Designing and Sensitivity Analysis of an Off-Grid Hybrid Wind-Solar Power Plant with Diesel Generator and Battery Backup for the Rural Area in Iran

Because of the lack of transmission and distribution grid of electricity in remote and inaccessible areas due to the high cost of construction of the transmission line along with the unsuitable geographical conditions and taking into account the factors aﬀecting sustainable energy production, renewable energy seems like a sensible solution. Therefore, in this paper, considering the solar and wind potential of Turkalan village located in East Azerbaijan Province, the combined solar-wind-diesel generator system with battery bank and independent of the grid was evaluated. Sensitivity analysis and optimal measurement of the studied system were performed by HOMER software. Sensitivity analysis was performed on the parameters of solar radiation, light reﬂection from the environment, and wind speed. The goal was to supply 22 kWh/d of energy with a maximum load demand of 2.5 kW. The four hybrid systems proposed by the software considering the total net present cost (NPC) were solar-generator-battery, solar-wind-generator-battery, solar-battery, and solar-wind-battery, respectively. The studies were conducted to determine which of the systems is more suitable for the area.


Introduction
Today, the use of renewable resources is on the agenda of many countries around the world, and an important investment process in the world is being developed in dispersed products. Regarding environmental issues and global warming, the use of these renewable energies has become necessary in the past [1][2][3]. By 2016, worldwide electricity generation from fossil fuels and renewable resources is 75.5% and 24.5%, respectively, of which energy produced by countries of China, America, Brazil, Germany, and Canada is superior in this area [4][5][6]. Renewable energy use is an alternative to fossil power plants due to its easy access and the renewable energy structure, lack of transmission and distribution network in remote areas due to the high cost of construction of the transmission line along with the inadequacy of the geographical conditions, and taking into account the factors affecting the sustainable energy production. e use of an independent grid system is a convenient option to meet the need to use electricity [7][8][9]. Over the years, researchers have been struggling to address the weakness of renewable resources by concentrating on the use of these resources combined with overcoming the weakness of these resources, making progress on the use of these distributed resources independently of the network or connected to the network [10][11][12][13]. However, in the design of dispersed production systems, it has combined challenges such as energy management, due to the intermittent nature of renewable resources and the diversification of energy demand [14][15][16], but the need for energy at all times of day and meeting consumer needs in mind getting system reliability due to unstable weather conditions in the area during daylight hours is used to store excess energy at times that require reduced energy consumption and the use of this energy when needed by the storage or battery [17,18]. e necessity of acquiring accurate region information and the overall view of the design of the system to meet the demands of the year in hybrid systems is crucial for obtaining optimum size [19]. In this context, software such as HOMER and iHOGA can be used to obtain the optimum size and design of the hybrid system [20,21]. Homer software is provided by the National Energy Laboratory of the United States to design a variety of microgrid systems, connected to the network, isolated from the network, and access to the climate database, with economic evaluation and analysis of the sensitivity of existing parameters, including energy cost and strategy to meet the load and obtain the lowest final cost of the system; and it proposes an optimal solution system for load balancing [22][23][24]. e disadvantages of software can be high computational time and not able to optimize multiobjectives [25]. In these articles, a general review is provided using this software for optimal combination programming. Research findings [26] analyze the cost of wind and solar hybrid systems with access to solar and wind resources in a region of Georgia, based on a combination of the independent network of wind and solar power plants and considering the life span of 25 years for the design project. Also in referring [27] has used a 5 kW microturbine in Nigeria to meet the design needs of the project. Combined systems are typically designed from two or more dispersed generation sources such as biomass, the geothermal, wind, solar, and microturbine water with a backup source for energy access throughout the hours. In the meantime, the use of solar and wind combinations has been of particular interest in many parts of the world [28]. e use of batteries or power grids is for easy access to energy at times when the production of energy from renewable sources due to climate change in the region's climate increases the reliability of the system. In the latest research, hydrogen can be used as a high-efficiency source compared to batteries [29]. e selection of each component of the hybrid power plant considers the climate and geography of the region depending on the needs of the consumer, considering the costs of construction, exploitation, social and environmental costs, and finally options which have the most favorable economic and environmental conditions than other options. In Figure 1, a hybrid system is shown. e purpose of this study is to find the annual electricity production of the microgrid system and the optimal capacity of system components and compare between different modes. From the types of equipment, the most economical type of combination is selected, and finally, the net profit of the whole system, which is calculated according to the net present cost method, is expressed along with the relevant analyses.

Material and Method
Accurate information about the geographical environment is very important for analyzing renewable energy systems. Because renewable energy sources are highly dependent on environmental factors, the intensity of sunlight and wind is a function of time. So, the first step in designing production systems based on renewable sources is to determine renewable energy sources. e most important factor in the use of renewable energy is economic parameters; in this study, HOMER software has been used for this work and determination of economic indicators. Figure 2 shows an overview of the system being designed. e flowchart of software performance is shown in the figure below. e type and number of inputs required to perform simulation, optimization, and economic ranking calculations are shown in the flowchart. Also, technicaleconomic-energy-environmental outputs show the high ability of software to analyze issues related to renewable energy.

Climatic Conditions of Solar Energy.
e sun is a massive source of energy that supplies our power to direct and indirect forms and causes natural processes such as the displacement of the air. e Earth's share of energy from the sun is a small amount of total solar radiation. Solar energy can be one of the most important renewable energies for replacing fossil fuels. As a result, this emerging source has become a priority in many countries, such as China, to increase energy production and greater access [2]. Solar energy is converted into electrical energy by no solar cell [19]. Iran is one of the countries with a good potential to invest in this area in terms of geographical location in terms of sunlight. In this study, the rural Turkalan area located near the city of Ahar in East Azerbaijan Shargi Province has been studied. Using the HOMER software, the amount of sunlight in the region studied is shown in Figures 3 and 4.
In the HOMER software, by specifying the area required by latitude and longitude, the average sunlight according to Figure 3 is introduced with the main index. Sensitivity analysis was performed by entering two different indexes of 4 and 5 (kWh/m2/d). Also, in Figure 5, the amount of received sunlight is shown in different months and at different times. e power produced by solar cells (P PV ) is calculated from the following equation by the HOMER software [31]: where Y pv is the output power of the PV panels in the standard conditions (kW), f PV is the derating factor, G T is the solar radiation received to the collector surface (kW/m 2 ), and G T,STC is the value of G T in the standard conditions (1 kW/m 2 ). e angle of the solar cells is equal to the latitude of the studied station [31].    Journal of Engineering the variability of production at different times and low reliability [20]. To obtain the wind speed in the area, using the Meteororm software, wind speed information is obtained according to Figures 6 and 7. Despite environmental factors such as ripples affecting wind speed, various wind speeds of 2.5 m/s and 4 were used for the assessment and analysis of sensitivity [32]. e output power of a wind turbine depends on its altitude [33]. e output power of wind turbine is calculated by the following equation by the HOMER software [34]: where ρ is the air density in real conditions, ρ 0 is the air density in standard conditions, and P WTG, STP is the output power (kW) which is obtained from the turbine power curve.
Wind turbines are used to generate electricity, while small wind turbines have been used to save costs. ese types of turbines have low-diameter rotors, which are intended here on the consumer side to charge the batteries. e cost of a one-kilowatt turbine with a life span is 1,200 $, the cost of replacement and repairs and maintenance for the year is 770 $ and 10 $/yr, respectively, and the production characteristic curve is shown in Figure 8.

System Configuration, Operation, and Optimization.
In this system, photovoltaic unit and wind turbine are present as renewable energy sources, diesel generator as support for power generation, and batteries to store excess  Journal of Engineering energy and improve system reliability. In some systems, a storage system (battery bank) is used when the power generated by renewable energy sources (P re ) at time t is not sufficient to supply the power load (P l ). If the load demand is high and the energy storage system is not able to supply this total energy, the diesel generator intervenes to meet the remaining load demand. is mechanism is based on the following three steps: (1) First step: If it is P rs (t)<P l (t), the third step should be done. Otherwise, the second step is done. (2) Second step: Set the battery bank charge to t � t+1 and then perform the first step. (3) Discharge the battery bank. If it is SOC < SOC min , the diesel generator will start; otherwise, the time will be set to t � t+1 and then the first step will be done.
e output power of each photovoltaic system (P PV ) at moment t can be calculated based on the following relation of solar radiation: In this regard, I is solar radiation, A is the cross section of the photovoltaic system, and η PV is the total efficiency of the photovoltaic system panels and the DC/DC converter.
For a wind turbine, if the given wind speed exceeds the cutoff value, the wind turbine will start producing. If the wind speed exceeds the nominal value of the wind turbine speed, the turbine will start producing a constant amount of output power. If the wind speed exceeds the high cutoff value, the wind turbine generator will stop to protect the turbine. e output power of each wind turbine (P WT ) at moment t is as follows: In this regard, v is wind speed, P r is nominal wind turbine powers, v cut-in is low wind turbine cutoff speeds, v cutout is high wind turbine cutoff speeds, and v r is nominal wind turbine speeds.
As a backup power system, the diesel generator will start operating when the power output is insufficient and the power level of the energy storage system is low. In this case, the diesel generator starts working and compensates for the power shortage.
Diesel generator Cons D � (1/h) fuel consumption depends on the output power and is defined as follows: In this regard, P D N is the nominal power, P D is the output power of the diesel generator, and two are the parameters BD and AD of the fuel curve coefficients, which are defined as BD � 0.0845(l/kWh) and AD � 0.246(l/kWh). e hourly cost of fuel consumption can be obtained as follows: P fuel is the cost of fuel. Due to the variable behavior of photovoltaic panels and wind turbines, the capacity of the battery bank in the hybrid system is constantly changing. On some systems, the battery charge mode can be achieved as follows: When the output power of photovoltaic panels and wind generators exceeds the load energy, the battery bank will be in the charging position.
E Batt (t) and E Batt (t−1) are the amount of battery charge in moments t and t-1, respectively, σ hourly self-discharge rate, η Inv inverter efficiencies, E load load demand, and η Batt battery bank charge efficiencies.

Other Equipment and Financial
Calculation. e battery in order to save energy and deliver the energy required in different situations, the battery bank in the system is considered. Regarding the types of models available in the software, the vision model 6FM200D with characteristic (200 Ampere, 12V, 917 kWh) is reviewed at HOMER. e cost of the used battery is 287 $, and the replacement and maintenance costs are 266 $ and 1 $/yr, respectively.
For limited use of diesel generators, increasing fuel costs and limiting the supply of diesel fuel, it is therefore emphasized that renewable energy can be used as much as possible. e generator price in this analysis is 164 $/kW, and replacement and maintenance costs are 131 $ and 0.001 $/hr, respectively. Converter power is needed to communicate between the consumer and the power generator. For a 1 kW system with 90% efficiency and a life span of 15 years, the cost of installation and replacement is 300 $ and 249 $, respectively. e intended consumer in this design is considered the domestic load of 22 kWh/d with a maximum load power requirement of 2.5 kW.
where P gen is the total electricity produced by generator (kWh/y), _ m fuel is the total fuel consumption (kg/y), and LHV fuel is the low heating value of the fuel (MJ/kg). e generator efficiency is calculated by the following equation by HOMER software [35].
HOMER software presents a list of classified systems based on the total NPC which is calculated by the following equation [36]: where C ann, total is the total annual cost ($), CRF is the capital recovery factor, i is the real interest rate, and R proj is the project lifetime. e CRF that represents the capital return in N years is calculated by the following equation [37]: e COE in terms of $/kWh during the project lifetime is also calculated by the following equation [38]: where E Load Served is the actual electrical charge by the hybrid systems in kWh/y that is priced in dollars.

Limitations.
For photovoltaic-wind-diesel generatorbattery system, the following conditions must be met: In these relationships, N max PV , N Wind , and N Batt , respectively, are the most available amount of photovoltaic panels, wind turbines, and batteries. Limitations for battery model: Initial battery power SOCintial: Minimum and maximum energy stored in the battery: Minimum and maximum battery charge capacity: Minimum and maximum battery discharge capacity: e battery cannot be charged or discharged at the same time: Power at any time for the battery: Minimum and maximum diesel power:

Results
In Table 1, the cost of the applicable systems along with the optimal equipment sizes is shown by taking into account the analysis of various parameters. e four proposed hybrid systems by the software, taking into account the NPC, are, respectively, solar-generator-battery, solar-wind-generatorbattery, solar-battery, and solar-wind-battery. e three wind speed parameters, the amount of sunlight, and the reflection of light from the surface in this analysis have been used as sensitivity variables. To find the optimal HOMER software system, among the various combinations and layouts of the system in the software search space, with an analysis of 8760 hours, all of the possible scenarios for the system are simulated with respect to the required electrical charge, and all the impossible situations deleted to categorize according to the NPC. e optimization results presented in Figures 9-11 give the high potential of using sunlight and relatively low wind speed, and the region of analysis of the amount of sunlight relative to the constant of the other variables. It is possible to use more solar power in different radiation levels around the area in question. According to Table 1, the sensitivity analysis of the system results from the proposal of two systems with accurate weather data, which is the difference between the two systems in the amount of light reflected from the environment. Because of the Journal of Engineering   Journal of Engineering particular climatic conditions in the area, light reflections are considered in the least conditions. erefore, the system to run in the area with accurate weather data using a solardiesel combined system with a 20% light reflection battery is an appropriate option for the implementation of the design at the desired location. Considering the villages around the area that are different from the light and wind speed, one can conclude that by increasing the amount of sunlight, the wind speed, and the amount of light reflected from the environment, the final net cost plus cost of energy production is reduced. With the observations in the precise weather data of the software, Figure 12 shows that increasing the amount of light reflections from the environment on the surface of the solar panels has a positive effect, which increases the amount of energy produced and reduces the net system cost.
In Figure 13, for comparison of the cost of diesel fuel with the cost of solar panel production, taking into account the amount of light reflection from the environment of 20% and wind speed of 15.3 m/s, it is indicated by the variability of the amount of sunlight by increasing the amount of sunlight, energy costs are much lower than diesel fuel. According to Table 2, the cost of generator fuel is estimated at 4 $/L. For the photovoltaic/diesel generator system, which is the battery as an energy storage system, NPC for this system is $ 27020, to supply energy with this system to 13 kW for the solar panel, and 17 batteries are needed. In the grid-connected system, the following grid specifications are considered: 2,500$ per kilometer of transmission line construction, which for this distance is 100$ maintenance costs. In this study, the cost of buying and selling electricity to the grid is estimated at 0.02$. It is economically justified for electricity to run this project at a distance greater than 0.987 km. Figure 14 illustrates the distance between the use of a system independent of the network due to the high cost of construction of transmission lines in difficult areas and out of reach of transmission lines. Table 3 shows the cost of installing, replacing, repairing, and maintaining the system, the cost of fuel, and the cost of the sale of worn-out equipment. As the total cost of the system equipment is 13582 $, the replacement is 9694 $, and the   system repairs and maintenance is 334 $. e amount of energy produced in different months of the year in Figure 15 by solar panels and diesel generators is 89% and 11%, with a power output of 18587 kWh/yr and 2260 kWh/yr, respectively. Figures 16-19 show the output of solar panels and diesel generator at hours of the year. For Turkalan region, according to the solar radiation and wind speed, four models were defined. Due to the solar radiation of high sunlight and low wind speed, the diesel generator model with photovoltaic cell is more suitable. In this model, the cost of each unit of energy produced is 0.371$/kWh, which is much lower than other models.

Conclusion
Due to the lack of energy and the endlessness of renewable energy, new and clean energy has been used in many countries around the world. On the other hand, in remote areas of the grid, independent networks considering the environmental conditions of the region seem to be a sensible solution. Hence, Iran has the potential to use renewable energy as a suitable alternative to fossil fuels. erefore, in designing the system in HOMER software, the use of hybrid systems has been investigated to improve system reliability and load responses in the Turkalan rural area. In general, due to the increase in the amount of solar radiation, the wind speed, and the reflection coefficient of light from the existing system environment, the net cost is lower than the chosen system. Based on the results obtained from the simulation of the four proposed systems by the software, taking into account the NPC (solar-generator-battery, solar-wind-generator-battery, solar-battery, and solar-wind-battery) with the tests done, the lowest final net cost, respectively, is combined with a solar-generator system with a battery, which has a light reflection coefficient of at least the proportion of other systems at a cost of energy 0.371 $/kWh, and the amount of energy produced by solar panels and diesel generators is 89% and 11%, respectively, and the amount of energy is 18587 kWh/yr and 2260 kWh/yr, respectively, a good solution for supplying the load of the Turkalan area compared to other hybrid systems. e NPC is 3224 $ with a capacity of 13 kW of solar panels and 2 kW of diesel generator with 17 batteries.

Data Availability
All data used to support the findings of this study are included in the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.