Design and evaluation of pv-seawater based pumped storage hydroelectric power plant (DPHES)) system

In this study, an innovative photovoltaic–seawater-based pumped hydro energy storage (PV-DPHES) model, integrating a photovoltaic (PV) system with a seawater-based pumped hydro energy storage system (DPHES), was designed and evaluated from technical, economic, and environmental perspectives in the Kaş district of Antalya, Turkey. Today, with the increasing share of renewable energy sources, the need for continuity and storage in energy production has become a critical issue. The intermittent nature of solar and wind energy, in particular, threatens electricity supply security and necessitates effective energy storage solutions. In this context, a seawater-based pumped hydro energy storage system (DPHES) offers a sustainable, economical, and environmentally advantageous alternative, especially in regions where freshwater resources are limited. The system is designed with a 500-meter elevation difference and provides high energy conversion efficiency with a net head of 557.84 m during pumping and 442.16 m during discharge. A hexagonal HDPE-membrane-lined upper reservoir with a volume of 75,000 m³ and a 1,450-meter-long, 0.92-meter-diameter penstock are used. High-efficiency Francis-type pumps and turbines were selected. With 78,235 CWT285-60P polycrystalline PV panels, each with a capacity of 285 Wp, covering a total area of 133,000 m², the system can deliver up to 19 MW of power and operates at an efficiency of 79.1%. The most significant advantage of using seawater is its unlimited and continuous availability, compared to freshwater-based pumped storage systems. The limitations of freshwater sources, high investment and operational costs, and restricted storage capacity challenge the continuity and feasibility of conventional systems. In contrast, systems using seawater offer low-cost and sustainable water supply in coastal and mountainous regions, providing a major advantage for integration with solar and wind energy. As seen in the Okinawa Seawater Pumped Storage Power Plant in Japan, the environmental and technical challenges of seawater can be managed in a controlled manner, and the reliability of such systems has been demonstrated. The system operates with a 7 hours pumping and 5 hours discharge cycle, and continuity in energy production is managed via a constant flow–water level relationship. The total installation cost is calculated at USD 81.04 million, with annual operating costs of USD 955,100. The LCOE of the PV-DPHES system is USD 0.0778/kWh, while the LCOE of the PV system alone is USD 0.01391/kWh both significantly below the 2023 electricity sales price of USD 0.1591/kWh. The system generates a net annual revenue of USD 3.35 million and a total net profit of USD 86.4 million over 50 years. The payback period is 24.2 years, and the discount rate must not exceed 3.33% for the investment to be profitable. While the general payback period of PHES systems ranges from 30 to 50 years, different values between 21 and 80 years can be found in the literature. In conclusion, the proposed PV-DPHES system contributes to energy supply security as a sustainable, economical, environmentally suitable, and reliable energy storage solution for sunny coastal and mountainous regions. The system supports Turkey's energy independence goals and is open to reevaluation in line with market conditions after 2025.