Optimization Of Storage System Research Articles

Optimal energy storage sizing using equivalent circuit modelling for prosumer applications (Part II)

Abstract An optimal system design indirectly implies efficient use of available resources, i.e., minimum investment to achieve the desired outcome. An increased demand of energy storages highlights the importance of efficient use and optimal storage sizing. However, the variety of available and newly developed storage technologies complicates decision-making in choosing the appropriate technology to the compatible application. The characterization of storage types extends to the inherent dynamic behavior and technical limitations, which is imperative for storage system design. This paper proposes a brute-force method of optimal storage system sizing based on the equivalent circuit modeling while considering storage's operation constraints. The sizing routine is applied to a set of different energy storage technologies (lead-acid, Li-ion, vanadium-redox flow battery, double-layer capacitor, flywheel) to balance the energy demand of a single-family building supported by a 3.36 kWpeak photovoltaic system. This case focuses on the energy management application of energy storages. Additionally, a suitability index is introduced to determine the applicability of the investigated storages in reference to an ideal case.

Design optimization of hydraulic energy storage and conversion system for wave energy converters

Wave energy collected by the power take-off system of a Wave Energy Converter (WEC) is highly fluctuating due to the wave characteristics. Therefore, an energy storage system is generally needed to absorb the energy fluctuation to provide a smooth electrical energy generation. This paper focuses on the design optimization of a Hydraulic Energy Storage and Conversion (HESC) system for WECs. The structure of the HESC system and the mathematical models of its key components are presented. A case study and design example of a HESC system with appropriate control strategy is provided. The determination of the ratings of the HESC system is also investigated in order to achieve optimal system energy efficiency.

Optimization of a thermal energy storage system provided with an adsorption module – A GenOpt application in a TRNSYS/MATLAB model

The optimization and assessment study of a thermal energy adsorption storage system is presented. The system integrates an adsorption heat storage module in a conventional hot water storage tank of a solar thermal system, operating with the silica-gel/water adsorption pair. The system was modeled using TRNSYS® and MATLAB®, and was previously assessed and improved through a set of parametric tests for each main component. In this work, the GenOpt® optimization software was used to obtain the optimal performance of the whole system. It is found that a slender and lengthy adsorber with a large number of thin fins, a thick and lengthy condenser, and an evaporator with a large number of lengthy tubes improve the system’s performance, by increasing the heat transfer areas and the adsorbent mass. The performance also improves by controlling the adsorber-condenser valve only through the system’s pressure and opening the evaporator-adsorber valve at the hot water setpoint temperature. The optimized system presents a 16% saving in annual backup energy consumption compared with a similar conventional storage system, thus validating the results of the previous segregated parametric study. This optimized system operates at the highest performance with the same configuration in different locations/climates, as only the inclination of the solar collector affects the results: larger inclinations improve the system’s performance, by favoring its operation in Winter. Results present this system as a promising solution to increase the energy storage capacity of solar thermal systems, and potentially of systems using other primary energy sources.

Generation Scheduling Optimization of Wind-Energy Storage System Based on Wind Power Output Fluctuation Features

As the output from wind power generation is intermittent in nature, making the wind power output “dependable” is critical for seamless integration of wind generation. One of the most favorable solutions is incorporating energy storage system (ESS) with wind farms to establish a wind-energy storage hybrid system. Since it requires capital investment for ESS installation, it is important to estimate appropriate storage capacity and charging/discharging rate of ESS for desired applications. In this paper, the fluctuation feature of wind power output is analyzed both in time domain and frequency domain. The degree of fluctuation is extracted and illustrated as quantization index (QI). Based on QI clustering, the wind scenario with largest power fluctuation is selected as “worst performance,” according to which, scheduling time horizon, along with the capacity and charging/discharging power of ESS, can be determined. After the case study, the proposed model is proved to improve the generation scheduling process.

Hydroassets portfolio management for intraday electricity trading from a discrete time stochastic optimization perspective

Hydro storage system optimization is becoming one of the most challenging tasks in energy finance. While currently the state-of-the-art of the commercial software in the industry implements mainly linear models, we would like to introduce risk aversion and a generic utility function. At the same time, we aim to develop and implement a computational efficient algorithm, which is not affected by the curse of dimensionality and does not utilize subjective heuristics to prevent it. For the short term power market we propose a simultaneous solution for both dispatch and bidding problems. Following the Blomvall and Lindberg (Eur J Oper Res 143(2):452–461, 2002) interior point model, we set up a stochastic multiperiod optimization procedure by means of a “bushy”recombining tree that provides fast computational results. Inequality constraints are packed into the objective function by the logarithmic barrier approach and the utility function is approximated by its second order Taylor polynomial. The optimal solution for the original problem is obtained as a diagonal sequence where the first diagonal dimension is the parameter controlling the logarithmic penalty and the second one is the parameter for the Newton step in the construction of the approximated solution. Optimal intraday electricity trading and water values for hydroassets as shadow prices are computed. The algorithm is implemented in Mathematica.

Optimal design of hybrid wind/photovoltaic electrolyzer for maximum hydrogen production using imperialist competitive algorithm

The rising demand for high-density power storage systems such as hydrogen, combined with renewable power production systems, has led to the design of optimal power production and storage systems. In this study, a wind and photovoltaic (PV) hybrid electrolyzer system, which maximizes the hydrogen production for a diurnal operation of the system, is designed and simulated. The operation of the system is optimized using imperialist competitive algorithm (ICA). The objective of this optimization is to combine the PV array and wind turbine (WT) in a way that, for minimized average excess power generation, maximum hydrogen would be produced. Actual meteorological data of Miami is used for simulations. A framework of the advanced alkaline electrolyzer with the detailed electrochemical model is used. This optimal system comprises a PV module with a power of 7.9 kW and a WT module with a power of 11 kW. The rate of hydrogen production is 0.0192 mol/s; an average Faraday efficiency of 86.9 percent. The electrolyzer works with 53.7 percent of its nominal power. The availability of the wind for longer periods of time reflects the greater contribution of WT in comparison with PV towards the overall throughput of the system.

Influence of increasing numbers of RE-inverters on the power quality in the distribution grids: A PQ case study of a representative wind turbine and photovoltaic system

This paper presents the selected power quality (PQ) indicia of a wind generator and a photovoltaic installation considered to be the representative of medium voltage and low voltage distribution grids. The analysis of measured values suggests that the decrease in PQ is a case of specific combination of distributed generation, grid parameters and load behaviour. Modern generators have a limited impact on PQ. On the other hand, fluctuations in power generation are regarded as an emerging PQ indicator. The growing number of distributed renewable installations causes stochastic, variable, and hardly predictable power flows in the distribution grid. The nature of fluctuations in wind and solar generation is different. In both cases, new indexes for the quantification of fluctuations are needed and are yet not standardised. Proper assessment of these fluctuations enables definition of useful fluctuation limits and rules for optimal storage system integration.

Portfolio Management and Stochastic Optimization in Discrete Time: An Application to Intraday Electricity Trading and Water Values for Hydroassets

Hydro storage system optimization is becoming one of the most challenging task in Energy Finance. Following the Blomvall and Lindberg (2002) interior point model, we set up a stochastic multiperiod optimization procedure by means of a ''bushy'' recombining tree that provides fast computational results. Inequality constraints are packed into the objective function by the logarithmic barrier approach and the utility function is approximated by its second order Taylor polynomial. The optimal solution for the original problem is obtained as a diagonal sequence where the first diagonal dimension is the parameter controlling the logarithmic penalty and the second is the parameter for the Newton step in the construction of the approximated solution. Optimimal intraday electricity trading and water values for hydroassets are computed. The algorithm is implemented in Mathematica.

Research on Slotting Optimization of Storage System in the Provincial Measuring Center

With the development of State Grid Corporation and the expanding of storage and verification of electric energy measuring assets, efficiency plays a key role on storage system. In this paper, the slotting optimization of storage system in Measuring Center of State Grid Hunan Electric Power Corp is studied. To solve the problem of inefficient storage systems running causing by unreasonable location assignment, a scheme of applying genetic algorithm was proposed to optimize the efficiency of warehousing operation and the stability of racks A reasonable scheme of location assignment was obtained after simulation and analysis. This scheme improved the efficiency and stability of the storage system.

Multiobjective formulation of the integration of storage systems within distribution networks for improving reliability

A new approach to improve reliability in distribution networks using energy storage systems is presented in this paper. Electric utilities have been using switching devices in distribution networks mainly to improve network reliability considering sustained interruptions. Temporary interruptions have been relegated to second place. However in modern societies appliances with electronic components are becoming more sensitive to temporary interruptions. Because of this, reliability indexes like the Momentary Average Interruption Frequency Index (MAIFI) that considers temporary interruptions are receiving more attention by electric utilities. The integration of storage systems into the multiobjective planning of distribution networks is proposed in this paper, to improve the reliability index MAIFI. This approach considers the optimization of storage systems integrated in a problem with multiple objective functions. The reliability index MAIFI is the first objective function, minimized by optimally choosing the size and location of battery banks in the distribution network. The second objective function, System Average Interruption Frequency Index (SAIDI) is optimized by finding the optimal number and location of switching devices. The third objective function consists on the minimization of the equipment cost. The optimization of these conflicting functions is achieved by the use of the Non-Dominated Sorting Genetic Algorithm II (NSGA-II).

FEA and Optimization of Flywheel Energy Storage System

FEA and Optimization of Flywheel Energy Storage System

A cross-layer optimized storage system for workflow applications

This paper proposes using file system custom metadata as a bidirectional communication channel between applications and the storage middleware. This channel can be used to pass hints that enable cross-layer optimizations, an option hindered today by the ossified file-system interface. We study this approach in the context of storage system support for large-scale workflow execution systems: Our workflow-optimized storage system (WOSS), exploits application hints to provide per-file optimized operations, and exposes data location to enable location-aware scheduling. We argue that an incremental adoption path for adopting cross-layer optimizations in storage exists, present the system architecture for a workflow-optimized storage system and its integration with a workflow runtime engine, and evaluate this approach using synthetic and real applications over multiple success metrics (application runtime, generated network stress, and energy). Our performance evaluation demonstrates that this design brings sizeable performance gains. On a large scale cluster (100 nodes), compared to two production class distributed storage systems (Ceph and GlusterFS), WOSS achieves up to 6× better performance for the synthetic benchmarks and 20–40% better application-level performance gain for real applications.

Heat Transfer Characterization and Optimization of Latent Heat Thermal Storage System Using Fins for Medium Temperature Solar Applications

While solar thermal power plants are increasingly gaining attention and have demonstrated their applications, extending electricity generation after the sunset using phase change material (PCM) still remains a grand challenge. Most of the organic PCMs are known to possess high energy density per unit volume, but low thermal conductivity, that necessitates the use of thermal conductivity enhancers (TCEs) to augment heat transfer within PCM. In this paper, thermal performance and optimization of shell and tube heat exchanger-based latent heat thermal energy storage system (LHTES) using fins as TCE for medium temperature (<300 °C) organic Rankine cycle (ORC)-based solar thermal plant are presented. A commercial grade organic PCM, A164 with melting temperature of 168.7 °C is filled in the shell side and heat transfer fluid (HTF), Hytherm 600 flows through the tubes. A three-dimensional numerical model using enthalpy technique is developed to study the solidification of PCM, with and without fin. Further, the effect of geometrical parameters of fin, such as fin thickness, fin height, and number of fin on the thermal performance of LHTES, is studied. It is found that fin thickness and number of fin play significant role on the solidification process of PCM. Finally, the optimum design of the fin geometry is determined by maximizing the combined objective of HTF outlet temperature and solid fraction of PCM at the end of the discharging period. The latent heat thermal storage system with 24 fins, each of 1 mm thickness and 7 mm height, is found to be the optimum design for the given set of operating parameters.

Decentralized price-driven grid balancing via repurposed electric vehicle batteries

The share of electricity generated from intermittent renewable sources, e.g., wind and solar grows rapidly. This affects grid stability and power quality. If the share of renewable power generation is to be increased further, additional flexibilities must be introduced.Aggregating small, distributed loads and energy storage facilities is a good medium-term option. In this paper, the suitability of decentralized and on-site optimized storage system consisting of repurposed electric vehicle batteries for grid balancing is investigated. Battery operation is controlled via an optimization procedure, which relies on a one-way communicated pseudo-cost function (PCF). Day-ahead electricity stock market prices are used as the PCF.Based on one year simulations, a sequential quadratic programming (SQP) approach is compared to a dynamic programming (DP) and an integer linear programming (ILP) approach with respect to runtime and control objective. All approaches lead to very similar results, however ILP leads to the shortest runtimes. ILP is then used to investigate the grid balancing potential using last decade's hourly day-ahead prices. Higher market data resolutions featuring quarter-hours introduced in 2014 lead to higher earnings. For hourly day-ahead prices the optimal capacity-to-power ratio of the battery is approximately 6 h while for quarter-hourly prices it is about 3 h.

Performance analysis and framework optimization of open source cloud storage system

More and more embedded devices, such as mobile phones, tablet PCs and laptops, are used in every field, so huge files need to be stored or backed up into cloud storage. Optimizing the performance of cloud storage is very important for Internet development. This paper presents the performance evaluation of the open source distributed storage system, a highly available, distributed, eventually consistent object/blob store from OpenStack cloud computing components. This paper mainly focuses on the mechanism of cloud storage as well as the optimization methods to process different sized files. This work provides two major contributions through comprehensive performance evaluations. First, it provides different configurations for OpenStack Swift system and an analysis of how every component affects the performance. Second, it presents the detailed optimization methods to improve the performance in processing different sized files. The experimental results show that our method improves the performance and the structure. We give the methods to optimize the object-based cloud storage system to deploy the readily available storage system.

Optimization of a Sensible Thermal Storage System by a Lumped Approach

This study is focused on the optimization of a sensible thermal storage system subjected to a cyclic energy source. The objective is to minimize the system heat storage mass and its geometry to guarantee its operation within an admissible temperature range. The storage medium is modeled as a Lumped system and the working fluid by a non-capacitive energy balance. The storage medium is composed of an array of parallel flat plates submitted to an air stream. The optimization is based on an exhaustive search method. It is observed that the minimum heat storage mass is proportional to the mass airflow rate. An optimal relationship between the superficial heat transfer rate and the fluid flow inertia, given by the dimensionless parameter NTU, is found to be constant (4.03) and independent in respect to the mass flow rate. The system time constant was invariable (3,230 s) for the optimal relationship between the interface heat transfer rate and the system inertia.

Effect of kinetics on the thermal performance of a sorption heat storage reactor

To reach high solar fractions for solar thermal energy in the built environment, long-term heat storage is required to overcome the seasonal mismatch. A promising method for long term heat storage is to use thermochemical materials, TCMs. In this research, a lab-scale test thermochemical heat storage system is tested experimentally and modeled numerically. Water-zeolite 13X is used as the working pair in an open packed bed reactor. The purpose of this study is to understand the effects of the kinetic parameters for the adsorption of water vapor on zeolite 13X (2mm spherical beads), on the thermal performance of a sorption heat storage packed bed reactor. A mathematical model is developed incorporating the kinetics model and the isotherm curves and including the heat losses from the side wall of the reactor, and is validated by comparing the calculated temperature profiles with experimental ones from a lab-scale test setup. The numerical and experimental results are used to calculate the heat fluxes in the reactor and are compared to evaluate the thermal performance of the reactor. With the validated model, a parameter study is carried out into the effect of the reaction kinetics and the gas flow rate on thermal performance of a thermochemical heat storage reactor under full scale normal operating conditions. From this work, predictions of the thermal dynamics of an adsorption bed on reactor scale can be achieved, which can and will be used for further studies on the design and optimization of a thermochemical heat storage system.

Energy sovereignty in Italian inner areas: Off-grid renewable solutions for isolated systems and rural buildings

This paper deals with a compact system developed to assure energy independence to buildings located in inner rural areas: the Off-Grid Box. This system features a combination of techniques that assure the use of several renewable energy sources, their storage and the rationalization of consumption.This research studies the base model of the Off-Grid Box, which entails the presence of photovoltaic panels as the energy capture system.The aim of this research is to evaluate the opportunity of realizing a system to ensure energy autonomy of rural residential buildings. To achieve energy independence, for an isolated dwelling, this paper assesses the optimal storage systems that may be combined with a photovoltaic system. To this end, an Off-Grid Box has been installed in a residential unit in central Italy. Starting from the real case, two alternative energy storage scenarios were constructed. The results can be applied to a variety of geographical settings and prove the feasibility and strategic importance of total off-grid systems for individual residential units, when they are designed in integrated terms in the area to implement small-scale-smart-grids. In rural areas, these grids should also cater for small farming businesses that feature a different consumption distribution compared to dwellings.

Development of a small and flexible sensor-based respirometer for real-time determination of respiration rate, respiratory quotient and low O2 limit of fresh produce

Information on the respiration rate and the low O2 limit (LOL) is important for optimization of packaging and storage systems for fresh fruit and vegetables. In this study, a small and flexible sensor-based respirometer was developed for real-time determination of the respiration rate, respiratory quotient (RQ), and LOL of fresh produce. The respirometer consisted of a wide mouth 1-L glass jar with a screw-type metal lid and an electrochemical and an infra-red sensor mounted directly on the lid of the glass jar to take continuous and non-invasive measurements of the O2 and CO2 contents. Data from the respirometer was compared with data obtained from two fluorescence-based spot sensors (OpTech and PreSens) and a headspace gas analyzer (CheckMate). A test with strawberry showed that similar respiration rates (14.1–16.2mLO2kg−1h−1 and 13.4–16.4mLCO2kg−1h−1 at 10°C) were obtained with all instruments. Further on, a Savitzky–Golay smoothing filter was implemented on the data from the respirometer to estimate the real-time respiration rate. The result showed that the respiration rate could be acquired in 2–3h after filling of the respirometer or even after 1h if the produce was equilibrated to the target storage temperature before the measurements. Detailed information on the respiration rate of wild rocket, strawberry, and carrot showed that the respiration rate decreased with time as the O2 content decreased; however, the RQ remained almost constant throughout storage until the LOL was reached. Information on the RQ and the LOL value is rare in the literature; however, the RQ and the LOL could easily be determined by the use of the respirometer. The RQ was 1.0, 1.0–1.5, and 0.5 for wild rocket, strawberry, and carrot, respectively, during storage under an O2 content above >2.0kPa. As the O2 content dropped to 0.5, 1.0 and 2.0kPa O2, for wild rocket, strawberry, and carrot, respectively, the RQ values increased sharply. The described respirometer made it easy to analyze the impact of a dynamic temperature and O2 content on the respiration rate, the RQ, and the LOL as handling was limited and real-time data could be obtained. With such detailed information, a knowledge-intensive design of packaging and storage systems for fresh horticultural produce is enabled.

Experimental observation of polymerization from [formula omitted] to [formula omitted] in mixed-anion [formula omitted] (A = Rb+, Cs+)

It has often been suggested that reversible hydrogen storage is hampered by the formation of higher boranes MpBnHm (M = alkaline or earth alkaline metal), acting as a boron sink in the solid state during decomposition processes of the borohydride. The thermodynamic stability of these materials poses high barriers for rehydrogenation. Though assumed to be key component in storage system optimization, the ultimate proof, being the crystal structure, has never been determined on a higher borane in-situ during thermal decomposition. We herein present a case study on a double-perovskite, significantly substantiating such assumptions and providing thorough experimental evidence based on synchrotron X-ray diffraction. It is shown on the basis of thermogravimetric measurements (TGA), in-situ mass spectroscopy and ex-situ nuclear magnetic resonance (NMR) spectroscopy that the double perovskites Cs3Y(BH4)6 and Cs2LiY(BH4)6 release 2.9 mol H2 during polymerization to the inverse perovskite, Cs3BH4B12H12, containing both closo and borohydride anions. Novel phases are solved ab-initio and in-situ Raman and mass spectroscopy are employed to follow the polymerization reaction.