*3.6. Electric Vehicle*

The reference car used as EV is the Nissan Leaf 2018. It was selected because that model is one of the few electric cars certified for use in V2G applications [50]. Table 1 shows some of the car's technical characteristics. The Nissan Leaf features two charging sockets—Type 2 and CHAdeMO. The on-board charger has a rated power of 6.6 kW, while the CHAdeMO socket supports a rated output of up to 50 kW.



1"worst case" based on −10 ◦C and use of heating along a highway.

Concerning the effective charging power, it is important to keep in mind that the discriminant is the minimum value of the power between the supply equipment and the charger of the vehicle itself according to the following relation (Equation (1)):

$$P\_{\text{char}\,\text{ge}} = \min(P\_{EVSE}, P\_{EV}) \tag{1}$$

with:

> *Pcharge*: rated power of recharge;

*PEVSE*: rated power of the electrical vehicle supply equipment;

*PEV*: rated input power of the electrical vehicle charger.

The maximum power absorbed by the network that will be considered is that of the electric vehicle supply equipment (EVSE), which is equal to 10.5 kW. Of the 10.5 kW, 10 kW is actually used to recharge the vehicle, while the remainder represents the losses of the charging system. Figure 8 indicates the trend of the power absorbed by the grid at three different power levels, based on standard value.

### **4. Analysis of the Energy Absorption of the Car Park**

As seen so far, the car park under examination is equipped with a series of electrical loads, which, overall, indicates power absorption similar to that shown in Figure 9. The red dotted line represents the maximum power limit that can be absorbed by the car park's electrical system, which stands at around 14 kW. Figure 9 shows the basic load of the car park. Now, assuming that power absorbed by electric cars is added, it will derive a load curve that is similar to that in Figure 7, which assumed the simultaneous recharge of five EVs during the first peak. However, this assumption presents a rather burdensome situation, because it requires a considerable amount of energy to be absorbed from the grid over an extensive period. This is a classic example of an uncontrolled charging without the implementation of any smart charging feature.

**Figure 9.** Overall load curve of the car park.

The relative energy consumption is shown in Figure 10. Appreciably, greater energy absorption occurs between 7.00 a.m. and 10.00 a.m. and between 5.00 p.m. and 9.00 p.m., and as a result of which, two peaks of power are derived. The daily total energy absorbed is approximately 114 kWh.

**Figure 10.** Overall daily energy absorption of the car park (without Electric Vehicle Supply Equipment—EVSE).

Table 2 shows a summary of the overall energy absorption at the car park when deploying a full charge of five Nissan Leaf cars for every day of the year.


**Table 2.** Overall energy absorption of the car park.

### **5. Design of the Photovoltaic System**

One of the major criticisms also giving rise to skepticism about electric mobility is that the energy to recharge this fleet of vehicles must be sourced from somewhere. This point is not trivial should fossil fuels constitute and remain the source of this much-needed energy for the recharging of vehicles. It means that the thorny problem of environmental pollution remains unresolved, and the problem is transferred to the supply chain. In fact, if one considers the tank-to-wheel transformation chain, the CO2 emissions into the atmosphere of both the EV and the Internal Combustion Engine (ICE) become equivalent.

However, the problem does not arise (or, is mitigated) if instead, the energy used came from a renewable source. Therefore, concurrently with the development and widespread use of the EVs, it is important to launch initiatives that aim at a greater di ffusion of renewable energy sources [52,53]. Following from this, a photovoltaic power plant will be designed in this section in order to provide the car park's load demand. As already described, the reference car park is the parking lot adjacent to the railway station. In this car park, the installation of three EVSEs with V2G technology was planned. Geographically, the site of interest has an azimuth of 30◦ towards the west, as shown in Figure 11. The optimal tilt angle of the panels was instead set at 30◦.

**Figure 11.** Bird-eye view for the site of interest—the car park.

The average daily solar radiation of this site, characteristic for each month, was obtained from [52]. From these data, the graph depicted in Figure 12 was derived.

**Figure 12.** Daily irradiance in Ferrara for each month.

From the solar irradiance dataset, exploiting Equation (2) [53], the associated produced power can be computed as

$$P\_{out,puncl}(G\_t) = \begin{cases} P\_{\text{fl}} \cdot \left( \frac{G\_t^2}{G\_{\text{std}} \cdot R\_c} \right) \text{for } 0 < G\_t < R\_c\\ P\_{\text{fl}} \cdot \left( \frac{G\_t}{G\_{\text{std}}} \right) \text{for } G\_t > R\_c \end{cases} \tag{2}$$

where:

> *Ppv*(*Gt*): the output power from a single panel as a function of the solar irradiance *Gt*;

*Gt*: the forecasted solar irradiance measured in <sup>W</sup>/m<sup>2</sup> at a certain time t in a day;

*Pn*: the nominal output power of the photovoltaic panel chosen;

*Gstd*: solar radiation in the standard environment set as 1000 <sup>W</sup>/m2;

*Rc*: a certain radiation point set as 150 <sup>W</sup>/m2.

Considering that the data have been sampled at intervals of a quarter of an hour from one another, the energy can be easily obtained through Equation (3):

$$E\_t = P\_{\text{out,panel}}(G\_t) \cdot \Delta t \tag{3}$$
