4.1. Information and Simulation of the PV System
The case study applies the proposed model for the improvement of the PV system simulation model’s accuracy using 2-year measured data (2018–2019) from the PV system in the central region of Thailand (14°10′78.1″ north latitude and 100°16′94.9″ east longitude). The PV system consists of 48,980 PV panels and 12 inverters; one string consists of 24 PV panels connected in series, and two series are connected in parallel; seven arrays consisting of 10 strings are connected in parallel; two arrays consisting of eight strings are connected in parallel, and nine arrays are connected in one inverter. The experiment of the PV system is as shown in
Table 5. The PV system has monitoring systems for all of the parameters, which are recorded every 1 min.
The pyranometer uses the KIPP&ZONEN band (CMP series) by installing it on the same plane as the PV panel, and the thermometer is installed under the PV panel. The PV panels uses the REC peak energy series band (REC245PE), as shown in
Table 6.
In order to verify the accuracy of the proposed model with the application to the PV system simulation model, the testing and comparison of the simulation results with the actual measurement data can be divided into two conditions. These are the daily PV power output in two weather conditions (cloudy day and sunny day) and the effect of climate change for the electricity production of the photovoltaic systems. In this study, the model was designed to calculate the PV power output in different weather conditions, which are divided into seasons. These are in the summer (February–May), the rainy season (June–September), and the winter (October–January). The division of the seasons in Thailand was taken from the Thai Meteorological Department. The test uses data from photovoltaic systems in Thailand (2018–2019). In order to verify the model that was used to improve the accuracy, the most accurate results to compare the % RMSE [
22] values with the measured data is given by
where
is the simulation data,
is the measured data and
is the average value of the measured data.
4.3. Seasonal PV System Simulation
In order to compare the electricity generation data of the proposed model and the actual measurement, the conditions are divided into three seasons: the summer, the rainy season, and the winter. The climate in each season is different. The climate is an essential variable for the electricity generation of the PV system, including solar irradiance, ambient temperature, and module temperature, etc. In this research, the proposed model’s accuracy is checked with the PV system simulation model application that calculates the PV system’s electricity generation in all climatic conditions. In the test, this research randomly generated electricity for one week of the three seasons in 2019.
Figure 14 compares the PV power output between the proposed model and the actual measurement data for the random week of the different seasons. The simulation results of the sampling of the photovoltaic system’s electricity production, the simulation results, and the data from the actual measurements tend to show a similar trend. The daily electricity generation data for all three seasons have different weather conditions. However, the proposed model shows that this model can accurately simulate the electricity production in the different weather conditions.
The accuracy of the proposed model of the monthly PV energy simulation compared with the actual measurement data in 2018 and 2019. When analyzing the simulation results of each season, such as in the summer, the rainy season, and the winter in Thailand’s tropical climate, the proposed model can simulate the PV energy precisely in all weather conditions, as shown in
Figure 15.
Table 8 shows the proposed model of the monthly PV energy and the actual measurement data (2018). The proposed model results from 12 months of PV energy in Thailand, showing that the average PV energy is 1516 MWh/month, and the PV energy is 18193 MWh/year. The actual measurement data has an average PV energy of 1504 MWh/month, and PV energy of 18053 MWh/year. The nRMSE (normalized RMSE) ranges from 0.06% to 4.05%, which is very low. The average nRMSE (normalized RMSE) is 1.19% for 12 months (2018).
The test results of the PV energy of the proposed model and the actual measurement data on monthly basis (2019) showed that the average PV energy is 1453 MWh/month, and that the PV energy is 17440 MWh/year. The average PV energy is 1450 MWh/month, and the PV energy is 17406 MWh/year in the actual measurement data. The nRMSE (normalized RMSE) ranges from 0.07% to 2.91%, which shows that this value is deficient. The average nRMSE (normalized RMSE) is 1.26% for 12 months (in 2019).
In the comparison of the PV energy of the 24 months data of the proposed model (2018–2019) with the actual measurements for all three seasons, the average nRMSE (normalized RMSE) is 2.12% in the summer, 0.49% in the rainy season, and 1.08% in the winter. These are the results of the proposed model.
In the rainy season, the model is at its highest accuracy. We found that the solar cells in this area performed at their best because the dust was washed off the front of the solar panels by the rain, and because the temperature accumulation of the solar panels is not as high as it is in the summer. Because of this, it causes relatively little energy loss.
In the winter, the model is less accurate than it is in the rainy season, but more accurate than it is in the summer because there is a lot of dust on the front of the solar panel, which is a waste of energy for the solar cells. However, no heat is accumulated on the solar cells; thus, the models presented can be processed better than those in summer.
In the summer, the model is less accurate than both seasons because the summer temperature is high. The heat accumulation of the solar panel causes the temperature to rise.
In the actual case of a solar farm, the panel cleaning is not performed every day, but there is a cleaning cycle. Therefore, the accumulated dust affects the solar cell’s electrical power generation efficiency.
The main factors that affect the PV system’s electricity production are solar irradiance, which varies according to the solar cell’s current, and the panel’s temperature, which varies according to the voltage of the solar cell. The proposed model has a method that uses the relationship of solar irradiance and electricity generation to help improve the accuracy process, but the module temperature is not used as a parameter in this model. For this reason, the accuracy of the model in the summer is lower than it is in the rainy season.