An Examination of Hybrid PV-Biogas Power Plants for Electric Vehicle Charging Station Development in Indonesia

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Figure 1. Research flow diagram

2.2 An explanation of the design model for a hybrid PV-Biogas generation system

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Figure 2. Hybrid PV-Biogas generation system modeling scheme

The EV charging station's hybrid generator system setup is off-grid. To maximize system performance, the planned generating system needs several auxiliary parts. The generating system being designed in this design is modeled using HOMER software. Solar/PV panels, batteries, generators, and converters are necessary. Figure 2 shows the modeling of the hybrid generating system in the HOMER program.

The total daily load of four Hyundai Ioniq 5 prime Standard Range cars, each with a battery capacity of 58 kWh, is around 232 kW, according to the estimation of the electrical load consumption made by the HOMER program. Figure 3 provides an estimated profile of the charging station's electrical load.

Understanding the expenses associated with each component's investment is essential for conducting an economic analysis of this hybrid power plant. Table 1 lists the parts required to assemble a hybrid PV-Biogas EV charging station-producing system.

2.3 Description of location for design of hybrid PV-Biogas generating system

Four cities in Indonesia—Semarang, Surakarta, Bekasi, and Denpasar—will model the design of a hybrid PV-Biogas-producing system for EV charging stations. The simulation aims to identify which of these cities has the most economic potential for EV charging station construction. Figure 4 shows the position of the development plan location.

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Figure 3. EV charging station electrical load profile

Table 1. Hybrid PV-Biogas EV charging station generator system components

Parameter	Canadian Solar CS6X-325P	Enersys PowerSafe SBS 3900	KEHUA France KF-BCS250K-B	Generac 100kW SD100
Capital Costs	IDR 2,000,000.00	IDR 55,000,000.00	IDR 12,000,000.00	IDR 100,000,000.00
Replacement Cost	-	IDR 55,000,000.00	IDR 12,000,000.00	IDR 100,000,000.00
O&M Costs	IDR 200,000.00	IDR 5,500,000.00	IDR 700,000.00	IDR 20,000.00
Lifetime	30 years	15 years	15 years	15,000 hours

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(a) Semarang City generating system design location

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(b) Surakarta City generating system design location

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(c) Bekasi City generating system design location

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(d) Denpasar City generating system design location

Figure 4. Location of Hybrid PV-Biogas generating system design

2.4 Potential use of solar energy

The potential for using solar energy to become a hybrid power plant, which are Semarang City, Surakarta City, Bekasi City, and Denpasar City, can be processed using data regarding the intensity of solar radiation and regional temperature obtained from the NASA (National Aeronautics and Space Administration) website. Table 2 displays information on solar radiation intensity in various cities.

Table 2. Solar radiation intensity data

Note: 1. Semarang, 2. Surakarta, 3. Bekasi, 4. Denpasar. Radiation intensity data is in kWh/m² units.

Variability in sun irradiation levels causes a PV system's output power to fluctuate. In order to make up for energy shortfalls during periods of poor solar irradiation, a hybrid system can assist by utilizing biogas. The degree of output power efficiency that the producing system can provide increases with the intensity of solar radiation. The data above indicates that Denpasar City has the highest average solar radiation intensity of 4.58 kWh/m², making it the city with the most significant development potential for constructing this hybrid-producing system.

2.5 Potential use of biogas

According to data from research conducted by Santoso et al. [24], in Bali Province, biogas has a capacity to produce 1.16 GWh of electricity per day. The average total livestock population in Bali Province (19,183,779) is used to create this biogas. Based on information obtained from the Directorate General of Animal Health and Husbandry [25], the number of livestock populations in Bali Province is shown in Table 3.

Table 3. Livestock population data for Bali Province

Biogas production capacity can be estimated by calculating the amount of feces produced by each type of livestock per day using Eq. (1).

Feces production $=n \times$ total feces per day                      (1)

where,

n = Total livestock populations

After that, the dry matter content of each type of livestock can be calculated, as shown in Eq. (2).

$T D M C=$ feces production $\times D M C$                 (2)

where,

TDMC = Total dry matter content (kg)

DMC = Dry matter content (kg)

The biogas potential can be obtained, as shown in Eq. (3).

$B P=T D M C \times B L$           (3)

where,

BP = Biogas potential (m³)

BL = Biogas produced by livestock (m³/kg)

Biogas potential can be converted into electrical energy using Eq. (4).

$E=B P \times 4.7 \mathrm{kWh}$           (4)

where,

E = Electrical potential (m³.kWh)

2.6 Main components of a hybrid PV-Biogas generation system

2.6.1 Daily total load

This concept starts with figuring out the overall daily load used. The electrical load at charging stations, generally in a range of Solar Home Systems, displayed in Table 4, is the basis for the daily total load data.

Table 4. Daily total load data

2.6.2 Photovoltaic solar panels

Solar panels convert solar radiation into electrical energy by utilizing the photovoltaic effect on semiconductor materials [26]. The following formula may be used to determine the power generated by the solar panel module without considering the PV's temperature [27].

$P P V=F_{p v} \cdot Y_{p v} \frac{G_T}{G_{T, S T C}}$                     (5)     

where,

PPV: Power produced by the PV module (kW)

F_pv: PV derating factor

Y_pv: PV output power under standard conditions (kW)

G_T: Instantaneous radiation on the surface of the PV module (kW/m²)

G_{T, STC}: Instantaneous radiation under standard conditions (1kW/m²)

This time, the Canadian-made MaxPower CS6X-325P solar panel is utilized in the PLTS system. This solar panel is featured in Figure 5 and contains the specs listed in Table 5.

Table 5. Canadian Solar MaxPower CS6X-325P specifications

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Figure 5. Canadian Solar MaxPower CS6X-325P

2.6.3 Generator

An energy-conversion tool that transforms mechanical energy into electrical energy is a generator [28]. HOMER has various generators, including thermoelectric, fuel cell, thermo-photovoltaic, microturbine, and Stirling engine generators. The generator's fuel consumption may be determined using the following formula, which considers electrical output [27].

$F=F 0+F 1 . P_{g e n}$                     (6)

where,

P_gen: Generator output power (kW)

F: Fuel consumption rate (L/h)

F0: Fuel intercept coefficient curve (L/h/kW)

F1: Fuel curve slope (L/h/kW)

This design uses a Generac 100kW SD100 generator, whose specs are displayed in Figure 6 and Table 6.

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Figure 6. Generac 100kW SD100

Table 6. Generac 100kW SD100 specifications

2.6.4 Inverter

The direct current (DC) produced by solar panels is converted into alternating current (AC) using an inverter [29]. The KEHUA France KF-BCS250K-B inverter is the one utilized in this setup. Figure 7 depicts this inverter with the specs listed in Table 7.

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Figure 7. KEHUA France KF-BCS250K-B

Table 7. KEHUA France KF-BCS250K-B specifications

2.6.5 Battery

The battery stores energy the solar panels produce so that the generating system can run even at night [30]. In this setup, an EnerSys PowerSafe SBS 3900 battery is utilized. This kind of battery is seen in Figure 8 and has the specs listed in Table 8.

Table 8. EnerSys PowerSafe SBS 3900 battery specifications

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Figure 8. EnerSys PowerSafe SBS 3900

2.7 Economy

The design of generating systems heavily relies on the economic sector. The project duration, currency, discount value, and inflation value are the forms in which the input data is presented in the economic window. Due to the project's Indonesian setting, the rupiah is the currency. Data from Bank Indonesia is used to calculate the inflation rate, which is 4.97%, and the discount rate, which is 5.75%. The project has a 25-year duration in mind. The asset value of a project will be impacted by inflation and discount rates. However, if the fluctuation in value is manageable, it will not significantly impact the assets in a project. A sound business strategy is necessary to anticipate fluctuations in interest rates to prevent a decline in asset values.

2.7.1 Net Present Cost (NPC)

HOMER uses the Net Present Cost (NPC) value to display the overall costs required during the project [31]. All project-related expenses, such as component replacement, maintenance, fuel, and interest costs, are included in the total NPC costs. The NPC may be computed using the below formula [21].

$C N P C=\frac{C_{\text {ann }, \text { tot }}}{C R F . i \cdot R_{\text {proj }}}$           (7)

where,

$\mathrm{C}_{\text {ann, tot}}$: Total annual fee (Rp/year)

CRF: Capital recovery factor

i: Interest rate

$\mathrm{R}_{\text {proj}}$: Life of use (years)

2.7.2 Cost of Energy (COE)

The average cost of electricity spent per kWh, or COE, is the result of comparing the yearly operating expenses of a project with the annual energy consumption [31]. Through the COE value, it can be seen whether a designed generating system is profitable or not. COE can be obtained using calculations with the following formula [21].

$C O E=\frac{C_{\text {ann,tot }}}{L_{\text {prim }, A C}+L_{\text {prim }, D C}}$              (8)

where,

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

L_prim,DC: DC loads per year (kWh/year)

This study undertakes a comprehensive analysis of the layout of PV-Biogas hybrid power generating systems intended for EV charging stations across various Indonesian cities, namely Denpasar, Surakarta, Bekasi, and Semarang. The configured generating system is meticulously optimized and simulated through HOMER software, spanning a 25-year duration. The primary objective is to pinpoint the city exhibiting the most substantial potential for system design, considering parameters such as total electricity production, total electricity consumption, NPC value, COE value, and BEP value. Semarang City emerges as the most promising candidate for the hybrid PV-Biogas EV charging station generating system, boasting a total electricity production of 625.88 kWh/year, total electricity consumption of 551.03 kWh/year, NPC value of IDR 20,964,400,000.00, COE value of IDR 1,673.18, and BEP in year 7.05. The initial investment cost for establishing a hybrid generating system in Semarang City is estimated at IDR 2,454,489,904.74.

This research is envisioned to contribute significantly to future studies, providing a foundation for the refinement of component selection. Enhancing the efficiency of electricity production and minimizing the design costs of hybrid systems can be achieved through the judicious selection of components. The ongoing optimization of component costs aligns with future investment objectives, ensuring the sustained development of hybrid systems. Supportive regulations promoting the continued and expanded utilization of renewable energy sources facilitate the realization of hybrid system designs. This, in turn, has the potential to catalyze numerous advancements in renewable and hybrid energy research.