## 6 Grid Impact
### Smart Charging/Charge Management and Location  
The high and disruptive level of EV penetration expected over the coming years [118] will reduce fossil fuel usage while entailing high electrical demand from distribution networks which were not originally designed for this purpose, resulting in network impacts, current congestion, and voltage drops in lines and transformers [104; 119]. This challenge can be addressed through the design and operation of high-quality smart grids and the use of local RES generators. These can allow surplus electricity to be stored in EVs, granting DSOs greater flexibility in managing demand peaks and valleys, active and reactive power in the network, frequency control, and spinning reserves [120]. For a better understanding of this section, Figure 20 presents a diagram showing the stakeholders and principal elements in the network. The main network stakeholders are EVs, aggregators, and DSOs. Aggregators are an interface between EVs and DSOs that unifies a set of EVs and their individualized state variables, such as the state of charge (SoC). They are necessary for V2G strategies and are able to achieve significant loads, which can then be intelligently managed by DSOs. EV charging and discharging orders are sent to the aggregator by the DSOs based on network need. DSOs are dedicated to optimizing large electricity flows, while aggregators individualize these orders to each customer. This strategy is economically and operationally the best for all stakeholders [121]. Electricity generation, transmission, and distribution are affected differently as EV penetration increases. Generation and transmission have a wide overload safety margin by design, and as such are not greatly affected. In contrast, distribution is affected, as it has not been designed for either the level of overload that EVs can produce or for electricity generation at the distribution level. In addition, fast chargers can significantly affect \begin{table}
\begin{tabular}{c c c} \hline \hline
**Subcategory** & \(\textit{KPI}_{\textbf{1}i}\) **[\%]** & \(\textit{KPI}_{\textbf{2}i}\) \\ \hline Increments in EV and solar facilities & 29.19 & 0.94 \\ \hline Shortage and quality of production (RES penetration issues) & 21.92 & 0.72 \\ \hline Operational cost management (users and companies) & 14.7 & 0.86 \\ \hline Emission reduction management & 10.85 & 1.05 \\ \hline Energy efficiency vs. fossil consumption & 8.79 & 1.01 \\ \hline Energy management among EV, PV and HVAC & 5.46 & 1.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: _KPI_ analysis of _SP_ subcategories. distribution, a situation that could be partially alleviated if some of them were installed in the transmission part to minimize the effects. Each case should be studied separately [122]. Transmission system operators (TSOs) and DSOs are affected differently by EVs. EVs limit the variations of RES energy in transmission, absorbing energy when there is a surplus and giving it up when there is not enough renewable production. Therefore, TSOs are favored by further stabilization of the network. In the case of DSOs, high penetration of EVs produces extra loads as well as loss of quality and stability of the electrical wave, which significantly impacts the distribution network. There may sometimes be conflicts between stakeholders due to the priority of EV storage resources in terms of need. The authors of [123] proposed a list to solve these problems: (1) (TSO) emergency actions; (2) (TSO/DSO) alert actions; (3) (DSO) local voltage control; (4) (DSO) peak-shaving; (5) (TSO) voltage support; (6) (DSO) Mvarbands (7) frequency control; (8) (TSO) other ancillary services; (9) (aggregator) imbalance issues; and (10) power quality [124]. EVs connected to the grid generate different problems, such as unbalanced grid areas due to high fast-changing demands, harmonic injection, and low-power factors. Thus, it is estimated that EV penetration of 10% will increase peak demand by 17.9%, while 20% penetration will increase it to 35.8%.