**2. Vehicle to X (V2X)**

Prior to learning about the V2G and V2H technologies mentioned in the title, it is important to know about their brothers, generalized by the term V2X, where X is a variable. When studies conducted in the literature are examined, it is seen that the name of the energy transfer technology depends on the target system to which the energy produced by the electric vehicle is transferred, that is, the recipient of energy [16]. As depicted in Figure 3, if an electric vehicle transfers the energy to another electric vehicle, the technology is called vehicle-to-vehicle (V2V); if the electric vehicle

charges an electronic device, the technology is called vehicle-to-device (V2D); if the electric vehicle transfers the energy to the grid, the technology is named V2G; if the electric vehicle provides energy to a house, the technology is called V2H, or if the energy is transferred to a building, the technology is referred to as vehicle-to-building (V2B) [17]. In general, V2X technology provides a safe, sustainable, and competitive energy supply [18].

**Figure 3.** Different interaction modes of electric vehicles [18].

The amount of energy transferred from the vehicle to the grid depends on the number of vehicles in connection. For instance, V2H requires at least 1 or 3 vehicles, V2B requires at least 1 or 30 vehicles, and V2G requires at least 5 or 50 vehicles. The energy transfer from vehicle to the grid has to be achieved smoothly without changing the voltage, the power factor, or the frequency of the grid [19].
