3.5.3. The Renewable Fraction (*RF*)

The *RF* is the gross amount of electricity produced by sustainable resources compared to the gross energy generated from the whole hybrid EV charging scheme [70]. The *RF* is computed with regard to the output power of the sustainable resources as illustrated below:

$$RF(\%) = \left(1 - \frac{\sum P\_{diesel}}{\sum Pren}\right) \times 100\tag{11}$$

#### 3.5.4. The Unsatisfied Load

The unsatisfied load is the electric charging load that the hybrid EV charging station system model cannot fulfill. This occurs when the load requirement is greater than the electric supply. The unfulfilled load is computed as a ratio of the annual non-served load to the gross annual demand as given below [67]:

$$\text{Unfull filled load} = \frac{\text{Annual Non} - \text{served Load}}{\text{Annual Entire Load}} \tag{12}$$

#### **4. Results Analysis and Discussion**

In this study, an EV charging scheme based on renewable energy resources and storage devices is designed and analyzed using the *HOMER Pro*® software. The simulation software utilizes the GPDO techniques to secure the most economically feasible system configurations that can sufficiently supply the EV charging demand. Nigeria is divided into six geo-political zones with different meteorological features, and the renewable energy resources are weather dependent. Therefore, to conduct a more comprehensive investigation and to have a detailed overview of the operational performance of the proposed system, six different locations, each from one of the six geo-political regions, are considered. Furthermore, three different combinations of energy sources with storage systems were investigated for the hybrid EV charging station system in the six sites.
