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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] This paper studies the experimental and exergy analysis of solar still with the sand heat energy storage system. The cumulative yield from solar still with and without energy storage material is found to be 3.3 and 1.89 kg/m2, respectively for 8-h operation. Results show that the exergy efficiency of the system is higher with the least water depth of 0.02 m (mw = 20 kg). Competitive analysis of second law efficiency shows that the exergy efficiency improves the system by 30% than conventional single slope solar still without any heat storage. The maximum exergy efficiency with energy storage material is found as 13.2% and it is less than the conventional solar still without any material inside the basin.
[en] Full text: This paper points out one of the critical issue overlooked for fusion to become a viable energy source in the future, quantitatively analyzes the requirements, and suggests a possible solution. Future grids in possible markets and the impact of fusion introduction was analyzed with numerical model, and the limitation and requirements of the generation capacity of fusion plant is shown as the function of grid capacity, composition and stability. There are very limited opportunity of 1 GW or above for fusion in most of the emerging grids, and fusion will need smaller capacity, or better ancillary service including innovative storage. Almost all the fusion reactor designs assume large and stable electricity grids to connect and expect unlimited large pulsed power supply for starting plants. Unlike in the grids in the countries where fusion research is currently pursued, majority of the future grids where fusion would be deployed are anticipated to be significantly different. Even in the large grids in advanced countries, future system will be rather unstable because of the larger renewable fraction and trends to free electricity markets. Majority of the electric grids in the world will be still far smaller than 50 GW at the middle of this century, where introduction of fusion electricity over 1 GW would be difficult. This paper analyzes the impact of fusion electricity on small size grids. Fusion plants requires large electricity for startup, and in the case of disruption or other unexpected shut down, loss of electricity in a short time would disturb the stability of the grids. The authors established a simplified Heffron–Philips model constructed in Matlab/Simulink™. This model analyzes quantitative impacts of fusion on a given grid size and composition, and provides limits and requirements for fusion to be installed. This concept suggests the possibility of faster and easier introduction of fusion energy in the future, with reduced difficulty and with larger and more attractive market possibility. Majority of sales of fusion, if it would be viable, is in the developing countries rather than the mature markets where growth is not expected, and thus encompassing such a business model could justify the investment for fusion development. (author)
[en] Understanding charge carrier transport in Na2O2, being one of the possible storage materials in the non-aqueous Na–O2 battery, is key to the development of this type of energy storage system. The electronic and dynamic properties of Na2O2 are expected to greatly influence the overall performance and reversibility of the discharge process. Thus far experimental studies on this topic are rare. To measure the extremely low conductivities setups with sufficiently high sensitivity are needed. Here we studied the partial electronic conductivity σ eon of nanocrystalline Na2O2 by potentiostatic polarization measurements which we carried out at room temperature. σ eon turned out to be in the order of 8.8 × 10−14 S cm−1; with a very poor total conductivity of σ total = 17 × 10−14 S cm−1 we obtained σ total/ σ eon ≈ 2 clearly showing that ionic transport of Na ions is strongly coupled to electronic dynamics. (paper)
[en] The inclusion of solar thermal energy into energy systems requires storage possibilities to overcome the gap between supply and demand. Storage of thermal energy with closed sorption thermal energy systems has the advantage of low thermal losses and high energy density. However, the efficiency of these systems needs yet to be increased to become competitive on the market. In this paper, the so-called “charge boost technology” is developed and tested via experiments as a new concept for the efficiency increase of compact thermal energy storages. The main benefit of the charge boost technology is that it can reach a defined state of charge for sorption thermal energy storages at lower temperature levels than classic pure desorption processes. Experiments are conducted to provide a proof of principle for this concept. The results show that the charge boost technology does function as predicted and is a viable option for further improvement of sorption thermal energy storages. Subsequently, a new process application is developed by the author with strong focus on the utilization of the advantages of the charge boost technology over conventional desorption processes. After completion of the conceptual design, the theoretical calculations are validated via experiments. (paper)
[en] Concentrating solar power plants represent low cost and efficient solutions for renewable electricity production only if adequate thermal energy storage systems are included. Metal hydride thermal energy storage systems have demonstrated the potential to achieve very high volumetric energy densities, high exergetic efficiencies, and low costs. The current work analyzes the technical feasibility and the performance of a storage system based on the high temperature Mg2FeH6 hydride coupled with the low temperature Na3AlH6 hydride. To accomplish this, a detailed transport model has been set up and the coupled metal hydride system has been simulated based on a laboratory scale experimental configuration. Proper kinetics expressions have been developed and included in the model to replicate the absorption and desorption process in the high temperature and low temperature hydride materials. The system showed adequate hydrogen transfer between the two metal hydrides, with almost complete charging and discharging, during both thermal energy storage and thermal energy release. The system operating temperatures varied from 450°C to 500°C, with hydrogen pressures between 30 bar and 70 bar. This makes the thermal energy storage system a suitable candidate for pairing with a solar driven steam power plant. The model results, obtained for the selected experimental configuration, showed an actual thermal energy storage system volumetric energy density of about 132 kWh/m3, which is more than 5 times the U.S. Department of Energy SunShot target (25 kWh/m3).
[en] Energy systems are meaningful devices which are based on basic laws of physics to take energy at one end and transform it into another form with optimum efficiency. Scientists, engineers always strive to make systems more efficient and lighter. This motive acts as driving force to bring about new technologies, materials and alternative approaches. Nanofluids are that kind of materials which have revolutionized energy absorbing, transporting and storage systems. Various parameters which are cardinal in thermal performance enhancement are drastically modified when material changes into nanoform. These parameters are thermal conductivity, heat transfer coefficient, optical extinction coefficient, electrical conductivity, viscosity, density, metallic property. When materials changes its phase from bulk to nano, surface to volume ratio changes tremendously. In our experimental analysis we have chosen nanofluids (MgO+CNTs)/H2O Hybrid for evaluating performance of and flat plate solar collector for exergy efficiency, entropy generation and thermal efficiency. Exergy efficiency indicates how system is efficient to convert available energy into useful work. We have gone through preparation of nanofluid along with characterization. Experimental analysis established that at 1% volume concentration and the flow rate 21/min exergetic efficiency (second law efficiency) for (MgO+CNTs)/H2O nanofluid is enhanced by ∼28 % compare to water, ∼13% compare to MgO. Entropy generation rate, which is penalty increases insignificantly at lower concentration for MgO hybrid compare to MgO. But enhancement in exergy efficiency dominates over increment in entropy generation rate. We can conclude that nanofluid based energy transporting systems are more efficient in terms of performance and energy saving. (author)
[en] The charging rates of commercial high-energy Li-ion cells are limited by the manufacturer's specifications leading to lengthy charging times. However, these cells are typically capable of much faster charging, if one ensures that the thermal and electrode-specific voltage profiles do not exceed safety limits. Unfortunately, precise and in-situ measurements of these parameters have not been achieved to date without altering the operation of these cells. Here we present a method to assess the maximum current for commercial 18650s, using novel instrumentation methods enabling in operando measurements. We found the maximum charging current that could be safely applied to the evaluated high-energy cells is 6.7 times higher than the manufacturer-stated maximum. Subsequently a rapid-charging protocol was developed that leads to over five-fold reduction in charging times without compromising the safety limits of the cells. We anticipate our work to be a starting point for a more sophisticated understanding of commercial Li-ion cells through deployment of diverse in-situ sensor systems. This understanding will enable advances in battery materials science, thermal engineering and electrical engineering of battery technology. Furthermore, this work has the potential to help the design of energy storage systems for high performance applications such as motor racing and grid balancing.