This article reviews the latest progress in thermal storage material research. It focuses on phase-change thermal storage materials covering the organic, molten salt and alloy and composites. Discussion is made on materials composition, preparation process and characteristics of the thermal storage materials. It is concluded nano-and micro-structured composite materials should play a significant role in the future phase change materials research and development.

Hydrate is a solid material formed by guest molecules and host water molecules under certain temperature and pressure. The water molecules are able to form a clathrate structure through hydrogen bonds. The clathrate structure can entrap gases such as CH4 and H2 to form a stable solid material, thus achieving the storage of energy. In the same time, the formation and dissociation of hydrates incurs heat release (exothermic process) and heat absorption (endothermic process), respectively. These characteristics could make them feasible materials for storing thermal energy. In this paper, current status of the use hydrates for energy storage is discussed and future research needs are proposed.

Wind power is generation is characterized by large extents of fluctuations in power quality and frequency stability due to the randomness and intermittence of wind speed and direction. Large-scale applications of wind power have a great impact on the stability of electrical grids. Compared with other energy storage technologies, flywheel energy storage (FES) has advantages of high round-trip efficiency and little environmental impact. FES is capable of helping low voltage ride through and smooth power output with appropriate control strategies and electronic control devices. FES can also enhance frequency stability and improve power quality of wind generator delivered to the grid. This paper introduces the background of the use of FES in wind power, explains the principles of FES, and reviews current status in the control strategies of FES.

This paper introduces flywheel energy storage system (FESS) with particular focus on motors and controllers. The paper covers the principle and characteristics of permanent magnet brushless DC motors, permanent magnet synchronous motors, induction motors and switched reluctance motors, which are usually used in flywheel energy storage system. Various control strategies associated with the four types of motors are discussed. Advantages and disadvantages of the motors and their control strategies are analyzed.

As a critical technology for renewable integration, energy storage development is driven by growth in renewable energy sources. With long development history, physical energy storage methods have successfully achieved commercial operations. As a representative technology of physical storage, pumped hydro accounts for the majority of market size, and is a key generation resource for grid side. However, pumped hydro storage, in addition to compressed air energy storage (CAES), is highly restrained by geographical conditions and environmental requirements. Physical storage technology is experiencing reforms among both traditional and new application models as well as R&D for new technologies. Although pumped hydro, CAES and flywheels are based on different operational principles, their applications, development trends, technological breakthroughs, policy aspects and funding support are all key drivers for the their future developments.

Compressed air energy storage is one of the most promising large scale electrical energy storage technologies. A techno-economic model of compressed air energy storage system is constructed. The techno-economic analysis is carried out under the conditions with and without the subsidy policy of a compressed air energy storage system with thermal energy storage for the scenario of being applied to an industrial plant. The results without subsidy policy indicate that the internal rate of return of this system is 16.3%, and the dynamic investment pay-back period is 9.2 years, and the results with subsidy policy indicate the above evaluation index is 23.8% and 6.2 years. Furthermore, the economical sensitivity factors are illustrated through the uncertainty analysis including the break-even analysis and the sensitivity analysis. In addition, the policy support plays an important role for the lower risk and improve return of the compressed air energy storage power plant. The study of this paper can provide theoretical reference and engineering instruction for the research and engineering application of compressed air energy storage system.

The work reported in this paper concerns the heat transfer behaviour of thermal energy storage components using composite phase change materials. Components with a single and a concentric configuration are designed and investigated. The composite materials consist of a molten salt based phase change material (PCM), a thermal conductivity enhancer material (TCEM) and a ceramic skeleton material (CSM). A mathematical model is established for the transient heat transfer in the composite materials and the components. The model is first compared with experimental data, showing a reasonably good agreement, and indicating the validity of the numerical model. Extensive modelling is then carried out to study the heat transfer behaviour under different conditions, particularly the influences of materials properties and geometrical design of the composite material module as well as heat transfer fluid velocity. The results show that an increase in the mass fraction of the TCEM, the thickness of the composite material module, or the velocity of the heat transfer fluid enhances the heat storage and release rate and improves the heat transfer performance of thermal energy storage components. The concentric tube configuration offers a better performance than the single tube configuration.

Two major challenges in wind power generation are weak low voltage ride through (LVRT) capability and unstable power output. A superconducting fault current limiter-magnetic energy storage system (SFCL-MES) has been proposed to address the two challenges. Simulations on the proposed system have been carried out using a single wind power generator, and validated the system performance. This paper extends the concept of SFCL-MES to a wind farms. Simulations are carried out on the extended systems and the effect of the use of the SFCL-MES on the LVRT capability and power output of the wind farms are analyzed. Great enhancement of the LVRT capability of wind power generator is observed. The use of the SFCL-MES has also been shown to smooth the active output power of the wind farm. Considering complementary effect of generators in wind farms, power capacity requirements for the SFCL-MES for a whole wind farm is expected to be considerably lower than the summation of the requirements of individual wind power generator. The total cost is therefore expected to be reduced.

Due to large heat transfer area, compact size and easy handling, cross flow tubular heat exchangers have a potential for a wide range of applications in latent heat energy storage. A two dimensional unsteady-state model is established for this type of heat exchangers contacting phase change materials (PCMs) to study the heat transfer behavior during phase change. Effects of various factors on the charging process are studied, including Stefan number, Reynolds number, thermal conductivity of PCM, arrangement of tubes, and the number of fins (N_fn). The motion of solid-liquid interface is analyzed. The results show that the heat transfer process can be significantly enhanced by the use of fins; The melting time of PCM in a two-fin unit could be reduced by 52.6% compared with a non-fin unit when the thermal conductivity of PCM is lower than 1.0 W/(m·K).

Two-tank sensible heat storage using molten salt is a relatively mature technology. However, the cost for the storage method is high. A new single tank based storage method is proposed by using immersed heat exchangers for charging and discharging processes. Analyses are carried out on the newly proposed system. Further analyses are done on the natural convective heat transfer of molten salt around two vertically aligned horizontal cylinders. The results show that the natural convection heat transfer of molten salt around the array of cylinders can be enhanced if the vertical distance between the cylinders is not too small, whereas the horizontal distance between them is not too big. The results may serve as guidance for the design of single thermal energy storage tanks.

This paper proposes the use of a flywheel based energy storage device at the power output end of wind farms. A control strategy is put forward based on the characteristics of both wind farms and flywheels. The proposed system is simulated in the Matlab/Simulink environment. The results show that the proposed control strategy could attain the target of smoothing grid side active power and reduce fluctuations of active power.

This paper reports a study on the use of flywheel technology for energy storage in a 1.5 MW wind generator. The results show that the system performance meets the requirements of smoothing power output. Further discussion is made on the charge/discharge modes for energy conversion system.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 1890 papers online from Dec. 1,2014 to Jan. 31,2015. 100 of them were selected to be highlighted. Layered oxide and high voltage spinel cathode materials are still under extensive investigations for the structure evolution and modifications. Large efforts were devoted to Si and Sn based anode material. There are a few papers related to electrolyte additives, solid state electrolyte, Li/S battery, Li-air battery and more papers related to cell analyses, theoretical simulations, and modeling.

With the rapid development of modern physical theory and computational technology, computer simulations have become efficient methods in materials science, which are also extensively used in the study of lithium ion batteries. In this paper, we introduce the basic principles of commonly used calculation methods in different space and time scales, e.g. Ab initio calculation, density functional theory, molecular dynamics, monte carlo, phase field simulation, force field and finite element method. Their applications in the fundamental research of lithium ion batteris, such as the calculation of the cell voltage, electronic sturcture, band gap, ion transport mechanism in bulk and various microstructures, and the distribution of temperature field and stress field in electrode materials, are also discussed.