## 1 Introduction
### Hybrid Wind-Powered Pumped-Hydro Energy Storage  
Increasing interest in the hybrid wind electric generation with pumped-hydro energy storage systems is evident through recent publications in the field studying the technological, environmental, and economic aspects of such projects. In [9], the pump and the pipe storage system is thoroughly studied in addition to the possible structure of the system under the condition of variable wind energy as an electric power source in order to determine the challenges and obstacles to compose a grid connected wind-hydro-pumped storage station. Obstacles such as control and dispatch of the system consisting of wind turbines and pumps when connected to the grid, stability of system, and proper allocation (capacity ratio) and efficiency of each system component were studied focusing on discussing the power balance in the grid connected system. It was found that the biggest challenge for power balance in a wind driven pump storage system is whether or not the power regulation range of pumps may cover the fluctuation range of wind energy for a given head lift and a certain flow. [PERSON] et al. in [10] proposed a method to design wind-solar hybrid power supply system with pumped storage to replace the use of batteries in order to overcome the combined shortage in wind-solar hybrid system power generation and electricity load's imbalance due to uncertainty of resources. According to the authors, the method proposed can produce a reasonable configuration for the system capacity according to the user's electricity load and resource condition and can ensure system reliability of power supply and reduce the cost of the power generation system. [PERSON] et al. in [11] investigated the contribution of pumped-hydro energy storage to the operation of electric system with high wind penetration with the help of a weekly optimal operation-scheduling model. The system was based on programming to get the optimal hourly thermal, hydro, and pumping powers for minimizing the production cost of the system. The system operation was studied under different demand and wind speed scenarios to scale the system according to different wind penetration levels. It was concluded that pumped-storage plants contribute in all cases analyzed to the reduction of the system operation costs, the magnitude of the reduction increased as the level of wind power penetration increases. Regarding the technology of wind farms, authors in [12; 13] fully investigates the trends of wind energy technologies. Outcomes of this study showed that within the next two-three decades the vertical axis wind turbine is expected to dominate the field as it requires less land space and can produce higher energy. They also forecasted that the demand for energy storage systems combined with wind farms will rise highly. Many areas, however, still require technological upgrading for the reduction of its cost. The authors in [14] discuss the importance of carrying out performance forecasts for renewable energy systems to maximize the resultant benefits and to keep the reliability indicators at the required level. Additionally, recent developments in the forecasting and management fields provide essential means for manage renewable energy projects. The publication also indicates that storage units should be used when the level of renewable energy projects integrated in the power system becomes significant. The adoption of probabilistic approaches for energy forecasts is said to aid in setting correct storage requirements leading to economic dispatch with higher success. Multiple recent studies were focused on the prospects of hybrid wind generations systems with pumped-hydro energy storage [15; 16; 17; 18; 19; 20; 21; 22]. Those studies were distributed in different areas of the globe; however, most of them were focused on integrating this type of system into autonomous grid systems in remote islands.