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The roof-mounted solar PV system is located in a heavily forested area east of Trinidad. The climate in Trinidad is characterized by a humid tropical environment with significant rainfall and consistent temperatures throughout the year [10]. The solar PV system will power equipment and fixtures in an existing structure that is used for the care and rehabilitation of local reptiles and birds, in particular reptiles and birds that are affected by onshore and offshore oil and other chemical spills. The site is remote and not connected to the electrical grid. Diesel-powered generators met the site''s electricity needs.
A site visit was conducted, and the slope and orientation of the roof were measured. The tilt and azimuth of the roof were measured as 200 and 0, respectively. The electrical load was calculated by recording the power consumption of the electrical appliances and their usage patterns. The average daily consumption was calculated as 10.1 kWh/day, and the daily average electrical consumption pattern is provided in Fig. 1. The site was unaffected by shading at the time of the site visit.
Using information from the site visit and the National Solar Radiation Database (NSRDB), which provided solar irradiance data for the site, the off-grid roof-top solar PV system was designed using the industry-leading software PVsyst. The solar PV design was then used to inform a request for proposals, which resulted in the purchase of solar PV equipment and the contracting of a solar contractor to install the system. The system was installed to meet National Electric Code (NEC) 2020 standards. The performance data for the solar PV system was logged by the energy management component of the system for every 5-minute interval from September 2023 to March 2024. This data was used in the analysis that follows.
The results of the solar PV design and simulation are provided in this section, along with the data logged during the 6 months of operation of the system. The design performance is then compared against the real-life performance of the system. The main components of the system and their rating are provided in Table I.
The single-line diagram of the system is provided in Fig. 2. The system meets NEC 2020 requirements.
This section focuses on the presentation and analysis of actual performance data taken from the data logging and energy management system of the solar PV system.
Fig. 4 presents that daily variation of solar irradiance data over the data collection period. It should be noted that during the reporting period, 1000 W/m2 irradiance levels were never attained. Fig. 5 presents the Cumulative Frequency Distribution (CFD) curve and the calculated median solar irradiance value of 423 W/m2. The histogram in Fig. 6 illustrates that the highest frequency of solar irradiation observations falls within the 100 to 500 W/m2 range, suggesting that these are the most common irradiance levels during daylight hours.
The average daily yield (kWh) value from October and November 2023 is presented in Fig. 7. The mean value is approximately 11.86 kWh. This is 49% of the simulated average daily yield value of 24.15 kWh. The daily variation in solar PV power is presented in Fig. 8. During the reporting period, the system rarely reaches or exceeds its installed capacity of 5.34 kW. Fig. 8 also illustrates that PV production peaks between 9 am and 10 am regularly.
The daily variation in electrical demand is presented in Fig. 9, and the corresponding electrical demand histogram in Fig. 10. Fig. 9 illustrates that the electrical demand is fairly consistent throughout the reporting period, and the histogram in Fig. 10 highlights that the highest bin covers the range from 219.8 W to 303.6 W, indicating this is the most frequently observed range of AC power consumption. The second highest bin covers the range from 136.0 W to 219.8 W, showing this as the next most common range of consumption.
The daily charging and discharging of the battery bank are presented in Fig. 11. The battery bank charging pattern does follow the solar PV power production pattern. The discharging of the battery bank, especially at night when there is no solar, matches the electrical load demand profile presented in Fig. 9. The battery bank histogram presented in Fig. 12 shows that the highest bin covers the range from approximately −423.2 W to −220.3 W, and the second highest bin covers the range from approximately −626.2 W to −423.2 W. This exceeds the range provided for the electrical power demand in Fig. 10.
The interplay between solar PV power production, battery charging, and discharging, and electrical load consumption is presented in Fig. 13.
Lead carbon batteries specifically for solar PV energy storage were used. Fig. 14 presents the variation in battery voltage for a typical day. Battery voltage is a direct indication of the state-of-charge of the battery bank. The red dashed line in Fig. 14 represents the battery voltage when fully discharged, and the higher two dashed lines represent the voltage range when the battery bank enters the float stage. The battery bank reaches close to fully discharged at around 6 am and spends a short time in the float stage before it is discharged again.
The percentage of power loss during charging and discharging of the batteries is presented in Figs. 15 and 16, respectively. Both figures illustrate that at low load power consumption, there are instances of high losses, exceeding 50%. However, the charging power losses at low load power consumption are regularly less than 20%, and for discharging, it is also regularly less than 20%.
The breakdown of the equipment cost of the solar PV system is provided in Fig. 17. The equipment was provided by a separate vendor and not the solar installer for this project. The cost of the battery bank is the most significant cost, consuming 37% of the total equipment cost.
Fig. 18 shows the installation labour cost to be greater than the installation equipment cost. The installation equipment cost, in this case, is the electrical equipment and materials required to interconnect the solar PV system with the existing electrical infrastructure of the existing building. The total installation cost exceeds the total equipment cost for this project. The total equipment cost refers to the cost of the major solar PV components and the balance of the system required to interconnect the system. The total equipment cost does not include the cost of equipment that interconnects the solar PV system with the existing electrical system. This breakdown in cost is presented in Fig. 19.
The parameters used to calculate the Levelized Cost of Electricity (LCOE) using the real-life energy production data and cost are provided in Table III.
The LCOE for your solar installation, before adjusting for the discount rate, is approximately $0.588/kWh. After adjusting for the discount rate on the operation and maintenance (O&M) costs over the system''s lifetime, the LCOE is approximately $0.567/kWh.
The system has a 5 kW inverter installed but rarely operates at this rated power and operates mostly at 1.5 kW output. An inverter typically has lower efficiency when operating at a lower output power. This is illustrated in Fig. 16, where there are mainly losses of around 20% when operating at a power output of 1.5 kW and less.
The cost to install the system exceeded the total cost of the equipment and the cost of the labour component of the installation exceeded the cost of the equipment, and materials to perform the installation. This is illustrated in Figs. 18 and 19. The cost is directly reflective of the remote nature of the site and the unavailability of an electrical connection during the installation of the solar system.
After analyzing the system''s performance, the following recommendations are being made: It is uncommon to perform a solar resource assessment for small domestic and light commercial installations; however, for off-grid, remote systems, a one-to three-month long logging of solar irradiance data using a low cost digital pyranometer can greatly benefit the technical design and financial analysis of the solar PV system. The high labor cost for this project, mainly caused by the remote and off-grid nature of the site, would decrease in the short and medium term as the local solar PV market grows, and the global decline in energy storage costs would also benefit off-grid sites [13].
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
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