Techno-Economical Planning of an Off-Grid Integrated Renewable Energy System

This paper focuses on reducing the LCOE (Levelized Cost of Energy), the unmet load, Net Present Cost (NPC) and the greenhouse gas emissions by the utilization of an optimized off-grid integrated renewable energy system. The LCOE has been reduced by 14.8% of that of DG and by 28.6 % of Diesel Generator (DG) with Battery System, whereas the NPC has been reduced by 14.7% of DG only system and by 28.7% of DG with Battery System. A comparison analysis has also been presented based on the performance of the proposed system and most recently published similar studies. To achieve these objectives, an optimization algorithm has been developed and simulated in Hybrid Optimization Model for Multiple Energy Resources (HOMER) software with different combinations of IRES, DG and battery systems. Similarly, intending to analyze the feasibility and performance in terms of the technical and economic aspects of the proposed system, HOMER is used. Based on the obtained results, broadly, it is examined that the proposed system decreases diesel consumption by around 8113 liters/year and the total emissions of greenhouse gas by about 21545 kg/year in the study area; thereby, it can be foreseen as a viable and sustainable option(s) for the development of more such systems in remote locations.


Introduction
Obtaining an inexpensive and dependable electricity supply is currently essential for the economic growth and stability of a nation. Due to technical and economic issues, the electrification of the grid of hilly, remote and scarcely populated regions is very difficult (Uwineza, Kim, and Kim 2021). A DG is often used as a source of energy for such situations. However, it leads to global warming as well as climate change by producing greenhouse gases (Shan et al. 2017). To address these problems, it is crucial to utilize a renewable energy source that does not create greenhouse gases. Fortunately, the majority of hilly communities are located in regions with tremendously improved development of renewable energy sources, both of which are cost-free and environmentally preferable to fossil fuels (Gioutsos et al. 2018). Thus, distributed power generation based on renewable energy is a viable alternative to fossil fuels and lowers their detrimental impact on human existence. Because of these pragmatic considerations, the production of energy from locally accessible

Methodology
This section explains the methodology employed for this investigation. It also provides a comprehensive explanation of the study area's location, load estimation, meteorological parameters, and resource estimation. As shown in Figure 1, the complete methodology may be separated into three major phases: pre-Homer process, Homer analysis, and post-Homer analysis. In Homer analysis, the HOMER Pro software is applied with input factors such as solar irradiation, etc., to determine the ideal size of a resource component. In the post-HOMER study, produced findings are compared technically, economically, and environmentally with basic instances (DG and DG/Battery) in order to identify the IRES's major benefits. Figure 2 is a flowchart that explains the entire optimization approach employed in this investigation.

Location of study area
The study area, i.e., Dewal, is a small village located at 〖78.439903〗^o N latitude and 〖 30.733299〗^0 E longitude in the Mori block, Uttarkashi district, Uttarakhand in India. Dewal's total area is 36.88 hectares (0.37 km2. There are 19 families and 108 inhabitants in the village of Dewal, among which 60% constitute males and 40% constitute females. The literacy level of Dewal is 66.7%, whereas the labour force participation rate is approximately 44.4%. They are mostly involved in the production of woollens, blankets and shawls (Directorate of Census Operations 2014a, 2014b).

Load estimation of study area
Dewal is a village in the Mori Block of the Uttarkashi district in the Indian state of Uttarakhand. The overall population of the Dewal is 108, composed of 60 men and 48 women. The primary data for calculating the minimum essential load comes from a study of the local region, from which the daily household energy demand has been assessed. To estimate a household's daily power demand, the devices and their corresponding daily working hours are evaluated in Table 2. It is projected that the village's total land area energy consumption, average demand, and peak power are 64.6 kWh/day, 2.69 kW, & 13.72 kW, respectively. Figure 3 depicts the peak load of a normal day in the research area during the month of January.

Weather characteristics study area
The meteorological data of the research area is a crucial factor in determining the location of IRES. The average annual temperature of the research area ranges from -10 to 11 degrees Celsius, with a mean temperature of 1.25 degrees Celsius. The National Aeronautics and Space Administration (NASA) provides the monthly average temperature variation of the research area using the HOMER software, as depicted in Figure 4 (NASA, n.d.).

Study area's resource estimation
The focus of this research is on exploiting the resources of solar energy in the study region. The sum of the beam combined with diffusion irradiance is referred to as daily sun irradiance. NASA data gathered by using HOMER software suggest that the study area receives an average of 4.63 kWh/m2/day of solar radiation on a horizontal plane. The daily solar irradiance with clearness index for the study area is given in Figure 5. The greatest value of solar irradiation for a region of study is 6.10 kWh/m2/day in June, while the minimum value is 2.85 kWh/m2/day in January. In both February and October, the greatest and minimum clearness index values are 0.658 and 0.479, respectively (NASA, n.d.).

HOMER software as IRES optimization tool
The HOMER is regarded as the international benchmark for simulating and improving renewable energy systems. It is utilised to design and evaluate the economic and technical viability of a hybrid renewable energy system. Economic feasibility, as well as sensitivity analysis, are used to assess the effectiveness of the renewable system. HOMER takes as input

Daily Radiation
Clearness Index data regarding renewable resources, energy needs, and the technical and economic aspects of the components and runs thousands of simulations to determine the ideal match between energy consumption and energy supply.

Composition of IRES
As illustrated in Figure 6, the planned IRES for the research region is designed with SPV, BES, and converters. Throughout this IRES, the SPV's DC output is connected to the DC bus. The load demand is deemed AC and is fed directly through the AC bus. AC and DC buses are coupled via a bidirectional converter operating in inverter mode. A BES is also implemented into the IRES to mitigate the random nature of SPV output.

Solar PV
In the current review, a generic photovoltaic panel with a derating factor of 80% and a 25-year lifetime was investigated. The derating ratio is the adjustment factor used to scale the loss in SPV production under real-world conditions, such as the existence of dirt, snow, and shade, as well as the heating of solar panels. The SPV power output is based on the incident solar irradiation and solar panel area, as defined by Equation (1) (Rajanna and Saini 2016).

Battery energy storage
To mitigate for the stochastic nature of SPV output, an energy storage system must be incorporated. A BES is also incorporated into the IRES created for the study area due to the numerous advantages afforded by batteries, like strong operating conditions, simplicity of operation, and low maintenance needs, etc. For the BES, the maximum value of stored energy can be assessed as given in Equation (2).
Where, ƞ _ is the charge-storage efficiency of the battery.
Where m, 1 , Δt, E, c, , , , and are the storage rate constant (h-1), available energy in the starting time step (kWh), duration of the time step (h), the energy available in the first-time step (kWh), capacity ratio, maximum charge rate (A/Ah), the total capacity of storage (kWh), number of batteries, maximum charge current (A) and the nominal voltage of the battery respectively.

Converter
Several AC and DC buses in this investigation were powered by a system converter with a 1kW capacity. The effectiveness and lifespan of a converter operating in inverter mode are estimated to be 95% and 15 years, respectively. Table 3 outlines several additional economic and technical characteristics applied in this research for converter sizing (Kumar et al. 2019).

Financial metrics
Using the suggested IRES, the primary goals of this research are to minimize LCOE, NPC, unfulfilled load percentage, as well as greenhouse gas emissions. To evaluate the economic viability of the suggested IRES, the LCOE is a crucial criterion. Therefore, the LCOE is estimated using the HOMER software tool, as well as the minimal LCOE is used as an objective function throughout this research to assess the IRES's technical and economic viability. The levelized cost of energy (LCOE) is the ratio of the overall cost incurred throughout the lifetime of an IRES project to the entire amount of electricity generated over the lifespan of that IRES project. In this analysis, a discount rate of 8%, an inflation rate of 2%, and a project duration of 25 years were assumed accordingly. The LCOE can indeed be determined mathematically using Equation (6).
Where, , , ( ) and the discount rate is assumed to be 8% per year, the project's duration is assumed to be in years, while IRES produces energy output in hours while total actual cost is measured in dollars ($) accordingly. The total NPC consists of the installation cost, operations cost, and total revenue generated by IRES over its lifetime. It is calculated using equation by the HOMER programme (7) (Shan et al. 2017).
Where, is the total annualized cost and CRF is the Capital Recovery Factor for IRES. It can be calculated with Equation (8): In the HOMER programme, it is assumed that all prices increase at the same rate; hence, it uses a real annual rate of interest rather than a nominal one. The equation for calculating the recovery cost of an IRES component is included in HOMER (9) (Agyekum and Nutakor 2020; Shan et al. 2017).
Where RC represents the replacement cost of IRES system components in dollars ($), represents the residual lifetime of IRES parts of the system, and represents the total lifespan of IRES system components in years.

Constraints
IRES design is subject to various physical and functional restrictions. Such constraints must be met for the entirety of the optimization programme. Listed below are the restrictions examined in this study.

Power Balance Constraint
The total hourly power dissipated by all operating units must meet the energy requirement of the scheduled load, as given by Equation (10) (Agyekum and Nutakor 2020).
Where, PSPV(t), PBES (t), ( ) and ƞ represent the total SPV output power, total BES output power, total power that is not being supplied, and efficiency of the inverter, respectively. d l NPC

SPV Power Output Limit
Equation (11) describes the relationship between SPV output power and incident solar irradiation (Shan et al. 2017).
Where and represents solar irradiance given time (W/m2), the overall power output of SPV, overall typical solar irradiance assumed to be 1000 (W/m2), cut in irradiance value assumed to be 150 (W/m2), as well as SPV rated electrical output under standard conditions. Similarly, several BES design limitations are defined as follows.

BES Power and State of Charge Limit
The BES must never be over-discharged or over-charged. Therefore, for the battery bank's safety procedures, the energy limit and state of charge limitations indicated by Equations (12) and (13) Where and represents the minimum as well as the maximum power capacity range and state of charge, respectively.

Simulation Results and Discussions
In this section, simulated results from the HOMER software are presented, along with a discussion of their interpretation. The HOMER software optimizes to lower LCOE as well as total NPC while taking capacity shortage limits into account. A capacity deficiency is the difference between the IRES's specified operating capacity and its actual operating capacity. HOMER maintains track of these shortages and computes their annual total. The IRES is optimized to meet the study area's overall load requirement. In addition, the inflation rate, as well as the discount rate, are considered in the sensitivity analysis to establish their tradeoff with the economic and technical feasibility of the IRES. The daily load demand of the study area, as estimated by the HOMER software, is around 64.6 kWh/day and the average load and peak load demand are assessed as 2.69 and 13.72 kW, respectively.

Technical and economic analysis
The current study simulated a total of 504 options, of which just 360 were feasible and 144 were impossible due to capacity deficit restrictions. Table 4 presents the optimization findings for the SPV/BES resources combination. To achieve the optimum solution, the SPV of 21 kW rating, 2718 numbers of BES, and a 12kW rating of converter (inverter) are utilized. It can be noticed from the results shown in Table 2 that the optimum values of total NPC and LCOE for SPV/BES-based IRES are 43738.53 $and 0.143515 $/kWh, respectively. The running cost and initial investment cost of the complete SPV/BES IRES are estimated to be 860,0656 $ and 32,620.02 $, respectively. The initial cost of a single SPV is $1,934,91, and its annual energy output is 3,1522.08 kWh. The annual output of BES is 14904.53 kWh per year. BES's normal capacity is 2788.229 kWh/year, while its normal useable capacity is 1672.937 kWh/year. The converter is used as a 2.6912 kW average inverter. The net present value and the yearly value of SPV/BES IRES are 43738.537 $ and $ 3383.37 dollars, respectively, according to Table 5, cost overview of IRES components.    In addition, 61.11 percent of such capital cost is borne by SPV, 33.89 percent by BES, and 5 percent by both the converter system. The BES replacement cost is the largest due to its shorter life span of five years, whereas the SPV replacement cost is null due to the SPV's enormous life span, which really is relatively similar to the IRES life of the project of 25 years. The contract price of the converter is moderately priced and equal to 34% of the capital cost of the converter. The negative character of the BES and converter salvage costs implies that these represent expenditures rather than profits. There is no requirement to replace SPV over the IRES project's 25-year lifespan. Therefore, it has no salvage value. Figure 7 reveals that perhaps the SPV system, BES, as well as converter contributed to 51.47 percent, 42.82 percent, and 5.71 percent of annualized capital cost, respectively. Table 6 details the summary electric results of the planned IRES. The production of energy by IRES is contingent on incident sun irradiation. Annually, the SPV/BES power system generates 31,522 kWh of energy. The annual demand for service load is 23,575 kWh. This value is important enough even to define the SPV/BES system to be selfsufficient for powering the study region. The system capacity deficit is also negligible, with a value of 0.0596%. In October and February, the minimum and maximum power outputs are 3,254.09 kW and 2,034.423 kW, respectively, according to the quarterly power output curve in Figure 8. The quantity of extra electrical energy produced is a function of the entire area generation and load profile. The surplus power is generated mostly during periods of low load curves and high solar irradiation. The excess electrical energy output for the SPV/BES electric power system is 4,393 kWh/year, or 13.9% of the overall electrical energy generated. This could be sold or used for commercial purposes. The annually generated excess power is shown in Figure 9. Further, the accessibility of surplus power and 0.02% unmet load demonstrated that the proposed IRES power system is not just self-sufficient in meeting current energy needs but is also capable of meeting future energy needs in a cost-effective and environmentally beneficial manner.  Figure 10 illustrates the proposed IRES's 24-hour functioning on a normal day during the month of June so that its energy management can be comprehended. SPV serves the load during the day, whereas BES is utilised whenever solar irradiance is unavailable. As depicted in Figure 11, 24-hour demand profile on a typical June day, the BES alone serves the load from

Total Load Served
Load served by SPV Load served by BES 1h to 6h when solar output is unavailable. 7 h to 18 h, when solar irradiance is sufficient, the load is handled by SPV alone and extra energy is used to charge the BES, as seen by the negative load supplied by the BES during this time. Between 18h to 19h, the solar radiation intensity is available but insufficient; therefore, the load is serviced by SPV and BES jointly. From 19h to 24h, there is no sun irradiation; consequently, the entire load is supplied by BES alone. Figure 11: Solar irradiance and the SPV output profile on a typical day of the month of the June Figure 11 depicts the incident solar irradiation and matching output curve of SPV for a typical June day. According to the results collected, the SPV-rated capacity is 21.0 kW, the average power output is 3.60 kW, the capacity factor is 17.1%, and the total power produced is 31,522 kWh/year. In addition, it is determined that the levelized cost for SPV is 0.143515 $/kWh with 4,379 operational hours per year.  Figure 12 depicts the 24-hour charging/discharging cycle of the BES on a typical July day in order to explain the role of the BES in the energy management of the planned IRES. In the lack of sufficient solar irradiation, a very slow discharge between 1h and 4h and a moderate discharge between 4h and 8h are seen. The BES is charged between 8h and 18h, as indicated by the BES's negative output power throughout this time frame. It is discharged gradually between 18h and 24h if the load need is large and cannot be met by SPV production alone.  Figure 13 depicts the yearly state of charge (SOC) for BES for such SPV/BES IRES system. Input and output energy amounts for BES are 16,051 kWh/year & 13,738 kWh/year, respectively. In contrast, the BES offers a throughput of 14,905 kWh/year with losses arising of 2,426 kW/year. The overall energy production of the system converter operating in inverter mode during 8760 hours per year is 23,575 kWh per year. It requires a total input energy of 24,816 kWh/year, with losses totaling 1,241 kWh/year. The mean output of the converter and its capacity factor is 2.69 kW and 22.4%, respectively. Presently, the one and only source of electrical power in the community of Dewal is a diesel generator set. Throughout this research, the diesel generator serves as a baseline for comparing the relative performance of designed IRES. According to the simulation results, the payback method of the designed IRES is 8.91 years. In the architecture of IRES, inflation rate increases result in a quick increase in the total cost of the system. Throughout this research, inflation rates ranging from 1% to 6% were employed to determine their impact on system cost characteristics like total NPC as well as LCOE. The data also indicate that an increase in inflation rates resulted in a decrease in the price of energy.

Comparative analysis with recent renewable study
Due to its fortunate location within the solar belt (40°S to 40°N), India is one of the world's leading recipients of solar energy. India has tremendous potential for solar-powered energy systems. There are numerous remote highland regions in India wherein grid extension is not economically viable. Multiple researches on the economic and technical viability of renewable energy systems for low-load profile areas have been conducted and published in the literature. Efforts have been undertaken to evaluate some of these investigations with the current one, as presented in Table 7. By implementing the suggested SPV/BES system under the different climatic circumstances of the study area, significantly lower LCOE and NPC values are attained in the current study, as shown by the comparison analysis. These findings are highly relevant for determining investment policies for generating power to the home load in the study region or any other low-load profile location with comparable climatic circumstances.

Comparative analysis with base case 1 and 2
Oil prices in the country are highly volatile due to global factors, including international crude oil prices, currency exchange, as well as inflation rates. As of July 12, 2020, diesel costs 1.02 dollars per litre in the research region. For the purpose of validating the effectiveness of the proposed IRES, its efficiency is also compared to that of two base cases. For base case-1, a diesel generator is examined for electricity supply to the study region. For base case-2, a diesel generator and a battery energy storage system are evaluated. Table 8 contains the technical details of the diesel generator under evaluation. In addition, as indicated in Table 9, a comparative cost study between base cases-1 and 2 and the proposed IRES has been conducted.     Table 5 and Table 6 reveals that the proposed IRES generates electricity at a significantly lower value of LCOE, NPC, and operating cost to zero greenhouse gas emissions but also guarantees the saving of at least 14,800 litres of diesel fuel and reduction of approximately 21545kg/year of overall harmful greenhouse gases in the climate of the region of the study region in comparison to base case-1 and base case-2.

Conclusions
The objective of this study was to evaluate the technical and economic viability of a solar photovoltaic/battery energy storage off-grid integrated renewable energy system for low load profile hilly isolated areas, such as the village of Dewal, Mori block in Uttarkashi district, Uttarakhand, India. Using HOMER Pro software was utilized to size resource components optimally in order to create a cost-effective power supply for the research area. The LCOE and total NPC for SPV/BES-based IRES are 0.143 dollars per kWh and 43738.53 dollars, respectively. Using the suggested SPV/BES-based IRES reduces the LCOE to 14.8% of the DGonly system and 28.8% of the DG-plus-batteries system. NPC is reduced to 14.7% of the DGonly system and 28.7% of the DG-plus-battery system. In the SPV/BES function, 4,393 kWh/year of extra energy is generated at 0.02 percent of the unmet load. This surplus electricity could be sold or used for commercial purposes. By implementing the suggested SPV/BES operations, diesel fuel consumption and GHG emissions can be decreased from a minimum of 8113 liters/year and 21545 kg, respectively. In conclusion, an SPV/BES-based IRES is proposed for powering the study region or other hilly, isolated areas. Not only is it capable of powering the study area alone, but it can also partially meet future energy demands in an inexpensive and environmentally responsible manner. In conclusion, an SPV/BES-based IRES is proposed for powering the study region or other hilly, isolated areas. Not only is it capable of powering the study area alone, but it can also partially meet future energy demands in an inexpensive and environmentally responsible manner. This research does not cover the