MPPT by the perturb and observe method (P&O) is used when the characteristic of these cells have a single maximum point. However, when PV cells are under partial shade, MPPT by particle swarm optimization (PSO) is used, which can be applied to PV characteristics with multiple maximum points. Therefore, in this study, we propose MPPT by PSO of PV cells for managing solar radiation intensity, which changes with time. Using simulation, we examine the effectiveness of this proposed method. The results show that in environmental conditions, where solar radiation intensity changes with time, it is possible to produce power efficiently through MPPT by PSO.