An updated review of energy storage systems: Classification and applications in distributed generation power systems incorporating renewable energy resources

The demand of electric energy is increasing globally, and the fact remains that the major share of this energy is still being produced from the traditional generation technologies. However, the recent trends, for obvious reasons of environmental concerns, are indicating a paradigm shift towards distributed generation (DG) incorporating renewable energy resources (RERs). But there are associated challenges with high penetration of RERs as these resources are unpredictable and stochastic in nature, and as a result, it becomes difficult to provide immediate response to demand variations. This is where energy storage systems (ESSs) come to the rescue, and they not only can compensate the stochastic nature and sudden deficiencies of RERs but can also enhance the grid stability, reliability, and efficiency by providing services in power quality, bridging power, and energy management. This paper provides an extensive review of different ESSs, which have been in use and also the ones that are currently in developing stage, describing their working principles and giving a comparative analysis of important features and technical as well as economic characteristics. The wide range of storage technologies, with each ESS being different in terms of the scale of power, response time, energy/power density, discharge duration, and cost coupled with the complex characteristics matrices, makes it difficult to select a particular ESS for a specific application. The comparative analysis presented in this paper helps in this regard and provides a clear picture of the suitability of ESSs for different power system applications, categorized appropriately. The paper also brings out the associated challenges and suggests the future research directions.     

A six-phase synchronous generator for stand-alone renewable energy generation: Experimental analysis

This paper presents the steady-state behavior of a SPSG (six-phase synchronous generator) configured to operate as a stand-alone electric energy source in conjunction with a hydro power plant. A purely experimental treatment is provided with the emphasis placed on operating regimes that illustrate the advantages of using SPSG. In particular, it is shown that the generator can supply two separate three-phase loads which represent an additional advantage. Last but not least, outputs of the two three-phase windings can be used to supply a single three-phase load through an interconnecting six-phase to three-phase transformer, in which case failure of one three-phase winding does not lead to the system shutdown and the load can be still supplied from the remaining healthy winding. Experimental results include loading transients with independent three-phase resistive load at each of the two three-phase winding sets, and measured steady-state characteristics for various configurations and operating conditions.     

Grid-connected versus stand-alone energy systems for decentralized power—A review of literature

The decentralized power is characterised by generation of power nearer to the demand centers, focusing mainly on meeting local energy needs. A decentralized power system can function either in the presence of grid, where it can feed the surplus power generated to the grid, or as an independent/stand-alone isolated system exclusively meeting the local demands of remote locations. Further, decentralized power is also classified on the basis of type of energy resources used—non-renewable and renewable. These classifications along with a plethora of technological alternatives have made the whole prioritization process of decentralized power quite complicated for decision making. There is abundant literature, which has discussed various approaches that have been used to support decision making under such complex situations. We envisage that summarizing such literature and coming out with a review paper would greatly help the policy/decision makers and researchers in arriving at effective solutions. With such a felt need 102 articles were reviewed and features of several technological alternatives available for decentralized power, the studies on modeling and analysis of economic, environmental and technological feasibilities of both grid-connected (GC) and stand-alone (SA) systems as decentralized power options are presented.     

Artificial neural networks in renewable energy systems applications: a review

Artificial neural networks are widely accepted as a technology offering an alternative way to tackle complex and ill-defined problems. They can learn from examples, are fault tolerant in the sense that they are able to handle noisy and incomplete data, are able to deal with non-linear problems and, once trained, can perform prediction and generalisation at high speed. They have been used in diverse applications in control, robotics, pattern recognition, forecasting, medicine, power systems, manufacturing, optimisation, signal processing and social/psychological sciences. They are particularly useful in system modelling such as in implementing complex mappings and system identification. This paper presents various applications of neural networks mainly in renewable energy problems in a thematic rather than a chronological or any other order. Artificial neural networks have been used by the author in the field of solar energy; for modelling and design of a solar steam generating plant, for the estimation of a parabolic trough collector intercept factor and local concentration ratio and for the modelling and performance prediction of solar water heating systems. They have also been used for the estimation of heating loads of buildings, for the prediction of air flow in a naturally ventilated test room and for the prediction of the energy consumption of a passive solar building. In all those models a multiple hidden layer architecture has been used. Errors reported in these models are well within acceptable limits, which clearly suggest that artificial neural networks can be used for modelling in other fields of renewable energy production and use. The work of other researchers in the field of renewable energy and other energy systems is also reported. This includes the use of artificial neural networks in solar radiation and wind speed prediction, photovoltaic systems, building services systems and load forecasting and prediction.     

A review of heat pipe systems for heat recovery and renewable energy applications

Advancements into the computational studies have increased the development of heat pipe arrangements, displaying multiphase flow regimes and highlighting the broad scope of the respective technology for utilization in passive and active applications. The purpose of this review is to evaluate current heat pipe systems for heat recovery and renewable applications utility. Basic features and limitations are outlined and theoretical comparisons are drawn with respect to the operating temperature profiles for the reviewed industrial systems. Working fluids are compared on the basis of the figure of merit for the range of temperatures. The review established that standard tubular heat pipe systems present the largest operating temperature range in comparison to other systems and therefore offer viable potential for optimization and integration into renewable energy systems.     

A review of electrical energy storage technologies for renewable power generation and smart grids

储能技术是突破可再生能源大规模开发利用瓶颈的关键技术,是智能电网的必要组成部分.在储能市场商业化雏形阶段,系统性的比较分析各类储能技术的性能特点,为未来市场发展提供筛选技术路线的框架基础至关重要.本文阐述了储能技术在可再生能源发电和智能电网中的作用,对物理储能(抽水蓄能,压缩空气储能,飞轮储能),电化学储能(二次电池,液流电池),其它化学储能(氢能,合成天然气)等储能技术进行了系统的比较与分析,最后提出储能技术的发展趋势.     

Simulation and optimization of stand-alone hybrid renewable energy systems

Stand-alone hybrid renewable energy systems usually incur lower costs and demonstrate higher reliability than photovoltaic (PV) or wind systems. The most usual systems are PV–Wind–Battery and PV–Diesel–Battery. Energy storage is usually in batteries (normally of the lead-acid type). Another possible storage alternative, such as hydrogen, is not currently economically viable, given the high cost of the electrolyzers and fuel cells and the low efficiency in the electricity–hydrogen–electricity conversion. When the design of these systems is carried out, it is usually done resolve an optimization problem in which the Net Present Cost (NPC) is minimized or, in some cases, in relation to the Levelized Cost of Energy (LCE). The correct resolution of this optimization problem is a complex task because of the high number of variables and the non-linearity in the performance of some of the system components. This paper revises the simulation and optimization techniques, as well as the tools existing that are needed to simulate and design stand-alone hybrid systems for the generation of electricity.     

Why are remote Western Australians installing renewable energy technologies in stand-alone power supply systems?

As people living in remote areas rely on SPS systems for their electricity and water needs, they hold a practical and non-idealistic perspective towards using renewable energy technologies. This research explores pastoral owner-operators’ personal experience and opinion of stand-alone power supply (SPS) systems over 30 years in remote pastoral regions Western Australia (WA). This research was undertaken qualitatively in terms of the experience of remote Australians of energy service delivery and SPS system performance to obtain personal opinions of remote pastoral people who rely on SPS systems to provide basic needs. This research concluded that the impressive growth in total renewable energy capacity in remote off-grid SPS systems in WA is primarily due to subsidies that aim to fuel-switch to renewable energy sources. Despite this, other major reasons for the increases in renewable energy capacity are escalating conventional fuel costs, difficulties in attracting qualified service contractors, increasing desire for quiet, 24-h energy services, and a range of unique situations. Despite the increased use of renewable energy technologies, this research reinforced previous research conclusions that consistently found both the conventional and renewable energy service sector wanting in remote areas. Three areas needing attention to sustain the growth in renewable capacity are: technical SPS system integration, service infrastructure, and technical reliability.     

Modeling and analysis of six-phase synchronous generator for stand-alone renewable energy generation

This paper presents a mathematical model of six-phase synchronous generator (SPSG) for analysis of its transient and dynamic behavior for stand-alone renewable energy generation in conjunction with a hydro power plant. In the analytical model, effect of common mutual leakage reactance between the two three-phase winding sets, and the mutual leakage coupling between d- and q-axis of the two stator windings have been considered. Paper also discusses the applicability of SPSG for supplying two individual loads by presenting the results of analytical and experimental study of transient and steady-state behavior under various operating conditions. It is shown that it can be used to supply two independent three-phase loads. While the interaction between the two windings is inevitable and variation of load at one winding set changes the operating conditions at the other winding, the situation is still satisfactory for a wide range of rural resistive loads.     

Techno-economic analysis of the integration of hydrogen energy technologies in renewable energy-based stand-alone power systems

A large number of stand-alone power systems that are based on fossil fuel or renewable energy (RE) based, are installed all over Europe. Such systems, often comprising photovoltaics (PV) and/or diesel generators provide power to communities or technical installations, which do not have access to the local or national electricity grid. The replacement of conventional technologies such as diesel generators and/or batteries with hydrogen technologies, including fuel cells in an existing PV-diesel stand-alone power system providing electricity to a remote community was simulated and optimised, using the hybrid optimisation model for electric renewables (HOMER) simulation tool. A techno-economic analysis of the existing hybrid stand-alone power system and the optimised hydrogen-based system was also conducted. The results of the analyses showed that the replacement of fossil fuel based gensets with hydrogen technologies is technically feasible, but still not economically viable, unless significant reductions in the cost of hydrogen technologies are made in the future.     

Selection of capacitance for self-excited six-phase induction generator for stand-alone renewable energy generation

This paper presents a simple method for finding the suitable value of shunt and series capacitance necessary to initiate self excitation and self-regulation (voltage regulation) in a self-excited six-phase induction generator (SPSEIG) for stand-alone renewable energy generation in conjunction with the hydropower. The problem is formulated as multivariable unconstrained nonlinear optimization problem. The admittance of the equivalent circuit of SPSEIG is taken as an objective function. Frequency and magnetic reactance or speed and magnetic reactance or frequency and capacitive reactance are selected as an independent variables depending upon the operational condition of the machine. Fmincon method is used to solve the optimization problem. Computed results were experimentally verified to validate the analytical approach presented in the paper.     

可再生能源发电的展望

21世纪能源结构将会发生根本的变化。寻找和开发利用清洁高效的可再生能源，将是世界能源发展的必然趋势。文章介绍了国内外新能源发电技术的现状与前景，针对中国所面临的挑战，提出了可再生能源发电问题的建议。     

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.     

Optimization of control strategies for stand-alone renewable energy systems with hydrogen storage

This paper presents a novel strategy, optimized by genetic algorithms, to control stand-alone hybrid renewable electrical systems with hydrogen storage. The strategy optimizes the control of the hybrid system minimizing the total cost throughout its lifetime. The optimized hybrid system can be composed of renewable sources (wind, PV and hydro), batteries, fuel cell, AC generator and electrolyzer. If the renewable sources produce more energy than the one required by the loads, the spare energy can be used either to charge the batteries or to produce H₂ in the electrolyzer. The control strategy optimizes how the spare energy is used. If the amount of energy demanded by the loads is higher than the one produced by the renewable sources, the control strategy determines the most economical way to meet the energy deficit. The optimization of the various system control parameters is done using genetic algorithms. This paper explains the strategy developed and shows its application to a PV–diesel–battery–hydrogen system.     

Direct coupling photovoltaic power regulator for stand-alone power systems with hydrogen generation

This paper describes a photovoltaic power regulator aimed for photovoltaic stand-alone hydrogen-backup power systems. The main characteristics of the regulator are the following; it employs a modular approach where each power cell has three ports, one input and two outputs, the input port is connected to a photovoltaic source while the two output ports are connected to a battery and to an electrolyser, respectively. A second characteristic is that the proposed regulator is driven sequentially, minimising the regulator losses. The operation and features of the photovoltaic regulator are presented and analyzed. Design guidelines are suggested and experimental validation is also given for a 2 kW prototype.     

Pre-feasibility study of stand-alone hybrid energy systems for applications in Newfoundland

A potential solution for stand-alone power generation is to use a hybrid energy system in parallel with some hydrogen energy storage. In this paper, a pre-feasibility study of using hybrid energy systems with hydrogen as an energy carrier for applications in Newfoundland, Canada is explained. Various renewable and non-renewable energy sources, energy storage methods and their applicability in terms of cost and performance are discussed. HOMER is used as a sizing and optimization tool. Sensitivity analysis with wind speed data, solar radiation level, diesel price and fuel cell cost was done. A remote house having an energy consumption of 25 kW h/d with a 4.73 kW peak power demand was considered as the stand-alone load. It was found that, a wind–diesel–battery hybrid system is the most suitable solution at present. However, with a reduction of fuel cell cost to 15% of its current value, a wind–fuel cell system would become a superior choice. Validity of such projection and economics against conventional power sources were identified. Sizing, performance and various cost indices were also analyzed in this paper.     

Utilization of renewable energy sources for power generation in Iran

Utilization of non-renewable energy sources not only results in environmental deterioration but also confronts us with the dilemma of a rapid rate of depletion of such resources, while renewable energy sources can serve us indefinitely with minimal environmental impacts as compared with fossil and nuclear fuels.This article deals with the extent of harnessing renewable energy sources for power generation in Iran, a Middle Eastern Asian nation.     

Performance evaluation of series compensated self-excited six-phase induction generator for stand-alone renewable energy generation

This paper presents the steady-state behavior of a series compensated (short-shunt) self-excited six-phase induction generator (SPSEIG) configured to operate as stand-alone electric energy source in conjunction with a hydro power plant. A purely experimental treatment is provided with the emphasis placed on operating regimes that illustrate the advantages of using SPSEIG. In particular, it is shown that the SPSEIG can operate with a single three-phase capacitor bank, so that the loss of excitation or fault at one winding does not lead to the system shutdown. The generator can also supply two separate three-phase loads, which represent an additional advantage. Experimental results include loading transients with independent three-phase resistive and resistive–inductive load at each of the two three-phase winding sets, and measured steady-state characteristics for various load and/or capacitor bank configurations. Practical results for long-shunt configuration are also given for comparative performance evaluation of series compensated SPSEIG.     

A comprehensive review of renewable energy resources for electricity generation in Australia

Recently, renewable energy resources and their impacts have sparked a heated debate to resolve the Australian energy crisis. There are many projects launched throughout the country to improve network security and reliability. This paper aims to review the current status of different renewable energy resources along with their impacts on society and the environment. Besides, it provides for the first time the statistics of the documents published in the field of renewable energy in Australia. The statistics include information such as the rate of papers published, possible journals for finding relative paper, types of documents published, top authors, and the most prevalent keywords in the field of renewable energy in Australia. It will focus on solar, wind, biomass, geothermal and hydropower technologies and will investigate the social and environmental impacts of these technologies.     

Electrical integration of renewable energy into stand-alone power supplies incorporating hydrogen storage

A stand-alone renewable-energy system employing a hydrogen-based energy store is now being commissioned within the HaRI project at West Beacon Farm, Leicestershire, UK. The interconnection of the various generators, loads and storage system is made through a central DC busbar: an arrangement that is believed to be unique within systems of this type and scale. The rotating generators, such as the wind turbines, are connected through standard industrial drives operating in regenerative mode, while the DC devices—electrolyser, fuel cell and solar photovoltaic array—employ custom DC–DC converters. This paper reviews the design philosophy of the electrical system and the various converters required. Modelling and simulation of the system is discussed along with practical lessons learnt from its implementation and some initial results are presented.