## 6 Challenges and Future Directions  
In Section 2, some challenges regarding V2G and its implementation are discussed. These challenges encompass the dynamic nature of the problem, including fluctuating electricity prices throughout the day and ensuring a reliable supply of energy and EVs to support grid stability. Additionally, the costs associated with upgrading the power infrastructure and gaining public acceptance are significant obstacles that V2G must overcome for a successful implementation. For a V2G system to become fully operational, a large number of EVs are required. However, one of the significant limitations of EVs is their battery capacity. The limited capacity of current EV batteries restricts their driving range, leading to a phenomenon known as range anxiety, which is the primary concern of potential EV buyers [43]. Consequently, when coupled with the lack of EV charging stations, EV users tend to be reluctant to participate in V2G systems, as they prefer to have a guaranteed amount of battery stored in case of emergencies or unforeseen circumstances. Therefore, the EV state of charge needs to be considered in order to reduce EV users' rejection of participating in V2G systems. Finding a balance between maximizing the primary objective of V2G systems and making them appealing to a wide range of drivers is essential when developing the V2G scheme and algorithm [44] since it is possible that maximizing the need for energy storage could conflict with the willingness of drivers to engage in V2G systems, which is often fueled by concerns like range anxiety. To mitigate these concerns, it is necessary to educate consumers about the benefits and safety of V2G systems. Providing assurances and guarantees, such as ensuring the guaranteed availability of a certain state of charge, can also help alleviate drivers' apprehensions. Moreover, other challenges encountered when dealing with V2G systems is grid control. In a V2G system, each EV serves as a generator, but a significant number of EVs are required to ensure grid stability. The grid operator needs to continuously monitor the condition and availability of these EV generators, as well as their willingness to participate, to identify those that are suitable for drawing energy from a specific battery pack [45]. Integrating advanced grid management systems can help handle the complexity of V2G operations, and upgrading the infrastructure can make it more flexible and resilient. Another highly influential parameter to consider is the degradation of EV batteries. While using EVs as energy storage units offers a valuable asset for balancing the electric grid's supply and demand, it also has a negative impact on their batteries. Battery cells deteriorate over time due to irreversible chemical reactions, leading to a reduction in the number of available lithium ions and subsequently, a decrease in cell capacity [46]. This capacity variation depends on various parameters, including temperature, depth of discharge (the portion of the battery's capacity missing from its full capacity), and charge and discharge rates. Consequently, different challenges arise due to the impact of these parameters, including increased complexity of the problem due to the added restrictions and optimization of benefits, as degraded batteries negatively affect the potential benefits. Moreover, as emphasized in [47], V2G systems have the potential to adversely affect battery lifespan if not implemented correctly. A smart grid system, however, should have mechanisms in place to avoid or minimize this issue. Nonetheless, while lithium-ion batteries currently dominate the market, models must acknowledge that maximizing return on investment for EV owners may not always be feasible, partly due to the societal constraints previously discussed. In such cases, energy trading between the grid and the vehicle should be based on prognostics [48].