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[en] Highlights: • A single energy storage can always be split into two hybrid energy storages. • These hybrid storages have the same total energy and power as the single storage. • The potential for storage hybridisation depends on the shape of the power profile. • A higher potential allows a higher spread of the power/energy-ratios of the storages. • Automobile and pulsed power applications are well suited for storage hybridisation. - Abstract: Aim of a storage hybridisation is a beneficial usage or combination of different storage technologies with various characteristics to downsize the overall system, decrease the costs or to increase the lifetime, system efficiency or performance. In this paper, the point of interest is a different ratio of power to energy (specific power) of two storages to create a hybrid energy storage system (HESS) with a resulting specific power that better matches the requirements of the application. The approach enables a downsizing of the overall system compared to a single storage system and consequently decreases costs. The paper presents a theoretical and analytical benchmark calculation that determines the maximum achievable hybridisation, i.e. possible spread in specific power, while retaining the original total energy and power capacities of an equivalent single storage system. The theory is independent from technology, topology, control strategy, and application and provides a unified view on hybrid energy storage systems. It serves as a pre-dimensioning tool and first step within a larger design process. Furthermore, it presents a general approach to choose storage combinations and to characterize the potential of an application for hybridisation. In this context, a Hybridisation Diagram is proposed and integral Hybridisation Parameters are introduced.
[en] Highlights: • An optimal planning model for DESSs in SOP-based active distribution networks is proposed. • The power flow controllability of SOP is modeled and optimally coordinated with DESS operation. • Inverter-based DG reactive power capability and short-term network reconfiguration at the hourly timescale are incorporated in the planning. • The proposed DESS planning model is formulated as a computationally efficient MISOCP problem. - Abstract: The integration of high-penetration distributed generators (DGs) with smart inverters and the emerging power electronics technology of soft open points provide increased controllability and flexibility to the operation of active distribution networks. Existing works on distributed energy storage planning have not fully considered the coordinated operation of these new power electronic devices with distributed energy storage systems, leading to less economic investment decisions. This paper proposes an optimal planning model of distributed energy storage systems in active distribution networks incorporating soft open points and reactive power capability of DGs. The reactive power capability of DG inverters and on load tap changers are considered in the Volt/VAR control. Moreover, soft open points are modeled to provide flexible active and reactive power control on the associated feeders. Hourly network reconfiguration is conducted to optimize the power flow by changing the network topology. A mixed-integer second-order cone programming model is formulated to optimally determine the locations and energy/power capacities of distributed energy storage systems. Finally, the effectiveness of the proposed model is validated on a modified IEEE 33-node distribution network. Considering soft open points, DG reactive power capability, and network reconfiguration, the results demonstrate the optimal distributed energy storage systems planning obtained by the proposed model achieves better economic solution.
[en] Highlights: • An automated search for reaction systems suitable for thermochemical energy storage was performed. • Algorithm to build reaction systems for thermochemical energy storage is presented. • Close to 1000 possible reaction systems for 5 different reactive gases were found. • The VIENNA TCES-database for thermochemical energy storage materials is presented. - Abstract: Thermochemical energy storage (TCES) is considered as an emerging green technology for increased energy utilization efficiency, thereby achieving a reduction of greenhouse gases. Various reaction systems based on different substance classes (e.g. hydrates, hydroxides, oxides) were suggested and investigated so far. Nevertheless, the number of know reactions which are suitable is still limited, as the main focus concentrates on the investigation of a handful known substances, their further improvement or applicability. To find novel promising candidates for thermochemical energy storage and also to allow for a broader view on the topic, this work present a systematic search approach for thermochemical storage reactions based on chemical databases. A mathematical search algorithm identifies potential reactions categorized by the reactant necessary for the reaction cycle and ranked by storage density. These candidates are listed in the online available VIENNA TCES-database, combined with experimental results, assessing the suitability of these reactions regarding of e.g. decomposition/recombination temperature, reversibility, cycle stability, etc.
[en] Highlights: • Novel analysis of unique building with integrated pumped hydro energy storage system. • Full parameterisation of pumped hydro energy storage in buildings. • Feasibility of pumped hydro energy storage in buildings is studied. • Conditions for a better competitiveness of this technology are discussed. - Abstract: The growing use of variable energy sources is pushing the need for energy storage. With Pumped Hydro Energy Storage (PHES) representing most of the world’s energy storage installed capacity and given its maturity and simplicity, the question stands as to whether this technology could be used on a smaller scale, namely in buildings. In this paper, the feasibility of such an installation is analysed by modelling each one of its components and applying it to several installation scenarios. Proposed and existing installations are also reviewed, including a first-time analysis of an installation in France, which is presumably the only existing building with an integrated PHES system. It was found that the economies of scale that render large PHES installations competitive are not present in small installations. This limitation, associated to other important disadvantages, such as the large volume required, seem to point out PHES as an ill-suited solution for energy storage in buildings, an important finding for building design and energy policy. Nevertheless, if synergies with existing reservoirs could be found (for example for a building on a riverside), costs could be significantly lowered. Further research on possible synergies with other building systems as well as a life-cycle assessment analysis are recommended.
[en] Highlights: • Sharing economy as new business model for Energy Storage Operators. • More attractiveness of Battery Storage Systems. • Optimal Dimensioning of Battery Storage Systems for sharing economy application. - Abstract: Energy storage systems (ESS) are the candidate solution to integrate the high amount of electric power generated by volatile renewable energy sources into the electric grid. However, even though the investment costs of some ESS technologies have decreased over the last few years, few business models seem to be attractive for investors. In most of these models, ESS are applied only for one use case, such as primary control reserve. In this study, a business model based on the sharing economy principle has been developed and analyzed. In this model, the energy storage operator offers its storage system to different kinds of customers. Each customer uses the ESS for their single use case. A set of different use cases has been identified to make the operation of the ESS profitable (e.g. peak shaving, self-consumption and day-ahead market participation). Different kinds of stationary batteries (lithium-ion, sodium-sulfur and vanadium redox-flow) have been considered as energy storage technologies, which differ both in their investment costs and their technical properties, such as round-trip efficiency. The simulation of the business model developed showed that a sharing economy-based model may increase the profitability of operating a battery storage system compared to the single use case business model. Additionally, larger battery dimensions regarding power and capacity were found to be profitable and resulted in an increased revenue stream.
[en] Highlights: • We present a MILP to co-optimize generation, transmission, and storage investments. • We find significant value in co-optimized storage via investment deferrals. • Operational savings from bulk services are small relative to investment deferrals. • Co-optimized energy storage significantly reduces prices associated with RPS. - Abstract: Worldwide, environmental regulations such as Renewable Portfolio Standards (RPSs) are being broadly adopted to promote renewable energy investments. With corresponding increases in renewable energy deployments, there is growing interest in grid-scale energy storage systems (ESS) to provide the flexibility needed to efficiently deliver renewable power to consumers. Our contribution in this paper is to introduce a unified generation, transmission, and bulk ESS expansion planning model subject to an RPS constraint, formulated as a two-stage stochastic mixed-integer linear program (MILP) optimization model, which we then use to study the impact of co-optimization and evaluate the economic interaction between investments in these three asset classes in achieving high renewable penetrations. We present numerical case studies using the 24-bus IEEE RTS-96 test system considering wind and solar as available renewable energy resources, and demonstrate that up to $180 million/yr in total cost savings can result from the co-optimization of all three assets, relative to a situation in which no ESS investment options are available. Surprisingly, we find that co-optimized bulk ESS investments provide significant economic value through investment deferrals in transmission and generation capacity, but very little savings in operational cost. Finally, we observe that planning transmission and generation infrastructure first and later optimizing ESS investments—as is common in industry—captures at most 1.7% ($3 million/yr) of the savings that result from co-optimizing all assets simultaneously.
[en] Highlights: • An analytical methodology for the optimal sizing of energy storage is proposed. • Different analytical approximations are discussed and compared. • A general procedure is identified which takes into account various storage technologies and scenarios. • A parametric approach allows identifying the strategy for energy and cost savings. • The methodology is verified through numerical applications on an actual test network. - Abstract: In this paper, an analytical approach that deals with the optimal sizing of energy storage systems in direct current networks is proposed. In modern power systems, the widespread use of power electronics, storage devices, and automation is driving power engineers to focus on the use of direct current networks. This new focus requires specific tools for the optimal planning and operation of these networks in order to increase energy efficiency and reduce operating costs. This paper is focused on the improvements in the efficiencies of direct current networks, which are characterized by the presence of loads, units for the generation of renewable power, and storage devices. Based on the calculus of variations, an original matrix formulation which starts with the nodal representation of the direct current network is proposed. Two attractive closed-form solutions are presented for minimizing power losses, i.e., (1) a solution based on the approximation of considering the voltage constant at all the network’s busses and (2) a solution based on the linear approximation of the load flow. In both cases, the goal is to minimize losses over a given time horizon (e.g., the daily cycle). The formulation of the problem allows an analytical solution to be obtained that represents a suitable tool for the purpose of designing storage. In addition, the proposed approach can be applied and extended to the optimal sizing of storage systems. The proposed sizing procedure, which uses an analytical approach, is formulated in a general manner that can be used for various storage technologies. The results of numerical applications clearly have demonstrated both the feasibility and accuracy of the methodology to be used in the proposed design. We also propose an interesting parametric study in order to determine the optimal technology and the optimal size of the storage device.
[en] Highlights: • Renewable HPS for the train start-up within feeding durations. • Dynamic modelling of the modern HPS applied to traction systems. • Port-Controlled Hamiltonian (PCH) design for supercapacitors’ charge/discharge operation. • Experimental validation and applicability of HPSs for energy management in eco-tractions. - Abstract: Electrochemical capacitors, called supercapacitors (SCs) or ultracapacitors, are devices conveniently used for embedded electrical energy management owing to their huge capacitance, low internal resistance and flexible control through power electronic conversion. This paper proposes a main power supply of hybrid Wind Generator (WG)–SC within the train station for feeding the traction onboard SC through specified limited feeding transit durations. Onboard SCs provide the train with the requested start–up self–energy. The hybrid WG–SCs system is an environmental–friendly source that enables the independency on national grid and guarantees an efficient bidirectional power transfer for energy management with enhanced dynamic performance. Therefore, the dynamic modelling and the experimental analysis of the modern hybrid WG–SCs used for managing the charge/discharge operation of SCs at Unity Power Factor (UPF) mode are presented. For this purpose, the Port–Controlled Hamiltonian (PCH) methodology is deduced and explicitly presented. Simulation results, via MATLAB™, reveal that the proposed PCH control methodology can be successfully implemented to ensure acceptable system dynamic behavior. Numerical results are validated with experimental measurements to investigate the significance of the PCH approach for the energy management operation in eco-tractions.
[en] Highlights: • Proposes an advanced microgrid interface based on MMC and energy storage system for multiple microgrids. • Proposes a novel architecture for multiple microgrids with hybrid AC/DC connection. • Proposes different control schemes for multiple microgrids under various operation conditions. • The large-scale integration of distributed renewable energies in multiple microgrids is enhanced. • The optimal use of distributed generators in multiple microgrids is realized. - Abstract: Microgrid provides an effective approach to utilize distributed renewable energies (DREs). Given the ongoing transformation of distribution system with high penetration of DREs, coordinating and consuming a large amount of distributed generators (DGs) within one single microgrid has become increasingly infeasible. Interconnecting multiple microgrids as a microgrid cluster is an effective way to improve the operation quality of large-scale DG integration. As the keys to the microgrid clusters, the flexible configurations and coordinated operation among multiple microgrids have not been adequately addressed. In order to solve this problem, a novel architecture for multiple microgrids and its coordinated control schemes are designed. Firstly, the advanced microgrid interface named hybrid unit of common coupling (HUCC) is designed and utilized in replacement of the conventional point of common coupling (PCC). The HUCC employs modular multilevel converter (MMC) as its core component and provides both AC and DC interfaces. Then, this paper puts forward a HUCC-based architecture for multiple microgrids where microgrids are grid-connected via the AC interfaces and interconnected via the DC interfaces. Based on the proposed architecture, coordinated control schemes under different operation scenarios are came up with at last. A case study of the HUCC-based multiple microgrids is performed in PSCAD/EMTDC on the basis of the demonstration project in Guangxi, China. The simulation results show that the interconnected microgrids with the proposed architecture and control schemes operates effectively and efficiently under different operation scenarios. The proposed architecture and control schemes not only enhance the large-scale integration of DREs, but realize the optimal use of DGs as well.
[en] Highlights: • A DSM minimizes both nodal operational cost and network power losses is proposed. • Uncertainties in distribution grids are captured with stochastic programming. • An ADMM based distributed method is applied for scalability and privacy preserving. - Abstract: The trending integrations of Battery Energy Storage System (BESS, stationary battery) and Electric Vehicles (EV, mobile battery) to distribution grids call for advanced Demand Side Management (DSM) technique that addresses the scalability concerns of the system and stochastic availabilities of EVs. Towards this goal, a stochastic DSM is proposed to capture the uncertainties in EVs. Numerical approximation is then used to make the problem tractable. To accelerate the computational speed, the proposed DSM is tightly relaxed to a convex form using second-order cone programming. Furthermore, in light of the continuous increasing problem size, a distributed method with a guaranteed convergence is applied to shift the centralized computational burden to distributed controllers. To verify the proposed DSM, real-life EV data collected on UCLA campus is used to test the proposed DSM in an IEEE benchmark test system. Numerical results demonstrate the correctness and merits of the proposed approach.