Technical and economic parameters regarding the operation of wind parks and pumped hydro storage systems in autonomous and in interconnected insular electrical systems

The scope of this article is to investigate the technical and economic feasibility of a wind park – Pumped Hydro Storage (PHS) system both in autonomous, insular grids and in interconnected electrical systems. As a case study, the island of Leros, Greece, was introduced, currently non-interconnected, yet planned to be interconnected with the mainland grid in the approximate future. A specific site for the PHS and the wind park installation was selected in the island and essential operation parameters of the plant's operation were defined, such as the available wind potential and the upper reservoir's volume storage capacity and absolute altitude. Given the inadequate rainfalls in the island, the PHS system will operate with seawater, using the sea as the lower reservoir. Two alternative operation algorithms – concepts were introduced, referring to the plant's operation in the alternatively examined electrical systems. The annual operation of the plant was computationally simulated for both scenarios. The work was integrated with the accomplishment of economic evaluations. In the scenario of the non-interconnected system, the goal was the real-time power demand coverage. The wind park and the PHS system operate as an integrated system, the so-called “hybrid power plant”, assuming a feed-in-tariff pricing for the produced electricity. The PHS operation depends exclusively on the electricity storage from the wind park production. Given that the insular grid is non-interconnected, the electricity penetration is limited by the insular power demand. The plant's sizing was optimized through iterative executions of the computational simulation, aiming to achieve at least 80% annual electricity penetration. The investment exhibits positive internal rate of return for a minimum electricity selling price of 0.14 EUR/kWh, revealing the competitiveness of the proposed plant, given that the current electricity production specific cost in the autonomous grid was given 0.28 EUR/kWh by the utility. In the scenario of the interconnected system, the wind park and the PHS system operate independently, following the electricity pricing fluctuation of the liberalized electricity market. The upcoming interconnection allows for the full utilization of the wind park's generation in the mainland grid and maximum exploitation of the PHS storage capacity, eliminating the penetration constraints occurring in the autonomous scenario, thereby significantly increasing the total electricity yield. The hydro power plant injects electricity in the grid during the peak demand periods, while, during the rest of the day, electricity can be absorbed by the pumps for storage. Hence, it operates as an independent storage plant, not directly connected to the wind park. The wind park's produced electricity can be either sold directly to the grid or stored in the PHS system, during periods of low selling price. Two alternative sub-cases were investigated regarding the plant's size. Firstly, the plant's size remains the same with the scenario of the non-interconnected system. Secondly, the hydro turbines and pumps nominal power increases approximately 30%, so as to maximize the available storage capacity of the PHS upper reservoir. In both sub-cases, the corresponding investments exhibit payback period at the range of 7 years, proving the economic viability of the examined power plants.