the Pareto-optimal frontier of the sizes of the storage elements along with the corresponding optimal operating strategy. Thus, as long as the performance objective of a storage application (such as an off-grid microgrid) can be expressed as a linear combination of the underlying storage sizes, the optimal vector of storage sizes falls somewhere on this frontier. We present two case studies to illustrate our approach, demonstrating that a single storage technology is sometimes inadequate to meet application requirements, unlike an HESS designed using our approach. We also find simple, near-optimal, and practical operating strategies for these case studies, which allows us to gain several new engineering insights

Peak Forecasting for Battery-based Energy Optimizations in Campus Microgrids

Battery-based energy storage has emerged as an enabling technology for a variety of grid energy optimizations, such as peak shaving and cost arbitrage. A key component of battery-driven peak shaving optimizations is peak forecasting, which predicts the hours of the day that see the greatest demand. While there has been significant prior work on load forecasting, we argue that the problem of predicting periods where the demand peaks for individual consumers or micro-grids is more challenging than forecasting load at a grid scale. We propose a new model for peak forecasting, based on deep learning, that predicts the k hours of each day with the highest and lowest demand. We evaluate our approach using a two year trace from a real micro-grid of 156 buildings and show that it outperforms the state of the art load forecasting techniques adapted for peak predictions by 11-32%. When used for battery-based peak shaving, our model yields annual savings of $496,320 for a 4 MWhr battery for this micro-grid.Comment: 5 pages. 4 figures, This paper will appear in the Proceedings of ACM International Conference on Future Energy Systems (e-Energy'20), June 202

Techno-economic analysis of storage degradation effect on levelised cost of hybrid energy storage systems

Abstract: The inclusion of storage systems in renewable-based energy systems is a promising option to boost the reliability of power supply for offgrid communities. A major consideration is the cost and performance of the selected storage system. This study investigates different energy storage combinations to form a hybrid energy storage system (HESS). The goal is to exploit the complementary characteristics of each storage system. The effects of system degradation on energy output and replacement costs over a 20-year period are analysed and used in obtaining the Levelised Cost of Hybrid Energy Storage Systems (LCOHESS); which can be used as a basis for comparing the techno-economic benefits of different HESS configurations. The model is run with data for a community in the Northern Cape Province, South Africa, to show the best HESS option that could be deployed by rural electrification planners and investors, based on the value of LCOHESS obtained

Smart management strategies of utility-scale energy storage systems in power networks

Power systems are presently experiencing a period of rapid change driven by various interrelated issues, e.g., integration of renewables, demand management, power congestion, power quality requirements, and frequency regulation. Although the deployment of Energy Storage Systems (ESSs) has been shown to provide effective solutions to many of these issues, misplacement or non-optimal sizing of these systems can adversely affect network performance. This present research has revealed some novel working strategies for optimal allocation and sizing of utility-scale ESSs to address some important issues of power networks at both distribution and transmission levels. The optimization strategies employed for ESS placement and sizing successfully improved the following aspects of power systems: performance and power quality of the distribution networks investigated, the frequency response of the transmission networks studied, and facilitation of the integration of renewable generation (wind and solar). This present research provides effective solutions to some real power industry problems including minimizationof voltage deviation, power losses, peak demand, flickering, and frequency deviation as well as rate of change of frequency (ROCOF). Detailed simulation results suggest that ESS allocation using both uniform and non-uniform ESS sizing approaches is useful for improving distribution network performance as well as power quality. Regarding performance parameters, voltage profile improvement, real and reactive power losses, and line loading are considered, while voltage deviation and flickers are taken into account as power quality parameters. Further, the study shows that the PQ injection-based ESS placement strategy performs better than the P injection-based approach (in relation to performance improvement), providing more reactive power compensations. The simulation results also demonstrate that obtaining the power size of a battery ESS (MVA) is a sensible approach for frequency support. Hence, an appropriate sizing of grid-scale ESSs including tuning of parameters Kp and Tip (active part of the PQ controller) assist in improving the frequency response by providing necessary active power. Overall, the proposed ESS allocation and sizing approaches can underpin a transition plan from the current power grid to a future one

Multifunktionaler Einsatz von Batteriespeichern in elektrischen Verteilnetzen: Optimale Auslegung und Betrieb

Der zunehmende Bedarf an Flexibilisierungsmöglichkeiten des elektrischen Energiesystems ist als direkte Folge des strukturellen Systemwandels zu sehen. Veränderungen in allen drei Bereichen des Stromnetzes (Erzeugung, Verbrauch, Transport) führen zu einer wachsenden Volatilität des Energieflusses, welche durch geeignete Maßnahmen aufgefangen werden muss. Während netzbasierte Energieüberschüsse vor allem durch Netzausbau und konventionelle Netzführung ausgeglichen werden können, verlangen marktbasierte Überschüsse mit zunehmendem Volatilitätsgrad in der Erzeugung nach Möglichkeiten der zeitlichen Verschiebung. Die Nutzung neuartiger Energiespeichertechnologien, wie Batteriespeichersysteme, ist einerseits notwendig auf Grund des fehlenden Ausbaupotentials konventioneller Pumpspeicher, aber andererseits auch mit Unsicherheiten angesichts fehlender Betriebserfahrungen im großtechnischen Einsatz und den aktuell noch hohen Investitionskosten verbunden. Die vorliegende Arbeit betrachtet den Einsatz von Batterieenergiespeichern (BES) im elektrischen Verteilnetz und ist dabei in die komplexe Auslegung und Betrieb unter jeweils verschiedenen Optimierungszielen aufgeteilt. Dies beginnt mit der Analyse der regulatorischen Rahmenbedingungen und der darauf aufbauenden Betrachtung potentieller Anwendungsfälle. Durch die Kombination unterschiedlicher Modellierungsansätze auf Zellund Batteriesystemebene wurde anschließend die Grundlage für die Bewertung ausgewählter Anwendungsfälle aus verschiedenen Gebieten sowie deren möglicher Kombination mit Zusatzanwendungen geschaffen. Des Weiteren wurde mit Hilfe eines modifizierten Zyklenzählverfahrens sowie einer auf Messwerten basierenden Wichtung entsprechend der Zyklierungstiefe ein Modell zur Nachbildung der Alterungseffekte für BES konzipiert und umgesetzt. Die Szenarien werden hinsichtlich Wirtschaftlichkeit unter Beachtung der genannten Aspekte bewertet. Die theoretischen Analysen werden anschließend im Vergleich zu einem realen Feldtest unter Nutzung einer 1 MW / 0,5 MWh-Referenzanlage betrachtet und der Speichereinsatz bewertet. Abschließend wird ein Ansatz zur Bestimmung eines online BES-Zustandsindizes, welcher auf einfachen Betriebsdaten beruht und weder zusätzliche Messdaten benötigt, noch den laufenden Betrieb beeinflusst, vorgestellt

Green Mobile Networks: from self-sustainability to enhanced interaction with the Smart Grid

Nowadays, the staggering increase of the mobile traffic is leading to the deployment of denser and denser cellular access networks, hence Mobile Operators are facing huge operational cost due to power supply. Therefore, several research efforts are devoted to make mobile networks more energy efficient, with the twofold objective of reducing costs and improving sustainability. To this aim, Resource on Demand (RoD) strategies are often implemented in Mobile Networks to reduce the energy consumption, by dynamically adapting the available radio resources to the varying user demand. In addition, renewable energy sources are widely adopted to power base stations (BSs), making the mobile network more independent from the electric grid. At the same time, the Smart Grid (SG) paradigm is deeply changing the energy market, envisioning an active interaction between the grid and its customers. Demand Response (DR) policies are extensively deployed by the utility operator, with the purpose of coping with the mismatches between electricity demand and supply. The SG operator may enforce its users to shift their demand from high peak to low peak periods, by providing monetary incentives, in order to leverage the energy demand profiles. In this scenario, Mobile Operators can play a central role, since they can significantly contribute to DR objectives by dynamically modulating their demand in accordance with the SG requests, thus obtaining important electricity cost reductions. The contribution of this thesis consists in investigating various critical issues raised by the introduction of photovoltaic (PV) panels to power the BSs and to enhance the interaction with the Smart Grid, with the main objectives of making the mobile access network more independent from the grid and reducing the energy bill. When PV panels are employed to power mobile networks, simple and reliable Renewable Energy (RE) production models are needed to facilitate the system design and dimensioning, also in view of the intermittent nature of solar energy production. A simple stochastic model is hence proposed, where RE production is represented by a shape function multiplied by a random variable, characterized by a location dependent mean value and a variance. Our model results representative of RE production in locations with low intra-day weather variability. Simulations reveal also the relevance of RE production variability: for fixed mean production, higher values of the variance imply a reduced BS self-sufficiency, and larger PV panels are hence required. Moreover, properly designed models are required to accurately represent the complex operation of a mobile access network powered by renewable energy sources and equipped with some storage to harvest energy for future usage, where electric loads vary with the traffic demand, and some interaction with the Smart Grid can be envisioned. In this work various stochastic models based on discrete time Markov chains are designed, each featuring different characteristics, which depend on the various aspects of the system operation they aim to examine. We also analyze the effects of quantization of the parameters defined in these models, i.e. time, weather, and energy storage, when they are applied for power system dimensioning. Proper settings allowing to build an accurate model are derived for time granularity, discretization of the weather conditions, and energy storage quantization. Clearly, the introduction of RE to power mobile networks entails a proper system dimensioning, in order to balance the solar energy intermittent production, the traffic demand variability and the need for service continuity. This study investigates via simulation the RE system dimensioning in a mobile access network, trading off energy self-sufficiency targets and cost and feasibility constraints. In addition, to overcome the computational complexity and long computational time of simulation or optimization methods typically used to dimension the system, a simple analytical formula is derived, based on a Markovian model, for properly sizing a renewable system in a green mobile network, based on the local RE production average profile and variability, in order to guarantee the satisfaction of a target maximum value of the storage depletion probability. Furthermore, in a green mobile network scenario, Mobile Operators are encouraged to deploy strategies allowing to further increase the energy efficiency and reduce costs. This study aims at analyzing the impact of RoD strategies on energy saving and cost reduction in green mobile networks. Up to almost 40% of energy can be saved when RoD is applied under proper configuration settings, with a higher impact observed in traffic scenarios in which there is a better match between communication service demand and RE production. While a feasible PV panel and storage dimensioning can be achieved only with high costs and large powering systems, by slightly relaxing the constraint on self-sustainability it is possible to significantly reduce the size of the required PV panels, up to more than 40%, along with a reduction in the corresponding capital and operational expenditures. Finally, the introduction of RE in mobile networks contributes to give mobile operators the opportunity of becoming prominent stakeholders in the Smart Grid environment. In relation to the integration of the green network in a DR framework, this study proposes different energy management policies aiming at enhancing the interaction of the mobile network with the SG, both in terms of energy bill reduction and increased capability of providing ancillary services. Besides combining the possible presence of a local RE system with the application of RoD strategies, the proposed energy management strategies envision the implementation of WiFi offloading (WO) techniques in order to better react to the SG requests. Indeed, some of the mobile traffic can be migrated to neighbor Access Points (APs), in order to accomplish the requests of decreasing the consumption from the grid. The scenario is investigated either through a Markovian model or via simulation. Our results show that these energy management policies are highly effective in reducing the operational cost by up to more than 100% under proper setting of operational parameters, even providing positive revenues. In addition, WO alone results more effective than RoD in enhancing the capability to provide ancillary services even in absence of RE, raising the probability of accomplishing requests of increasing the grid consumption up to almost 75% in our scenario, twice the value obtained under RoD. Our results confirm that a good (in terms of energy bill reduction) energy management strategy does not operate by reducing the total grid consumption, but by timely increasing or decreasing the grid consumption when required by the SG. This work shows that the introduction of RE sources is an effective and feasible solution to power mobile networks, and it opens the way to new interesting scenarios, where Mobile Network Operators can profitably interact with the Smart Grid to obtain mutual benefits, although this definitely requires the integration of suitable energy management strategies into the communication infrastructure management

A peer-to-peer exchange framework for microgrids to improve economic and resilient operation

Ph. D. ThesisPeer-to-peer (P2P) exchange is an emerging approach in smart grids which enables users to share their energy production or storage surplus or the flexibility of their demand with other end-users. This provides benefits to both energy producers and consumers. In this work, a P2P exchange framework methodology is developed. It relies on a Time-of-Use (ToU) tariff scheme to value the benefit in time-shifting demand to low cost / low carbon periods. Two groups of stakeholders are considered, the local distribution network operator (DNO) and the microgrid (MG) users. Energy trading follows three principles: First, energy sharing occurs by using the storage and renewable assets of the microgrid. Second, P2P exchange is enabled during the high-tariff period and third, it is based on cooperation to achieve mutual benefits for the DNO and the MG users. The stakeholders share the cost and benefits of P2P energy trading. The main steps of the developed methodology include a battery sizing process, user categorization and priority order, zoning and optimum battery discharging. The electrical limits of transformer and storage inverter power are considered in the process. The developed methodology investigates the benefits gained by the DNO and MG users. Benefits are examined in terms of economic benefits for the stakeholders (profits), system resilience in case of faults, carbon emissions reduction and energy storage lifetime increase. Case studies are used to illustrate the capabilities of the methodology in determining the expected performance of a P2P scheme under a range of conditions and geographical locations. The results show that this method of P2P exchange will have significantly different impacts depending upon the local conditions for demand, generation, resilience standards and tariff structure.Enzen Global Solutions Lt

Aportaciones al dimensionamiento y gestión de energía de un tren de potencia eléctrico híbrido para vehículos industriales con ciclos de conducción repetitivos y agresivos

Currently, the interest for helping mitigate the emission of greenhouse gases caused by high fuel consumption in industrial vehicles has increased. In order to the reduction of fuel consumption in an industrial vehicle, it has been proposed to incorporate into the powertrain a system capable of storing and supplying electrical energy. Consequently, the design of a hybrid electric powertrain is required, based on the interconnection of the elements (topology), the sizing of the elements and/or the energy management strategy of the powertrain. This paper presents a methodology for the design of a hybrid electric vehicle for refuse collection, which presents a repetitive and aggressive drive cycle as a result of work activity. The proposed methodology consists in modeling the behavior of a hybrid electric powertrain, considering the electrical behavior of various energy accumulation elements (batteries and supercapacitors). An embedded system is used to perform the experimental characterization of a cell and a commercial supercapacitor, in order to approximate the behavior through an electric model. In accordance with a real drive cycle of a refuse collection vehicle, the energy demand for a hybrid electric refuse collection vehicle is determined. On the other hand, the fuel consumption is calculated from a hybrid electric powertrain that integrates an energy storage system or a hybrid energy storage system. A bio-inspired metaheuristic based on a stochastic population (particle swarm optimization and genetic algorithm) is developed, in order to determine an optimal solutions space. Subsequently, the optimal sizing of an energy storage system (batteries) and a hybrid energy storage system (batteries and supercapacitors) is performed, considering different mono-objective and multi-objective optimization problems. Based on the results of each optimization problem, a comparative analysis is carried out with an element of commercial accumulation. Considering a hybrid electric powertrain that integrates a hybrid energy storage system (batteries and supercapacitors), an energy management strategy based on fuzzy logic is developed. This includes the identification of the vehicle status from a real drive cycle. Finally, the validation of the energy management strategy is carried out through the model of a hybrid electric vehicle for refuse collection.Actualmente, se ha incrementado el interés por mitigar la emisión de gases de efecto invernadero que se produce por un elevado consumo de combustible en vehículos industriales. Con la intención de contribuir en la reducción del consumo de combustible de un vehículo industrial, se ha propuesto incorporar al tren de potencia un sistema capaz de almacenar y suministrar energía eléctrica. En consecuencia, surge la necesidad de realizar el diseño de un tren de potencia eléctrico híbrido, a partir de la interconexión de los elementos (topología), el dimensionamiento de los elementos y/o la estrategia de gestión de energía del tren de potencia. En el presente trabajo se presenta una metodología para realizar el diseño de un vehículo eléctrico híbrido de recolección de basura, que presenta un ciclo de conducción repetitivo y agresivo como resultado de la actividad laboral. La metodología propuesta consiste en modelar el comportamiento de un tren de potencia eléctrico híbrido, considerando el comportamiento eléctrico de diversos elementos de acumulación de energía híbrido (baterías y supercapacitores). Se emplea un sistema embebido para realizar la caracterización experimental de una celda y un supercapacitor comercial, con el propósito de aproximar el comportamiento a través de un modelo eléctrico. En función de un ciclo de conducción real de un vehículo de recolección de basura se determina la demanda de energía para un vehículo eléctrico híbrido de recolección de basura. Por otra parte, se calcula el consumo de combustible a partir de un tren de potencia eléctrico híbrido que integra un sistema de almacenamiento de energía o un sistema de almacenamiento de energía híbrido. Se desarrolla una metaheurística bio-inspirada basada en una población estocástica) para determinar un espacio de soluciones óptimas. Posteriormente, se realiza el dimensionamiento óptimo de un sistema de almacenamiento de energía (baterías) y un sistema de almacenamiento de energía híbrido (baterías y supercapacitores), considerando diferentes problemas de optimización mono-objetivo y multi-objetivo. Con base en los resultados de cada problema de optimización, se procede a realizar un análisis comparativo con un elemento de acumulación comercial. Considerando un tren de potencia eléctrico híbrido que integra un sistema de almacenamiento de energía híbrido (baterías y supercapacitores), se desarrolla una estrategia de gestión de energía basada en lógica difusa, que incluye la identificación del estado del vehículo a partir de un ciclo de conducción real. Finalmente, se realiza la validación de la estrategia de gestión de energía a través del modelo de un vehículo eléctrico híbrido de recolección de basura.Postprint (published version

Aportaciones al dimensionamiento y gestión de energía de un tren de potencia eléctrico híbrido para vehículos industriales con ciclos de conducción repetitivos y agresivos

Currently, the interest for helping mitigate the emission of greenhouse gases caused by high fuel consumption in industrial vehicles has increased. In order to the reduction of fuel consumption in an industrial vehicle, it has been proposed to incorporate into the powertrain a system capable of storing and supplying electrical energy. Consequently, the design of a hybrid electric powertrain is required, based on the interconnection of the elements (topology), the sizing of the elements and/or the energy management strategy of the powertrain. This paper presents a methodology for the design of a hybrid electric vehicle for refuse collection, which presents a repetitive and aggressive drive cycle as a result of work activity. The proposed methodology consists in modeling the behavior of a hybrid electric powertrain, considering the electrical behavior of various energy accumulation elements (batteries and supercapacitors). An embedded system is used to perform the experimental characterization of a cell and a commercial supercapacitor, in order to approximate the behavior through an electric model. In accordance with a real drive cycle of a refuse collection vehicle, the energy demand for a hybrid electric refuse collection vehicle is determined. On the other hand, the fuel consumption is calculated from a hybrid electric powertrain that integrates an energy storage system or a hybrid energy storage system. A bio-inspired metaheuristic based on a stochastic population (particle swarm optimization and genetic algorithm) is developed, in order to determine an optimal solutions space. Subsequently, the optimal sizing of an energy storage system (batteries) and a hybrid energy storage system (batteries and supercapacitors) is performed, considering different mono-objective and multi-objective optimization problems. Based on the results of each optimization problem, a comparative analysis is carried out with an element of commercial accumulation. Considering a hybrid electric powertrain that integrates a hybrid energy storage system (batteries and supercapacitors), an energy management strategy based on fuzzy logic is developed. This includes the identification of the vehicle status from a real drive cycle. Finally, the validation of the energy management strategy is carried out through the model of a hybrid electric vehicle for refuse collection.Actualmente, se ha incrementado el interés por mitigar la emisión de gases de efecto invernadero que se produce por un elevado consumo de combustible en vehículos industriales. Con la intención de contribuir en la reducción del consumo de combustible de un vehículo industrial, se ha propuesto incorporar al tren de potencia un sistema capaz de almacenar y suministrar energía eléctrica. En consecuencia, surge la necesidad de realizar el diseño de un tren de potencia eléctrico híbrido, a partir de la interconexión de los elementos (topología), el dimensionamiento de los elementos y/o la estrategia de gestión de energía del tren de potencia. En el presente trabajo se presenta una metodología para realizar el diseño de un vehículo eléctrico híbrido de recolección de basura, que presenta un ciclo de conducción repetitivo y agresivo como resultado de la actividad laboral. La metodología propuesta consiste en modelar el comportamiento de un tren de potencia eléctrico híbrido, considerando el comportamiento eléctrico de diversos elementos de acumulación de energía híbrido (baterías y supercapacitores). Se emplea un sistema embebido para realizar la caracterización experimental de una celda y un supercapacitor comercial, con el propósito de aproximar el comportamiento a través de un modelo eléctrico. En función de un ciclo de conducción real de un vehículo de recolección de basura se determina la demanda de energía para un vehículo eléctrico híbrido de recolección de basura. Por otra parte, se calcula el consumo de combustible a partir de un tren de potencia eléctrico híbrido que integra un sistema de almacenamiento de energía o un sistema de almacenamiento de energía híbrido. Se desarrolla una metaheurística bio-inspirada basada en una población estocástica) para determinar un espacio de soluciones óptimas. Posteriormente, se realiza el dimensionamiento óptimo de un sistema de almacenamiento de energía (baterías) y un sistema de almacenamiento de energía híbrido (baterías y supercapacitores), considerando diferentes problemas de optimización mono-objetivo y multi-objetivo. Con base en los resultados de cada problema de optimización, se procede a realizar un análisis comparativo con un elemento de acumulación comercial. Considerando un tren de potencia eléctrico híbrido que integra un sistema de almacenamiento de energía híbrido (baterías y supercapacitores), se desarrolla una estrategia de gestión de energía basada en lógica difusa, que incluye la identificación del estado del vehículo a partir de un ciclo de conducción real. Finalmente, se realiza la validación de la estrategia de gestión de energía a través del modelo de un vehículo eléctrico híbrido de recolección de basura