This research focuses on generating electrical energy using a power plant that employs reverse pump technology.The installation involves eight pumps operating in parallel,with the efficiency calculated under various conditions by altering parameters such as head, flow rate, and output pressure. The performance curve for the reverse pump was created for a centrifugal pump model 33-250.The design was conducted for three scenarios: normal (full capacity), average (neither full nor low capacity), and finally for a minimal (low capacity) water level in the reservoir. These three scenarios were also analyzed under three different output pressures: 1.5 bar, 2.5 bar, and 3.5 bar. The results indicated that in the optimal condition, the efficiency of the reverse pump would reach 83%. The maximum power extracted from the plant was calculated to be 947.312 kW. The electrical energy generated over 345 days, operating continuously for 24 hours, amounted to approximately 9335468.16 kWh.
Introduction:The world is gradually heading toward a severe energy crisis, as energy demand is exceeding supply. Humans have realized that daily-used energy is not infinite, yet often take it for granted—overlooking the finite nature of oil, gas, electricity, and even accessible water. The rising demand and limited availability of energy resources have led to increased prices(Manieniyn, Thambiduri, and Selvakumar,2009). Energy remains a vital component of economic infrastructure. The integration of renewable sources such as hydro, wind, solar, tidal, and biogas has transitioned electricity generation toward cleaner, cost-effective technologies. Hybrid systems combining hydro and wind power enhance energy value and improve water resource flexibility(Shahinejad and Kakavand, 2016; Gondhali et al, 2020). The water-energy nexus is essential for sustainable development(Walker, Lv, and Masanet, 2013; Chen, and Chen, 2016; Jiang, Wang et al, 2016). Large-scale hydropower has declined in developed nations due to environmental impacts and depleted water sources. This has shifted focus toward small-scale hydropower, especially in remote areas. Pumps as turbines (PATs) have emerged as a low-cost alternative to traditional turbines, with easy maintenance and broad availability(Chapallaz, Eichenberger, and Fischer, 1992; Liu, Tan, and Cao, 2019). Centrifugal pumps operating in reverse can recover energy efficiently(Gülich, 2010). This unconventional approach is gaining traction in mechanical and energy engineering(Kusakana, 2014). PATs are increasingly adopted in small hydro plants to replace expensive hydraulic turbines(Pourrajabian, Hamekhani, Fatahi, Dehghan, and Rahgozar, 2018; Nejadali, 2021). However, manufacturers often do not provide performance curves in turbine mode, posing a key challenge(Williams, 1994; Barbarelli et al, 2016). This study designs a small hydropower plant using PAT technology for the Shahrchai Dam in Urmia, Iran. It analyzes its performance across three water levels using both maximum and minimum output scenarios, highlighting the potential of PATs in enhancing clean energy production aligned with sustainable economic goals.
Methodology: In recent years, the growing global demand for energy, coupled with the depletion of fossil fuel resources, has increased the focus on renewable energy sources(Manieniyn, Thambiduri, & Selvakumar,2009; Shahinejad and Kakavand, 2016; Gondhali et al, 2020). Electricity generated from renewables such as water, wind, and solar is considered a sustainable and cost-effective solution(Shahinejad and Kakavand, 2016; Gondhali et al, 2020). A novel approach in hydropower generation involves using pumps as turbines (PAT)( Chapallaz, Eichenberger, and Fischer, 1992; Liu, Tan, and Cao, 2019), where centrifugal pumps operate in reverse mode to convert hydraulic energy into electricity(Gülich, 2010). This method is gaining attention, especially in developing countries, due to its low cost, ease of maintenance, and wide availability of components(Kusakana, 2014; Pourrajabian, Hamekhani, Fatahi, Dehghan, and Rahgozar, 2018; Nejadali, 2021).
This study presents the design and performance analysis of a small-scale hydropower plant using PAT technology, intended for installation on the drinking water transmission line of Shahrchai Dam in Urmia, Iran. The proposed system includes eight pumps arranged in parallel. Its operation was evaluated under three hydrological scenarios (wet, normal, and dry years) and at three different outlet pressures (1.5, 2.5, and 3.5 bar). The results demonstrated that the reverse pump efficiency could reach up to 83%. The maximum power output was calculated to be 947.312 kW, with an estimated annual energy production of 9,335,468.16 kWh under optimal 24-hour operation for 345 days. The generated electricity can supply the local facilities and also be connected to the national grid. PAT technology represents a promising and economical alternative for enhancing renewable energy production and effectively utilizing existing hydraulic infrastructures.

Results and Discussion: The objective of this study is to optimize the use of the water transmission line from Shahrchai Dam in Urmia for hydroelectric power generation.As shown in Eqs 1 - 12, Figs 1,2 and Tab1 Initially, the system curve and the head-discharge curve of the power plant were calculated using hydraulic equations and dam data. As shown in Eq 13, Figs 2-4, after selecting a suitable pump from the catalog, the pump-turbine's performance in both turbine and pumping modes was analyzed, and curves for head-discharge, power-discharge, and efficiency were plotted.As shown in Figs 5-8, The power plant includes eight pump-turbines operating in parallel. Key variables such as the dam water level and the outlet pressure to Urmia’s Water Treatment Plant No. 2 were analyzed for their effects on flow rate, output power, and overall efficiency. As shown in Tables 2-8 , results showed that under various conditions (high flow, average, and drought) and different outlet pressures, the plant could generate power with over 80% efficiency across a wide range of flows. The parallel operation of turbines allows flexible power regulation and improved efficiency.The working point of the system is determined by the intersection of the system curve and the head-discharge curve. Using the Darcy-Weisbach equation, the total head loss was calculated, and with known dam elevation, turbine installation level, and outlet pressure (2.5 bar), the design head was estimated at 34.5 meters. Each turbine's flow rate was found to be 0.32 m³/s, and the specific speed was 59.6 rev/min.By applying conversion factors between pump and turbine modes, design variables were adapted for catalog selection. The chosen pump (model 250-33 by Pumpiran) operates at 1450 rev/min. Converting pump performance data to turbine conditions and estimating maximum/minimum conversion coefficients, the turbine’s operational limits were defined.Comprehensive calculations and data showed that the plant operates efficiently with variable flow conditions and number of turbines in operation. For example, at 2.5 bar outlet pressure, annual energy production ranges from 0.7 to 9.3 MWh depending on water availability. When outlet pressure is increased or decreased (1.5–3.5 bar), the head and flow characteristics change, affecting power output and efficiency.The system’s modular design allows operation from 1 to 8 turbines, adapting to seasonal variations in water demand. Even under low-flow or high-pressure scenarios, the plant maintains a performance efficiency above 80% in most configurations, demonstrating the viability and flexibility of using pump-turbines for energy recovery from water transmission systems.

Conclusion: Pumps are among the most widely used turbomachines in both industrial and domestic applications. Improving their efficiency and optimizing their performance can significantly reduce energy consumption. Centrifugal pumps, in particular, are commonly used in water facilities and are also applicable as pump-turbines. The primary objective of this study is to design a pump-turbine hydroelectric power plant for the Shahrchai Dam in Urmia. Using pump-turbine equations, key operational parameters were calculated. Design charts were then developed, and a suitable pump model (the 250-33 single-suction volute pump) was selected from the Pumpiran company catalog. The power output from eight parallel pump-turbines was subsequently estimated. The results indicate that the energy of water in transmission pipelines can be effectively recovered and converted into valuable electrical energy without environmental pollution, unlike thermal power plants. Additionally, operating pump-turbines in parallel allows for flow regulation and enables the system to function as a pressure-reducing valve.