Electricity Production Performance Of A 70 Kwp Pv System

Study Case ELECTRICITY PRODUCTION PERFORMANCE OF A 70 kWp PV SYSTEM AT THE ICT CENTER BUILDING, USA Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract Solar energy is one of the most promising renewable energy sources. This energy can be converted into electricity through photovoltaic (PV) panels and used for daily needs. A solar power generation system (PV system) with an on-grid configuration was installed on the ICT building of a university in the United States. This system was designed with a capacity of 70 kWp, which can supply approximately 15%–20% of the building's power needs. The installation consists of 336 solar panels with a capacity of 200 Wp per unit and three on-grid inverters with capacities of 25 kW, 25 kW, and 20 kW, respectively. Performance test results show a maximum output power of 42,152.4 W, equivalent to 62.7% of the total installed electrical load. Keywords: On-Grid PV System, Photovoltaic Panels, On-Grid Inverters, PV System Performance INTRODUCTION University campuses in the United States generally consist of lecture buildings and supporting facilities, one of which is the ICT Center. This building requires a stable supply of electrical energy, which can come from the utility grid (e.g., from a local power company), renewable energy, or a combination of both. To meet renewable energy needs, a solar power generation system was chosen. A PV system is a renewable energy technology that converts solar radiation into electrical energy using photovoltaic cells (PV cells). Physically, PV cells work similarly to diodes with pn junctions. Sunlight is absorbed by these junctions and converted into electrical current that is fed into a circuit [1]. PV cells are then assembled into modules MICHAEL KURNIAWAN 1 Study Case or panels. In general, PV systems are divided into two types: on-grid and off-grid [1,2]. Offgrid systems operate independently without being connected to the electricity grid. Since the energy supply depends solely on the sun, an energy storage medium in the form of batteries is required. This system is typically used in remote areas without access to the electricity grid [2,3]. Conversely, on-grid systems work by connecting solar panels to the power grid. The electrical energy generated can be used directly for building loads, and if there is excess, it can be exported to the grid [2,4]. This system does not require batteries. The application of rooftop PV is increasingly widespread in various buildings [3,5]. Various studies on the performance of PV systems have also been conducted [6,7]. In this case, the ICT Center uses an on-grid PV system. The electrical energy generated by the PV system is used as the main source for the building, while the shortfall is covered by supply from the utility grid. This article discusses the electricity production performance of the installed PV system. METHODOLOGY The initial stage involved collecting data related to site conditions, solar radiation intensity, and electricity requirements. Next, the on-grid PV system components were selected, including solar panels, inverters, protection devices, and connection equipment. The system design and implementation process is shown in Figure 1. After installation, electrical parameters (voltage, current, and total power) were measured for each string. The total electricity production was calculated from this data. Solar Panels Panel selection considers power requirements, capacity, price, availability in the US market, and after-sales warranty. The system capacity is set at around 70 kWp (15%–20% of the building's electricity needs). The panels used have a capacity of 200 Wp per unit, with specifications listed in Table 1. On-Grid Inverter This system uses a three-phase grid-tie inverter, which is capable of synchronizing with the power grid [8]. For safety reasons, the inverter automatically stops working when the grid goes down. During operation, energy from the PV is the main source of power, while any shortfall is supplied by the grid. The total inverter capacity is approximately 70 MICHAEL KURNIAWAN 2 Study Case kW, divided into three units: • Inverter 1 = 25 kW • Inverter 2 = 25 kW • Inverter 3 = 20 kW The specifications of the three-phase on-grid inverter are shown in Table 2 (25 kW) and Table 3 (20 kW). Figure 1. Diagram of the System Design and Implementation Stages Table 1. Solar Panel Specifications MICHAEL KURNIAWAN 3 Study Case Table 2. 25 kW Inverter Spec ifications Table 3. 20 kW Inverter Specifications To achieve 70 kWp, the panels are arranged in series-parallel. The series arrangement forms strings to match the inverter input voltage. The number of panels per string is calculated using formula (1): The calculation shows that 24 panels are needed per string. The power capacity of each string = 24 × 200 Wp = 4,800 Wp. The number of strings is calculated using formula (2): MICHAEL KURNIAWAN 4 Study Case This results in 14–15 strings to approximate 70 kWp. The installation uses 14 strings with the following distribution: • Strings 1–5 → Inverter 1 (25 kW) → 120 panels • Strings 6–10 → Inverter 2 (25 kW) → 120 panels • Strings 11–14 → Inverter 3 (20 kW) → 96 panels Total panels: 24 × 14 = 336 units Total capacity: 336 × 200 Wp = 67.2 kWp PV System Circuit The system block diagram is shown in Figure 2. Fourteen strings are grouped into three inverter units through a DC combiner box (Figure 3). Next, the output of the three inverters is combined through an AC combiner box (Figure 4) before entering the building's main low-voltage distribution panel. Figure 2. ICT Building PV System Diagram Figure 3. DC Combiner Panel and Three-Phase On-Grid Inverter MICHAEL KURNIAWAN 5 Study Case Figure 4. AC Combiner Panel Location Initially, the system was planned as a rooftop PV system. However, after considering the roof area, shape, and structural strength, it was decided to install the panels in a ground-mounted configuration. Based on Table 1, the panel dimensions are 1249 × 975 × 35 mm ≈ 1.22 m². With 336 panels, an area of >410 m² is required. The installation location was chosen in an open area of ±870 m² with minimal shade and close to the building, resulting in low transmission losses. Figure 5 shows the selected location. MICHAEL KURNIAWAN 6 Study Case Figure 5. Location of the PV System around the ICT Building RESULTS AND DISCUSSION PV System Circuit All solar panels were successfully connected in a series circuit to form strings, and each string could generate electrical power. In the DC combiner box, the strings were connected in parallel so that the power could be combined and fed into the inverter. Each inverter was also successfully connected to the electrical grid through the AC combiner box. The synchronization process between the inverter and the utility grid, as well as between inverters, ran smoothly. This ensured that all strings could transmit electrical energy to the grid and to the ICT building's electrical load. Electrical Power Production The evaluation of electrical power production was carried out for one day, from 09:00 to 14:00. The voltage and current output of the panels were measured every hour for each string, then the power was calculated. The output power data for strings 1 (S1) to 14 (S14) were grouped based on three inverters. Tables 4, 5, and 6 present the electrical power output results from each string connected to inverters 1, 2, and 3. From the output data for each string during the test period, the maximum value was selected (all achieved at 12:00 p.m.). Table 7 shows the percentage of maximum power output for each string (S1–S14). This value was compared to the maximum capacity of each string based on the manufacturer's specifications, namely: MICHAEL KURNIAWAN 7 Study Case Table 4. String Output Power on Inverter 1 Table 5. String Output Power on Inverter 2 Table 6. String Output Power on Inverter 3 Table 7. Maximum Output Power Percentage per String MICHAEL KURNIAWAN 8 Study Case The results show variations in power between strings. String 8 produces the highest output (81.3%), while string 14 produces the lowest (51.1%). The factors causing these differences may originate from material quality, installation methods, or differences in circuit impedance. In addition, the effectiveness of Maximum Power Point Tracking (MPPT) in determining the optimal operating point also has an effect [8]. However, the power differences in strings 1–5 and 6–10 are relatively small. This is because strings connected to the same DC combiner box and inverter tend to operate at similar operating points and impedances. Furthermore, the output power per inverter and the total PV system power for each hour are shown in Table 8 and visualized in Figure 6. Inverters 1 and 2 have different output powers due to variations in power between strings, while inverter 3 produces less power because it consists of only four strings. Table 8. Output Power per Inverter and Total System Power Figure 6. Output Power per Inverter and Total System Graph The total PV system power fluctuates between 9:00 a.m. and 2:00 p.m., influenced by solar radiation intensity, weather conditions, and location. Maximum power production was recorded at 12:00 p.m. at 42,152.4 W, or 62.7% of the total installed load. MICHAEL KURNIAWAN 9 Study Case CONCLUSION The on-grid PV system on the ICT building has a capacity of 67.2 kWp, consisting of 336 solar panels (200 Wp per panel), three on-grid inverter units with capacities of 25 kW, 25 kW, and 20 kW, and is supported by a DC combiner box and an AC combiner box. The PV array is arranged in 14 strings, each consisting of 24 solar panels. Inverter 1 is connected to five strings, inverter 2 to five strings, and inverter 3 to four strings. This system is successfully connected to the electricity grid through a Low Voltage Main Distribution Panel (LVMDP). The maximum power output obtained from the system is 42,152.4 W, equivalent to 62.7% of the installed load capacity, achieved at 12:00 noon. MICHAEL KURNIAWAN 10 Study Case REFERENCE MICHAEL KURNIAWAN 11 Study Case MICHAEL KURNIAWAN 12