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[en] In order to resolve the problems arising from the fact that the production and consumption of electricity are at distinctly levels through much of the day, the electric power companies have been led to adopt different solutions, from the financial inducements to customers to limit their use of appliances, to the design of electric power stations with daily or weekly compressed air energy storage. Faced with fluctuating energy demand situation, the electric power companies are developing an electric base load, produced by basic power stations, hydroelectric (river) stations, nuclear and steam stations. They respond to the fluctuation of demand by starting up stations powered by fuel-oil by more or less sophisticated gas turbine, by hydroelectric energy, or as at Huntorf, by pneumatic stored energy. In this communication, we present the results, the capital cost and the operating cost concerning the combination of pneumatic storage with reciprocating engine and gas turbine. (author)
[en] The major types of energy storage systems (including conventional batteries, compressed air energy storage, pumped hydro and superconducting coils) are discussed in this paper. 8 bibliographies
[en] This article examines how the ability to ''store'' electricity can pay handsome dividends in a competitive environment. Priorities change when industries are deregulated. Indeed, new priorities are being established for electric generation--low cost, efficiency, product distinction for marketing purposes, etc. are all more critical today. Perhaps not so obvious is the fundamental role of energy storage in a fully competitive marketplace. In fact, rarely do a technology development and a changing business climate play off against each other so nicely. Consider the function of the emerging electricity broker, or power marketer. Imagine the premium that broker could command with access to a large increment of electricity--purchased at a low price--and supplied at a moment's notice for a substantially higher price. Storage of electricity would mean that the investment in excess available generation capacity to supply so-called peak demand could be avoided. It also means that electricity could be brokered like other commodities--that is purchased, stockpiled, and sold to reflect market conditions across a wider geographical region and time spain. Benefits accrue to transmission and distribution, in addition to generation. Energy storage helps to manage the increasing stress placed on the grid as a result of intermittent sources of power and large numbers of cogenerators and small power producers. On the customer side, any ratepayer large or small could, theoretically, play the spot market in electric supply with a reserve to tap in emergencies. For a parallel in other deregulated markets, recall how storage has become an important factor in natural-gas contracting. Quality of electricity also can be improved by applying storage to stabilize the grid, especially along the distribution system at substations. And the opening of vast markets for electricity consumption, such as electric vehicles, depends in large measure on electric storage
[en] This document describes the main characteristics of various electric power storage methods and their application domains. The large-scale storages include the hydraulic systems, those using compressed air, the batteries or those implementing a thermal way. The small-scale storages are electrochemical as the accumulators, the super-capacitors, mechanical as the flywheel, magnetic or also by the hydrogen use. The first part presents the necessity of the electric power storage, the second part the places of these storage. The third part details the forms of storage. (A.L.B.)
[en] Wind energy is an important field of development for the island of Gotland, Sweden, especially since the island has set targets to generate 100% of its energy from renewable sources by 2025. Due to the variability of wind conditions, energy storage will be an important technology to facilitate the continued development of wind energy on Gotland and ensure a stable and secure supply of electricity. In this study, the feasibility of utilizing the Middle Cambrian Faludden sandstone reservoir on Gotland for Compressed Air Energy Storage (CAES) is assessed. Firstly, a characterization of the sandstone beneath Gotland is presented, which includes detailed maps of reservoir thickness and top reservoir structure. Analysis of this information shows that the properties of the Faludden sandstone and associated cap rock appear favorable for the application of CAES. Seven structural closures are identified below the eastern and southern parts of Gotland, which could potentially be utilized for CAES. Scoping estimates of the energy storage capacity and flow rate for these closures within the Faludden sandstone show that industrial scale CAES could be possible on Gotland.
[en] Electricity generated from renewable wind sources is highly erratic due to the intermittent nature of wind. This uncertainty of wind power can lead to challenges regarding power system operation and dispatch. Energy storage system in conjunction with wind energy system can offset these effects, making the wind power controllable. Moreover, the power spectrum of wind power exhibits that the fluctuations of wind power include various components with different frequencies and amplitudes. Thus, the hybrid energy storage system is more suitable for smoothing out the wind power fluctuations effectively rather than the independent energy storage system. A hybrid energy storage system consisting of adiabatic compressed air energy storage (A-CAES) system and flywheel energy storage system (FESS) is proposed for wind energy application. The design of the proposed system is laid out firstly. The A-CAES system operates in variable cavern pressure, constant turbine inlet pressure mode, whereas the FESS is controlled by constant power strategy. Then, the off-design analysis of the proposed system is carried out. Meanwhile, a parametric analysis is also performed to investigate the effects of several parameters on the system performance, including the ambient conditions, inlet temperature of compressor, storage cavern temperature, maximum and minimum pressures of storage cavern. - Highlights: • A wind-hybrid energy storage system composed of A-CAES and FESS is proposed. • The design of the proposed hybrid energy storage system is laid out. • The off-design analysis of the proposed system is carried out. • A parametric analysis is conducted to examine the system performance
[en] The idea of storing compressed air in submerged flexible fabric structures anchored to the seabed is being investigated for its potential to be a clean, economically-attractive means of energy storage which could integrate well with offshore renewable energy conversion. In this paper a simple axisymmetric model of an inextensional pressurised bag is presented, along with its implementation in a constrained multidimensional optimization used to minimise the cost of the bag materials per unit of stored energy. Base pressure difference and circumferential stress are included in the optimization, and the effect of hanging ballast masses from the inside of the bag is also considered. Results are given for a zero pressure natural shape bag, a zero pressure bag with circumferential stress and hanging masses, and a nonzero pressure bag with circumferential stress and hanging masses.
[en] Highlights: • A novel supercritical compressed air energy storage system is proposed. • The energy density of SC-CAES is approximately 18 times larger than that of conventional CAES. • The characteristic of thermodynamics and exergy destruction is comprehensively analysed. • The corresponding optimum relationship between charging and discharging pressure is illustrated. • A turning point of efficiency is indicated because of the heat transfer of crossing the critical point. - Abstract: A novel supercritical compressed air energy storage (SC-CAES) system is proposed by our team to solve the problems of conventional CAES. The system eliminates the dependence on fossil fuel and large gas-storage cavern, as well as possesses the advantages of high efficiency by employing the special properties of supercritical air, which is significant for the development of electrical energy storage. The thermodynamic model of the SC-CAES system is built, and the thermodynamic characters are revealed. Through the exergy analysis of the system, the processes of the larger exergy destruction include compression, expansion, cold storage/heat exchange and throttle. Furthermore, sensitivity analysis shows that there is an optimal energy releasing pressure to make the system achieve the highest efficiency when energy storage pressure is constant. The efficiency of SC-CAES is expected to reach about 67.41% when energy storage pressure and energy releasing pressure are 120 bar and 95.01 bar, respectively. At the same time, the energy density is 18 times larger than that of conventional CAES. Sensitivity analysis also shows the change laws of system efficiency varying with other basic system parameters. The study provides support for the design and engineering of SC-CAES.
[en] In this report a survey of different techniques for storage of electrical energy. The following alternatives are described regarding method, characteristics, potential and economy. Batteries; Capacitors; Flywheels; Pump storage hydro power plants; Hydrogen gas generation; Air compression. Regarding evaluation of methods for storage of electrical energy. Battery storage: The development of Lithium-ion batteries are of great interest. In the present situation it is however difficult of classify battery storage as a good alternation in applications with frequent re-charging cycles and re-charging of large energy volumes. The batteries have limited life length compared to other alternatives. Also the power is limited at charging and discharging. Energy storage in capacitors: 'Super-capacitors' having large power capacity is considered to be of interest in applications where fast control of power is necessary. The ongoing development of based on carbon-nanotubes will increase the energy storage capacity compared with the today existing super-capacitors. This can in the future be an alternative to battery storage. Of further interest is also the idea to combine battery and capacitor based storage to achieve longer life-time of the batteries and faster power control. Flywheel energy storage: The energy storage capacity is relatively limited but power control can be fast. This system can be an alternative to capacitor based energy storage. Pump-storage hydro power plant: This type of energy storage is well suited and proven for time frame up to some days. In the Swedish power system there is today not any large demand of energy storage in this time frame as there is a large capacity in conventional hydro power plants with storage capacity. Pump-storage can however be of interest in the southern part of Sweden. In some operation stages the grid is loaded up to its limit due to large power transmission from the north. The pump-storage can reduce this power transfer during critical periods and can therefore be an alternative to new power lines. Hydrogen energy storage: The handling (storage and transfer) of hydrogen is considered to be difficult and dangerous. Air-compression energy storage: This method is combined with gas turbine plants. During periods with surplus of energy in the power system this surplus energy is used to compress air and store it. This compressed air is used in the operation of gas turbine power plant where the compressed air is used instead of the normal use where the gas turbine makes the compression. The possibility should be considered in the future if new gas turbine power plants are to be built in Sweden. This is not the situation today. Different application areas where the energy storage can be used are discussed, such as: Electrical supply quality improvement; Improvement of power system transient stability; Damping of electromechanical oscillations in the power system; Spinning disturbance power reserves; Power system frequency control; Fast disturbance power reserves (activated within 15 minutes); Optimization of energy production dispatch; Increase of power grid transmission capacity. In the scientific world the technical development is very active within areas regarding batteries, capacitors with very large storage capacity, flywheels, etc. As the progress is very fast and this report gives only a brief survey of the research within the area, there is a need to continuously follow the technical development. The judgement is done that there is demand for evaluation of the value of energy storage for different applications and to identify suitable methods to be used in the different applications. Regarding conditions and demands in Sweden and the other Nordic countries research and development activities should be done as: Identify application areas where there are requirements of improvements in the power system. From the identified demands it should be analysed if electrical energy storage can be used to achieve the required improvements. For each application area different alternatives for energy storages are evaluated regarding technical feasibility, environmental influence and economy. During the next 2-4 years conceptual solutions should be presented for application where electrical energy storage is considered to be technically and economically feasible. These applications should be linked to new requirements in the power system due to increased volume of distributed power generation (for example wind power), increased consumptions of electrical energy due to new load objects (for example electrical cars), changed structure of the distribution grids, etc. Evaluation of the different concepts is done as soon as the above described conceptual studies allow. Prioritization of realization should be done. Within 5 years from now realization of pilot projects are started. The project time for the different projects will probably vary significantly due to different technical solutions. Evaluation of the pilot projects are done as soon as possible with the goal for further implementation within 10 years
[en] This paper presents an overview of all currently commercially available options of energy storage in the power distribution network. The paper puts forward arguments for energy storage in the distribution network as well as requirements that must be met by the relevant energy storage systems. The paper describes 7 technologies allowing the solution of energy storage problems, including their basic principles and summarizing benefits and drawbacks of individual solutions. (authors)