Techno-Economic Assessment of Solar Power Plants on River Land in Indonesia Using HOMER Pro

The need for clean energy in the 21st century is increasing [1]. This is brought on by the usage of fossil fuels, which contribute to global climate change [2]. The solution to the issue of the need for clean energy is to shift our reliance on fossil fuels to renewable energy sources [3]. Renewable energy has the characteristic that it is environmentally friendly because it produces almost zero pollutants, so this gets more attention from the public [4]. Several countries in Asia, Australia, and Europe have set a target: by 2040, renewable energy sources must contribute more than 50% to meet total electricity needs [5]. Renewable energy is available on earth and is still being developed to produce electricity, namely wind, solar, water, geothermal, biomass, and marine energy [6].

One renewable energy source that is widely available on Earth and may be used without restriction is solar energy [7]. The sun emits rays with an amount of energy of 3.8×1023 kW, and that which is intercepted by the earth is 1.8×1014 kW [8]. Solar energy potential is enormous for tropical regions that receive constant sunshine. Indonesia can use 4.5–4.8 kWh/m$^2$/day of solar energy [9]. With the potential that Indonesia has, of course, this will be an advantage in meeting electricity needs in Indonesia.

Solar energy used to supply electricity requires a conversion tool in the form of a solar panel, which will later convert solar radiation into electricity [10]. However, due to the low efficiency of solar panels, a large enough land area is needed to meet electricity needs [11]. Therefore, this is usually overcome by building on the roof of a building or open land for use on a larger scale [11], [12]. According to data from the Geospatial Information Agency, Indonesia's land area is 1,905 million km$^2$, where rivers are a characteristic part of the land in Indonesia [13]. This river area has the potential to be used as land for generating solar electricity by floating solar panels on the river, commonly known as floating PLTS. There are several advantages to be gained from implementing floating solar power plants, namely optimizing the water area so that water can be used to cool the panels so that efficiency is maintained [14]. Then another advantage of implementing floating PLTS is that it can reduce water evaporation so that if it is applied to water areas such as reservoirs, it will be helpful, especially when experiencing drought situations [15]. However, like technological innovation, the implementation of floating PLTS cannot be separated from several challenges ranging from technical aspects such as design to sustainability aspects and environmental impacts, especially on aquatic ecosystems, so studies are needed to minimize the effects of implementing floating PLTS.

The purpose of this study was to model the use of river land at Solo's Tirtonadi Dam as a solar power plant. The techno-economic analysis of the PLTS system—which examines the variables influencing cost-effectiveness—was conducted through simulation to ascertain if investing in the project is feasible. The HOMER program was used for the techno-economic study. Both off-grid and on-grid studies are performed by connecting the system to the PLN electricity network and the system to the PLN electricity network, respectively.

The research began with a literature study, data collection, simulation, and analysis of results. Simulation of river land use for on-grid and off-grid PLTS using HOMER software to determine the ideal solar power plant configuration, as shown in Figure 1.

HOMER software can simulate small-scale generating system models (micropower) in on-grid and off-grid networks. This software makes it possible to compare different design options based on technical requirements and economic benefits [16]. The process in HOMER Pro begins with inputting data related to the energy system to be analyzed, such as the type of energy sources, energy load, and location characteristics. Users then define system design options, including the type and size of components such as solar panels, wind turbines, batteries, and diesel generators. Afterward, HOMER Pro performs simulations to evaluate various system configurations, considering technical and economic aspects to determine the most efficient configuration. The software generates reports that include graphs, tables, and summaries of the analysis results, helping users understand system performance and make better decisions. Economic analysis assesses investment costs, operational costs, and return on investment (ROI), providing a clear picture of the financial feasibility of different design options. By simulating this device, the results will be used to determine a feasible configuration to meet electricity needs with estimated installation and operating costs during the project [17]. NPC is the basis for selecting the economic factors used to find the optimal configuration. The total of all component costs (capital costs), component replacement costs, fuel expenses, operating and maintenance costs, and component residual costs is known as the NPC [18]. The PLTS system design scheme in this research can be completed using two methods, namely the on-grid and off-grid systems.

a. On-grid System

Solar panels and the PLN electrical network are the two energy sources of the on-grid PLTS paradigm. Since the PLTS system at the research location only provides electricity for 14 hours a day, an implementation design like this is expected to reduce energy use from the PLN network by increasing the amount of energy used. Solar panels and PLTS connected to the electricity network provide electricity for households for 24 hours. Figure 2 shows how the on-grid PLTS system is modeled using this approach.

b. Off-grid System

Off-grid solar Power Generation Systems (PLTS), known as stand-alone PV, use solar energy as the primary source. A series of photovoltaic modules are used to generate electricity for households. Areas that do not have a PLN electricity supply usually use this system. The model of the off-grid PLTS system can be seen in Figure 3.

The PLTS architecture shown in the above image relies on a generating system linked to the PLN electrical network and a producing system not to supply the demands for electricity. Meanwhile, Figures 4 and Figure 5 show the loads or electrical requirements that must be supported in this PLTS system.

The required electrical components are determined after the electrical load requirements have been determined. The elements that must be resolved include solar panels, inverters, and batteries. Table 1 shows the components used in the simulation and economic data on each element.

The location for the PLTS system design was carried out on the Bengawan Solo River, Tirtonadi Dam Park, Nusukan, Banjarsari District, Surakarta City, as shown in Figure 6. This aims to utilize river land for solar power plants in Surakarta. In urban planning, implementing solar PV in riverine areas can improve land use efficiency and support renewable energy development in urban areas. It can also promote greener transport policies by reducing dependence on fossil fuels. In addition, the involvement of community stakeholders in the project is essential to ensuring social acceptance and long-term sustainability. The government and relevant parties need to integrate the results of this study into broader development policies and programs.

The distribution of solar radiation and the sun's intensity in an area. Influences the process of converting electrical energy from solar energy [7]. The higher the solar intensity value, the more electricity produced [20]. Direct Normalized Irradiance data in Surakarta is shown in Figure 7 and Table 2.

Daily Load Data applied to the system analysis is shown in Figure 8 and Table 3.

Solar panels are a tool used to convert solar energy into electrical energy [22]. Solar panels capture solar radiation with a semiconductor material, which causes electrons in the semiconductor to move, thereby generating an electric current. In this simulation, a Schneider Conext CL25000 E with a generic PV solar panel is used with the specifications shown in Table 4.

An inverter is a device used to convert DC (Direct Current) current into AC (Alternating Current) current [23]. This device converts the DC electricity generated by solar panels into AC electricity. This conversion is necessary because most electrical devices used in daily life operate on AC power. In this PLTS design simulation, the type of inverter used is KEHUA France KF-BCS 630K-B, whose specifications can be seen in Table 4.

The battery functions as a place to store electrical energy [24]. In this PLTS system, batteries are used to store electricity that solar panels have produced during the generation process. The higher battery capacity is better because the electricity generated by the solar panels requires storage space for use at specific times. The battery used is EnerSys PowerSafe SBS 970, with the specifications in Table 4.

NPC is the cost that must be incurred both during installation and during the project. In the HOMER simulation, NPC values are sorted from the lowest value. NPC costs include component costs, component replacement costs, operation and maintenance costs, fuel costs minus the cost of remaining components at the end of the project period, and annual interest rates. The NPC value calculation can be done with the following equation [25].

$N P C=\frac{C_{\text {ann, tot }}}{C R F, i . R_{\text {proi }}}$

where,

NPC : Net Present Cost

Cann, tot : Total annual fee (Rp/year)

CRF : Capital recovery factor

i : interest rate

Rproj : life of use (years)

Energy costs are calculated by comparing the total annual costs of the system divided by the energy produced during the same period. The COE value can be calculated using the following equation [26].

$\operatorname{COE} = \frac{C_{\text {ann}, \text { tot }}}{L_{\text {prim }, A C}+L_{\text {prim}, D C}}$

where,

COE: Cost of energy

Lprim, AC: AC loads per year (kWh/year)

Lprim, AC: AC loads per year (kWh/year)

The simulation procedure was executed using the HOMER software optimization technique, enabling the optimal configuration for the created system. With HOMER, configuration is done on a machine that is both connected to PLN (on-grid) and disconnected from PLN (off-grid) [27]. The study was conducted by Kumar et al. on the development of river solar power plants in India using on-grid and off-grid scenarios. The results showed that the on-grid system is more economical in the long run, with a higher ROI. In contrast, the off-grid system is more suitable for remote areas not covered by the electricity grid. The data shows that the energy conversion efficiency of the on-grid system reaches 17.8%, while that of the off-grid system is around 15.6% [28]. Homer's simulation for this system can be seen in Figure 9. The following summarizes the simulation results of two categories and two systems designed using HOMER, shown in Table 5.

The overall electrical power generation of the on-grid system is 887,798 kWh/year, and the Off Grid system is 2,153 kWh/year, according to simulation data in Table 5.

Calculating the River PLTS system with NPC efficiently utilizes solar panels to produce electrical energy. For the economics of PLTS Sungai, the leading indicator used to measure the financial efficiency of the project is the COE. The concept of BEP is also relevant in determining how long it will take for a river PLTS investment to reach the BEP, where the income generated is equivalent to the initial investment cost. The results of PLTS economic calculations can be seen in Table 6.

a. NPC

The quantity of NPC determines the best possible system setup outcomes. All project-related expenses, including component costs, replacement costs, maintenance costs, fuel costs, and financing rates, are included in the overall NPC cost. Homer ranks the optimization results based on the lowest NPC since NPC is the total cost of the system over a certain amount of time [29]. Based on the simulation, the NPC value shows that the On-Grid system has an NPC value of 1,805,634.01 USD and the off-grid system of 1,970.18 USD.

b. COE

The average cost per kWh of electrical energy produced by the system may be used to calculate the energy cost. The yearly cost of producing electrical energy is divided by the entire amount of electrical power utilized by the system to get COE. Since kWh is the COE unit used in the Homer simulation, we can determine the electricity rate and revenue from energy sales by knowing the COE [3]. Based on the data in Table 5, it is found that the on-grid system has a COE value of 0.09 USD, and the off-grid system is 0.10 USD.

c. BEP

When income and investment value reach point 0, or when there is neither a profit nor a loss, this is referred to as a BEP [30]. The BEP value is employed in economic operations to ascertain the system's potential level. A lower BEP value indicates a higher system potential value. Table 5 data suggests that the BEP value for the on-grid system is 0.54 years.

The optimal configuration is ascertained from the results of the HOMER simulation, which uses two systems: on-grid and off-grid. The simulation was conducted at the Tirtonadi Solo Dam on the Bengawan Solo River. A comparison of many criteria, including total electrical energy generated, total electrical energy used, NPC value, COE value, and BEP value, is the outcome of optimization using HOMER software. Figure 10 displays the monthly power generation based on the system setup. Figure 11 and Table 7 below demonstrate the cash flow in the suggested model from the HOMER simulation using these two systems.

After carrying out a simulation using the HOMER application, a comparison of the electricity production results of the on-grid and off-grid systems can be seen in Figure 12 below.

The total electricity production output using the on-grid system tends to be higher than that of the off-grid system because it can utilize more extensive and continuous resources from the PLN electricity network. Meanwhile, the total electricity production output with an off-grid system depends on local resources such as solar panels, wind turbines, or power generators. The production capacity of off-gird systems is also more limited and influenced by fluctuations in weather or environmental conditions.

This study created two PLTS systems, the on-grid, and off-grid systems, particularly for the Bengawan Solo riverfront region near Tirtonadi Dam in Surakarta. Optimizing the integration of renewable resources, such as solar panels, in power-producing systems was the goal of the research. This research provides insight into how river PLTS can improve energy efficiency in urban and rural areas. Using this method, the researchers examined several scenarios of resource allocations and energy storage systems to reduce operating and capital expenses while maintaining the stability of the electrical supply. The total amount of energy produced and consumed, the NPC value, the COE value, and the BEP value are critical variables used to evaluate the possibility of creating this system. The system project is planned to last for 25 years. The on-grid system produces 885,358 kWh/year, while the total electricity consumption is 887,798 kWh/year. Apart from that, the NPC value is USD 1,805,634.01, and the COE value is USD 0.09, with a BEP in the year of 0.54. The initial cost to build an on-grid PLTS at Tirtonadi Dam is estimated at around USD 47,782.10. Meanwhile, the off-grid system produces 34,400 kWh/year, while the total electricity consumption is 2,153 kWh/year. Apart from that, the NPC value is USD 1,970.18, and the COE value is USD 0.10. The initial cost to build a grid PLTS at Tirtonadi Dam is around USD 1,923.77. This research introduces a hybrid model of river PLTS in the Tirtonadi Dam area, Solo, which can be integrated into both on-grid and off-grid electricity systems. The results of this research are expected to provide technical and economic guidance for implementing solar power plants in similar locations while offering a more environmentally friendly and sustainable option for urban areas with similar potential.