Because of the world's increased population and developing industries, the demand for electrical energy is increasing. It is known that the fossil-based sources will be consumed in the future, therefore, sustainable and renewable types of energy resource such as wind energy has become very popular in the past decade. Wind energy has a wide range of applications that are rapidly expanding, unlimited, environmentally friendly, and cost-effective. It has a bright feature, however, due to its stochastic and intermittent nature, it is hard to predict accurately (Xiaochen et al., 2011; Yang et al., 2013; Yang & Shaoshuai, 2016).
Wind power forecasting is highly dependent on the wind speed forecasting process. The wind power forecast is essential and significant for determining the locations of wind plants to be built in (Varanasi & Tripathi, 2016), power system quality, grid reliability, energy planning (Rahmani et al, 2013; Lund, 2005; Debbağ & Yilmaz, 2015), energy transformation efficiency and interconnected network operations (Riahy & Abedi, 2008).
The wind parameters such as wind speed, wind direction, temperature, humidity, and pressure must be measured and recorded for at least 12 months to determine the power of the wind power plant to be constructed. This period may be extended due to climate changes caused by global warming (Kerem et al, 2014). The most accurate wind power forecasting studies depending on the collected data might be encouraging and motivating for investors by providing light on future concerns. Thus, the significance of accurate wind power forecasting studies is once again highlighted.
The wind is a flow of air in motion and there is the kinetic energy of an object in motion. Thus, the theoretical power obtained from the wind can be calculated with (1) (Patel, 1942; Golding, 1955);
Pr = ½ ρa AT Vr3 (W) (1)
where, air density (ρa: 1.225 kg/m3), wing sweeping area (AT, m2) and wind speed (Vr, m/s). Temperature, atmospheric pressure, slope and air components are effective in air density. Thus, the air density can be calculated with (2) if the temperature (T) and height (Z) of the zone are known;
ρa = ( 353.049 / T). e (−0.034^Z/T) (2)
The above equations explain the theoretical wind power. In fact, according to Betz Law, the power value to be taken from the unit wind is 59% of the wind power it carries (Cp=0.59). The max power to be taken from the wind turbine is calculated in (3) (Ragheb & Ragheb, 2011; Gourieres, 1982);
Pr = ½ ρa AT Vr3 Cp (W) (3)
Figure 1 Kinetic energy flow of wind around a wind turbine (Rahmani et al., 2010)
Energy of the air passing through the wings can be defined as follows (4) (Çetin, 2006);
Ek= EkIn - EkOut (Nm) (4)
Kinetic energy (Ek) of the wind in motion is calculated in (5) and wind power (PT) is shown in (6);
Ek = ½ ρa AT Vr1 (Vr2 - Vr22) (Nm) (5)
PT = Ek/t = ½ ρa AT Vr1 (Vr2 - Vr22) (W) (6)
In literature, Rahmani et al., (2013) developed a hybrid model of Ant Colony Optimization (ACO) and PSO for short term wind energy estimation. To observe the performance of the hybrid model they used 364 days data from Binaloud wind farm. The proposed model predicted wind power as 3.513% using MAPE. Pousinho et al., (2010) developed a hybrid model of Particle Swarm Optimization (PSO) and Adaptive Neuro-Fuzzy Inference Systems (ANFIS) models for short-term wind power estimation. They analyzed the performance of the model and found the Mean Absolute Percent Error (MAPE) as 5.41%. Liang et al., (2015) designed a hybrid model of Hilbert Hur Huang Transform (HHT) and Hurst Analysis (HA) for wind power estimation. Using the Empirical Mode Decomposition (EMD) + Least Square Support Vector Machine (LSSVM) + Extreme Learning Machine (ELM) hybrid models they decreased to error values from 49.45% and 44.30% to 37.96 and 27.12%, respectively. Zhang et al., (2015) designed a hybrid estimation model of EMD + Support Vector Machine (SVM) for wind power estimation. They used the EMD to convert the wind energy sequence into a variety of internal functions, and the SVM used to optimize the optimal parameters and each component of the kernel function. According to analysis results, it is observed that the developed EMD + SVM hybrid model has significantly increased the wind power estimation accuracy. Kassa et al., (2016) designed a hybrid estimation model that includes ANN based Genetic Algorithm (GA) + Back Propagation (BP) models for wind power prediction. GA -optimized and BP - trained algorithm of multi-layer ANNs were used in this model. In order to test the performance of the model, they used the data of 2.5 MW wind turbine in Beijing. Catalao et al., (2011) developed a triple hybrid prediction model of Wavelet + PSO + ANFIS models for short term wind power estimation. In order to test the performance of the proposed model, they used data from the National Electricity Network (REN) in Portugal. They were compared to the success of the new model with other models such as Persistence, NRM, ARIMA, Neural Networks (NN), NNWT, NF and Wavelet + Neuro + Fuzzy (WNF). It was observed that the new hybrid model had better MAPE and NMAE error values. Osório et al., (2015) developed a hybrid estimation model of Wavelet Transform (WT), ANFIS, Evolutionary Particle Swarm Optimization (EPSO) and Mutual Information (MI) algorithms for short term wind power estimation. They observed the performance of the WT + ANFIS + EPSO + MI hybrid model were more successful than previous prediction algorithms. Azimi et al., (2016) designed a hybrid model based on time series that includes Time-Series Based K-Means Clustering Method (TSBK) and Cluster Selection Algorithm (CSA) for wind power estimation. In this model TSBK, Discrete Wavelet Transform (DWT) and Harmonic Analysis Time Series (HANTS) and Multilayer Perceptron Neural Network (MLPNN) algorithms were used to increase the accuracy of wind energy estimation. The task of TSBK is to separate the data into separate groups, identifying abnormal and irregular patterns and providing more appropriate learning for neural networks. That improves the accuracy of the estimated results. They applied the CSA to identify the best-trained cluster for MLPNN. The data were separated by Daubechies D4 wavelet transform and filtered by HANTS. They tested the performance of the developed model on the data obtained from different wind farms in the USA. The new hybrid model showed superior success according to the results of the analysis. Liu et al., (2015) developed a hybrid Relevance Vector Machine (RVM) model for wind power estimation. There are five Kernel Functions in this model that Gaussian Kernel, Laplacian Kernel, Cauchy in Distance Kernel, R (distance) Kernel and Thin-plate spline Kernel (Tps). The SVM prediction model used one by one with each Kernel. According to the analysis they observed that the proposed hybrid RVM model was more compatible with the Kernel parameters and obtained more accurate results than the other individual kernel models. Haque et al., (2014) designed the WT + FA + FF + SVM hybrid model for wind power estimation consisting of WT, Fuzzy Artmap (FA), Firefly (FF) and SVM. They have combined WT and FA algorithms for wind power estimation and optimized with FF. They used SVM to minimize wind power estimation errors obtained from WT + FA + FF. They tested the success of the hybrid model by using the wind power data from the Cedar Creek wind farm in Colorado. Chitsaz et al., (2015) used the Wavelet Neural Network (WNN) model trained with the Enhanced Clone Selection Algorithm (CSA) for wind power estimation. They used the Maximum Correntropy Criterion (MCC) instead of MSE in the estimation process. They used real-time hourly data of the wind turbine in Alberta, Canada in order to test the performance of the model. They compared the success of the model with other techniques and observed that this new model obtained more successful results. Osório et al., (2012) developed a hybrid prediction model of the WT, EPSO and ANFIS models for short-term wind power estimation. They found that the proposed model had MAPE of 4.28% and calculation time of less than 1min. Thus, they have obtained much more accurate estimation and short computation time than the other techniques in the literature. Kusiak et al., (2009) designed the MLP + kNN hybrid model for wind power estimation. And, they presented two basic estimation studies. The first one is the direct prediction model where the power estimate is derived directly from the weather forecast data. The other one is an integrated forecasting model which is produced by the estimated air data of the wind speed and then generated by the estimated wind speed and power. They examined the performance of the model for different time periods of 12 hours and 84 hours. They observed that the direct prediction model had better prediction performance than the hybrid prediction model. Catalao et al., (2011) developed a new hybrid model based on the WT model and a hybrid of NNs + Fuzzy Logic (FL) model for short term wind power estimation in Portugal. The proposed WNF hybrid model obtained MAPE value as 5.99%. Sharifian et al., (2018) designed a new hybrid prediction model called T2FNN + PSO to develop Type-2 Fuzzy Neural Network (T2FNN). This new model combines both the expert knowledge of the fuzzy system and the ability of the NNs to learn for accurate estimation of wind power.
In this study, to make a highly accurate wind power prediction, a newer and powerful hybrid metaheuristic approach called ANNs+(PSO-RMO) was used. Data was gathered from Wind Measuring Stations (WMS) located at various locations in the Burdur and Osmaniye cities for WMS-1 and WMS-2, respectively. To compare the effectiveness of ANNs+(PSO-RMO) approach, the other hybrids such as ANNs + ACO, ANNs + GA, ANNs + PSO, ANNs + RMO were designed. 50run was used to evaluate the performance of all developed hybrid metaheuristic models.
The main contributions of this study are;
1. Accurate wind power forecasting can be encouraging and motivating for investors to shed light on future uncertainties caused by global warming. Thus, CO2 and other greenhouse gases will not be released into the atmosphere as a consequence of focusing energy generation to clean, ecologically friendly, and renewable energy rather than fossil-fueled power plants.
2. The ANNs+(PSO-RMO) model is able to perform wind power forecasting studies with high accuracy, rapid and reliability without needing wind speed data, which is a vital parameter.
3. Wind power forecasting studies could be performed despite the height differences between the sensors. That is, wind power forecasting studies at 61m and 60.3m were performed using temperature (3m), humidity (3m) and pressure (3.5m) data for WMS-1 and WMS-2, respectively.
4. The effectiveness of the designed hybrid metaheuristic approach has been tested on real-time data taken from two distinct coordinates and the model success has been confirmed even at abrupt fluctuations.
5. This proposed model is proved to be more effective than the GA, ACO, PSO, and RMO models commonly used in the literature.
6. With this study, the wind power forecasting studies have been applied to ANNs+(PSO-RMO) model for the first time in the literature.