This paper presents an analysis concerning to the slow and fast dynamics for DC/DC Boost converters in photovoltaic applications.Two converters with classical Proportional Integrative (PI) control and Maximum Power Point Tracker (MPPT) with the same parameters and operation conditions are implemented by means of simulation.Simulations were done in OpenModelica using specialized libraries with solar modules, power electronics components and controls blocks.Results show that simulations with irradiance data and MPPT considering fast dynamics are only viable for short time periods due to it is necessary high computer resources.In contrast, results taking into account slow dynamics allow more large simulations with minor computational cost due to there are only considered average values of fast dynamics.Therefore, slow dynamics could be considered to simulate systems as micro-grids in OpenModelica.