Superconducting magnetic energy storage

Superconducting magnetic energy storage (SMES) is an energy storage technology that stores energy in the form of DC electricity that is the source of a DC magnetic field. The conductor for carrying the current operates at cryogenic temperatures where it is a superconductor and thus has virtually no resistive losses as it produces the magnetic field. The overall technology of cryogenics and superconductivity today is such that the components of a SMES device are defined and can be constructed. The integrated unit appears to be feasible for some utility applications at a cost that is competitive with other technologies. SMES is the only technology based on superconductivity that is applicable to the electric utilities and is commercially available today. In addition to today's power quality application, the historical development of SMES starting with the concept of very large plants that would store hundreds of megawatt hours of energy and were intended for diurnal load leveling are described.     

Superconductive magnetic energy storage

Technical and economic aspects of large scale superconductive magnetic energy storage are discussed. This paper is a review of a program which has been under way at the University of Wisconsin since 1970. Early work between 1970 and 1976 was primarily involved in proving economic and technical feasibility of the concept The present program deals with component development and detailed design ultimately leading to construction of a large superconducting magnet capable of storing 1000–10,000 MWh. The magnet is a single-layered segmented solenoid of approx. 100 m radius. Energy containment is achieved economically by burying the magnet underground in bedrock tunnels. Magnetic loads are transmitted from the conductor to bedrock through glass fiber reinforced composite struts. The conductor consists of a composite of aluminum and NbTi and is designed for full cryogenic stability in 1.8 K superfluid helium. The dewar-conductor assembly will be rippled in a l m radius of curvature to reduce the hoop stress tension. A Graetz bridge is required to convert the d.c. superconducting current into a.c. current in the three-phase power system. Economic analysis indicates that superconductive magnetic energy storage is competitive with alternative large scale storage schemes for units greater than 1000 MWh size.     

高潜热相变砂浆与相变板墙体性能对比研究

相变储能墙体面临着相变温度不适宜、储能能力低、构建形式多但缺乏性能对比分析等问题。以相变砂浆、相变板墙体为对象,对其性能进行优化和对比研究。采用固、液石蜡、高密度聚乙稀(HDPE)按比例熔融混合制备出相变温度约为34.000℃的定形相变材料,该材料无泄漏、形状稳定,潜热为现有文献的2.00倍多。基于该材料制备出相变砂浆、相变板材,并构建两类相变-混凝土墙体结构,研究在相同边界条件和初始条件下两者的传热特性及节能效果。结果表明,以普通砂浆墙体为对照,相变砂浆、定形相变板可将内壁面最高温降低0.730、1.760℃,定形相变板保温隔热性能最优。定形相变板可将空调热负荷降低21.9%,高于相变砂浆;但其原料成本为普通砂浆的3.38倍;成本增幅较相变砂浆高出32.8%,而成本回收周期低33.3%。     

Design,modeling, and analysis of a high performance piezoelectric energy harvester for intelligent tires

Basic parameters affecting vehicle safety and performance such as pressure, temperature, friction coefficient, and contact‐patch dimensions are measured in intelligent tires via sensors that require electric power for operation and wireless communication to be synchronized to the vehicle monitoring and control system. Piezoelectric energy harvesters (PEHs) can extract a fraction of energy that is wasted as a result of deflection during rolling of tires, and this extracted energy can be used to power up sensors embedded in intelligent tires. A new design of PEH inspired from Cymbal PEHs is introduced, and its performance is evaluated in this paper. Cymbal PEHs are proven to be useful in vibration energy harvesting, and in this paper, for the first time, the modified shape of Cymbal energy harvester is used as strain‐based energy harvester for the tire application. The shape of the harvester is adjusted in a way that it can be safely embedded on the inner surface of tires. In addition to the high performance, ease of manufacturing is another advantage of this new design. A multiphysics model is developed and validated to determine the output voltage, power, and energy of the designed PEH. The modeling results indicated that the maximum output voltage, the maximum electric power, and the accumulated harvested energy are about 3.5 V, 2.8 mW, and 24 mJ/rev, respectively, which are sufficient to power two sensors. In addition, the possibility is shown to supply power to five sensors by increase in piezoelectric material thickness. The effect of rolling tire temperature on the performance of the proposed PEH is also studied.     

Advanced configuration of superconducting magnetic energy storage

\Superconducting Magnetic Energy Storage (SMES) is very promising as a power storage system for load leveling or a power stabilizer. However, the strong electromagnetic force caused by high magnetic field and large current is a serious problem in SMES systems. To cope with this problem, we proposed the concept of Force-Balanced Coil (FBC), which is a helically wound toroidal coil. The FBC can minimize working stresses by selecting an optimal number of poloidal turns. However, the winding of the FBC has a complex three-dimensional shape that can make the manufacturing of the helical windings difficult. To overcome this difficulty, a helical winding machine was developed. From winding tests, the possibility of the coil construction was demonstrated. Moreover, a small helical coil using high temperature superconductors was designed and fabricated in order to estimate the problems of helical winding technique through the experimental results with liquid nitrogen cooling. This paper describes the design condition of the Force-Balanced Coil in order to reduce structure requirements and proposes a solution to the problems of helical winding technique by using experimental devices.     

Application of magnetic energy storage unit as load-frequencystabilizer

Fast-acting energy storage devices can effectively damp electromechanical oscillations in a power system because they provide storage capacity in addition to the kinetic energy of the generator rotor, which can share the sudden changes in power requirement. The effectiveness of small-sized magnetic energy storage (MES) units (both superconducting and normal loss types) for this application is shown, and means of best utilizing the small energy storage capacity of such units to improve the load-frequency dynamics of large power areas are suggested. The proposed method of improving the load frequency control of power systems has the advantage that it does not require the governor or any other part of the power system to perform any sophisticated control action. The control logic suggested for this purpose takes the area control error as its input and uses inductor current deviation feedback. In a power system with a SMES (superconducting MES) unit, the optimal setting of the integrator gain is altered to a higher value. With the suggested control measure, SMES units of 4-6 MJ capacity would suffice in reducing the maximum deviations of frequency and tie-line power flow by about 40% in power areas of 1000-2000 MW capacity     

Hybrid energy storage systems for stand-alone electric power systems: optimization of system performance and cost through control strategies

The development of remote, renewable-based energy is hindered in part by the lack of affordable energy storage. Requiring power-on-demand from an energy system powered by intermittent or seasonal sources may necessitate one-month’s energy storage—an expensive proposition using conventional storage technologies. If multiple energy storage devices with complementary performance characteristics are used together, the resulting ‘hybrid energy-storage system’ can dramatically reduce the cost of energy storage over single storage systems. The coupling of conventional storage batteries with emerging hydrogen technologies provides one such hybrid system. Hydrogen energy storage in this context includes an electrolyzer, hydrogen storage tank, and a fuel cell. An additional component that must be considered is the control system that determines when the various components are used. Since the control system has an effect on component sizes and thus system and operating costs, the control algorithm must be carefully considered for any system with energy storage. For this study, a time-dependent model of a stand-alone, solar powered, battery-hydrogen hybrid energy storage system was developed to investigate energy storage options for cases where supply and demand of energy are not well matched daily or seasonally. Simulations were performed for residential use with measured solar fluxes and simulated hourly loads for a site at Yuma, Arizona, USA, a desert climate at 32.7 N latitude. Renewable-based power not needed to satisfy the load is stored for later use. Two hybrid energy-storage algorithms were considered. The first is a conventional ‘state-of-charge’ control system that uses the current state of the storage system for control. The second control system presumes knowledge of future demand through a feed-forward, neural net or other ‘intelligent’ control systems. Both algorithms use battery storage to provide much of the daily energy shifting and hydrogen to provide seasonal energy shifting, thus using each storage technology to its best advantage. The cost of storing energy with a hybrid energy-storage scheme was found to be much less expensive than either single storage method, with a hybrid system storage costing 48% of the cost of a hydrogen-only system and only 9% of the cost of a conventional, battery-only system. In addition, the neural-net control system is compared to a standard battery state-of-charge control scheme, and it is shown that neural-net control systems better utilize expensive components and result in less expensive electric power than state-of-charge control systems.     

Improving the technical, environmental and social performance of wind energy systems using biomass-based energy storage

A completely renewable baseload electricity generation system is proposed by combining wind energy, compressed air energy storage, and biomass gasification. This system can eliminate problems associated with wind intermittency and provide a source of electrical energy functionally equivalent to a large fossil or nuclear power plant. Compressed air energy storage (CAES) can be economically deployed in the Midwestern US, an area with significant low-cost wind resources. CAES systems require a combustible fuel, typically natural gas, which results in fuel price risk and greenhouse gas emissions. Replacing natural gas with synfuel derived from biomass gasification eliminates the use of fossil fuels, virtually eliminating net CO₂ emissions from the system. In addition, by deriving energy completely from farm sources, this type of system may reduce some opposition to long distance transmission lines in rural areas, which may be an obstacle to large-scale wind deployment.     

Operation principle and applications of multiterminalsuperconductive magnetic energy storage systems

The basic operation principle of a multiterminal superconductive magnetic energy storage (MSMES) system is introduced. The motivation for developing the MSMES systems is to combine and maximize the flexibility benefits provided by energy storage and the controllability benefits provided by power electronic systems. A MSMES system can be used simultaneously as an energy storage device and a power flow control device. This attribute enables MSMES systems to perform some unique functions in electric power systems. Potential applications of MSMES systems and their impact on solving the problems faced by power systems today are discussed     

Design and performance of hot-oil storage tanks

Because the ratio of surface area to capacity decreases with increasing volume for a particular shaped hot-oil storage tank, there is a trend towards larger tanks in order to incur only relatively small heat losses per unit capacity. The present investigation suggests, for conditions encountered in the UK, that the aspect ratio (i.e. height-to-radius) for least heat losses from bare or fully insulated hot-oil tanks should be approximately 0·4. If the cylindrical walls of the tank are to be insulated, the roof remaining bare, then the optimal aspect ratio should be appropriately greater. However, when designing a tank, the running cost is only one of several considerations—although an increasingly important one as fuel costs inflate—the capital investment in the tank and site also radically affect the choice. The economically most favourable aspect ratio, i.e. that leading to the least total financial expenditure over the lifetime of the tank, is considerably in excess of the optimal aspect ratio corresponding to minimum rate of energy loss. This maximum energy thrift or minimum financial expenditure dichotomy is now serious when neither sufficient, cheap fuel nor adequate industrial investment is available.     

Liquid hydrogen storage system for heavy duty trucks: Configuration,performance, cost,and safety

We investigate the potential of liquid hydrogen storage (LH₂) on-board Class-8 heavy duty trucks to resolve many of the range, weight, volume, refueling time and cost issues associated with 350 or 700-bar compressed H₂ storage in Type-3 or Type-4 composite tanks. We present and discuss conceptual storage system configurations capable of supplying H₂ to fuel cells at 5-bar with or without on-board LH₂ pumps. Structural aspects of storing LH₂ in double walled, vacuum insulated, and low-pressure Type-1 tanks are investigated. Structural materials and insulation methods are discussed for service at cryogenic temperatures and mitigation of heat leak to prevent LH₂ boil-off. Failure modes of the liner and shell are identified and analyzed using the regulatory codes and detailed finite element (FE) methods. The conceptual systems are subjected to a failure modes and effects analysis (FMEA) and a safety, codes, and standards (SCS) review to rank failures and identify safety gaps. The results indicate that the conceptual systems can reach 19.6% useable gravimetric capacity, 40.9 g-H₂/L useable volumetric capacity and $174–183/kg-H₂ cost (2016 USD) when manufactured 100,000 systems annually.     

Application of magnetic energy storage unit as continuous VArcontroller

It is shown that magnetic energy storage units can simultaneously operate as continuous VAr (volt-ampere reactive) controllers while performing the role of load-frequency stabilizers in electrical power systems. This is achieved by operating the converter in the buck-boost mode with a switched capacitor bank placed across its terminals. The P versus Q modulation ranges of the 12-pulse converter depend on the source inductance, secondary voltage of the input transformers, and output current. Once the input transformer is chosen, the Q modulation range depends on the active power transfer and the current through the inductor at any instant of time. The actual reactive power consumption of the converter is varied continuously, depending on the requirements of the power system, while keeping within the Q-modulation range. Switching of the capacitor bank keeps the required Q consumption of the converter within the available range. It is shown that this mode of control improves the overall performance of the power system in P-f and Q-V loops and obviates the use of any additional VAr compensator in the power area where the SMES (superconducting magnetic energy storage) unit is located     

Impact of superconductive magnetic energy storage on electric powertransmission

The authors demonstrate that a superconductive magnetic energy storage (SMES) system can provide a significant positive impact on electric power transmission. By using SMES, transmission-line loadings during heavy load hours can be reduced if the SMES system is located near the major load. Transmission losses as well as the fuel cost for the losses over a 24 hr period can also be decreased. An SMES scheme, the SMES-DC link, is introduced for energy storage and control of power flow. The operation of this scheme and the benefits it provides are described     

Variable geometry wind turbine for performance enhancement,improved survivability and reduced cost of energy

The conceptual design and proof‐of‐concept testing of a furling vertical axis wind turbine, suited to large‐scale offshore deployment, is described. Through the implementation of variable geometry capabilities, extreme storm loads can be reduced, and unsteady flow‐related fatigue loads can be minimized thereby reducing capital (structural) and maintenance costs. Moreover, annual power generation can be optimized in real‐time to account for unsteady wind effects related to weather and siting thus improving efficiency and annual power generation. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessing long-term performance of centralized thermal energy storage system

A validated computational fluid dynamics simulation tool is used to study the long-term performance of a centralized latent heat thermal energy storage system (LHTES). The LHTES system is integrated with a building mechanical ventilation system. Paraffin RT20 was used as a phase change material (PCM) and fins are used to enhance its performance.To reduce the computational time, artificial neural networks (ANN) was used to relate the relationships between the LHTES inputs and output parameters. Extensive CFD simulations were carried out to identify all the influential parameters for the development of ANN. They include phase change temperature range, air flow rate, the geometrical configuration of a LHTES system, fin size, and the unit's length. Further CFD simulations were carried out to provide sufficient data for proper training and testing of the ANN. The ANN model was used to predict the LHTES's outlet air-temperature. There was a good agreement between the ANN prediction and CFD model's prediction.The ANN model then was used to study the annual performance of a LHTES for application in Montreal. We found that the potential of use the centralized LHTES system to reduce the cooling load is high with a wider phase change temperature range. The centralized LHTES system contributes to reducing the cooling load from 21% to 36% when the length of the centralized LHTES system is increased from 500 to 650 mm at a flow rate of 1.5 m/s.     

Thermal performance of a two-phase thermosyphon energy storage system

This article presents an energy storage system, which can be readily integrated with the building structure. It stores heat supplied by solar energy via the two-phase closed loop thermosyphon to storage tank and releases stored heat in energy storage material via two-phase closed thermosyphon to the heat exchanger through the flow of transport fluid. The functions of such energy storage system have three operating modes, i.e., heat charge, heat discharge, and simultaneous charge and discharge. The thermal performance of the system with alcohol and water as working fluid is experimentally investigated. The results show that the storage system employing alcohol as working fluid in the loop thermosyphon provides better performance; the system gives optimum heat charge and discharge performance under 35–40% fill ratio, regardless whether the working fluid is water or alcohol. The system displays optimum charge efficiency of 73% and optimum discharge efficiency of 85% with alcohol as working fluid.     

Application of superconducting magnetic energy storage in electrical power and energy systems: a review

Superconducting magnetic energy storage (SMES) is known to be an excellent high‐efficient energy storage device. This article is focussed on various potential applications of the SMES technology in electrical power and energy systems. SMES device founds various applications, such as in microgrids, plug‐in hybrid electrical vehicles, renewable energy sources that include wind energy and photovoltaic systems, low‐voltage direct current power system, medium‐voltage direct current and alternating current power systems, fuel cell technologies and battery energy storage systems. An extensive bibliography is presented on these applications of SMES. Also, some conclusive remarks in terms of future perspective are presented. Also, the present ongoing developments and constructions are also discussed. This study provides a basic guideline to investigate further technological development and new applications of SMES, and thus benefits the readers, researchers, engineers and academicians who deal with the research works in the area of SMES. Copyright © 2017 John Wiley & Sons, Ltd.     

Improvement of synchronous generator damping throughsuperconducting magnetic energy storage systems

Stabilization of a synchronous generator through control of firing angle of the power converters in superconducting magnetic energy storage (SMES) systems is considered. An optimum strategy of the firing angle control is designed so as to eliminate the transients in minimum time. A nonlinear model of a synchronous generator, its governor and exciter systems, and an SMES system connected to the generator terminal is considered. The optimum firing angle control is derived retaining the nonlinearities of the system dynamics. Digital simulation results indicate that the proposed strategy controls the slowly growing as well as first swing instabilities very effectively     

Minimizing the energy cost for microgrids integrated with renewable energy resources and conventional generation using controlled battery energy storage

This paper presents a methodology to minimize the total cost of buying power from different energy producers including renewable energy generations particularly within the context of a microgrid. The proposed idea is primarily based on the controlled operation of a battery energy storage system (BESS) in the presence of practical system constraints coupled with our proposed cost optimization algorithm. The complex optimization problem with constraints has been solved using the well-known concept of dynamic programming. The methodology has been assessed using actual power and price data from six different power generation sites and cost reduction has been calculated for a number of BESSs by varying their energy and power capacities. Twofold benefits of the proposed methodology lie in minimizing the total cost along with the constraint-based efficient operation of the BESS. Simulation results depict that the given power demand at a particular region can be fulfilled properly at all times using a BESS and multiple power generation.