# The Synergy of Renewable Energy and Desalination:
## 5 Energy Efficient Operation of Centrifugal Pumping System in Desalination  
Centrifugal pumping plants (CPPs) play a pivotal role in the desalination process, particularly in systems utilizing membrane technologies such as reverse osmosis, nanofiltration, and forward osmosis. CPPs are essential for ensuring that seawater or brackish water is effectively transported and pressurized to facilitate the desalination process. In reverse osmosis desalination, high-pressure centrifugal pumping plants are responsible for drawing water from its source and delivering it to the membrane units at the high pressures necessary for overcoming osmotic pressure. The efficiency of these pumps directly influences the overall energy consumption of the desalination plant [74]. Given that energy costs often represent a significant portion of operational expenses, sometimes accounting for up to 60 percent, the importance of energy-efficient pumping solutions cannot be overstated. Energy efficiency in CPPs is crucial not only for cost savings, but also for environmental sustainability. Traditional pumping systems can consume vast amounts of energy, contributing to greenhouse gas emissions and increasing the carbon footprint of desalination operations. By utilizing advanced pump designs, variable frequency drives (VFDs), and optimized control strategies, desalination plant operators can enhance the energy efficiency of CPPs. For instance, VFDs allow for real-time adjustments to pump speed based on demand, ensuring that energy is used only as needed. Moreover, the integration of energy recovery devices (ERDs) within the RO systems can further improve the overall energy efficiency of the desalination process. ERDs capture and reuse energy from the pressurized brine stream, significantly reducing the energy required by the CPPs to maintain optimal pressure levels. The energy efficiency, reliability, and maintenance of CPPs are critical factors in ensuring the uninterrupted operation of desalination plants. Enhancing centrifugal pumps' energy efficiency and minimizing losses are essential for determining the optimal operation of the desalination system powered by RES. A system should be designed to be as productive as is feasible in order to maximize its potential. Several researchers have provided some optimization strategies, which are listed below. The three primary optimization strategies are shown in Figure 9.  
In [75], the authors found out that certain high-speed centrifugal pumps show signs of instability in their cavitation and hydraulic performance. Using the orthogonal experimental design approach, the turbulence model was developed in order to examine the effects of these parameters on the net positive suction head (NPSH). Rotating cavitation was observed at part-load in a visual high-speed photography test setup. A numerical model that closely resembles the experimental cavitation characteristics was developed by comparing the cavitation and pressure counters with high-speed photographic photos. This simulation approach helps to identify the optimal sizing for the CPP to avoid cavitation and increase the efficiency of the pumping unit. In order to maximize the capacity sizes of various CPP components employing water tank storage, the authors of [76] suggested an ideal sizing approach. The suggested model considers the pumping system's submodels and employs two optimization criteria: the life-cycle cost (LCC) for the economic assessment and the loss of the power supply probability (LPSP) model for reliability. A very important role in the energy efficiency of CPP is played by the control approach. Most of the centrifugal pump systems are driven by induction motors (IMs). In RES-powered pumping systems, there are two primary methods for controlling the IM. Scalar control is the first, and vector control is the second. The authors in [77] suggested using direct torque control (DTC) in conjunction with a hybrid control algorithm that was developed for pressure maintenance (Figure 10).