Analysis of the combined use of wind and pumped storage systems in autonomous Greek islands

In autonomous islands, the wind penetration is restricted due to technical reasons related with the safe operation of the electrical systems. The combined use of wind power with pumped storage (WPS) systems is considered as a means to exploit the abundant wind potential, increase the wind installed capacity and substitute conventional peak supply. An approach for the simulation of the autonomous electrical systems is proposed and applied in three islands. The simulation is based on the non-dynamic analysis of the electrical system, in order to calculate the energy contribution of the different power units. The aim is to analyse the prospects of WPS systems to decrease the electrical system's cost. The results show that the integration of WPS in autonomous islands may decrease the system's electricity production cost     

A simplified model for estimating the monthly performance of autonomous wind energy systems with battery storage

This paper presents a simplified algorithm to estimate the monthly performance of autonomous small-scale wind energy systems with battery storage. The novel model is drawn based on the simulation results, using eight-year long hour-by-hour measured wind speed data from five different locations throughout the world. An hourly constant load profile is used. The renewable energy simulation program (ARES) of the Cardiff School of Engineering is used. The ARES simulates the battery state of voltage (SoV) and is able to predict the system performance.The monthly performance values obtained from the simulations are plotted against increasing energy to load ratios for varying battery storage capacities to obtain performance curves. The novel method correlates the monthly system performance with the parameters of the Weibull distribution function, thus offering a universal use. The monthly performance curves are mathematically represented using a 2-parameter function. The novel method is validated by comparing the simulated performance values with those estimated from the simplified algorithm. The standard errors calculated in estimation of the system performance using the simplified algorithm are further presented for each battery capacity.     

The role of pumped storage systems towards the large scale wind integration in the Greek power supply system

In the recent years, the debate on the necessity of pumped storage systems in the Greek power supply system has started. In the current decade, the Greek power system will gradually try higher RES penetration, mainly due to wind energy and photovoltaics integration. Variability of wind and PV generation and the current structure of the Greek power system introduce technical constraints, which should be taken into consideration in the forthcoming large scale RES integration. This paper examines the ability of the Greek power system to absorb renewable power and the necessity of pumped storage systems. The feasibility of pumped storage systems is discussed in three different scenarios of wind–photovoltaics integration. Results show that for the gradual increase of variable output RES, pumped storage systems are required, but the feasibility of pumped storage systems is not proved in the intermediate scenarios of RES integration.     

Exploitation of moderate wind resources by autonomous wind electric pumping systems

A laboratory test rig has been developed, in order to analyse the mutual interaction of the different components of a low power WEPS, in the presence of arbitrarily chosen wind intensity. The performances with moderate wind speed of a system composed by a horizontal axis, fixed-pitch wind turbine, a synchronous generator and a centrifugal electric pump have been investigated, both at the start and under steady-state conditions. A control strategy of the alternator field voltage, which facilitates the starting of the pump in the presence of modest wind intensity and maximises average water discharge under any wind condition, has been defined, implemented on an electronic board and tested.     

Pumped storage in systems with very high wind penetration

This paper examines the operation of the Irish power system with very high levels of wind energy, with and without pumped storage. A unit commitment model which accounts for the uncertainty in wind power is used. It is shown that as wind penetration increases, the optimal operation of storage depends on wind output as well as load. The main benefit from storage is shown to be a decrease in wind curtailment. The economics of the system are examined to find the level at which storage justifies its capital costs and inefficiencies. It is shown that the uncertainty of wind makes the option of storage more attractive. The size of the energy store has an impact on results. At lower levels of installed wind (up to approximately 50% of energy from wind in Ireland), the reduction in curtailment is insufficient to justify building storage. At greater levels of wind, storage reduces curtailment sufficiently to justify the additional capital costs. It can be seen that if storage replaces OCGTs in the plant mix instead of CCGTs, then the level at which it justifies itself is lower. Storage increases the level of carbon emissions at wind penetration below 60%.     

Development of wind energy systems for New England islands

The 3000 plus islands of New England with their varying electrical needs and high electricity costs present an opportunity for renewable energy development. This paper summarizes the results of ongoing wind energy projects carried out by the University of Massachusetts for the development of renewable energy on several of these islands. In addition to technical–economic issues, the work has addressed potential environmental and political problems that might arise with the installation of such systems. Summaries of four selected case studies involving this work are given in this paper. The overall analysis method used to study each of these studies is described, and the example case studies present a status of the work to date on each of these projects.     

Smooth transition from wind only to wind diesel mode in an autonomous wind diesel system with a battery-based energy storage system

High wind penetration wind diesel hybrid systems (WDHS) have three modes of operation: Diesel Only (DO), Wind Diesel (WD) and Wind Only (WO). The WDHS presented in this article consists of a wind turbine generator (WTG), a diesel engine (DE), a synchronous machine (SM), the consumer load, a battery-based energy storage system (BESS), a discrete dump load (DL) and a distributed control system (DCS). The DE can be engaged (DO and WD modes)/disengaged (WO mode) from the SM by means of a clutch. The DCS consists of a sensor node, which measures the SM and DE speeds, calculates the reference active power P_REF necessary to balance the active power in the WDHS and communicates this P_REF value with a message to the BESS and DL actuator nodes. In the WO mode, the power sources are the WTG and the BESS (temporary) and if there is an active power shortfall, the DCS, to prevent a frequency collapse, must order to start the DE, wait until the DE reaches the SM speed and lock the clutch, changing to the WD mode. With the clutch locked, the combined actuation of the DE+BESS will raise the system frequency to the rated value. This WO to WD transition is simulated in this article showing graphs for frequency, voltage and active powers for the elements of the system. These graphs are compared with the ones obtained if the BESS does not actuate in WD mode. The comparison results show that with the BESS actuation in WD mode the settling time is reduced a 50%, the over and under shooting in the system frequency are eliminated and the system voltage variations are reduced a 40%.     

On the wind power rejection in the islands of Crete and Rhodes

Crete and Rhodes represent the two biggest isolated power systems in Greece. The energy production in both islands is based on thermal power plants. The annual wind energy rejection percentage is calculated for Crete and Rhodes in this paper. The rejected wind energy is defined as the electric energy produced by the wind turbines and not absorbed by the utility network, mainly due to power production system's stability and dynamic security reasons. A parametric calculation of the annual wind energy rejection percentage, in terms of the installed wind power, the power demand and the maximum allowed wind power instant penetration percentage, is accomplished. The methodology takes into account (i) the wind power penetration probability, restricted by the thermal generators technical minima and the maximum allowed wind power instant penetration percentage over the instant power demand; and (ii) the wind power production probability, derived by the islands' wind potential. The present paper indicates that isolated power systems which are based on thermal power plants have a limited wind power installation capacity—in order to achieve and maintain an adequate level of system stability. For a maximum wind power instant penetration percentage of 30% of the power demand, in order to ensure an annual wind energy rejection percentage less than 10%, the total installed wind power should not exceed the 40% of the mean annual power demand. The results of this paper are applicable to medium and great size isolated power systems, with particular features: (i) the power production is based on thermal power plants; (ii) the power demand exhibits intensive seasonal variations and is uncorrelated to the wind data; (iii) the mean annual power demand is greater than 10MW; and (iv) a high wind potential, presenting mean annual wind velocity values greater than 7·5ms^?1, is recorded. Copyright © 2007 John Wiley &Sons, Ltd.     

Optimization of autonomous hybrid systems with hydrogen storage: Life cycle assessment

The design of autonomous systems for the rural electrification is a complex task due to the diversity of variables involved in such processes. The absence of programs and methods that carry out this task in a clear and precise manner constitutes a barrier to the dissemination of these systems, although some tools have been developed that present other possible limitations. The exclusion of the environmental dimension in the design and evaluation process of hybrid systems means that the true benefits are not evaluated in terms of quality and quantity. In an attempt to overcome such deficiencies, this work presents a new method of design; approached from the multi‐objective optimization of systems. The multi‐objective optimization by means of enumerative search implemented by the Hybrid Optimization Model for Electric Renewable program is used to generate a set of solutions optimized economically by the value of the net present cost (NPC). The analysis of greenhouse gas emissions (in tCO₂‐eq.) in the life cycle of each one of the system components is carried out and a set of solutions with the values of the two objective functions is generated, namely NPC and NAE_SLC (net avoided emissions in the system life cycle). The method is applied to a case study in a Cuban rural community. The compromise solution obtained by means of the proposed algorithm includes a wind turbine (WT) of 25.4 and 8 kW of photovoltaic panels, while that of the HOGA includes a WT of 76 and 21 kW of photovoltaic panels. Both commitment solutions consider hydrogen storage instead of storage in batteries, as a better option for the energy storage. Copyright © 2011 John Wiley & Sons, Ltd.     

Computational environment to investigate wind integration into small autonomous systems

This paper presents briefly the methodologies and the respective computational tools for the investigation of the wind power exploitation in small autonomous power systems supplying the load demand of small islands. The proposed methodology examines the wind power penetration from both technical and economic point of view. It comprises tools for load forecasting and management, power system analysis and generation system simulation and planning.     

Optimisation and techno-economic analysis of autonomous photovoltaic–wind hybrid energy systems in comparison to single photovoltaic and wind systems

A techno-economic analysis for autonomous small scale photovoltaic–wind hybrid energy systems is undertaken for optimisation purposes in the present paper. The answer to the question whether a hybrid photovoltaic–wind or a single photovoltaic or wind system is techno-economically better is also sought. Monthly analysis of 8 year long measured hourly weather data shows that solar and wind resources vary greatly from one month to the next. The monthly combinations of these resources lead to basically three types of months: solar-biased month, wind-biased month and even month. This, in turn, leads to energy systems in which the energy contributions from photovoltaic and wind generators vary greatly. The monthly and yearly system performances simulations for different types of months show that the system performances vary greatly for varying battery storage capacities and different fractions of photovoltaic and wind energy. As well as the system performance, the optimisation process of such hybrid systems should further consist of the system cost. Therefore, the system performance results are combined with system cost data. The total system cost and the unit cost of the produced electricity (for a 20 year system lifetime) are analysed with strict reference to the yearly system performance. It is shown that an optimum combination of the hybrid photovoltaic–wind energy system provides higher system performance than either of the single systems for the same system cost for every battery storage capacity analysed in the present study. It is also shown that the magnitude of the battery storage capacity has important bearings on the system performance of single photovoltaic and wind systems. The single photovoltaic system performs better than a single wind system for 2 day storage capacity, while the single wind system performs better for 1.25 day storage capacity for the same system cost.     

Optimization of integrated photovoltaic–wind power generation systems with battery storage

In this paper, a new method for optimization of a wind–PV integrated hybrid system is presented. Based on deficiency of power supply probability (DPSP), relative excess power generated (REPG), unutilized energy probability (UEP), life cycle cost (LEC), levelized energy cost (LEC) and life cycle unit cost (LUC) of power generation with battery bank, the method addresses a specific location and employs an iterative scheme. A simulation software code has been developed to carryout the analysis for optimizing the size of the integrated system for a given location. Also, a case study using the software on the selection of optimal size of the integrated system for the site Pompuhar, Tamil Nadu state in India has been presented.     

Techno-economic comparison of energy storage systems for island autonomous electrical networks

The oil-dependent electricity generation situation met in the Aegean Archipelago Islands is in great deal determined by increased rates of fuel consumption and analogous electricity production costs, this being also the case for other island autonomous electrical networks worldwide. Meanwhile, the contribution of renewable energy sources (RES) to the constant increase recorded in both the Aegean islands’ annual electricity generation and the corresponding peak load demand is very limited. To compensate the unfavorable situation encountered, the implementation of energy storage systems (ESS) that can both utilize the excess/rejected energy produced from RES plants and improve the operation of existing thermal power units is recommended. In the present study, a techno-economic comparison of various RES-ESS configurations supported by the supplementary or back-up use of existing thermal units is undertaken. From the results obtained, the shift of direction from the existing oil-dependent status to a RES-based alternative in collaboration with certain storage technologies entails – apart from the clear environmental benefits – financial advantages as well.     

The value of compressed air energy storage with wind in transmission-constrained electric power systems

In this work, we examine the potential advantages of co-locating wind and energy storage to increase transmission utilization and decrease transmission costs. Co-location of wind and storage decreases transmission requirements, but also decreases the economic value of energy storage compared to locating energy storage at the load. This represents a tradeoff which we examine to estimate the transmission costs required to justify moving storage from load-sited to wind-sited in three different locations in the United States. We examined compressed air energy storage (CAES) in three “wind by wire” scenarios with a variety of transmission and CAES sizes relative to a given amount of wind. In the sites and years evaluated, the optimal amount of transmission ranges from 60% to 100% of the wind farm rating, with the optimal amount of CAES equal to 0–35% of the wind farm rating, depending heavily on wind resource, value of electricity in the local market, and the cost of natural gas.     

Impact of wind power forecasting error bias on the economic operation of autonomous power systems

Many efforts have been presented in the literature for wind power forecasting in power systems and few of them have been used for autonomous power systems. In addition, some recent studies have evaluated the impact on the operation of power systems and energy markets that the improvement of wind power forecasting can have. In this paper, the value of the information provided to the operators of autonomous power systems about forecasting errors is studied. This information may vary significantly, e.g. it can be only the normalized mean absolute error of the forecast, or a probability density function of the errors for various levels of forecasted wind power, which can be provided either during the evaluation phase of the wind power forecasting tool or by online uncertainty estimators. This paper studies the impact of the level of detail provided about wind power forecasting accuracy for various levels of load and wind power production. The proposed analysis, when applied to the autonomous power system of Crete, shows significant changes among the various levels of information provided, not only in the operating cost but also in the wind power curtailment. Copyright © 2008 John Wiley & Sons, Ltd.     

Review of flywheel energy storage systems for wind power applications

风力发电可以解决能源短缺和环境污染等问题,但由于风速随机性和间歇性的特点导致风电输出电压、功率和频率存在较大波动,因此风电的大规模并网会对现有电网的稳定运行造成不利影响。飞轮储能是一种高效无污染的储能技术,而且通过合理的控制策略和控制设备可实现电网调频及短时间调峰以解决大规模风电并网带来的问题。本文主要介绍了飞轮储能在风力发电领域的应用背景、飞轮储能的结构原理和目前国内外在飞轮储能控制策略方向的研究进展。     

An analysis of the Greek photovoltaic market

The number of photovoltaic applications has increased slightly over the last 10 years in Greece, with a forecasted 40% increase in the annual rate of sales over the next few years, a target similar to the rest of the EU Member States. This article: (i) presents an analysis of the current situation on the photovoltaic market in Greece and attempts to segment this market; (ii) investigates the existing incentives policy, as well as the crucial barriers for the wide dissemination of the photovoltaic applications, and (iii) records the market actors’ aspects and predictions for the future. Furthermore, in order to supply essential information for business development, the current investment and legislative framework is presented.     

Operation planning of hydrogen storage connected to wind power operating in a power market

In this paper, a methodology for the operation of a hybrid plant with wind power and hydrogen storage is presented. Hydrogen produced from electrolysis is used for power generation in a stationary fuel cell and as fuel for vehicles. Forecasts of wind power are used for maximizing the expected profit from power exchange in a day-ahead market, also taking into account a penalty cost for unprovided hydrogen demand. During online operation, a receding horizon strategy is applied to determine the setpoints for the electrolyzer power and the fuel cell power. Results from three case studies of a combined wind-hydrogen plant are presented. In the first two cases, the plant is assumed to be operating in a power market dominated by thermal and hydropower, respectively. The third case demonstrates that the operating principles are also useful for isolated wind-hydrogen systems with backup generation.     

Review on combined wind power generation and energy storage systems

储能系统由于能够实现电能的时空平移,具有响应速度快,规模化等优点,是改善风电波动性,提高其并网能力的有效手段,构建风储联合发电系统成为目前研究重点.简单介绍了风电并网对电力系统的影响及不同类型电池储能技术的发展现状,给出了部分国内外风储联合发电系统的示范工程,并分析了平滑风电功率波动,跟踪计划出力曲线和削峰填谷3种主要运行方式,重点阐述了目前风储联合发电系统控制策略和储能容量配置研究现状,对进一步开展风储联合发电系统的研究进行了展望,指出经济性仍然是制约储能技术应用的关键问题之一,提高包含储能单元的风储联合发电系统的经济性是今后的研究重点.