# The Synergy of Renewable Energy and Desalination:
## 2 Overview of Desalination Technologies
### Thermal-Based Methods  
Multi-stage flash (MSF) desalination is a widely used thermal process that converts seawater into freshwater through a series of stages. In MSF, seawater is preheated and then introduced into a series of chambers, or stages, where the pressure is progressively reduced. This reduction in pressure causes a portion of the seawater to \"flash\" or vaporize rapidly [26]. The vapor produced in each stage is collected and condensed, resulting in freshwater. The remaining brine is then directed to the next stage for further processing. One of the key advantages of MSF is its ability to produce large volumes of freshwater, making it suitable for coastal regions with high water demand [27]. MSF plants are often designed for high efficiency, utilizing waste heat from power generation or industrial processes to minimize energy consumption. However, the initial capital investment and operational costs can be significant. Additionally, MSF systems require careful management to handle scaling and corrosion issues due to the saline environment. MSF remains a  
Figure 1: Commercial and emerging desalination processes. vital technology for addressing water scarcity in arid regions and supporting agricultural and urban needs. Typical operation temperature for MSF method varies in the range of 90 to 120 degree Celsius [28]. At 30% power plant efficiency, MSF's average thermal energy consumption ranges from 191 MJ/m\({}^{3}\) to 290 MJ/m\({}^{3}\), or 15-25 kWh/m\({}^{3}\)[29]. MSF technology dominated in the 1980s and 1990s because of its reliable functioning and year-round availability. Yet, the most recent advancements in MED and RO methods took over MSF's global installations. Multi-effect distillation (MED) is an efficient thermal desalination method that leverages the principle of using vapor from one stage to heat the next. In this process, seawater is heated in a series of evaporators known as \"effects\". Each effect operates at a lower pressure than the previous one, allowing the vapor generated from boiling seawater in one effect to be used to heat the incoming seawater in the subsequent effect [30]. This cascading effect minimizes energy consumption and maximizes the use of available heat. MED systems are known for their energy efficiency and lower operational costs compared to other thermal desalination methods. They can be designed to operate with both low-grade heat sources, such as waste heat from power plants, and renewable energy sources. The modular design of MED units allows for scalability, making them suitable for various applications, from small communities to large industrial operations [31]. Despite its advantages, MED does have some limitations, such as sensitivity to scaling and fouling, which require regular maintenance and monitoring. Nevertheless, MED continues to be an important option for sustainable water production in many regions facing freshwater shortages. The typical operation temperature for MED method varies in the range of 60 to 90 degrees Celsius [32]. Depending on top brine temperature (TBT), the thermal energy needed for MED operation ranges from 145 MJ/m\({}^{3}\) to 230 MJ/m\({}^{3}\), or 12-19 kWh/m\({}^{3}\) based on power plant efficiency. Vapor compression (VC) is a desalination technique that utilizes mechanical or thermal energy to compress vapor, raising its temperature and pressure for the purpose of producing freshwater. In VC systems, seawater is heated to generate vapor, which is then compressed using either mechanical compressors or steam ejectors. The compression process increases the temperature of the vapor, allowing it to be condensed on a heat exchanger where it transforms back into liquid water [33; 34]. This results in freshwater while leaving behind concentrated brine. One of the significant advantages of VC technology is its high energy efficiency, particularly in smaller-scale desalination applications.