Optimal Design of a Hybrid PV Solar/Micro-Hydro/Diesel/Battery Energy System for a Remote Rural Village Under Tropical Climate Conditions

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Article Optimal Design of a Hybrid PV Solar/Micro-Hydro/Diesel/Battery Energy System for a Remote Rural Village under Tropical Climate Conditions

Jamiu Omotayo Oladigbolu * , Makbul A. M. Ramli and Yusuf A. Al-Turki Renewable Energy Research Group, Department of Electrical and Computer Engineering, King Abdul-Aziz University, Jeddah 21589, Saudi Arabia; [email protected] (M.A.M.R.); [email protected] (Y.A.A.-T.) * Correspondence: [email protected]; Tel.: +234-7035634424 or +966-5-5768-3955

Received: 21 July 2020; Accepted: 2 September 2020; Published: 11 September 2020

Abstract: Recently, off-grid renewable power generation systems have become good alternatives for providing reliable electricity at a low cost in remote areas. According to the International Renewable Energy Agency, more than half the population of Nigerian rural communities are outside the electricity coverage area. This research examines the potential application of hybrid solar photovoltaic (PV)/hydro/diesel/battery systems to provide off-grid electrification to a typical Nigerian rural village. The performance of four different hybrid systems was evaluated via techno-economic and environmental analysis, and the optimized solution was selected using the HOMER analysis tool. The simulation results revealed that a hybrid PV solar/hydro/diesel with battery storage was the optimized solution and most suitable with the least net present cost (NPC) of $963,431 and a cost of energy (COE) of $0.112/kWh. The results also revealed that the optimal system prevented about 77.1% of CO2 gas emission from being released to the surrounding air as compared with the PV/diesel system (worst case). In addition, the results also showed better performance in technical aspects, making the system appropriate and ideal for rural electrification and clean energy development. Furthermore, the effects of varying some variables such as interest rate, solar radiation, water discharge, capacity shortage, and battery minimum state of charge on the system cost and operational performance were discussed via the sensitivity analysis because these parameters influence the economy and technical aspect of the power system.

Keywords: solar PV; power generation system; optimized solution; oﬀ-grid electriﬁcation; hydro; rural community; HOMER

1. Introduction Various reforms have been established in the Nigerian power sector since the beginning of the democratic ruling by the Nigerian Power Supply Industry and Nigerian Electricity Regulatory Commission. These reforms led the country to privatize its electricity production and distribution companies in 2013 [1]. To some extent, these reforms have contributed to improving the existing power infrastructure to support the ever-growing electricity needs of the masses. Rural communities are generally dispersed; geographically isolated; faced with high illiteracy levels; and lack access to good health care delivery, clean water supply, and power connection. As a result, these areas have poor standards of living as compared with urban areas where the use of electricity is common [2], and many rural communities rely on diesel generator systems to supplement the unstable grid supply or on the local kerosene-powered lighting system. According to the International Renewable Energy Agency, more than half the population of Nigerian rural communities are out of the electricity coverage [3].

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This situation is worsening because of limited progress recorded towards rural electrification coupled with the high cost of grid expansion. However, off-grid small-scale electricity generation represents one of the most appropriate solutions to this issue, serving also as a building block for future distributed generation development. Providing reliable electricity to rural areas is essential in the sense that it improves the standard of living of rural dwellers, in addition to its positive impact on healthcare delivery and creates an ideal environment for infrastructure development and industrialization. However, unreliability and lack of access to the national grid and the high cost of grid expansion to the villages coupled with other constraints have led to an inadequate supply of power to rural communities [4]. In addition, approximately 8500 MW of power is generated by various thermal power plants in Nigeria, representing 81% of the total installed capacity, showing an overdependence on thermal sources for electricity generation. Because of high operation and maintenance costs, coupled with the release of carbon dioxide (CO2) and other harmful gases that are responsible for global warming, this necessitates the inclusion of renewable power resources, such as hydro, wind energy, and solar, into the energy mix of Nigeria’s power sector [1]. According to [5], the value of solar energy per year is around 27 times the gross fossil energy sources of the country in units of energy and is over 115,000 times the power generated, whereas the country’s hydroelectric potential is estimated to be 14,750 MW, showing the apparent abundance of these resources in electricity production which could meet the growing and increasingly affluent Nigeria population. As stated in the UN Framework Convention on Climate Change (UNFCCC), industrialized nations have agreed to mitigate their combined greenhouse gas (GHG) and pollutant emissions by 5.2% in the first phase to achieve a minimum of 18% below the initial levels by the end of 2020 [6]. This shows that more must be done to mitigate the amount of GHGs released into the atmosphere in order to limit the global warming effect. Moreover, according to the World Bank Sustainable Energy for All (SE4ALL), the global renewable energy (RE) consumption rate stands at a low value of 18.054% of the gross final energy consumption as compared with that of fossil fuel which stands at 80.04% [7]. Hence, the global warming effect [8], the increased energy demand because of the high level of industrialization and economic activities expected in Nigeria as measured by the gross GDP [9], and the high operational cost associated with the use of systems based on fossil fuels for power generation [10] are expected to increase the use of renewable energy (RE) resources to achieve the electrification goals of the nation, while creating a safe and clean environment. Furthermore, various RE technologies are becoming more attractive for electricity generation in rural and semi-urban areas because of their decreased damage to the environment in addition to the fact that they are an abundant and natural free energy source. Many research projects have been performed globally to estimate and determine the feasibility of applying one or more renewable resources in conjunction with a fossil fuel-based system for generating electricity to be used in different applications and in different human settlements. The results have shown their excellent contributions for reducing GHGs emissions and increasing sustainability and cost-effectiveness while in operation and serving the fast-growing energy demand, although their initial capital cost seems to be relatively high [11–16]. However, the recent reduction in the cost of renewable energy technologies (RET) has shown their cost competitiveness in meeting power demand and more than half of the RETs capacity is expected to generate cheaper energy than any of the conventional energy sources (oil, coal, etc.) [17,18]. A feasibility study, conducted on renewable energy sources (RESs) and their application in hybridized form for power supply to a typical residential load in Somaliland, showed a 30% reduction in electricity cost as compared with serving the local energy demand with diesel-only power systems at an energy cost of $0.408/kWh [19]. Similarly, [20] presented a detailed economic viability analysis in addition to developing a model to examine the costs and benefits of a decentralized photovoltaic (PV) system. Their findings indicated that the economic viability of the system was absolutely site dependent based on variations of some determinant factors. The optimized PV/battery system showed better economic prospects as the gross net present value stood at $589,852 at an energy selling price of $0.4/kWh, Electronics 2020, 9, 1491 3 of 22 which was lower than the unit price of $0.62/kWh for the diesel system. In [21], an evaluation of a biogas-driven cogeneration system, which could supply power and cold storage for “yam bank” within a rural village was carried out, where they considered about 200 households in a Nigerian community. Their findings, however, revealed that the system configuration could store 3.6 tons of yam tubers each year, as well as generate sufficient power for domestic and commercial use. The application of hybrid energy systems (HESs) for power generation at an off-grid remote location was demonstrated in [22]. The authors used two different RES integration approaches, and confirmed that a HES was the best electricity supply option for the selected areas with regards to cost and environmental sustainability. The possibility of a HES for electricity production in Yanbu, Saudi Arabia, was investigated by [23]. They stated that the study location had enormous potential for RESs. Moreover, the energy contribution from a wind energy conversion system was less than that of the PV system of the same size but the energy cost of the wind, i.e., $0.149/kWh, was more expensive than that of the solar energy which stood at $0.0637/kWh. A model and assessment of a PV/wind/diesel hybrid energy system for rural electrification in Kaduna State (Nigeria) were presented in [24]. The authors found that the PV/wind/diesel/battery hybrid system was the most economically feasible and environmentally friendly because it reported a substantial savings in the cost of electricity and mitigated pollutant emissions remarkably. In another study [11], the potential implementation of a HES to meet the energy demand of Godagari of the Rajshahi division in Bangladesh was investigated. The HES was found to reduce CO2 gas emission by about 62% and a further 67% as compared with the kerosene-based and on-grid systems. In [25], the authors used an optimization tool (HOMER) and assessed the economic feasibility and environmental benefit of establishing a HES in Giri village (Nigeria). They concluded that the implementation of HESs in Giri village had great economic prospects with less environmental effect because they supplied power at a minimum net present cost (NPC) of $1.01 m and emitted a tolerable amount of GHGs, i.e., 2889.36 kg/year. The techno-economic feasibility of a HES comprised of solar PV, wind turbine, diesel generator, and a battery storage device were studied in [26] for power generation at a rural village in Sri Lanka. Their outcomes showed that the optimal system could supply electricity at a cost of $ 0.34/kWh. In addition, in Nigeria, many research articles have examined the potential, utilization, and evaluation of technical and economic aspects of using RESs for power production in remote, rural, and semi-urban areas [27–30]. However, most of these studies have focused on solar and wind energy in combination with conventional energy sources. From previous studies, it has been established that no research has been conducted to investigate the feasibility of PV/hydro/diesel with a storage system for providing off-grid electrification in Nigeria. The hydropower system has received less application in this regard due to the lack of hydro resource data. According to [5], there are about 277 potential sites for small hydropower (SHP) applications in the country, but only five sites among these have been developed. Many viable SHP applications are run-of-river schemes that require less civil works, and existing dams can be transformed into SHP sites to make its implementation more attractive and cost-effective. In addition, with the networks of rivers where at least one river flows through most of the states in Nigeria coupled with the potential of small-scale hydropower estimated to be 734 MW [31], a small hydropower project would be a viable solution for the power crisis that occurs in most of rural Nigeria [3]. The reliability and environmental impact of a HES are related to hours of operation of diesel generators, fuel availability and costs, O&M issues, stability issues, etc. On the one hand, if a HES involves more than one RE resource, the reliability can be maximized and GHG emission can be reduced since there is compensation between resources for power production. On the other hand, a system with one RE technology, for example, PV, requires more storage capacity to guarantee the reliability, which increases investment costs. However, using multiple RE technologies can make the power generation more reliable, in addition to fuel consumption savings and CO2 reduction. This was demonstrated in [12], where the system with one RES was unable to meet an annual load of about 57 kWh as compared with that of the configuration with two RE technologies. Electronics 2020, 9, 1491 4 of 22

In addition, the environmental benefit of the latter technologies showed a reduction in CO2 emission of approximately 7167 kg/year. This research aims to support the development and implementation of the hydroelectric system by providing techno-economic feasibility and environmental analysis to develop and establish a standalone hybrid PV/hydro/diesel power system with continuous power generation for an isolated rural area with a tropical climate. The simulation is performed based on the hydro resources available with the level of global solar radiation, and the diesel plant and battery storage are included because of the intermittent nature of RESs to ensure a continuous supply of power. Different system configurations were simulated and analyzed, in addition to conducting a sensitivity evaluation to check the economic as well as the operational performance of the HES over variation in some parameters such as the real interest rate, RE component (solar irradiation and hydro stream flow rate), capacity shortage, and battery minimum state of charge (SOC). The RE potentiality, in addition to the proper way of implementation in this part of the country, is also discussed to serve as a guide for implementing the Renewable Energy Master Plan (REMP) that has set a target of meeting at least 10% of the country’s total energy consumption by RESs by the end of 2025 [32].

2. Potential Renewable Energy Resources in Nigeria The endowment of waterfalls and large rivers in Nigeria can make hydropower resources the main sources of power production and continuous supply. However, out of about 277 potential locations for small hydroelectric applications with a gross output of around 734 MW, only 32 MW were exploited, representing only 4.3% of the available hydro capacity [5]. Consequently, hydro resources have not been fully utilized in Nigeria as SHP for power generation. Moreover, hydropower application is a viable option for electricity generation in the southern region because of the perennial rainfall with the required hydraulic heads that have been favored by the topology [31]. However, considering the dams that have already been built, the implementation of hydro systems should be more cost-effective with less civil work. In this area, the hydroelectric profile of the three major rivers (Otamiri, Bumaji, and Njaba rivers) as reported in [33,34] shows a peak season discharge rate and a total head in the range of 2.65 to 9.25 m3/s and 3 to 40 m, respectively. In addition, Nigeria’s global solar irradiation is well distributed with a yearly daily average ranging from around 3.5 kWh/m2 (12.6 MJ/m2/day) in the coastal area to 7.0 kWh/m2 (25.2 MJ/m2/day) in the remote part of the northern region [35]. Nigeria has a large potential for solar energy application because of its observable abundance, i.e., about 3.8 1023 kW of energy is emitted from the sun, corresponding to about 1.082 million tons of oil daily × at a mean solar gain of 5.535 kWh/m2/day [5]. Solar photovoltaic (PV) is becoming a suitable energy option for countries with average solar irradiation in the range of 3 to 6 kWh/m2/day [36]. The solar radiation and hydropower potential in different states of Nigeria are presented in Figure1. From the aforementioned data, it is evident that a considerable amount of electricity can be produced if a small hydropower/PV system can be established in this area that can adequately serve remote rural areas across the country. Electronics 2020, 9, 1491 5 of 22 Electronics 2020, 9, x FOR PEER REVIEW 5 of 22

FigureFigure 1. Map 1. Map of Nigeria. of Nigeria. (a) ( aHydrological) Hydrological river river basins;basins; (b(b)) Solar Solar radiation radiation and and solar solar electricity electricity potential. potential.Reproduced Reproduced from referencesfrom references [37,38 [37,38].].

3. Methods3. Methods and andMaterial Material SelectingSelecting suitable suitable analysis analysis criteria criteria is crucial is crucial to properly to properly evaluate evaluate the operational the operational performance performance of of variousvarious schemes schemes in renewable in renewable energy-based energy-based systems. systems. The Thefollowing following evaluation evaluation outlines outlines were were used used in in this thisstudy: study: specifications specifications of the of theselected selected site, site, the theproposed proposed HES HES and and load load profile, profile, design design specification specification of of thethe HES, HES, hybrid hybrid system system components components and and costs, costs, and and the the mathematical mathematical model. model. 3.1. Specifications of the Selected Location 3.1. Specifications of the Selected Location Mboke is a village located in the township of Ihiagwa that is situated 12 km south of Owerri Mboke is a village located in the township of Ihiagwa that is situated 12 km south of Owerri in in Nigeria’s southern region, which was considered in this research. The area is about 235 miles Nigeria’s southern region, which was considered in this research. The area is about 235 miles south south of the country’s capital. The village is located at 5 24.3 N and 7 0.7 E and is characterized of the country’s capital. The village is located at 5°24.3′ N and◦ 7°0.70 ′ E and◦ is0 characterized by a by a tropical wet monsoon climate. There is a power supply from the national grid, as electricity in tropical wet monsoon climate. There is a power supply from the national grid, as electricity in this this region is supplied by the Affam Genco power company [39]. The electricity supply is unstable region is supplied by the Affam Genco power company [39]. The electricity supply is unstable and and unreliable, with many residents who have been exposed to frequent blackouts [40]. Moreover, unreliable, with many residents who have been exposed to frequent blackouts [40]. Moreover, the the educational centers, as well as a marketplace such as the Nkwo Ukwu’ market, are among the educational centers, as well as a marketplace such as the Nkwo Ukwu’ market, are among the minimal infrastructure and economic developments in this area, and their daily operation and services minimal infrastructure and economic developments in this area, and their daily operation and could be improved through off-grid electrification [41]. According to the Nigerian Economic Summit services could be improved through off-grid electrification [41]. According to the Nigerian Economic Group and Heinrich Böll Stiftung Nigeria, the average cost of a diesel generator is around $0.3/kWh [42], Summit Group and Heinrich Böll Stiftung Nigeria, the average cost of a diesel generator is around which has always been the alternative option for power supply in this area. The diesel system has high $0.3/kWh [42], which has always been the alternative option for power supply in this area. The diesel operational maintenance costs and poses a serious environmental threat through the combustion of system has high operational maintenance costs and poses a serious environmental threat through the fossil fuel [43]. This community is expected to be provided with electrification using renewable sources combustion of fossil fuel [43]. This community is expected to be provided with electrification using and a conventional energy system in an off-grid mode. The Otamiri River supports the residents with a renewable sources and a conventional energy system in an off-grid mode. The Otamiri River supports potable water supply. According to [44], about 2.28 108 m3 volume of water is available and around the residents with a potable water supply. According to× [44], about 2.28 × 108 m3 volume of water is 1.89 MW of power can be produced from this river. Consequently, using a hydropower system is a available and around 1.89 MW of power can be produced from this river. Consequently, using a feasible option for producing electricity at these locations. hydropower system is a feasible option for producing electricity at these locations. 3.2. Proposed Hybrid Generation System and Load Profile Analysis 3.2. Proposed Hybrid Generation System and Load Profile Analysis The proposed hybrid system is comprised of four major components that consist of a PV system, hydroelectricThe proposed system, hybrid batteries,system is andcomprised a diesel of generator four major (DG), components as illustrated thatin consist Figure of2. a The PV system, application hydroelectricof a hybrid system, system batteries, for power and generationa diesel generator is more (DG), cost-e asff illustratedective with in highFigure reliability 2. The application than a single of a sourcehybrid system system (hydro-alone for power generation/photovoltaic-alone is more cost-effective systems). For with instance, high itreliability was shown than in a [12 single] that the source system (hydro-alone/photovoltaic-alone systems). For instance, it was shown in [12] that the hybrid system could reduce the energy cost by about $0.369/kWh as compared with a PV-alone system. Moreover, the effect of global warming could be reduced when renewable and nonrenewable

Electronics 2020, 9, x FOR PEER REVIEW 6 of 22 energy resources were used together to serve a particular load, as demonstrated in [13]. The proposed system configuration considered the 24 h load of a total of 250 households in the village. The village load profile was estimated based on the data presented by Akinyele [30]. The Nigeria southern region energy consumption pattern was considered in that study; thus, a similar power consumption pattern was used in this paper. The loads usually consisted of refrigerators, compact fluorescent lamps, fans, televisions, and a few other appliances. The total electricity demand of the site, therefore, was computed in HOMER as the hourly load data to obtain the daily and monthly load profiles for the Electronicswhole year.2020 ,The9, 1491 village hourly and yearly load profiles are presented in Figure 3a,b for an annual6 of 22 average daily load demand of 3375 kWh per day with a peak demand of 357 kW. In general, most of the loads operated for a few hours daily, while a high percentage of the hybrid system could reduce the energy cost by about $0.369/kWh as compared with a PV-alone system. electricity demand in the remote area was attributed to the lighting and cooling devices. The lighting Moreover, the effect of global warming could be reduced when renewable and nonrenewable energy load was mostly operated during the night hours, with the peak time between 19:00 and 22:00, while resources were used together to serve a particular load, as demonstrated in [13]. The proposed system the cooling load varied according to the community’s seasonal conditions. Additionally, there was configuration considered the 24 h load of a total of 250 households in the village. The village load low-energy demand in the morning from 7:00 to noontime because of the presence of the sunlight profile was estimated based on the data presented by Akinyele [30]. The Nigeria southern region and low temperature, reducing the working hours of the lighting and fan loads. However, a 10% day- energy consumption pattern was considered in that study; thus, a similar power consumption pattern to-day and time step random variability was used in HOMER for better system reliability. An optimal was used in this paper. The loads usually consisted of refrigerators, compact fluorescent lamps, fans, design assessment of PV/diesel, PV/hydro/battery, PV/hydro/diesel/battery, and PV/diesel/battery televisions, and a few other appliances. The total electricity demand of the site, therefore, was computed was conducted to obtain optimal system configuration along with a sensitivity analysis to examine in HOMER as the hourly load data to obtain the daily and monthly load profiles for the whole year. the system's operational behavior, while varying some parameters that could affect hybrid system The village hourly and yearly load profiles are presented in Figure3a,b for an annual average daily performance. load demand of 3375 kWh per day with a peak demand of 357 kW.

Figure 2. Schematic diagram diagram of of the the proposed proposed photovolta photovoltaicic (PV)/hydro/diesel/battery (PV)/hydro/diesel/battery hybrid hybrid energy energy Electronics 2020, 9, x FOR PEER REVIEW 7 of 22 system (HES).

FigureFigure 3. Load profile profile of Mboke village. ( (aa)) Hourly Hourly load load profile; profile; ( (bb)) Yearly Yearly load load profile. profile.

3.3. HybridIn general, System most Design of theSpecifications loads operated for a few hours daily, while a high percentage of the electricity demand in the remote area was attributed to the lighting and cooling devices. The lighting The monthly average solar irradiation and clearness index obtained from NASA [45], and shown load was mostly operated during the night hours, with the peak time between 19:00 and 22:00, in Figure 4, were inputted in HOMER as solar global horizontal irradiance data with annual average while the cooling load varied according to the community’s seasonal conditions. Additionally, irradiation and a clearness index of 4.71 kWh/m2 daily and 0.474, respectively. The results showed that the months from July to September recorded low daily radiation, as well as a low clearness index because of the high rainfall experienced during these periods, revealing that the PV power production level was smaller than in other months. In addition, the ambient temperature influenced the operational performance and the electricity generation level of the solar PV system; consequently, there was a need to consider temperature variation of the selected location. The average monthly temperature is depicted in Figure 5. The maximum ambient temperature occurred in April, the minimum temperature occurred in August, and the annual average temperature was 24.91 °C. The hydrological data of the Otamiri River considered in this research paper were taken from [46]. The hydrological graph, shown in Figure 6, showed that the chosen site experienced a high- water flow rate for considerable power generation from the hydropower turbine. The peak water discharge was observed in October, while a low stream flow of 6.14 m3/s was recorded in April. An annual average discharge of 7.67 m3/s was found. The nominal power of 94.08 kW was determined for the water turbine through the available head and design stream flow rate.

6 1

5 0.8 4 0.6 3 0.4 2 Clearness index Clearness 1 0.2

Daily Radiation (kWh/m2/day) Radiation Daily 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Daily Radiation Clearness Index

Figure 4. Monthly average solar irradiation for the village of Mboke.

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Electronics 2020, 9, 1491 7 of 22

there wasFigure low-energy 3. Load demand profile of inMboke the village. morning (a) Hourly from 7:00 load toprofile; noontime (b) Yearly because load profile. of the presence of the sunlight and low temperature, reducing the working hours of the lighting and fan loads. However,3.3. Hybrid a System 10% day-to-day Design Specifications and time step random variability was used in HOMER for better system reliability. An optimal design assessment of PV/diesel, PV/hydro/battery, PV/hydro/diesel/battery, The monthly average solar irradiation and clearness index obtained from NASA [45], and shown and PV/diesel/battery was conducted to obtain optimal system configuration along with a sensitivity in Figure 4, were inputted in HOMER as solar global horizontal irradiance data with annual average analysis to examine the system’s operational behavior, while varying some parameters that could affect irradiation and a clearness index of 4.71 kWh/m2 daily and 0.474, respectively. The results showed hybrid system performance. that the months from July to September recorded low daily radiation, as well as a low clearness index 3.3.because Hybrid of Systemthe high Design rainfall Specifications experienced during these periods, revealing that the PV power production level was smaller than in other months. In addition, the ambient temperature influenced the operationalThe monthly performance average solar and irradiation the electricity and genera clearnesstion index levelobtained of the solar from PV NASA system; [45 consequently,], and shown inthere Figure was4 ,a were need inputted to consider in HOMER temperature as solar variatio globaln horizontalof the selected irradiance location. data The with average annual monthly average 2 irradiationtemperature and is adepicted clearness in indexFigure of 5. 4.71 The kWh maxi/mmumdaily ambient and 0.474, temperature respectively. occurred The results in April, showed the thatminimum the months temperature from July occurred to September in August, recorded and the low annual daily radiation, average temperature as well as a lowwas clearness24.91 °C. index becauseThe of hydrological the high rainfall data experiencedof the Otamiri during River these consi periods,dered in revealing this research that the paper PV power were taken production from level[46]. wasThe smallerhydrological than in gr otheraph, months.shown in In Figure addition, 6, theshowed ambient that temperature the chosen influenced site experienced the operational a high- performancewater flow rate and for the considerable electricity generation power generation level of thefrom solar the PVhydropower system; consequently, turbine. The therepeak waswater a needdischarge to consider was observed temperature in October, variation while of thea low selected stream location. flow of The6.14 average m3/s was monthly recorded temperature in April. An is depictedannual average in Figure discharge5. The maximum of 7.67 m ambient3/s was temperaturefound. The nominal occurred powe in April,r of the94.08 minimum kW was temperature determined occurredfor the water in August, turbine and through the annual the available average head temperature and design was stream 24.91 ◦flowC. rate.

6 1

5 0.8 4 0.6 3 0.4 2 Clearness index Clearness 1 0.2

Daily Radiation (kWh/m2/day) Radiation Daily 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Daily Radiation Clearness Index

Electronics 2020, 9, x FORFigure PEER REVIEW 4. Monthly average solar irradiation for the village of Mboke. 8 of 22 25.76 25.68 25.77 25.65 C) 25.35 O 24.77 24.71 24.68 24.45 24.15 24.05 23.94

ambient temperature ( temperature ambient

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 5. Monthly average ambient temperat temperatureure for the village of Mboke.

9 8.29 8.3 8.48 8.47 8.4 7.8 7.87 7.69 8 7.46 6.74 7 6.14 6.38 6

/s) 5 3 4 (m 3 2 1 Average water discharge Average water discharge 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 6. Monthly average water discharge [46].

3.4. Hybrid System Components and Costs The input parameters and pricing of the various components used in this paper are given in Table 1. Different sizes of the system components were evaluated to find the best and appropriate size suitable for the location. Two dispatch strategies (DS), i.e., load following (LF), and cycle charging (CC), were strategically implemented for the energy management systems to properly investigate the hybrid system techno-economic performance. On the one hand, in the cycle charging strategy, the diesel generator runs at its maximum rated power to serve the load in addition to feeding the surplus power for charging the storage device. On the other hand, the diesel system operates just to sufficiently satisfy the load demand without charging the battery storage in the case of a load- following strategy. The operating reserve as a percentage of load and renewable output was set at 10% of the load in the current time step, and 25% of solar power output, while 3% was selected for the maximum annual capacity shortage which was within the range recommended by [47]. The project lifetime is 25 years at a diesel fuel price of $0.63/l. and a discount rate of 13.5%.

Table 1. System component specifications and costs.

Component Parameters/Reference Specification 1. PV panel [12,40] Efficiency at the standard test condition 13% Temperature coefficient −0.48%/°C Initial cost $3200/kW Cost of replacement $3000/kW Operating and maintenance cost $5/kW/year 2. Hydropower system [12] Initial cost $1700/kW Cost of replacement $500/kW Operating and maintenance cost $100/year

Electronics 2020, 9, x FOR PEER REVIEW 8 of 22 25.76 25.68 25.77 25.65 C) 25.35 O 24.77 24.71 Electronics 2020, 9, 1491 24.68 8 of 22 24.45 24.15 24.05 23.94 The hydrological data of the Otamiri River considered in this research paper were taken from [46]. The hydrological graph, shown in Figure6, showed that the chosen site experienced a high-water flow rate for considerable( temperature ambient power generation from the hydropower turbine. The peak water discharge was observed in October, while a low stream flow of 6.14 m3/s was recorded in April. An annual average Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec discharge of 7.67 m3/s was found. The nominal power of 94.08 kW was determined for the water turbine through theFigure available 5. Monthly head average and design ambient stream temperat flowure rate. for the village of Mboke.

9 8.29 8.3 8.48 8.47 8.4 7.8 7.87 7.69 8 7.46 6.74 7 6.14 6.38 6

/s) 5 3 4 (m 3 2 1 Average water discharge Average water discharge 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 6. Monthly average water discharge [[46].46].

3.4. Hybrid System Components and Costs The input parameters and pricing of the various components used in this paper are given in Table1 .1. Di Differentfferent sizes sizes of of the the system system components components were were evaluated evaluated to findto find the the best best and and appropriate appropriate size suitablesize suitable for the for location. the location. Two dispatchTwo dispatch strategies stra (DS),tegies i.e., (DS), load i.e., following load following (LF), and (LF), cycle and charging cycle (CC),charging were (CC), strategically were strategically implemented implemented for the energy for the management energy management systems to properlysystems to investigate properly theinvestigate hybrid systemthe hybrid techno-economic system techno-economic performance. performance. On the one On hand, the one in thehand, cycle in the charging cycle charging strategy, thestrategy, diesel the generator diesel generator runs at itsruns maximum at its maximum rated power rated power to serve to serve the load the inload addition in addition to feeding to feeding the surplusthe surplus power power for chargingfor charging the the storage storage device. device. On On the the other other hand, hand, the the diesel diesel system system operates operates just just to suto ffisufficientlyciently satisfy satisfy the loadthe load demand demand without without charging charging the battery the battery storage storage in the case in the of a case load-following of a load- strategy.following The strategy. operating The reserveoperating as reserve a percentage as a percentage of load and of renewable load and renewable output was output set at 10%was ofset the at load10% of in the currentload in timethe current step, and time 25% step, of solar and power25% of output,solar power while output, 3% was while selected 3% for was the selected maximum for annualthe maximum capacity annual shortage capacity which shortage was within which the rangewas within recommended the range by recommended [47]. The project by lifetime[47]. The is 25project years lifetime at a diesel is 25 fuel years price at a of diesel $0.63 /fuell. and price a discount of $0.63/l. rate and of 13.5%.a discount rate of 13.5%.

Table 1.1. System component speciﬁcationsspecifications and costs.

ComponentComponent Parameters Parameters/Reference/Reference Specification Specification 1.1. PV panel PV panel [12,40 [12,40]] Efficiency at the standard test condition 13% Efficiency at the standard test condition 13% TemperatureTemperature coeffi coefficientcient −0.48%/°C0.48%/ C − ◦ InitialInitial cost cost $3200/kW $3200/kW CostCost of replacement of replacement $3000/kW $3000/kW OperatingOperating and and maintenance maintenance cost cost $5/kW/year $5/kW/year 2. Hydropower system [12] 2. Hydropower system [12] Initial cost $1700/kW CostInitial of costreplacement $500/kW $1700/kW Cost of replacement $500/kW Operating and maintenance cost $100/year Operating and maintenance cost $100/year Efficiency 75% Electronics 2020, 9, 1491 9 of 22

Table 1. Cont.

Component Parameters/Reference Speciﬁcation 3. Battery [43] Model Surrette 6CS25P Nominal voltage 6 V Nominal capacity 6.94 kWh Initial cost $1100 Cost of replacement $1100 Operating and maintenance cost $10/year 4. Converter [40] Capital cost $245/kW Cost of replacement $245/kW Operating and maintenance cost $10/year Eﬃciency 90% 5. Diesel generator [40] Initial cost $200/kW Cost of replacement $200/kW Maintenance cost $0.05/kW/h Minimum load ratio 25%

3.5. Mathematical Model

3.5.1. Modeling of a Hydropower System The principle of power production by a hydro turbine is based on the transformation of the kinetic energy of falling water into mechanical power, which is, then, converted into electrical power by a generator. In HOMER, the below equation is used to determine the electrical power generated by the hydro turbine [12]: ηhyd hnet ρwater Qturbine g P = × × × × (1) hyd W 1000 kW 3 where ηhyd is the efficiency of the hydro turbine system (%), ρwater the water density (1000 kg/m ), 3 Qturbine refers to hydro turbine stream flow rate in m /s, g is the gravitational acceleration, and hnet is the effective head in meters, and is computed in [48] as:

hnet = h (1 f ) (2) × − h where h denotes available head in meters and fh, the pipe head loss. To determine the frictional losses, the Darcy–Weisbach equation given in [12] can be utilized for a circular pipe. ! L V2 h = f (3) L D D 2g where hL denotes the absolute head loss as a result of friction (in units of length), fD, the Darcy friction factor, L denotes the pipe length in meters, D the pipe diameter (m), and V is the ﬂow speed (m/s). There are various methods in which the Darcy friction factor fD can be determined, including the Moody diagram, which is a well-known diagram, as depicted in Figure7. Electronics 2020, 9, 1491 10 of 22 Electronics 2020, 9, x FOR PEER REVIEW 10 of 22

Figure 7.7. MoodyMoody diagram diagram showing showing friction friction factor factor and and relative pipe roughne roughnessss for different diﬀerent ﬂowflow regimes [[48].48].

3.5.2. Modeling of a PV System and Temperature PV modules modules consisting consisting of of solar solar cells cells are are used used to produce to produce electricity electricity for different for different purposes purposes (e.g., (e.g.,household household load, load, street street lighting, lighting, and and water water pumping). pumping). Furthermore, Furthermore, the the solar solar insolation insolation level level and temperature, as well as the cellcell materialmaterial of thethe photovoltaic,photovoltaic, are the main factors that influenceinfluence the energy productionproduction levellevel ofof aa PVPV panelpanel [[15].15]. The output power of thethe PV panel is es estimatedtimated in HOMER as follows [14]: as follows [14]: ! GT PPV = YPVfPV [1 + αP(TC TC,STC)] (4) G = ƒ( T,STC)[1 + ( −− ,)] (4) , where YPV denotes the PV power output under standard test conditions (STC) in kilo watts, fPV refers PV PV towhere the PVY deratingdenotes the factor PV inpower %, G Toutputrepresents under global standa solarrd test irradiation conditions incident (STC) in on kilo the watts, PV module ƒ refers in T theto the current PV derating time step factor in kilo in %, watts G represents per square global meter, solarGT,STC irradiationis the incident incident radiation on the underPV module STC (1 in kilo the T,STC wattcurrent per time square step meter), in kilo wattsαp refers per square to temperature meter, G coe ffiis cientthe incident of power radiation in %/◦ C,underTC denotesSTC (1 kilo the watt cell p C temperatureper square meter), of the PV α system refers (◦toC), temperature and TC,STC refers coefficient to TC atof STC power (25 ◦inC). %/°C, T denotes the cell temperaturePV efficiency, of the however,PV system decreases (°C), and as T theC,STC temperature refers to TC at rises. STC The (25 derating°C). factor of temperature is evaluatedPV efficiency, as [23]: however, decreases as the temperature rises. The derating factor of temperature is evaluated as [23]: TC,NOCT Ta,NOCT 1+ p Ta + IT − TC,STC ∝ IT,NOCT − f = − (5) temp , , η 1+∝ [ + TC,NOCT Ta,NOCT mp−,STC ,] 1+ I ( ,− P T IT NOCT 0.9 = ∝ , (5) , −, Ƞ , 1+∝ ( where Tc,NOCT is the nominal operating cell temperature, (◦C), Ta,NOCT0.9refers to the ambient temperature 2 at NOCT (20 ◦C), IT,NOCT represents the solar irradiation at NOCT (0.8 kW/m ), ηmp,STC denotes the where Tc,NOCT is the nominal operating cell temperature (°C), Ta,NOCT refers to the ambient temperature efficiency of the PV panel under maximum power at STC (%), and αp represents the power temperature at NOCT (20 °C), IT,NOCT represents the solar irradiation at NOCT (0.8 kW/m2), Ƞmp,STC denotes the coefficient (%/◦C). efficiency of the PV panel under maximum power at STC (%), and αp represents the power 3.5.3.temperature Modeling coefficient of Economic (%/°C). Parameters

3.5.3.The Modeling net present of Economic cost (NPC Parameters) comprising the cost of replacement, initial cost, fuel cost, salvage cost, and the operational maintenance cost is computed using the following equation [43]: The net present cost (NPC) comprising the cost of replacement, initial cost, fuel cost, salvage TAC cost, and the operational maintenance costC is computed= using the following equation [43]: (6) NPC ( ) CRFi, n = (6) (, )

Electronics 2020, 9, x FOR PEER REVIEW 11 of 22 Electronics 2020, 9, 1491 11 of 22 where TAC is the total annualized cost in $ per year; n and i refer to the project lifetime in years and the annual interest rate in percent, respectively; and the capital recovery factor (CRF) is given in [25] where TAC is the total annualized cost in $ per year; n and i refer to the project lifetime in years and the as a function of n and i: annual interest rate in percent, respectively; and the capital recovery factor (CRF) is given in [25] as a (1 + ) function of n and i: (, ) = (7) (1i( +1 )+i)−1N CRF(i N) = , N (7) The levelized cost of energy (COE) is the average(1 + i) cost1 per kilowatt hour of effective power − generatedThe levelizedby the system cost ofand energy is given (COE in [49]) is as: the average cost per kilowatt hour of eﬀective power generated by the system and is given in [49] as: = (8) TAC COE = (8) where Eanloadserved refers to the gross annual load (kWh)Eanloadserved served.

4.where ResultsEanloadserved and Discussionrefers to the gross annual load (kWh) served.

4. ResultsIn this and analysis, Discussion the HOMER simulation tool was used to determine the best system configuration through a techno-economic and environmental evaluation corresponding to the In this analysis, the HOMER simulation tool was used to determine the best system configuration selected remote location in Nigeria. A sensitivity evaluation was performed to determine system through a techno-economic and environmental evaluation corresponding to the selected remote performance, while varying variables that directly affect the operational behavior of hybrid systems. location in Nigeria. A sensitivity evaluation was performed to determine system performance, while The procedure for the economic evaluation to obtain the optimal configuration is illustrated in Figure varying variables that directly affect the operational behavior of hybrid systems. The procedure for 8. The maximum capacity shortage of 3% was set for 25 years of project lifespan and a diesel fuel the economic evaluation to obtain the optimal configuration is illustrated in Figure8. The maximum price of $0.63/L [50]. capacity shortage of 3% was set for 25 years of project lifespan and a diesel fuel price of $0.63/L[50].

Figure 8. Hybrid system economic evaluation ﬂowchart. Figure 8. Hybrid system economic evaluation flowchart.

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4.1. Optimization Results In this section, we discuss the optimization results of the power system produced at a fuel price of $0.63/L and a discount rate of 13.5%. The hybrid system configuration obtained from the simulation analysis is shown in Table2. The configuration includes PV /diesel, PV/hydro/battery, PV/hydro/diesel/battery, and PV/diesel with battery system configurations. The table reveals that PV/diesel/micro-hydro/battery configuration is a more economically optimal solution than other models and that the PV/diesel configuration has the worst economic prospect. The optimal system consists of a 50 kW PV, 94.1 kW hydro turbine with 111 kWh nominal battery capacity, 100 kW DG capacity, and a 50 kW converter. The operating cost for this optimized configuration is $83,667/year with a COE of $0.112/kWh and an NPC of $963,431 and an initial capital cost of $369,820. The results also indicate that the optimal configuration reduces the operating cost, COE, and NPC by 76%, 64%, and 64.3% as compared with the PV/diesel system (worst case), respectively. The renewable fraction representing the contribution of RESs in the total power generated by the entire system was found to be 77.2%. This result shows that the system produces more energy from renewable power sources with the additional energy supplied by the diesel system. The outcome also shows that dispatch strategy significantly affected the renewable penetration rate. For example, when the simulation was conducted for the optimal system using CC and LF strategy, the renewable fraction was found to be 77.2% and 81.6%, respectively, for the same load demand. The optimal dispatch strategy for the proposed system was found to be cycle charging, as shown in Table2. The optimized system produces an annual total of 1,518,895 kWh of energy, whereas the hydro turbine system contributes about 1,178,600 kWh/year which represents around 77.6% of the total production. The diesel plant system supplies a share of 18.3% (277,222 kWh/year), with the extra electricity provided by the PV system at a share of 4.15%. Figure9 shows the monthly power generation of each component.

Table 2. Categorized optimization results summary of the system conﬁgurations.

Operating Renewable Average PV DG Hydro Converter NPC COE Diesel Battery DS Cost Fraction Generator (kW) (kW) (kW) (kW) ($) ($/kWh) (L) ($/year) (%) Hours (h/yr) 50 100 16 94.1 50 CC 963,431 0.112 83,667 77.2 76,492 4705 200 - 376 94.1 200 LF 2.17 M 0.254 127,674 100 - - 50 220 48 - 100 CC 2.60 M 0.301 327,396 1.25 326,073 7577 50 250 - - 50 LF 2.70 M 0.312 348,970 1.30 334,200 8760 Electronics 2020, 9, x FOR PEER REVIEW 13 of 22

Figure 9. Monthly electric power production.

Furthermore, the PV/hydro/battery conﬁguration shows 100% renewable penetration with no fuel consumed because of the absence of a diesel plant. This system is superior in terms of environmental aspects because no pollutant emissions are reported. However, it has economic negatives because the NPC and COE are 125% and 127% more than that of the optimal conﬁguration. Moreover, the optimized system had a small unmet electric load of 15,412 kWh/year, which was only 1.25% with a capacity shortage of 35,816 kWh/year (2.91%) of total capacity. However, the capacity shortage was considered to be acceptable, showing that the system had the maximum uptime and was able to satisfy most of its electrical load. Figure 10. Monthly average fuel consumption of a 100 kW diesel generator (DG).

The cash flow summary, presented in Figure 11, reveals that both capital and fuel costs contribute to the highest share of the total system cost. The high capital cost was because of the amount of money spent on the installation of the hydro and PV system, whereas the fuel cost was attributed to the generator operating conditions. The maintenance of the moving part of the diesel plant also led to high operation and maintenance (O&M) costs of around $174,075. The replacement cost, however, was reported to be a low value of $78,515, because the renewable power systems incurred no cost from replacement, since their lifetime was the same as that of the project’s lifetime.

Cash flow summary 400000 350000 300000 250000 200000 150000 100000 50000 0 Net present cost ($) cost present Net -50000 Replacem Capital O&M Salvage Fuel ent Converter 12250 3547.48 4426.1 -258.35 0 PV 160000 1773.74 0 0 0 Hydro 159970 709.5 0 0 0 DG 20000 166909 37828.25 -133.57 341908 Batteries 17600 1135.2 36260.84 -494.91 0

Figure 11. Cash flow summary of PV/hydro/diesel/battery scheme.

4.2. Environmental Analysis The production of greenhouse gases (GHGs) and pollutant emissions in hybrid power systems are attributed to the fuel consumption level of the DG system. In this paper, CO2 and other GHGs emissions were used to determine the environmental effect of the HESs. The concentration of pollutants and GHGs produced is directly related to global warming, and a trillion tons of carbon

Electronics 2020, 9, x FOR PEER REVIEW 13 of 22

Electronics 2020, 9, 1491 13 of 22

Concerning the performance of the diesel plants, the outcome revealed that the optimal system had the lowest annual consumption of 76,492 L of fuel, at 8.73 L/h, as shown in Figure 10, when operated for about 4,705 h per year. The diesel fuel consumption of this system was 77.1% less than that of the PV/diesel conﬁguration (worst case). The generator operational life was found to be 3.19 years because it was considered to have a lifespan of 15,000 h [51]. Figure 9. Monthly electric power production.

Figure 10. Monthly average fuel consumption of a 100 kW diesel generator (DG).

The cashcash ﬂow flow summary, summary, presented presented in Figure in Figure 11, reveals 11, reveals that both that capital both andcapital fuel costsand contributefuel costs tocontribute the highest to sharethe highest of the totalshare system of the cost. total The system high capitalcost. The cost high was capital because cost of the was amount because of moneyof the spentamount on of the money installation spent on of the installation hydro and PVof th system,e hydro whereas and PV thesystem, fuel costwhereas was the attributed fuel cost to was the generatorattributed operatingto the generator conditions. operating The maintenanceconditions. Th ofe themaintenance moving part of the of the moving diesel part plant of alsothe leddiesel to highplant operationalso led to and high maintenance operation and (O&M) maintenance costs of (O&M) around costs $174,075. of around The replacement $174,075. The cost, replacement however, wascost,reported however, to was be a lowreported value to of be $78,515, a low because value of the $78,515, renewable because power the systems renewable incurred power no cost systems from replacement,incurred no cost since from their replacement, lifetime was since the same their aslifeti thatme of was the the project’s same lifetime.as that of the project’s lifetime.

CashCash flow flow summary 400000 400,000350000 350,000300000 300,000250000 250,000200000 200,000150000 150,000100000 100,00050000 50,0000 Net present cost ($) cost present Net -500000 Net present cost ($) -50,000 Replacem Capital O&M Replaceme Salvage Fuel Capital O&M ent Salvage Fuel nt Converter 12250 3547.48 4426.1 -258.35 0 Converter 12250 3547.48 4426.1 -258.35 0 PV 160000 1773.74 0 0 0 PV 160000 1773.74 0 0 0 Hydro 159970 709.5 0 0 0 Hydro 159970 709.5 0 0 0 DGDG 2000020000 166909 166909 37828.25 37828.25 -133.57 341908 BatteriesBatteries 1760017600 1135.2 1135.2 36260.84 36260.84 -494.91 0 0

Figure 11. CashCash flow ﬂow summary of PV/h PV/hydroydro/diesel/battery/diesel/battery scheme.

4.2. Environmental Analysis The production of greenhouse gases (GHGs) and pollutant emissions in hybrid power systems are attributed to the fuelfuel consumptionconsumption levellevel of thethe DGDG system.system. In this paper, COCO22 and other GHGs emissions werewere used used to determineto determine the environmentalthe environmen eﬀtalect ofeffect the HESs.of the The HESs. concentration The concentration of pollutants of andpollutants GHGs and produced GHGs isproduced directly relatedis directly to global related warming, to global and warming, a trillion and tons a trillion of carbon tons emitted of carbon can cause a peak warming of around 2 ◦C[8]. Ngan and Tan [52] recommended maintaining the amount of carbon release below a trillion tons to limit the eﬀect of global warming. The type and amount of Electronics 2020, 9, 1491 14 of 22

harmful pollutant emissions (CO2, CO, SO2, NOx, unburned hydrocarbons, and particulate matter) produced by the optimized system and PV/diesel conﬁguration (worst case) are shown in Table3. The optimum conﬁguration was considered to be environmentally friendly because it emitted the least pollutant gas as compared with the PV/diesel system and other system designs analyzed. The results also revealed that the optimal system prevented about 77.1% of CO2 gas emission from being released to the surrounding air as compared with the PV/diesel system (worst case). The table shows that the prime contributor to unhealthy atmospheric air in this location is carbon dioxide (CO2), followed by carbon monoxide, while particulate matter contributes the least to total pollutant emissions [51].

Table 3. Pollutant emissions produced by the optimal hybrid system and PV/diesel system (worst case).

Proposed Pollutant PV/Hydro/Diesel/Battery System PV/Diesel System (kg/year) (kg/year) Carbon dioxide 200,247 874,890 Carbon monoxide 1250 5461 Unburned hydrocarbons 55.1 241 Particulate matter 7.50 32.8 Sulfur dioxide 490 2142 Nitrogen oxides 1175 5133

4.3. Sensitivity Assessment Sensitivity analysis was performed on the optimized configuration by varying some variables that could directly affect the cost and its overall performance. In this section, the following parameters were analyzed: real interest rate, RE component (solar irradiation and hydro stream flow rate), capacity shortage, and battery minimum SOC.

4.3.1. Real Interest Rate The interest rate (RIR) is a function of both the nominal discount and expected inflation rates that are utilized in HOMER to compute from NPC, the discount factors, and annualized costs. The effects of varying this parameter from 12% to 18% on the operating cost, NPC, and COE are shown in Figure 12. The figure reveals that this variable is linearly related to the COE, as given in Equation (8), because the interest rate increases with an increase in total annualized cost (TAC), which is directly proportional to COE. However, the total NPC and operating cost decreases linearly as the interest rate increases. The COE increases from $0.108/kWh for a 12% interest rate to $0.124/kWh as the interest rate rises to 18%. The NPC decreases by approximately 20%, while the operating cost is affected slightly with about a 0.69% reduction, as the interest rate increases from 12% to 17%. Again, an increase in the interest rate by 50% is found to increase the COE by about 14.8%. Electronics 2020, 9, 1491 15 of 22 Electronics 2020, 9, x FOR PEER REVIEW 15 of 22

NPC ($) COE ($/kWh) Operating cost ($/year)

1,050,000 0.126 83,800 0.124

1,000,000 0.122 83,700 0.120 83,600 950,000 0.118

0.116 83,500

900,000 0.114 83,400 0.112

850,000 0.110 83,300

0.108 83,200 800,000 0.106 12 13 14 15 16 17 18 Interest rate (%)

Figure 12. EEffectﬀect of increasing interest rate on the oper operatingating cost, cost, net net present present cost cost (NPC), (NPC), and and cost cost of of energy (COE).(COE).

4.3.2. Renewable Energy Component Parameters The levellevel ofof global global solar solar irradiation irradiation (GSI) (GSI) and and availability availability of water of water stream stream flow flow (WSF) (WSF) rate in rate a place in a determinesplace determines the periods the periods it will take it will for take the PV for and the hydro PV and system hydro to system meet the to load meet requirement. the load requirement. High solar insolationHigh solar and insolation water discharge and water reduce discharge the working reduce hours the working of DG, as hours well as of the DG, fuel as consumption well as the rate,fuel andconsumption vice-versa. rate, Furthermore, and vice-versa. the amountFurthermore, of electricity the amount contributed of electricity by RE contributed systems (PV by RE and systems hydro) depends(PV and hydro) on the leveldepends of streamflow on the level and ofsolar streamflow radiation and and solar intensity; radiation thus, and varying intensity; these thus, parameters varying canthese aff parametersect the system’s can affect operational the system's performance operationa and cost.l performance In this case, and the cost. annual In this average case,global the annual solar 2 2 irradiationaverage global was solar increased irradiation from 4.71 was to increased 9.71 kWh from/m daily 4.71 to at an9.71 interval kWh/m of2 daily 1 kWh at/m an/day, interval whereas of 1 3 thekWh/m average2/day, annual whereas streamflow the average was variedannual instreamflow the range ofwas 7.67 varied to 8.67 in m the/s range with an of increasing 7.67 to 8.67 step m3 of/s 3 0.2with m an/s. increasing step of 0.2 m3/s. The eeffectsffects ofof varyingvarying solarsolar radiationradiation onon thethe COE,COE, NPC,NPC, andand operatingoperating costscosts are illustratedillustrated in Figure 1313,, and Figure 14 presentspresents a graphgraph ofof NPC,NPC, operatingoperating cost, and COE as a functionfunction of waterwater discharge variation. As indicated in Figure 13,13, the NPC and COE decrease by only 0.76% and 0.89%, respectively, whereas whereas the the operating operating cost cost reduces reduces by about by about 4.2% when4.2% thewhen level the of globallevel of solar global radiation solar 2 increasedradiation increased from 4.71 tofrom 9.71 4.71 kWh to/ 9.71m /day kWh/m in the2/day HES. in Again,the HES. similar Again, to similar solar radiation, to solar radiation, Figure 14 Figureshows that14 shows the NPC that decreasedthe NPC decreased linearly from linearly $963,431 from to $96 $920,0093,431 to (4.5% $920,009 reduction) (4.5% reduction) along with along the COE with that the reducedCOE that from reduced $0.112 from/kWh $0.112/kWh to $0.107/kWh to $0.107/kWh (4.46% decrease), (4.46% anddecrease), the operating and the cost operating reported cost the reported highest 3 3 reductionthe highest of reduction 8.8%, as theof 8.8%, water as discharge the wate rater discharge increased rate from increased 7.67 m from/s to 7.67 8.67 m m3/s/s. to The 8.67 amount m3/s. The of decreaseamount of in decrease NPC and in COE NPC in and both COE cases in could both becases justified could by be the justified reduction by the in diesel reduction consumption, in diesel asconsumption, shown in Figures as shown 15 and in 16 Figures, as well 15 as theand cost 16, relatedas well to as diesel. the cost Moreover, related the to renewablediesel. Moreover, penetration the raterenewable increased penetration as the GSI rate and increase WSF increased.d as the GSI The and results WSF increased. also show, The in the results case also of GSI, show, that in the the COE case 2 remainsof GSI, that constant the COE for remains solar irradiation constant abovefor solar 5.51 irradiation kWh/m / day.above The 5.51 results kWh/m clearly2/day. show The results the impact clearly of theseshow parametersthe impact of on these the overall parameters system on cost the asovera wellll assystem the electricity cost as well cost. as the electricity cost.

Electronics 2020, 9, x FOR PEER REVIEW 16 of 22 Electronics 2020, 9, 1491 16 of 22 Electronics 2020, 9, x FOR PEER REVIEW 16 of 22 NPC ($) COE ($/kWh) Operating cost ($/yr.) NPC ($) 84,000 964,000 COE ($/kWh) 0.1120 Operating cost ($/yr.) 83,500 963,000 84,000 964,000 0.11200.1118 83,000 962,000 83,500 963,000 82,500 961,000 0.11180.1116 83,000 962,000 82,000 960,000 82,500 961,000 0.11160.1114 959,000 81,500 82,000 960,000 958,000 81,000 0.11140.1112 959,000 81,500 957,000 80,500 958,000 81,000 0.11120.1110 956,000 80,000 957,000 80,500 45678910 0.1110 80,000 956,000 Solar radiation (kWh/m2/day) 45678910 Figure 13. Effect of global solar irradiationSolar radiation (GSI) (kWh/m2/day) on the NPC, COE, and operating cost of the HES.

Figure 13. EffectEﬀect of global solar irradiation (GSI) on th thee NPC, COE, and operatingoperating cost of the HES.

Figure 14. ImpactImpact of of water water streamflow streamﬂow (WSF) on the NPC,NPC, COE, and operating cost of the HES.

Figure 14. Impact of water streamflow (WSF) on the NPC, COE, and operating cost of the HES.

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Renewable fraction Fuel consumption

82 78,000 76,000 81 74,000 80 72,000 70,000 79 70,000 68,000 78 78 66,000 77 64,000 Renewable fraction (%) Fuel consumption (L/yr) consumption Fuel Renewable fraction (%) 62,000 62,000 (L/yr) consumption Fuel 76 60,000 75 58,000 4.71 5.71 6.71 7.71 8.71 9.71 Solar radiation (kWh/m2/day)

Figure 15. ImpactImpact of GSI on the renewable fractionfraction and annual fuel consumption.

Renewable fraction Fuel consumption

83 90,000 82 80,000 81 70,000 80 60,000 79 50,000 78 40,000 77 30,000 76 20,000 Renewable fraction (%) 76 20,000 Fuel consumption (L/yr) consumption Fuel Renewable fraction (%) Fuel consumption (L/yr) consumption Fuel 75 10,000 74 0 7.67 7.87 8.07 8.27 8.47 8.67 Water discharge rate (m3/s)

Figure 16. EffectEﬀect of WSF on the renewable fractionfraction and annual fuel consumption.

4.3.3. Maximum Annual Capacity Shortage (MACS) The maximum annual capacity shortage (MACS) shortage is the maximum allowable amount of the totaltotal deﬁcitdeficit that that occurs occurs between between the the required required capacity capacity and theand actual the actual capacity capacity the system the system can supply can dividedsupply divided by the total by the load, total whereas load, whereas the capacity the capacity shortage shortage fraction isfraction a function is a function of total capacity of total shortagecapacity andshortage the total and electrical the total loadelectrical [48], andload any [48], system and any having system a higher having amount a higher of thisamount fraction of this is considered fraction is toconsidered be unacceptable. to be unacceptable. The results The can beresults altered can in be some altered cases in some if a certain cases amountif a certain of capacityamount of shortage capacity is allowed,shortage suchis allowed, as the occurrence such as the of aoccurrence very high peakof a demandvery high lasting peak for demand a very shortlasting duration. for a very However, short selectingduration. zero However, for the selecting maximum zero annual for the capacity maximum shortage annual means capacity that the shortage system means must serve that the electricsystem loadmust atserve all times the electric including load the at veryall times high including peak demand. the very high peak demand. Givler andand LilienthalLilienthal [[47]47] recommendedrecommended varying varying this this parameter parameter within within a rangea range of of 0.5% 0.5% and and 5% 5% to determineto determine the the performance performance and and cost-e cost-effectivenesﬀectiveness of as REof system.a RE system. In this In part, this the part, maximum the maximum annual capacityannual capacity shortage shortage was allowed was allowed to vary between to vary 0%between (in which 0% (in the which system the must system serve must 100% serve of the 100% load of at allthe times) load at and all 5%times) (in which and 5% the (in system which must the servesystem 95% must of theserve load 95% at allof times)the load to checkat all times) the operational to check the operational and economic behavior of the HES. Figures 17 and 18 show that allowing a certain percentage of capacity shortage can significantly affect the system's total NPC and unserved annual

Electronics 2020, 9, 1491 18 of 22

Electronicsand economic 2020,, 9,, x behaviorx FORFOR PEERPEERof REVIEWREVIEW the HES. Figures 17 and 18 show that allowing a certain percentage18 of of22 capacity shortage can significantly affect the system’s total NPC and unserved annual load, as well as load,theload, energy asas wellwell cost asas and thethe operating energyenergy costcost cost. andand The operatingoperating NPC and cost.cost. COE TheThe of the NPCNPC system andand reduce COECOE ofof from thethe $1,069,184 systemsystem reducereduce to $915,297 fromfrom $1,069,184and from $0.122 to $915,297/kWh toand $0.108 from/kWh, $0.122/kWh respectively, to $0.1 when08/kWh, the respectively, MACS rises fromwhen 0% the to MACS 5%. In rises addition, from 0%this to increase 5%. In addition, causes a 17.6%this increase reduction causes in operatinga 17.6% reduction cost, while in operating the unfulfilled cost, while load increasesthe unfulfilled from load0.018%load increasesincreases to 2.68%. fromfrom 0.018%0.018% toto 2.68%.2.68%.

NPC COE

1,100,000 0.125

1,050,000 0.12

1,000,000 0.115 950,000 NPC ($) NPC ($) 0.11 COE ($/kWh) 900,000 COE ($/kWh)

0.105 850,000

800,000 0.1 00.511.522.533.544.55 Maximum annual capacitycity shortageshortage (%)(%)

Figure 17. ImpactImpactImpact ofof of increasingincreasing increasing thethe the maximummaximum maximum annualannual annual cacapacity capacity shortage shortage on onthe the NPC NPC and and COE COE of the of system.thesystem. system.

Operating cost Unmet load

100,000 3 90,000 2.5 80,000 70,000 70,000 2 60,000 50,000 1.5 40,000 1 30,000 Operating cost ($/yr) Operating Operating cost ($/yr) Operating Unmet electric load (%) load electric Unmet

20,000 (%) load electric Unmet 20,000 0.5 10,000 0 0 00.511.522.533.544.55 Maximum annual capacitycity shortageshortage (%)(%)

Figure 18.18. EffectEﬀect of increasing the maximum annual ca capacitypacity shortage on the operating cost andand unserved electric load.

4.3.4. Battery Minimum State of Charge (SOC min)))

The batterybattery systemsystem minimum minimum state state of of charge charge (SOC (SOCminmin) is)) isis the thethe relative relativerelative charge chargecharge state statestate below belowbelow which whichwhich the thestoragethe storagestorage system systemsystem is never isis nevernever drawn. drawn.drawn. Most MostMost storage storagestorage batteries babatteriestteries that thatthat are areare rechargeable rechargeablerechargeable are areare expected expectedexpected not notnot to betoto becompletely completely discharged, discharged, otherwise, otherwise, such actionsuch canaction permanently can permanently damage thedamage batteries. the Thebatteries. percentage The percentagerange from 30range to 50 from is normally 30 to 50 selected is normally for the batteryselectedlected SOC forfor tothethe avoid batterybattery an excessive SOCSOC toto dischargeavoidavoid anan thatexcessiveexcessive could discharge that could damage the battery bank and to increaseincrease thethe battery’sbattery’s lifetimelifetime [49].[49]. InIn thisthis analysis, the effect of varying the SOCmin inin thethe rangerange ofof 20%20% toto 50%50% inin 5%5% incrementsincrements onon thethe hybridhybrid system operational performance and the total cost was evaluated. The effect of increasing the SOCmin on the total NPC, COE, operating cost, and fuel consumption rate is illustrated in Figures 19 and 20

Electronics 2020, 9, 1491 19 of 22 damage the battery bank and to increase the battery’s lifetime [49]. In this analysis, the effect of varying Electronics 2020, 9, x FOR PEER REVIEW 19 of 22 the SOCmin in the range of 20% to 50% in 5% increments on the hybrid system operational performance Electronics 2020, 9, x FOR PEER REVIEW 19 of 22 and the total cost was evaluated. The effect of increasing the SOCmin on the total NPC, COE, operating The results show that a rise in the SOCmin from 20% to 50% causes the NPC and COE to increase by cost, and fuel consumption rate is illustrated in Figures 19 and 20 The results show that a rise in the 1.59%The results and 1.8%,show thatwhile a risethe inoperating the SOC mincost from and 20% annual to 50% consumption causes the NPCincrease and fromCOE to$79,093/yr. increase byto SOC from 20% to 50% causes the NPC and COE to increase by 1.59% and 1.8%, while the operating $83,658/yr.1.59%min and and1.8%, from while 62,812 the Loperating to 76,479 costL of andfuel. annualThe increase consumption in the annual increase liters from of fuel $79,093/yr. consumed to cost and annual consumption increase from $79,093/yr. to $83,658/yr. and from 62,812 L to 76,479 L of shows$83,658/yr. that andthe fromsystem 62,812 relies L moreto 76,479 on theL of DG fuel. in Th meetinge increase the inload the demandannual liters whenever of fuel the consumed battery fuel. The increase in the annual liters of fuel consumed shows that the system relies more on the DG minimumshows that SOC the increases.system relies In addition, more on the the results DG in show meeting that increasingthe load demand the SOC whenevermin poses a the significant battery in meeting the load demand whenever the battery minimum SOC increases. In addition, the results environmentalminimum SOC increases.challenge, In as addition, more carbon the results emissi showon thatwould increasing be produced the SOC becausemin poses of a significantits direct show that increasing the SOC poses a significant environmental challenge, as more carbon emission relationshipenvironmental with challenge, the amount asmin ofmore fuel in-takecarbon byemissi the dieselon would plant. be produced because of its direct wouldrelationship be produced with the because amount of of its fu directel in-take relationship by the diesel with the plant. amount of fuel in-take by the diesel plant.

NPC COE NPC COE 965,000 0.1125 965,000 0.1125 0.112 960,000 0.112 960,000 0.1115 0.1115 955,000 0.111 955,000 0.111

NPC ($) 950,000 0.1105 COE ($/kWh)

NPC ($) 0.1105 950,000 0.11 945,000 0.11 COE ($/kWh) 945,000 0.1095 0.1095 940,000 0.109 940,000 0.109 20 25 30 35 40 45 50 20 25 30 35 40 45 50 Battery SOCmin (%) Battery SOC (%) min

Figure 19. Impact of the battery minimum state of charge (SOCmin) on the system total NPC and Figure 19. Impact of the battery minimum state of charge (SOCmin) on the system total NPC and FigureCOE. 19. Impact of the battery minimum state of charge (SOCmin) on the system total NPC and COE. COE.

Operating cost Fuel consumption Operating cost Fuel consumption 85,000 90,000 84,00085,000 80,00090,000 83,00084,000 70,00080,000 82,00083,000 60,00070,000 81,00082,000 50,00060,000 80,00081,000 40,00050,000 79,00080,000 30,00040,000

Operating cost ($/yr) Operating 78,00079,000 20,00030,000 Fuel consumption (L/yr) consumption Fuel

Operating cost ($/yr) Operating 78,000 20,000

77,000 10,000 (L/yr) consumption Fuel 76,00077,000 010,000 76,000 20 25 30 35 40 45 50 0 20 25 30 35 40 45 50 Battery SOCmin (%) Battery SOC (%) min

Figure 20. Effect of battery SOCmin on the operating cost and fuel consumption rate of the HES. Figure 20. Eﬀect of battery SOCmin on the operating cost and fuel consumption rate of the HES. Figure 20. Effect of battery SOCmin on the operating cost and fuel consumption rate of the HES. 5. Conclusions 5. Conclusions In this article, we present an optimal design and environmental evaluation of an off-grid hybrid energyIn thissystem article, meant we topresent power an a optimalrural village design in anNigeria.d environmental The HOMER evaluation analysis of tool an off-gridwas employed hybrid forenergy the economic system meant evaluation to power of the a ruralproposed village energy in Nigeria. supply Thesystem HOMER along analysiswith the tooltechnical was employedfeasibility basedfor the oneconomic the energy evaluation sources of availablethe proposed in the energy southe supplyrn part system of the along country. with theFour technical different feasibility system configurationsbased on the energy from a sources combination available of hydro, in the DG,southe batteryrn part storage, of the and country. PV generation Four different system system were analyzedconfigurations during from the simulationa combination process of hydro, to obtain DG, the battery most suitablestorage, and and least PV generationexpensive option,system whilewere analyzed during the simulation process to obtain the most suitable and least expensive option, while

Electronics 2020, 9, 1491 20 of 22

5. Conclusions In this article, we present an optimal design and environmental evaluation of an off-grid hybrid energy system meant to power a rural village in Nigeria. The HOMER analysis tool was employed for the economic evaluation of the proposed energy supply system along with the technical feasibility based on the energy sources available in the southern part of the country. Four different system configurations from a combination of hydro, DG, battery storage, and PV generation system were analyzed during the simulation process to obtain the most suitable and least expensive option, while considering the environmental effect of each system design. The simulation results reveal that the hybrid system with 50 kW PV panels, 94.1 kW hydro system with 111 kWh nominal battery capacity, 100 kW DG capacity, and a 50 kW power converter is the most economically feasible option for this location as compared with the other models, with the lowest NPC and COE being $963,431 and $0.112/kWh, respectively. In addition, the area shows a high potential for RE projects, as the RE penetration stands at a high rate of 77.2% that has reduced the operating hours and consumption of the diesel plants to 4,705 h/yr. and 76,492 L of fuel; thus, this system is appropriate for the environment because it helps to maintain a clean and safe atmosphere because it has low pollutants and GHGs. The sensitivity assessment conducted on the optimum configuration shows that parameters such as the real interest rate, RE component (solar irradiation and hydro stream flow rate), capacity shortage, and battery minimum SOC have significant effects on the costs and operational performance of the system. The obtained results show that the total NPC and electricity cost varies whenever these parameters change at different rates, showing the sensitivity of the HES parameters toward variations in these variables. Lastly, the results of this work should assist in the implementation of rural electricity framework plans and increase the RE share in the total energy mix, supporting the limitation of the global warming effect. Further research is required involving the feasibility study of solar, wind, and hydro resources considering the six geopolitical zones of Nigeria.

Author Contributions: All authors contributed equally. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The support of the deanship of graduate studies at King Abdul-Aziz University for postgraduate scholarship is highly appreciated. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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