**1. Introduction**

The overall increase in population worldwide, accompanied by the contemporary technological revolution, has given rise to an excessively high rate of electricity consumption, a critical problem that necessitates sustainable energy solutions [1,2]. In the Nigerian power sector, most of the electricity supply is being secured through fossil fuels, namely natural gas, which accounts for about 80% of the total fossil sources, and oil, from which most of the remaining fossil power generation originates [3]. In fact, 80% of the country's energy mix takes the form of thermal generation sources, with the remaining 20% being derived from hydropower and other renewable energy (RE) sources. The per capita CO2 emissions in Nigeria had dramatically risen from about 0.08 metric tons in 1960 (when Nigeria attained independence from Britain) to 0.67 metric tons in 2018 [4]. In fact, the contribution of the country to the global pollutant emissions level has increased considerably over the past

**Citation:** Oladigbolu, J.O.; Mujeeb, A.; Imam, A.A.; Rushdi, A.M. Design, Technical and Economic Optimization of Renewable Energy-Based Electric Vehicle Charging Stations in Africa: The Case of Nigeria. *Energies* **2023**, *16*, 397. https://doi.org/10.3390/en16010397

Academic Editors: Saad Motahhir, Najib El Ouanjli and Mustapha Errouha

Received: 25 November 2022 Revised: 11 December 2022 Accepted: 23 December 2022 Published: 29 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

**<sup>\*</sup>** Correspondence: omotayooladigbolu@gmail.com (J.O.O.); arushdi@kau.edu.sa (A.M.R.); Tel.: +234-7035634424 (J.O.O.); +20-1128247509 (A.M.R.)

few decades. Nigeria's total energy consumption in 2020 is about 164,013 kilotonne of oil equivalent (ktoe), with the transportation sector alone contributing about 16,554 ktoe [5]. The transportation sector accounted for over 70% of Nigeria's energy use [6]. This sector has been the major consumer of fossil fuels in the past 20 years. Many countries, including Nigeria, are looking toward mitigating the usage of conventional energy sources where greenhouse gas (GHG) emission poses serious climate and environmental challenges. The Nigerian government strives to promote the use of electric vehicles (EVs) in the country to mitigate noise and air pollution, and in its effort toward that end, it is incorporating Evs in its development plan for the National Automotive Industry [7]. Environmental and noise pollution concerns, unstable cost and supply of petroleum products as well as efficiency are the driving factors for the development and implementation of alternative means of running vehicles in Nigeria.

Furthermore, the EV named Kona, which was the first one assembled in Nigeria, was unveiled in 2020 [8], and it was stated [9] that it can be charged anywhere within the five-year life of its storage device. The Nigerian JET Motor firm (JMF) launched its electric van JET EV [10,11] with a moving range of more than 250 km [12], and meanwhile, the Nigerian Siltech company introduced its electric bikes with a battery swapping technology. Recently, the National Automotive Design and Development Council (NADDC) of Nigeria, under the EV pilot program, has launched two solar energy-based EV charging stations (EVCSs) in the western Nigerian cities of Lagos and Sokoto with a capacity of 86.4 kilowatts per hour each [13]. The EVCS in the southeastern Nigerian city of Enugu is expected to be unveiled soon to boost the Nigerian government's commitment to efficient, cost-effective, and eco-friendly vehicles [14,15]. The Lagos state government has given assurance towards providing EVCSs to support the full utilization of EVs in the state [16]. The partnership between JMC and GIG logistics (the country's leading logistics company) to introduce the first electric vans (Jet Mover) has resulted in the installation of EV charging station infrastructures on the premises of this latter company. A charging station is capable of charging two EVs at the same time to full capacity with two hours of charging. Each EV van has a 107.8 kWh lithium-ion battery and can go a distance of about 300 km [17]. This shows that the government and the private sectors are highly committed to the establishment of EV pilot projects that support carbon neutrality. However, insufficiency in electrical power supply, which is essential for the utilization of EVs, and the shortage in EV charging station (CS) infrastructures are obstacles to a bright future for EVs in Nigeria.

In addition, wind and solar power have become essential and common technologies for electricity production due to the recent technological advancements in power electronic storage systems as well as the price reduction of the required devices [18]. According to Aliyu et al. [19], with an average of 6 h of daily sunshine being captured over 1% of land size for the solar photovoltaic (PV) system, Nigeria has the potential to generate annual electrical energy of about 1,850,000 GWh. The coastal and offshore regions, hilly areas of the north, middle belt mountainous terrains, as well as northern fringes of the country are windy with the potential for harvesting great wind power all over the year [20]. Moreover, it was indicated by Nehrir et al. [21] that renewable energy sources (RESs) such as solar energy (SE) and wind energy (WE) have more benefits in terms of electricity generation compared to other sources in addition to being freely available in nature. The integration of solar and wind systems with storage devices, either as standalone microgrids or with a utility grid network, has proven to save a substantial amount of carbon dioxide (CO2) and other pollutant emissions, thereby making such microgrids environment-friendly [22]. The microgrid could serve as a green solution for the EVCS energy demand. The utilization of solar and wind energies incorporated with a better end-use efficiency will almost definitely be needed to cope with the increasing energy charging demand from EVs for sustainable, eco-friendly, and affordable power supply as the use of fossil fuels is gradually destroying the atmosphere and creating adverse and alarming climatic conditions.

Additionally, to solve the problem of everyday power outages, which could affect the operational time and efficiency of EVs in the country due to insufficient generation, the Nigerian government has unveiled plans to increase the power generation from fossil fuels to 18,200 MW [23] and targeted 30% of the gross electricity generation from renewable energy (RE) resources by the year 2030 [24]. This shows that the future energy plan still targets enormous electricity generation from resources that pollute the environment and put the ecosystem in danger [25]. The sustainable development goal of the country can be accomplished via the adequate provision of reliable and affordable electricity supply from RE sources for various applications, including EVCS systems, in addition to preserving environmental integrity [26].

## **2. Literature Review**

Various studies have been carried out to optimally design and techno-enviro-economically investigate the performance of EVCS systems and the Vehicle-to-Grid (V2G) technology strategy using different techniques and tools. Among the works assessed in the literature, few have simultaneously considered locations with diverse geographical characteristics and climatic conditions for the design and analysis of EVCS systems. The system topology, operating mode, locations, sensitivity, and evaluation variables using different optimization strategies and methodologies for electric vehicle charging station (EVCS) design in many other parts of the world are given in Table 1. Both grid-tied, hybrid models and standalone systems for meeting EV charge demand have been effectively studied for EV charging applications, but at a smaller number in a few locations around the world. Some studies have shown the technical and economic advantages of using an off-grid system based on RESs for EV charging to mitigate the burden and protect the utility grid network [14], while others have indicated the environmental benefits of a standalone EVCS [26]. Observation of the various system designs in Table 1 for the power supply of an EVCS conforms to our belief that no study has been conducted so far in the whole of Africa, particularly in the Nigerian context, to design and conduct a detailed performance assessment of a standalone system based on available RESs for EV charging. Furthermore, a few studies (Table 1) have performed a sensitivity analysis to check the resilience of the optimized system against uncertain variables. However, none of the few studies that actually performed some sort of sensitivity evaluation has performed so as an in-depth sensitivity analysis considering variations in diverse, uncertain, and critical parameters against the technical and economic performance of the selected EV charging system.

By utilizing bio-gas sources, Karmaker et al. [27] designed a 20 kW EVCS with a detailed feasibility assessment. The technical, environmental, and financial perspectives relating to their proposed EV charging points were studied with the aid of the HOMER optimization tool. Their outcome reveals the economic and environmental benefits of the proposed EVCS system as compared to the utility grid-based charging points in Bangladesh. The design and viability study of a specialized EV charging station model was investigated using the grid analysis software tool known as HOMER (short for "Hybrid Optimization of Multiple Energy Resources"). Based on three various cases of EV charging points analyzed, a yearly profit of USD63,680 was provided in addition to recovering the charging station's installation costs in less than three years. The level-2 EVSE is the most effective, reducing greenhouse gas emissions by 104 t [28]. The investigation of the environmental effect of the carbon dioxide (CO2) emissions point of view embedded in green off-grid power schemes and the assessment of the environmental impact of their execution in the electricity supply of EVCS was conducted by Filote and Felseghi [29]. Their outcomes show that the clean power schemes represent viable solutions for the autonomous electricity support of EVCSs, being capable of supplying electric power based on 100% availability of on-site alternative energy resources. Moreover, the mean cost of 1 kWh of energy produced by the evaluated configurations is 4.3 times the mean unit cost of the EU electric distribution network electricity. Machado et al. [30] investigated the techno-economic viability evaluation on EV and RE integration as a case study, where three possible scenarios varying between a grid-alone operation, the integration of RESs for providing electric power to the EVs and a utility grid, together with the vehicle-to-grid (V2G) strategy were presented. The V2G

scheme and the RE integration outcome indicated cost benefits along with minimal power intake during the peak loading time of the design. The HOMER software was used by Boddapati and Venkatesh [31] for the design of an EVCS by utilizing hybrid power sources such as solar photovoltaic, wind, and diesel plants (DG). They indicated that the utility power network-tied EVCS is more cost-effective than the standalone charging scheme. Moreover, they also conducted a sensitivity evaluation to check the impact of some variable parameters on the EVCS.

Furthermore, another study by Ye et al. [32] assessed the feasibility of a solar-based EVCS model for application in Shenzhen City in China. The results of this study reveal prospects of the proposed model in terms of emissions minimization and the satisfaction of the huge demand needed for electric vehicles. The study also recommends that carbon pricing promotes RE only when the cost of carbon is more than USD20/t. Moreover, a technical and economic investigation of a standalone renewables-based EVCS to find the optimum system to produce the needed charging demand per day was performed [33]. The outcomes of this investigation revealed that the optimized solution for the chosen locations comprises a 250-kilowatt wind system with a 60 m hub height. Furthermore, the optimum scenarios' gross net present cost (NPC) varies between USD2.53M to USD2.92M, while the cost of energy (COE) varies between USD0.285 and USD0.329 per kWh. Based on the change in the feed-in tariff technique, a techno-economic performance investigation of the V2G system model in Indonesia's largest electricity grid network was performed [1]. The investigation indicated that the utilization of EVs can potentially reduce the peak hour supply by about 2.8% and 8.8%, respectively, for coal and gas. From the electricity company's point of view and because of fuel replacement, the annual revenue can be improved by around 3.65% with the vehicle-to-grid approach. The design and viability evaluation of a RE-based hybrid EVCS system was carried out to lessen the stress on the electric utility network system owing to the fast rise in electrical vehicles in Bangladesh [34]. The EVCS system in [32] is designed using solar PV and a biogas system. The system configuration estimates an energy cost of USD0.1302/kWh and a gross net present cost of USD56,202 at a running cost of USD2540. Moreover, the system model minimizes carbon dioxide emission by 34.68% in comparison to a traditional electric utility network-based CS.

Efficient, reliable, and cost-effective EV charging infrastructure is one of the main factors that can facilitate the utilization and adoption of electric vehicles in Africa, particularly in Nigeria, to support the decarbonization of the economy and environment. It is difficult to achieve an efficient and reliable EVCS in Nigeria with the current utility grid network because of the so-far erratic and unreliable nature of that network. Therefore, an autonomous RE-based system could provide clean, reliable, and cost-effective electricity for EV charging. Moreover, since the adequate and effective use of RE sources for power generation depends on the climatic conditions of a place and the massive and successful roll-out of EVs is a function of the availability of reliable and cost-effective EV charging infrastructures, it is important to come up with an alternative approach to designing an efficient EVCS that can generate reliable, clean and cost-effective electricity. Currently, there is no grid-independent hybrid EV charging station scheme under Nigerian conditions that are readily available in the open literature. Therefore, this study strives to carry out the design and performance assessment of a hybrid RE-based system to provide reliable, eco-friendly, cost-effective electricity with enhanced efficiency for EV charging stations. The proposed robust methodology intends to accurately investigate the establishment of EV charging stations in Nigeria. This methodology is examined by considering different optimal system configurations across the six geo-political zones with diverse geographical characteristics and climatic conditions.

The operational behavior of the charging system was tested via sensitivity analysis to check the robustness of the optimal charging scheme by varying some critical sensitivity parameters. The HOMER Pro® software has been employed for the sizing and performance assessment of the proposed charging station scheme owing to its precision, performance, and efficiency in evaluating the optimum hybrid energy system configuration [35]. The

grid-search and proprietary derivative-free optimization (GPDO) techniques were used in the microgrid analysis tool to obtain the cost-effective, viable charging system.

**Table 1.** The EVCS system designs and sensitivity analyses conducted in previous works in the open literature.


#### **3. Methodology**

*3.1. Microgrids Design and Optimization Tool (HOMER)*

The hybrid optimization model for electric renewable (HOMER) simulation tool is an important and widely used simulation software tool. It was developed in 1993 by the National Renewable Energy Laboratory (NREL) in the USA [41]. The software is utilized for analyzing various system design alternatives for both standalone and grid-tied designs in a simplified way for different applications. The optimal evaluation simulation procedure of the charging station models in the HOMER Pro® software is illustrated in Figure 1. Three major tasks are accomplished here: simulation, optimization, and sensitivity evaluation. For the simulation, HOMER models hourly the performance of each of the system subunits to ensure the optimal possible matching between the energy demand and supply. It models various system designs in the optimization section to find the systems that meet the technical constraints as well as fulfill the charge demand at a low life-cycle cost.

Lastly, HOMER performs numerous optimization operations with various ranges of input variables to check the effects of changes in input parameters on the selected system in the sensitivity analysis section [42]. The input data required by HOMER are load profile, meteorological resources, economic constraints, and system component specifications (prices and sizes), which are used to provide a list of ranked feasible systems according to the least total NPC and energy cost [43]. The modeling and optimization of different hybrid energy systems were previously studied in the literature in terms of diverse technoeconomic and environmental parameters. Such a study was accomplished with the aid of the HOMER analysis tools for both grid-connected and off-grid applications in different parts of the world are presented in Table 2. This shows that HOMER software is an important and widely used tool for the design and assessment of hybrid energy systems worldwide. Therefore, the HOMER Pro® simulation tool is employed in the present analysis for the optimal design and techno-economic viability analysis of the proposed renewable energy-based EV charging station. In order to obtain a cost-effective feasible system, the simulation tool utilizes the GPDO techniques [44].

**Figure 1.** The evaluation process of the hybrid RE-based charging stations in HOMER Pro®.

**Table 2.** Hybrid renewable energy-based system models that were studied in different parts of the world with the aid of the HOMER simulation tool.


#### *3.2. Sites Details and Operating Strategy*

The six locations selected in this study for the set-up of the proposed EV charging station are shown on the map of Nigeria displayed in Figure 2. The considered case study sites were selected from the North-Central (Minna), North-East (Maiduguri), North-West (Sokoto), South-West (Ikeja), South-East (Enugu), and South-South (Port-Harcourt) geopolitical zones. The geographical coordinates of the case study sites are given in Table 3. The selected and investigated locations are among the sites that the National Automotive Design and Development Council (NADDC) of Nigeria is considering for the EV pilot program initiatives.

**Figure 2.** The map of Nigeria showing the case study sites. The star in the middle denote Abuja, the Capital of Nigeria.


**Table 3.** Geographical coordinates of the case study sites.

The power flow diagram of the proposed hybrid RE-EV charging station is depicted in Figure 3. The wind turbines (WTs) are integrated into the hybrid charging station system via the alternating current (AC) link, while the PV panels and the batteries storage are connected through the direct current (DC) bus. The bi-directional converter keeps the flow of electric power between the AC bus and DC link devices. It converts the electrical power from DC to AC. In the inverter mode, it changes the electricity from DC to AC and from AC to DC while operating as a rectifier.

**Figure 3.** The energy flow schematic diagram of the suggested hybrid RE-based charging stations.

The flowchart for the assessment and the optimization evaluation utilized in the HOMER Pro® microgrid software is illustrated in Figure 4. The objective function is to find the sizes and working scenarios with the least lifespan and set up running costs among the viable systems that satisfy the charging point demand. The minimization of the objective function is based on certain constraint conditions. In this study, the following constraints are considered: the maximum yearly capacity shortage, the minimum renewable fraction, the renewable energy power output, and other standard technical constraints. The decision parameters explored in this analysis are the sizes of the integrated components, including the RE components, the battery storage device, and the converter. The values and specifications of the system control variables, economics, and constraints utilized in the analysis tool are given in Table 4. Because of the large financial cost produced by the battery device replacement, a charging control technique and control approach is needed to protect the storage device from over-charging and over-discharging [58]. The optimization evaluation and the outcomes are based on the constraints, objective function, and decision parameters. After calculating and modeling the load profile, inputting the resource data based on the geographical location of the case study sites, and identifying and specifying the predefined constraints and system components' technical and cost details, the analysis tool begins the simulation procedure. The simulation process ensured (via the optimization section) that the charging station models that satisfy the technological constraints and meet the EV charge demand at a low total net present costs are realized.


**Table 4.** The control variables, economics, and constraints utilized in the optimization tool [41,59,60].

**Figure 4.** Assessment flowchart and optimization process utilized in the HOMER Pro® microgrid tool.

The other part of this study assesses and discusses sensitivity evaluation through the variation of some system variables. Sensitivity analysis is capable of identifying the most important variables of an investment due to the possibility of knowing in advance the effect of input parameters with uncertainty on the system cost variables and can be utilized in different contexts as well as in the assessment of investment projects [61]. The intermittent nature of RESs [62] and the change in load demand are the two major parameters that influence the reliability and consistency in the power generation of any renewable-based energy system. These variables can also impact the present and future financial aspects of the system. Hence, sensitivity analysis is a more realistic and easier technique for determining whether a specific investment is feasible or not. In the present study, the wind speed, solar radiation, battery energy storage minimum state of charge (BES SOCmin), maximum yearly capacity shortage, and EV charge demand are used as sensitivity parameters.
