The assessment of the contribution of short-term wind power predictions to the efficiency of stand-alone hybrid systems
Highlights
► Analysis of a stand-alone wind turbine/fuel cell/battery hybrid system. ► The utilization of wind power predictions in order to optimize the hydrogen consumption. ► Application of fuzzy logic for hybrid system energy management. ► Evaluation of hybrid system performance with and without prediction based control.
Introduction
Wind power has become increasingly competitive with other conventional power generation systems over the last decade and the share of wind energy in worldwide electricity production has increased dramatically. The cost-effectiveness, reliability and efficiency of wind energy compared to those of other alternative sources can be regarded as the main reasons for this development. However, it is evident that a wind energy system cannot provide a continuous supply of energy due to the intermittent nature of wind. Therefore in order to meet sustained load demands, particularly in remote rural areas where economics are not favorable to extend the grid supply, different energy sources need to be combined. Thus, it may be likely to utilize alternative energy resources more efficiently and alleviate the power quality problems caused by wind power.
To this end, a great number of concepts and system designs have been studied in the literature over the past decade [1], [2], [3]. In order to maintain a constant power under all conditions, Kalantar and Mousavi present a stand-alone system of wind turbine (WT), microturbine, solar array and battery storage [4]. Another stand-alone wind/fuel cell (FC) hybrid system is proposed by Khan and Iqbal [5]. They propose to store superfluous energy from wind by producing hydrogen with the aim of later use. Taking this issue into account, many authors utilize the storage systems at different scales such as ultracapacitors, electrolyzer/FC systems, flywheels, pneumatic systems and batteries [6], [7], [8], [9], [10]. Hence a share of power can be supplied from these systems while decreasing the size and cost of the WTs.
Lately, exploiting the energy from WTs during periods of over-production and using this energy with a high efficiency when wind power is not sufficient become a promising research area where many researchers have contributed. With the objective of increasing the hydrogen production according to the wind conditions, Valenciaga and Evangelista [11] propose a stand-alone system consists of a wind energy generation module, an electrolyzer and a battery bank. Khalid and Savkin [12] utilize wind power prediction so as to provide an efficient control to smooth the wind power output and prolong the battery life in a hybrid energy system. Hence, it is inferred that accurate wind power predictions would be utilized to help in achieving energy efficiency to some extent apart from its main applications such as unit commitment, economic dispatch and participation in the electricity market.
This study gives a further step in terms of improving efficiency by making use of wind power prediction in a system created by the combination of a WT, an FC and a battery bank. Thus it is aimed to minimize the hydrogen consumption without putting at risk the quality and continuity of the energy provision and reducing the operative life of the battery bank. For this purpose, operation of a residential application primarily powered by a WT and supported by a hybrid system made up of a PEM (Proton Exchange Membrane) FC stack and a battery bank is modeled and simulated using MATLAB, Simulink and SimPowerSystems software packages.
In the proposed system, when the WT produces enough power, the load demand will be supplied entirely from wind energy. In the case of probable low wind conditions, the control system examines whether the predicted wind and battery power will be sufficient for net load according to the outputs from the wind prediction system. Otherwise, the deficit power can be supplied from the FC and/or the battery with respect to control system. If the output power from the WT exceeds demand, the excess power may be stored by the battery banks to be used for insufficient generation.
This paper is organized as follows: Section 2 presents the proposed system and gives a brief description of each component. The prediction model developed is explained in Section 3. The case study and simulation results are given in Section 4 and Section 5 concludes our study.
Section snippets
System description
A simulation model of the hybrid system is built in MATLAB/Simulink and SimPowerSystems in order to study the performance of the proposed control strategy. The main components in the system proposed are a 2 kW PEMFC model with a DC/DC converter, a battery bank with a reversible converter which is capable of either charging the battery or recovering the storage energy, and a 5 kW WT model as illustrated in Fig. 1.
Among the various types of FC systems, PEMFC has been found to be especially suitable
Wind power prediction model
As stated earlier, the wind power prediction model is integrated with the hybrid energy system so as to optimize the hydrogen consumption as well as to ensure the continuity of load supply. Therefore, the controller utilizes the inputs from the wind prediction model and power capacities of the hybrid system components. The proposed wind power prediction model consists of four processes, as given in Fig. 4.
The first process is to utilize wavelet transform to cut up the original wind speed series
Case study and results
The location selected for the simulations is on Aliaga (Izmir), a town in western Turkey (Fig. 6). This region is chosen because of its high wind potential during all seasons. For the simulation studies, a period of one day is chosen that is representative of the general situation which can probably be seen in this region for these wind speeds and load profile. In order to avoid data redundancy, simulations are only carried out with the values concerning the autumn of 2010, as depicted in Fig. 7
Conclusions
As WT output power varies with wind speed, it can be combined with FC stack and battery storage to satisfy the load demand under all conditions and to assure the required degree of reliability. In this study, the wind generation system is used as main energy source while the FC and battery are used as back-up energy sources.
The main contribution of this work is the minimization of hydrogen amount consumed in the FC system utilizing short-term wind power predictions. The simulation results show
Acknowledgments
This work was supported in part by “Yildiz Technical University Scientific Research Projects Coordination Department” under Grant 2011-04-02-DOP02”. Also the authors are gratefully acknowledged to the General Directorate of Electrical Power Resources Survey and Development Administration (EIE) for providing the real wind speed data required for this study.
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