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[en] Phase change material (PCM) can store large amount of thermal energy at phase change temperature. Determination of thermophysical properties of PCM plays an important role in estimation of energy stored or released in storage device. Properties of PCM are key factors for designing a latent heat thermal energy storage system. This paper deals with the study of effect of heating/cooling rate on thermophysical properties, especially on melting temperature and latent heat of fusion /solidification. Results indicate that latent heat of fusion has more dependence on heating/cooling rate than onset, peak and end temperature. (author)
[en] Highlights: • A complete set of contributions by storage in reducing system costs is analyzed. • A stochastic form of SCOPF identifies costs caused by wind variability. • Storage saves reserve cost by 48% in 2020 wind level by reducing wind variability. • Storage lowers generation cost by 2.1% in 2020 wind level by adopting more wind. • The benefit of storage capacity become larger with higher wind generation capacity. - Abstract: With the rapid increase in variable renewable sources in the power system, storage capacity is being considered as an effective solution, because its flexible charging-discharging characteristics enable the reduction of the variability of these sources. However, the value of energy storage has been estimated mostly based on arbitrage benefit, and this does not reflect the true contribution of energy storage to the power system, especially when it is integrated with high levels of wind generation. This study analyzes a more complete set of contributions made by energy storage toward reducing the total cost of supplying electricity to customers. A simulation based on a stochastic form of multi-period Security-Constrained Optimal Power Flow (SCOPF) is used to reflect the stochastic characteristics of wind resources. The results show that in addition to the arbitrage benefit, energy storage can generate an additional economic value by 1) reducing the variability of wind generation; 2) adopting more wind generation that is otherwise wasted because of high variability, and 3) lowering the peak capacity needed to meet system adequacy. Moreover, the results indicate that the benefit of energy storage is larger with higher wind generation capacity.
[en] A facile greener approach was adopted to synthesized the metal sulphide and its composite with carbon quantum dots for high performance supercapacitor application. Metal sulphides and oxides are providing high energy storage capacity due to the involvement of redox reactions in the energy storage process compared with carbonaceous materials where electrochemical double layer is primarily responsible for energy storage. The reversibility of the cycle has been optimized in the potential range from 0 V to 0.75V. The NiS/ C-dots nano structure composite exhibited high specific capacitance of 900 F/ g at the current density 2 Agt and the cyclic stability retained up to the tested cycles of 2000. Introduction of C-dots in the NiS nanostructure crystal indicated that the hybrid electrode material showed high performance of electrochemical application. (author)
[en] Highlights: • The ReSOC EES system can achieve LCOS • Balance-of-plant hardware can be compatible between operating modes. • Storage tank dynamics have minimal impact on system performance. • The ReSOC system can operate down to 15% of rated capacity and with RTE of 54%. • The ReSOC system investigated is economically competitive with other technologies. - Abstract: Reversible solid oxide cells may be a cost competitive energy storage technology at the distributed scale. Leveraging C–O–H chemistry and operating near 600 °C allows the cells to be exothermic in both modes, improving efficiency and operability. This study characterizes ReSOC balance-of-plant hardware off-design performance to investigate component mode compatibility, the effect of tank dynamics, and part-load performance for a 100 kW/800 kWh plant. We also introduce a variable volume floating piston tank concept to improve energy storage density and evaluate operability advantages. Results show that with proper system design, balance-of-plant components are compatible, and tank dynamics have minimal impact when tanks are uninsulated and designed for storage near ambient temperature. System AC roundtrip efficiency is between 53% and 54%, depending on the tank technology selected and the compressor operating approach. Energy density is 84.4 kWh/m3 for rigid tanks, and 146.1 kWh/m3 for the variable volume tank concept at 100 bar storage pressure. This study also shows that ReSOC systems can maintain high efficiency at part-loads as low as 15% of rated capacity. Economic analysis of the system estimates an installed capital cost of $422–452/kWh, and a levelized cost of storage of 18.8–19.6 ¢/kWh, values competitive with state-of-the-art battery technology.
[en] Flexible Cu–O thin films were grown on different metal coated non rigid polyimide substrates by the RF-magnetron sputtering and their microstructure and supercapacitive properties were studied. The Raman and XRD studies confirms the formation of a single Cu2O phase with predominant (111) orientation. Surface topography observations revealed that as the percentage of lattice mismatch of Cu2O lattice and substrate lattice is greater the average grain size tends to decrease. The Cu2O films deposited on Ti-Kapton, Ni-Kapton and Pt-Kapton substrates exhibited maximum specific capacitances of 255, 273 and 350 F g−1 correspondingly at a constant current density of 1 A g−1. The observed maximum specific capacitance for CuxO thin films deposited on Pt-Kapton substrates is due to the lower lattice mismatch, high work function of the metal, availability of (111) planes and highly available active area. (author)
[en] Highlights: • K0.7Fe0.5Mn0.5O2 is synthesized for the first time through a facile and simply organic-acid-assisted method. • K0.7Fe0.5Mn0.5O2 provides highly reversible layer spacing variations and an ultra-stable skeleton structure during the charge-discharge processes. • K0.7Fe0.5Mn0.5O2 displays both a high capacity (181 mAh g-1) and superior cycling stability (capacity retention of 85% after 1000 cycles). The delivery of cathodes with both high capacity and excellent cycling stability is a great challenge in the development of sodium-ion batteries (SIBs) for energy storage systems. Here, we exploited a novel potassium-ion-intercalated layered iron/manganese-based material (K0.7Fe0.5Mn0.5O2). On the basis of advanced in situ and ex situ X-ray diffraction analysis, we confirm that K0.7Fe0.5Mn0.5O2 can provide highly reversible layer spacing variations and an ultra-stable skeleton structure during the sodiation/desodiation processes. As a result, K0.7Fe0.5Mn0.5O2 displays superior performance, with both high capacity and superior cycling stability, as a cathode for SIBs. A high discharge capacity of 181 mAh g−1 is achieved at 100 mA g−1. Remarkably, even when cycled at high rate of 1000 mA g−1, 85% of the initial discharge capacity is maintained after 1000 cycles. These results indicate that K0.7Fe0.5Mn0.5O2 is a promising candidate for high-capacity and long-life SIBs. Additionally, this work will provide a unique insight into the development of high-performance cathodes for energy storages.
[en] The development of high-performance miniaturized electrochemical energy storage systems is one of the important technological challenges for innovative electronic gadgets. Flexible microelectromechanical systems-based supercapacitors are considered one of the most aggressive on-chip power sources for advanced integrated electronics. Achieving high power efficiency with excellent flexibility and transparency for the micro-supercapacitors is a major challenge nowadays. Generally, these characteristics of micro-supercapacitors are dependent on the fabrication methods, electrical, mechanical and electrochemical properties of the microelectrode materials, current collectors and electrolytes. In the present review, we have summarized the various strategies used in materials engineering to develop flexible micro-supercapacitors and their electrochemical performance characteristics. Meanwhile, this review presents the latest developments in the design, fabrication and application of flexible micro-supercapacitors. (topical review)
[en] Highlights: • An efficient modeling method for PCM solidification with fins was developed. • A finned heat pipe structure was optimized with negligible computational cost. • Suggestions to economically weld fins on a heat pipe are given. - Abstract: Phase Change Materials (PCMs) are gaining importance in energy storage applications. However, many PCMs are poor thermal conductors and thus can benefit from the optimal use of appropriate fins. This work introduces a PCM-fin structure optimization framework. Typically, the non-linear solidification process increases the complexity associated with solving the mathematical equations for the PCM-fin structure optimization problem, making it computationally expensive. In this paper a modeling approach called Layered Thermal Resistance (LTR) model is extended and developed in 2D cylindrical geometry in order to enable efficient PCM-fin structure optimization. The finned LTR model represents the nonlinear transient solidification process by analytic equations. This significantly reduces the computational cost associated with optimization. A finned heat pipe structure modeled by the finned LTR approach is optimized based on minimizing cost while meeting operational requirements. The optimal results imply that thinner fins result in lower system cost and that there is a thickness limit for the fins to be economically welded on a heat pipe. The finned LTR model also gives the optimal cost of material usage for a large scale latent thermal energy storage system in terms of dollars per kilowatt and it was found that the system cost is slightly lower by using carbon-steel as the construction material for the heat pipes and fins than by using Al 6061.
[en] This report has been prepared as part of an effort to design and build a Modeling and Simulation (M&S) framework to assess the economic viability of a Nuclear-Renewable Hybrid Energy System (N-R HES). In order to facilitate dynamic M&S of such an integrated system, research groups in multiple national laboratories and universities have been developing various subsystems as dynamic physics-based components using the Modelica programming language. In Fiscal Years (FYs) 2015, Idaho National Laboratory (INL) performed a dynamic analysis of two region-specific N-R HES configurations, including the gas-to-liquid (natural gas to Fischer-Tropsch synthetic fuel) and brackish water Reverse Osmosis (RO) desalination plants as industrial processes. In FYs 2016–2017, INL developed two additional subsystems in the Modelica framework: (1) a high-temperature steam electrolysis plant as a high priority industrial plant to be integrated with a light water reactor within an N-R HES and (2) a gas turbine power plant as a secondary energy supply. In FY 2018, the RO desalination system model developed in FY 2015 has been updated such that the model is compatible with the most recent version of the ThermoPower library. Special attention has been given to the controller settings based on process models, aiming to improve process dynamics and controllability. A dynamic performance analysis of the updated RO desalination plant was carried out to evaluate the technical feasibility (load-following capability) of such a system operating under highly variable conditions requiring flexible output. Simulation results involving several case studies show that the suggested control scheme could maintain the controlled variables (including the variable electrical load and RO feed pressure) within desired limits under various plant operating conditions. The results also indicate that the proposed RO plant could provide operational flexibility to participate in energy management at the utility scale by dynamically optimizing the use of excess plant capacity within an N-R HES. For a small-scale energy storage system, a sensible Thermal Energy Storage (TES) model has been developed in the Modelica Framework in FY 2018.