Off-grid Solar Power Plants (PLTS) have become an important solution in supporting the transition to renewable energy, particularly in tropical urban areas such as Jakarta. The performance of these systems is strongly influenced by environmental factors, especially solar radiation intensity and daily sunshine duration. This study aims to analyze the influence of these two variables on the electrical charge of PLTS batteries as the main energy storage component. The theoretical foundation covers the concepts of solar radiation intensity, sunshine duration, and battery charging mechanisms in photovoltaic systems, with an analytical approach using linear and nonlinear regression models (logarithmic, quadratic, and cubic). The data were obtained from operational records of the PLTS at Institut Teknologi PLN for the period January–December 2024, totaling 366 days of observation.
The results show that solar radiation intensity has a positive and significant effect on the charging current to the battery across all regression models, while sunshine duration has a positive but insignificant effect. The nonlinear models indicate a more complex relationship, particularly when ambient temperature and wind speed are included as mediating factors, where the influence exhibits saturation points at certain values.
In conclusion, solar radiation intensity is the dominant factor in determining the efficiency of PLTS battery charging, while sunshine duration plays a limited role. System performance can be improved through the integration of real-time radiation monitoring, the use of weather prediction technology, and the selection of high-capacity batteries suited to tropical climate conditions.