This paper proposes a methodology to model and analyze the security scheme required by a microgrid that considers the participation of intermittent energy sources, such as photovoltaic generators (PVG). This security scheme is represented by an up and down spinning reserve. The methodology consists of performing a four stages analysis, at each study hour of the next day: a load analysis, which evaluates the uncertainty in the forecast electricity demand; a generation analysis, that evaluates the uncertainty in the forecast power availability of the PVGs; a security analysis, which quantifies and evaluates the up and down spinning reserve required by the microgrid. This reserve allows to drive the system frequency to a steady state after the occurrence of events associated with forecast errors in both the electricity demand and the power availability of the PVGs; and a validation analysis, that verifies the proper sizing of the up and down spinning reserve. The proposed methodology was implemented on a real microgrid located at the Universidad Nacional de Colombia's campus. From this, it was concluded that the security scheme designed for the microgrid allowed to ensure efficiently the relation between generation and demand, at each study hour.