Revolutionizing Oman's energy network with an optimal mixture renewable energy source

Abbreviations:VRE: Variable Renewable Energy; PPAs: Power Purchase Agreements; GCC: Gulf Cooperation Council; RE: Renewable Energy; HRES: Hybrid Renewable Energy System; PV: Photo-voltaic; HOMER: Hybrid Optimization Model for Electric Renewables; Ret Screen: Renewable Energy Technologies Screen; OPWP: Oman Power and Water Procurement Company; MIS: Mian Interconnected System; Sm³: Standard Cubic Meter; OMR: Omani Rial; CO₂: Carbon Dioxide; GHG: Greenhouse gases; ℃ : Celsius Degree; GPP: Gross Domestic Products; DPS: Dofar Power System; bcm: Billion Cubic Meter; CPV: Concentrator Photovoltaic; PDO: Petroleum Development Oman; MSP: Miraah Solar Project; EOR: Enhanced Oil Recovery; AER: Authority for Electricity Regulation; Wh/m²: Watt Hour per Square Meter; NASA: National Aeronautics and Space Administration; HES: Hybrid Energy System; ＄: US Dollar; CF: Capacity Factor; PR: Performance Ratio; NREL: National Renewable Energy Laboratory; TOPSIS: Technique-for-Order-Performance-by-Similarity-to-Ideal-Solution; FC: Fuel Cell; DG: Diesel Generator; G: Gas; WT: Wind Turbine; KWp: Kilowatt Power; tCO₂: Tons Carbon Dioxide; STC: Standard Test Condition; IoT: Internet of Things; NASDA: National Space Development Agency; DC: Direct Current; AC: Alternating Current; GCR: Ground Coverage Ratio

1.   Introduction

With the steep growth of the world population and the prosperity of society, the consumption of fossil fuels gradually increases, aggravating plenty of global problems like energy crisis, air pollution, global warming and so on. Renewable energy with sustainable, clean and safe properties has attracted the attention of governments all over the world ^[1]. Hybrid renewable energy systems, such as solar PV systems, are critical for sustainability in certain areas, such as airport energy ecosystems with demand flexibility and power supply reliability ^[2].

The solar density in the Sultanate of Oman is very high. Some demand of Oman can be supplied through solar energy. Apart from the large availability of solar energy, the capacity of solar power plants in the country is very low. The solar insolation in Oman varies from 4.5 to 6.1 kWh/m², and the power is 1640 to 2200 kWh per year as per the renewable energy study. [https://energypedia.info/wiki/Oman_Energy_Situation]. Hence, the nation will have more solar insolation during summer in the desert areas than in the coastal areas. Thus, the country plans to extend power generation through solar energy and target to supply 30% of electricity through renewable energy by 2030.

The Gulf-Cooperation-Council (GCC) countries, which include Oman, Kuwait, Bahrain, Saudi Arabia, Qatar, UAE and Qatar, have many alternative energy sources like solar and wind. Nonetheless, it is observed that fossil fuels still dominate the primary energy consumption of the GCC, while less than 1% of total consumption is fed with renewable energy. The Gulf region has launched various renewable energy projects, initiatives and programs to meet its renewable energy targets. For example, the state had 146-GW of installed electricity capacity at the end of 2020, with renewable energy accounting for 3271-MW. Solar PV technologies remain the most dominant (71%) among other renewable energy sources. Oman's renewable energy total installed capacity is 159-MW as of 2020 ^[3].

Renewable energy sources provide highly reliable and environmentally beneficial solutions by reducing the GCC states' dependency on oil and gas for local energy production and consumption. Furthermore, the world's economies and nations support RE. GCC countries, if climate change is not addressed by enacting a proactive energy policy that minimizes dependency on fossil fuels, may become uninhabitable. In addition, because those nations have a high per capita carbon emission rate, they must transition to (RE) to comply with the Paris Agreement. Governments must enact laws that stimulate the use and investment in renewable energy technology at both the business and consumer levels ^[4].

In line with Oman's Vision for 2040, the country aims to reduce its reliance on nonrenewable energy and encourage the growth of clean energy sources as effectively as possible. Using renewable energy will positively impact the environment by lowering carbon dioxide emissions. As the renewable energy installations increase, private sector investments will be attracted, the production cost will reduce and more dependency on renewable energy will increase the competition in the renewable energy market.

To achieve Oman's targets in the sustainable renewable sector for Oman Vision 2040, finding alternative energy sources that are sustainable and reducing our dependence on non-renewable energy sources is critical. Thus, planning solar energy projects at a particular location is essential to ascertain the financial viability of a solar PV system with a specific capacity and module technology. New technology, modern software and programs can determine and simulate model projects with accurate data output. Design-Hybrid-Renewable-Energy-System (HRES) for electrification using simulation software HOMER/ETAP/PSSE/PSCAD/DIGSILENT/RET-SECREEN/MATLAB/PV-SYST/LAB SOLAR. Many scholars worldwide have conducted feasibility studies on solar PV systems, especially in European and Middle Eastern countries. Nevertheless, the research papers on the assessment of solar PV systems give little emphasis on the tropical climate, specifically in Oman. Typically, (HOMER) or Renewable Energy Technologies Screen (Ret-Screen) simulation software or Researchers have used satellite data to analyze the technical feasibility and financial viability of a photovoltaic (PV) system.

With the increase in power demand due to the increase in population, Oman targets Vision 2040 to combine renewable energy with conventional energy systems to produce cost-effective power generation. This paper proposes the optimal mixture of renewable energy sources like solar energy and an On-Grid system as conventional energy sources, which use natural gas or diesel.

Moreover, this paper will assess the optimal mixture of renewable energy sources like solar energy and combine it with an On-Grid system as conventional energy sources, which use natural gas or diesel. The work will also discuss the economic feasibility of using the combination of renewable energy sources along with conventional energy sources. It will also include comparing GHG emission reduction when using this combination. Furthermore, it will emphasize discussing the positive impact on the cost reduction of the power generation and tariff structure by considering the project's initial investment.

This study will use simulation software and will contribute for the appropriate and optimal mixture of renewable energy sources in Nizwa City, Oman.

The proposed research aims to determine the optimal mix of renewable energy sources using a micro solar PV integrated with the grid system. Using the simulation in HOMER software, various parameters like (CO₂) level, energy production and net present cost are estimated. The results obtained are compared with conventional models to show the feasibility of the proposed system.

2.   Literature review

There are various studies on the optimal mixture of solar energy sources, but there are limited studies in Oman. This part will illustrate Omani and international papers relevant to our field of research in the Continent of Asia Countries.

A summary of studies for several configurations on the HOMER software is illustrated below in Table 1, which includes or involves details: name of authors, project site, publication year and software used.

According to the above literature, implementing a hybrid system will reduce (CO₂) by up to 28% more than conventional systems. Similarly, to focus on achieving the Paris Agreement's long-term target of remaining well below 2%, aggressive mitigation steps are necessary beyond 2030 ^[26]. It also provides low Net Present Cost (NPC) and Cost of Energy (COE) compared to the existing system.

By conducting a brief literature survey, it is identified that most of the conventional systems have a higher percentage of (CO₂) emission. Also, the cost of energy production is significantly high. In this paper, it is proposed that by using an Optimal mixer of renewable energy source in the Omani network using a grid-connected photovoltaic system, the emission level of (CO₂) and cost of energy production can be reduced.

3.   Renewable energy in Oman

3.1.   Peak demand in Oman

Generally, the scenario of peak demand in Oman is changing. MIS has increased from 5,565 MW in 2015 to 6,473 MW in 2021 at an average annual growth rate of about 3% for MIS (As well as an increase by 4% in 2021 against 2020). DPS also shows that it increased at an average annual growth rate of around 1%, which increased from 495 MW in 2015 to 534 MW in 2021 and increased by 1% in 2021 compared to 2020 ^[27]. In Musandam, peak demand decreased by 6% in 2021 compared to 2020. So, total peak demand has increased from 6,837 MW in 2020 to 7,081 MW in 2021 ^[12].

3.2.   Renewable energy in Oman with including solar energy

The Sultanate has adopted regulations that encourage the extensive utilization of renewable energy sources. Production of electricity from renewable energy sources in Oman this year has reached 650 MW, a remarkable milestone since a modest beginning on a smaller scale in 2019 and will further be increased to 3,350 MW by 2027 [https://solarquarter.com/2022/08/26/oman-to-generate-3350-mw-capacity-of-renewable-energy-by-2027]. According to the latest five-year capability report of Oman Electricity Transmission Company or OETC, it expects to have up to 2.25 gigawatts of renewable energy connected to its transmission grid before 2026 [https://solarquarter.com/2023/05/09/oman-electricity-transmission-company-to-boost-renewable-energy-capacity-with-2-25gw-by-2026/].

On a smaller scale in 2013, the Authority for Public Services Regulation (formerly the Authority for Electricity Regulation) published the first strategy to promote the development of renewable energy technology in rural areas. The objective of the new plan was to integrate renewable energy sources into the existing diesel-based energy networks that supply electricity to remote areas. In response to this requirement, the 303-kW solar system known as Mazyonah Energies 2022 was constructed in an isolated area. Consequently, other rural area projects, such as a 500-kW wind-powered pilot project on Masirah's rural island, were constructed ^[3].

In Oman, there are numerous present and potential solar energy projects. The Miraah Solar Project (MSP), which is being sponsored jointly by (PDO) and Glass-Point Solar, is the most extensive solar power installation currently being built. With the use of Enhanced Oil Recovery (EOR) technology, this solar project is expected to create more than a thousand megawatts (MW) of power. The (MSP) will annually contribute to national efforts to reduce emissions of greenhouse gases by offsetting around 300,000 tons of carbon dioxide. To supplement the 7 MW EOR solar plant in southern Oman, the (MSP) project was initiated. The (EOR) Solar project has generated a significant amount of steam, which has made the use of (EOR) technology in oil production feasible. Oman's southernmost province of Amin is home to a 100-MW solar facility funded partly by (PDO). The award phase of a 25-year solar power project with the goal of supplying energy to assist meet the company's internal power demand and possibly reducing annual CO₂ emissions by 137,000. Building on the Ibri Solar PV Project in the northeastern part of Oman has commenced, thanks to the efforts of the Ministry of Housing (OMH) and the Power and Water Procurement Company (OPWP). This ＄ 500 million, 500 MW plant was operated in 2021, providing power to around 33,000 homes. As part of PDO's efforts to achieve long-term sustainability in energy generation, an estimated 18,500 PV car park installation was built in Mina Al Fahal. A total of one thousand (1,000) homes and numerous (PDO) business buildings have been supplied with power from this 5.92-MW capacity project since 2017. It amounts to nine (9) million kWh. As a result, annual CO₂ emissions were reduced by 6,662 tons. The authority for Electricity Regulation (AER) is now talking with key players to launch the Sahim Rooftop Solar Project as part of the government's rural electrification development strategy. The scheme is expected to deliver rooftop solar energy through PV technology to 3,000 houses.

Additionally, several other rooftop PV-installed powering projects in Oman's cities and provinces are in the planning stages. Rural locations include Al-Wusta (2,000 kW) in Dhofar province, Hiji (100–1,500 kW), Sohar (303 kW), Masirah Island (500 kW), Al Mazyonah (299 kW) and Al Mathfa (28 kW). Investing in these modest projects is predicated on the excellent outcome of the piloted on-grid PV solar concentrating system deployed in select Muscat homes ^[28].

According to Patrick's paper, Oman has planned investments in renewable energy for the past two decades, and it was during this time that the first wind-powered water turbines were installed in Muscat to assist in water distribution to residential properties. As part of the nation's national development priorities, several expansive renewable energy initiatives are planned to help establish future energy security and ensure socioeconomic development ^[28]. In a recent article published in 2022, the following names of active renewable energy projects in Oman give possible business prospects for experienced renewable energy firms.

4.   Study area

Nizwa is one of the largest states in the Dakhiliyah governorate in Oman. Nizwa is roughly 140 kilometers (87 miles) (1.5 hours) from Muscat, Oman's capital. Around 72,000 individuals are expected to live there. Nizwa has electricity demand for Annam around 191.5-MW in 2021 and increased the demand by 7% in 2022 that is 206.8 MW based on data given by Oman electricity transmission company. Nizwa's location is between 22° 56′ 0″ N, 57° 32′ 0″ E. Nizwa recorded the temperature max 43 ℃ during summer months and 12 ℃ in January. Unfortunately, Nizwa city has not implemented any project for renewable energy sources till now, and there is no study paper on those sources in Nizwa City.

4.1.   Geography and climate in Nizwa in Oman

Nizwa is surrounded by mountains on all sides. According to the Koppen climate categorization, Nizwa has an arid climate. Temperatures in January may drop to a pleasant 12 degrees Celsius, and the weather is generally a little cool from November through March. Extreme heat and dryness characterize the summers, approaching 43.5 ℃ in June, and the average high temperature a year is 35 degrees Celsius.

OPWP became involved with the Solar Project data, specifically with the two weather monitoring sites in Adam & Manah (Nizwa). The figures below represent the data trend for (DNI) and (GHI) during the period ^[6].

4.2.   Solar radiation in Nizwa-Oman

Oman's favorable geographic position between latitudes 168 and 268 N and longitudes 518 and 598 E makes it suitable for using PV and wind turbines to address the growing need for power ^[5]. The solar energy density in Oman is among the highest worldwide. Daily sun radiation in July averages between 5,500 and 6,000 Wh/m² and 2,500–3,000 Wh/m² in January throughout the nation ^[29].

Al-Badi et al. has found the overall solar radiation is barely higher than 4 kWh/m²/day at Sur and almost 6 kWh/m²/day at Marmul. Still, the average value at Oman's twenty-five sites is more than 5 kWh/m²/day and around 5.3 kWh/m²/day, and the average sunshine is 9 hours per day at the selected project area (Nizwa), as shown in Figures (4 and 5) ^[30].

The other latest study in 2016 in Nizwa station showed results of (GHI and DNI) as below in Table 2 ^[31].

The annual average DNI measured at Nizwa-Manah station was 7.51 kWh/m²/day, as the figure below illustrates measured solar data in February 2013. Additionally, based on an old study through Atsu S.S Dorvloa and David B Ampratwum that Oman has more than 9 sun hours per day, is shown in the below Figures 6 and 7 ^[32].

Based on the Global Solar Atlas website, Nizwa city has a high amount of GHI and DNI, at 2,256.5 kWh/m² and 2,140.2 kWh/m², respectively, with an Optimum tilt of PV modules OPTA (25/180°) as seen in Figure 8.

Another study by Ali Al-Lawati computed monthly average sunshine as below in Figure 9 ^[33].

4.3.   Data sources

Any location for a solar energy generation facility must be assessed for feasibility using solar radiation and temperature data. Moreover, to progress and analyze data of solar radiation, numbers of hours of sunshine per day and temperature in particular areas and any related data that has been recorded and knowing the peak hours of sun radiation is essential. Solar energy resource evaluation applications require precise radiation data over a few years. Solar radiation gathering may be accomplished in two ways: by measurement or through (NASA) surface meteorology and solar energy database (sites geographical).

In Oman, the most common way to get the data is to use the data provided by The Meteorological Office Oman and for implementation, which is actively processing data collected from installed and monitoring stations sensors in meteorological stations located within potential project site locations. Another way to get sun data is to use satellite data. This data is available online, and the researcher can get it from NASA or other websites. This data is not measured and is from the satellite, so it might be less accurate than Meteorological Office Oman data.

The simplest method of obtaining solar radiation data is by on-site measurements. However, depending on readings from in-situ meteorological stations, there may be less opportunity. Thus, due to the high cost of monitoring construction, the Long-term meteorological observation stations are not always located in all places favorable for solar farm construction. Luckily, solar radiation monitoring was installed in 2013 and 2016 in my selected location from my project in Nizwa City-Manah. Moreover, the monitoring concluded that the area had the highest radiation among Oman's cities. The power law indicates high output power from PV panels when it imposes high solar radiation.

By analyzing the above data from the sources, it is observed that the potential for implementing solar power in Nizwa is feasible.

5.   The configuration of the proposed solar energy system (SES)

The combined energy system must be feasible and sustainable, which means that at each time step, one or more energy systems must be available to fulfill electric load demand, such as primary generating, backup generation or storage. Components of a system can be designed and incorporated in various configurations. The sizing of system components using a probabilistic method has been carried out based on sun radiation, electric load demand and specific technical and physical parameters. The suggested (Renewable energy system) RES is schematically depicted in Figure 14.

5.1.   Solar system with on-grid system

For various reasons, solar energy systems with on-grid are an excellent compromise for most houses. They are much more cost-effective than stand-alone setups, and as long as the grid is up and running, you can count on having access to power even in cloudy climates.

On-grid PV systems generate electricity from solar photovoltaic harvesters and transfer it to a utility. Off-grid solutions, on the other hand, are not designed to be a substitute for grid power. Grid-connected systems are often found in metropolitan areas where main power is readily accessible, and the energy produced by the PV system is sent back into the grid rather than stored in batteries. The Grid serves as a storage medium in this strategy, and electricity may be imported from the grid when required in the building. One of the key benefits is that, unlike an off-grid system, the system does not need to supply enough energy to meet the property's power requirements. The PV system, the energy grid or a combination of the two may power the property, with the system being as little or as big as the owner desires. Excess electricity produced by the PV system will be exported to the power grid, and the system owner will be reimbursed in many locations with the highest profit. The essential components of a grid-connected PV system are the PV array, inverter and metering system. Cables, combiner boxes, protection devices, switches, lightning protection and signs are also needed in addition to these essential components.

5.2.   Solar system with on-grid system concept

When solar power systems are connected to the grid, their operation remains virtually unchanged. Solar panels keep converting solar energy into electricity, which powers your home. When a house is linked to the power grid, any shortfalls in the amount of solar energy generated by the solar panels in the home may be made up for by drawing electricity from the power grid.

Similarly, if you generate excess electricity at any time, such as while your family is away at work or school, your panels can feed it back into the grid. You will typically obtain credits for creating power for your electrical grid, which will frequently be sufficient to offset any electricity you consume from it.

It is simple to connect solar systems to the Grid. They are constructed using various quantities of photovoltaic (PV) panels, a solar grid-tie inverter and a net meter. The electricity produced by the solar panels is direct current (DC), but the solar grid-tie inverter changes it into alternating current (AC) that your home and the Grid may use. Net meters process the current following and track how much electricity you supply to the Grid and how much you get from it to calculate your monthly billing and credits with specified tariff rates.

5.3.   Fundamentals of solar power in residential systems with on-grid system

The solar panels mounted on roof space or on free land generate a direct flow of electrons producing direct current (DC). Electricity output is maximized based on average peak hours in a day, which is different for every state based on the solar irradiance levels. Since, using alternating current (AC) power supply in our households, (DC) electricity is converted to (AC) electricity through a macro-inverter connected to a distribution panel, which distributes electricity in our electrical devices and energy meters, displaying the amount of energy produced during the day. Sometimes to reduce the dependency on on-grid electricity, we install small battery banks to accommodate energy usage during night and off-peak hours.

6.   HOMER methodology

(HOMER) stands as a popular software that was developed in the United States of America by the National Renewable Energy Laboratory (NREL) with the intention of constructing and evaluating off-grid and on-grid power systems for remote, stand-alone and distributed production operations. The tool was created in the United States of America. At the time that this paper was written, more than 200,000 people were using the program all over the world. Depending on the quantity of information presented, the software demands a range of inputs from the user. The following are some of them: the need for energy, the availability of resources (including the possibility of using the grid) and the producing components, such as turbines or generators (with varied degrees of detail for each). In addition to this, the emission forecast is examined. Finally, the model can be constrained by several different constraints (such as a production limit or a scheduled output). HOMER performs mathematical computations and provides a list of viable configurations ordered by net present cost (NPC) and (COE) to assess alternative design combinations based on operational and economical rates. This list may then be compared to one another and then recommends, through the optimal configuration, one among them. HOMER's optimization and sensitivity analysis may be used to analyze different system configurations. HOMER models three primary activities in total: simulation, optimization and sensitivity analysis.

Dr. Peter Lilienthal initially devised the HOMER software at the NERL Laboratory in the United States. The software was refined into HOMER Pro® in 2014 (HOMERenergy.com, 2018). Using this software, we can model, optimize and analyze an integrated energy system primarily utilizing renewable and non-conventional resources. Modeling, optimization and analysis are available for both grid-connected and autonomous systems. The software can optimize the cost of the system by considering all relevant factors ^[35].

Any system's power consumption profile can be entered into HOMER Pro®, and renewable energy generation can be matched to the required demand. It allows users to evaluate microgrid potential, peak renewables penetration, renewables-to-total-energy ratio and grid resilience, especially for medium to large-scale projects. HOMER then determines if a design is practical, such as whether it can fulfill the needed power consumption. It estimates the cost of installing and running the system throughout the project's lifetime. The cost analysis approach includes capital, replacement, operation and maintenance, fuel and interest. This feature allows for cost savings and scenario optimization depending on several criteria. HOMER displays a list of configurations sorted by net present cost (life cycle cost) that can be utilized for comparing system design options after simulating possible system configurations.

A Few of the advantages of HOMER Pro® are stated as follows ^[36]:

■ Simulates a list of real technologies as a catalog of available technologies and components.

■ Very detailed results for analysis and evaluation.

■ Determines the possible combinations of a list of different technologies and their size.

■ It is quick to run many combinations.

■ Results could be helpful to learn system configuration and optimization.

The HOMER simulation paradigm is illustrated in Figure 16. For the modelling of hybrid renewable energy sources, simulation, optimization and sensitivity analysis are the three major functionalities of HOMER software. The output replicates all potential element combinations according to different conditions. HOMER filters and optimizes the optimal configuration before presenting a list of configurations based on lifespan cost. As in this study, the proposed hybrid PV system was developed around a PV system connected on-grid and a load profile. The HOMER model fed estimated daily load data, which are different in each hour per day, and supposed this data for one year and an average sun radiation. The program then does analysis and optimization, after which it selects the best and optimal feasible configuration based on previously stated economic parameters, such as (NPC) and (COE).

7.   The proposed energy system

The proposed research aims to analyze a simulated model for hybrid systems with a capacity of 30 kwh/day to meet the demand of residential buildings. Figure 20 presents the schematic diagram of 9-kW PV solar panels model (LONGi) Solar LR6-72PE 370 W is as part of a long-term energy system, this is envisioned. This PV module generates DC electricity directly linked to the inverter and converted to AC power to feed the load. This configuration provides the most efficient and effective use of the produced electrical energy, resulting in a decrease in using energy from grid, and the system also draws and exports the energy from or to the grid in a more efficient manner for controlling the generated electricity, resulting in a shorter payback period. This also provides a versatile and readily maintained system that may be used in a residential building as consumption of 30 kWh/day as shared in Figure 17.

Table 3 shows the system architecture. It illustrates that the optimized system consists of 25 panels of 0.370 kW PV panels with a total capacity of 9 kW and one inverter 9 kW.

The proposed system is a small PV Panels system placed in an open area but close to the residential buildings. The placement of 25 PV panels allows the system to generate a good amount of energy through peak hours throughout the year.

8.   Techno-economic model

To conduct techno-economic assessment, the capital cost, replacement cost, operation and maintenance (O & M), real interest rate, cost recovery factor, net present cost (NPC), internal rate of return (IRR), annual cost, annual benefit and cash flow calculations are shown for the most applicable PV system total of 9 kW, where each PV panel is a 0.370 kW with On-grid. Table 4 shows the technical data for RES.

The following parameters are used to make the techno-economic model results more accurate.

- The nominal interest rate is taken as 7.5%.

- The annual inflation rate is 2.06%.

- Overall project lifetime is 25 years.

Table 4 shows that the proposed PV energy system is a small solar generation plant placed on an open area to receive more solar irradiation and continues PV energy generation. The combined capital cost for (25 PV panels with each 0.370 kW) PV panels of the equipment is priced at only ＄ 3,408.99, replacement cost estimating to be 75% out of capital cost is ＄ 2,556.7425, and operation and maintenance that are approximately 10% out of the capital cost around ＄ 340.000, with an estimated average lifetime of 25 years for the entire system per piece of equipment. This allows time for the system to break even and start producing profit before any major repairs or changes are needed. One inverter with 9 kw and it has a capital cost of ＄ 3,408.99, a replacement cost of ＄ 2,556.7425 and (O & M) cost of ＄ 340.000. Though the full economic feasibility of the model will be discussed in further detail later, it is crucial to look at the main driving factor for increased production and thus increased profit, which is number of sun peak hours, and can still be unpredictable from time to time especially daily, regardless of intensive research. Establishing the system in open areas eliminates some of that uncertainty. Figure 21 shows the amount of power generated by the solar system throughout the day, the period between the hour 8 am and 5 pm around total 10 hours per day.

9.   Optimization

The proposed research considers various constraints involving load demand, radiation, temperature panel rating, interest rate and inflation rate. For optimization, simulation is performed using HOMER software. The target results obtained using the simulation are the energy cost, net present cost and amount of greenhouse gas produced.

HOMER can simulate a variety of equipment possibilities under a variety of limitations and sensitivities to optimize small power systems. The optimization result window will offer possible system configurations based on the Net Present Cost (NPC).

The system components are grouped in order of decreasing cost effectiveness. Table 5 below shows the most optimized system according to HOMER.

The proposed HOMER model allows for the most optimal generation structure with a complete outlook on its economic effect, allowing for a more comprehensive look at the feasibility and economic usefulness of such systems. Considering the cost of investment and maintenance, HOMER provides the means to make a precise assessment of the extent to which the installation is beneficial and allows for an accurate outlook about the time it might take for a return on investment to materialize. Table 5 above shows the optimized results of the proposed system. It shows that the system has a COE of O.R 0.017 or ＄ 0.044/kWh and compares this number with the Tariff from the Authority for Public Services Regulation, which is O.R 0.020 or ＄ 0.052/kWh ^[34]. It concludes that the system is feasible as its energy cost is almost the same or slightly below the Tariff the Authority for Public Services Regulation charges for each kWh usage.

10.   Electrical evaluation

To optimize and enhance the electrical production and demand system, it is necessary to consider the amount of surplus produced power or unmet load demand. There does not seem to be any systemic surplus or untapped power in this instance. Excess electricity is extra electrical energy that cannot be utilized to power a load and must be disposed of (or limited). Surplus power is produced when more energy is produced than is needed (whether from renewable sources or when the generator's low output exceeds the demand). The quantity of electricity the power system cannot deliver is an unmet load. This happens when the supply of power is insufficient to meet demand. It rarely occurs due to the combined system with the On-grid system, which generates power required to demand load for a long period of time.

10.1.   PV data part—LONGi Solar LR6-72PE-370W

The solar panel is the main part in the system that is used to absorb the sun's rays and convert them into electricity. In this study, we are using LONGi Solar LR6-72PE-370W. The PV panel's datasheet and details are in Figures 22–24.

10.2.   Converter data part—SolaX X3 Hybrid10-800-9KW

The converter is an essential part of the ESS system implemented as it converts the output DC power from PV panels to AC power that will flow and be utilized to the load. The datasheet with the rating is given below in Figure 25.

To further understand the equipment used, Table 6 provides the characteristics of the converter model used.

According to Table 6, the annual total of energy production is 4,362 hours. The total energy taken from the setup each year is 14,313 kWh, whereas the total energy fed into it each year is 14,756 kWh. Due to the inverter efficiency of 98%, the total energy lost in the device is 443 kWh/year.

The number of losses can be considered negligible, considering the amount of power the converter moves between the PV modules and the load. It can also be noticed that the converter is abundantly used throughout the year. With a lifetime of only 15 years, converters are the most vulnerable of the devices to breaking down or to be replaced. Solar generation requires the converter to run all the time, so the device can be expected to not last as long.

The inverter works at the same period and matches and parallels with PV solar panels from 8 am to 6 pm throughout the day, as shown below in Figure 26.

11.   Economical evaluation

11.1.   Capital cost

The capital cost is calculated by adding the PV panels system costs and the station's balance. Neither cost includes construction finance or financing costs, computed and applied separately via the fixed charge rate. Additionally, the expenses exclude a fund for debt payment reserves, which is assumed to be zero for balance sheet financing. The initial investment cost for each group is given independently in Table 7, and according to the capital cost of PV solar in Oman, that is around ＄ 0.378 US per Watt. Therefore, the system has (25) PV panels 0.370 kW for each and the total capital cost for PV solar is ＄ 3,408.99. In addition, 1 piece (9 kw) of the converter is used, and the capital cost per kW is ＄ 378.6 US in Oman.

11.2.   Replacement cost

As illustrated in Table 8, the replacement cost is a decreasing fund factor that accounts for long-term replacements and repairs of important PV panel components. However, much effort is being made to develop more of the PV panels model's efficiency worldwide. Considering the replacement costs of PV solar and converter are 75% of the capital cost for each. That is (75% of ＄ 3,408.99 for PV solar and the same case with converter 75% of ＄ 3,408.99), equal to ＄ 2,556.75 as replacement costs for each of them.

11.3.   Operations and maintenance cost (O & M Cost)

Operations and Maintenance O & M costs include all regular and unscheduled maintenance and operations costs associated with operating the PV panels system. Due to the various PV connections and installation designs, O & M expenses may vary. This enabled researchers to quantify the effect of various technical features on the cost of energy COE without considering the influence of operations and maintenance costs, which were exceedingly difficult to predict at the time. While more work is being conducted to determine O & M costs for existing PV energy conversion systems, the operating and maintenance costs are presented in Table 9 for this study. Considering (O & M) cost for both PV solar and converter is 10% of capital cost. Thus, 10% of ＄ 6,817.97 is ＄ 681.8.

The decided-upon O & M costs are theoretical. To find a more realistic estimate, a lot of factors should be taken into account, from the location of the plant, average salaries of technicians and equipment costs if the equipment fails, thus making this estimate to be representative of the highest expected O & M cost and is subject to change and be reduced as the technology spreads wider and becomes cheaper to produce and repair.

11.4.   Annual energy cost saving

The system's annual energy-saving cost can be determined from the annual energy production of the system. As indicated in Table 5, the annual energy production is 21,712 kWh per year. Then, using this annual cost saving can be determined using the current energy tariff in Oman for residential usage of ＄ 0.052 per kWh. Then, annual benefit can be calculated as:

- Annual grid rate = 21,712 kWh × ＄ 0.052 = (＄ 1,129.024)

- Annual proposed system rate = 21,712 kWh × ＄ 0.044 = (＄ 955.328)

- The annual benefit of the system is (＄ 173.696).

11.5.   Cash flow diagram for the system

This cash flow is operational in nature and depicts the capital, replacement, salvage and operating costs associated with the proposed system design. The discount factor is a ratio based on the discounted rate that is used to determine the present value of a cash flow that happens in any year of the project's lifetime. A discounted cash flow is a cash flow that has been discounted to zero for years. The results of the Cash Flow simulation are depicted in Figure 27. Each bar in Figure 27 reflects a single year's total cash inflow or outflow. The first bar, for year zero, represents the system's capital cost, which is also reflected in the optimization outcomes. A negative number indicates an outflow, expense for equipment replacements, or operations and maintenance (O & M). Furthermore, Figure 28 illustrates the cash flow for the project for each component in the configuration.

Figure 28 shows that the cost is drastically reducing as the operations get into action. With theoretical replacements being expected occasionally, the operating costs are relatively low and consistent, aside from the initial investment. As mentioned earlier, the converters are the part most prone to damage and this is considered as can be seen in Figure 28. The most expensive part to generally repair or replace would be the PV parts due to exposure to external environmental conditions. They are expected to require minimal maintenance or repairs unless there is an extreme weather phenomenon.

12.   CO₂ emission investigation

Deployment of renewable energy and improvement in energy efficiency is an effective carbon offset strategy, which can contribute to achieving carbon-neutrality targets worldwide ^[37]. Solar energy resources can be used for spatiotemporal energy sharing and decarbonization, which show promising prospects in many countries around the world ^[38]. Energy-efficient buildings with onsite renewable energy supply, such as solar energy sources, are effective to address the energy shortage crisis, reduce the consumption of fossil fuels and achieve carbon neutrality ^[39]. Carbon dioxide (CO₂) is one of the most significant pollutants among greenhouse gases. It is released when power plants that operate on fossil fuels produce emissions, and these emissions are to blame for environmental problems. As the demand for fossil fuels continuously rises, carbon dioxide (CO₂) emissions in Oman are rising, with 100 million tons in 2018 ^[40]. Therefore, diminution of carbon dioxide levels by entering renewable energy sources, such as PV solar, into the network system. Emission of CO₂ is now a serious concern worldwide.

Further, the proposed project revealed that it reduces the emission of greenhouse gases such as (CO₂) by a sufficient number of grams. According to the statistical report issued recently in 2020, to generate 1 kWh in Oman, 490 grams of (CO₂) will be released. Using conventional sources to generate 14,756 kWh/yr will emit (490 gm X 14,756 kWh/yr), which is about 7,230,440 kg, whereas using and entering the PV solar to the grid system will reduce to 4,396.001 kg to generate the same amount of electrical energy as illustrated in Figure 29.

13.   Conclusions

The global and Oman demand for electric generation is rising daily. This increase has begun to place a new strain on the grid's electrical energy supply. The design and optimization of a PV solar system-powered station was examined in this paper using Nizwa, Oman as a case study. Although the size research was conducted on a specific location, the conclusions and technique may be used globally by just modifying the solar irradiation energy statistics. Oman has renewable energy targets with Oman's vision 2040. Still, there are insufficient solar energy project stations to achieve this target, necessitating the development of a national road map for installation and production station size, regulation and other considerations. The first task was site survey and selection, and then collecting necessary data for the work, including power consumption in the residential building which is 30 kWh daily base consumption and having 3.51 kWh peak load consumed to feed the residential building in the proposed site.

According to measured HOMER software data, daily radiation at Nizwa is about 6 kWh/m²/day. Additionally, the current electricity tariff for residential consumers in Nizwa is about ＄ 0.052 per kWh and the grid sell-back is ＄ 0.066. These are key parameters in determining the feasibility of the PV project. Therefore, using this as a site-specific parameter, the feasibility study was undertaken using a software package HOMER to investigate the feasibility.

The following conclusions are derived based on all above calculations:

-The hybrid system produces 21,712 kilowatt-hours of electricity each year.

-The energy system is comprised of a 9 kW PV solar system.

-The hybrid system's Total Capital Cost is ＄ 6,817.97

-The hybrid system's Net Present Cost is ＄12,806.58

-The Cost of power generated is ＄ 0.044 per kilowatt-hour.

-Using and entering the proposed PV solar to the grid system will reduce (CO₂) emission from 7,230,440 kg to 4,396.001 kg to generate 14,756 kWh/yrs.

The study established that the suggested small-scale PV solar is technically possible, economically and environmentally viable as a renewable energy source using 9 kW PV combined with the public grid.

The proposed research work can be extended in future by adding wind energy systems to reduce the production cost further. Using advanced technology battery systems to store solar energy effectively is also recommended. Solar energy system performance can be improved by making the system more innovative, like solar tracking systems and automatic solar panel dust cleaning systems.

This work illustrates how sites with viable sun radiation resources can be economically feasible for the applying small-scale hybrid PV solar with On-grid system. This research used solar radiation data collected from measuring equipment in the site, previous research and concerned websites. There is probably missing and unrecorded data; therefore, acquiring the maximum degree of assurance regarding possible yields and the PV panel's environmental impact from increasing temperature and dust, especially in Oman's terrain, is essential.

Various recommendations are outlined in this section. We recommend the immediate implementation of certain types of renewable pilot projects, the development of policies to support and encourage renewable energy, and that the authority and other entities undertake further research and monitor developing renewable technologies. Our recommendations relate to different categories, and small scale and large scale of hybrid renewable energy sources should be implemented in Oman. These initial renewable energy projects would help demonstrate the technical and economic performance of renewable energy technologies under local conditions, and would, if implemented appropriately, facilitate the transfer of knowledge and know-how to relevant institutions and entities in Oman. The proposed project above is the type of renewable energy project we believe the Authority could approve for immediate implementation by the Rural Areas Electricity Company SAOC.

Before implementing these types of projects, we recommend that further detailed technical and economic analysis is undertaken to verify assumptions in this report and confirm the suitability of individual project locations.

The study has identified a significant potential source of renewable energy in the Sultanate of Oman. However, if solar energy resources are to be utilized on a large scale, as we believe they could, new policies and funding mechanisms will be needed to support and encourage renewable energy investment.

In addition, the implementation of Tax Credits and Investment Subsidies would be a matter for the tax authorities in Oman and the Ministry of Finance. However, we recommend the Authority in conjunction with relevant government authorities take steps in this field.

An additional thing is renewable energy quotas; the government might require, for example, renewable energy projects to account for X% of total system capacity by the next specified years. The authorities would then have to ensure that PWP and RAEC complied with the quotas in a cost effective and efficient manner, with regards to security of supply considerations and other relevant license conditions. Moreover, the Feed in tariffs; for large scale projects, we recommend authorities to develop feed in tariffs to support projects over several stages of development (in the expectation that tariffs in the latter stages of a project would be lower than in the initial stage due to the technology being proven, economies of scale and so on).

In summary, we recommend that the authorities act to remove barriers for utilizing renewable energy, whether these be technical, economic or legal barriers, so as not to hinder policy initiatives that aim to facilitate and promote renewable energy projects.

Use of AI tools declaration

The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.

Conflict of interest

The authors declare that there are no conflicts of interest in the execution and publication of this work.

Author contributions

Humaid Abdullah ALHinai and Azrul Mohd Ariffin conceived the review idea and developed the research theory, methodology and draft manuscript preparation.

Humaid Abdullah ALHinai drafted the manuscript and Azrul Mohd Ariffin and Miszina Osman performed study conception and reviewed the manuscript.

Humaid Abdullah ALHinai, Azrul Mohd Ariffin and Miszina Osman designed the proof outline and contributed to the implementation of the research.

In summary, all authors have participated in the conception and design, analysis and interpretation of the data and approval of the final version.