In a stand-alone solar streetlight system, a DC/DC converter for battery charging and a DC/DC converter for LED lighting control are used independently. In this way, there is a limits to the utilization rate of solar power generation because the use of a DC/DC converter having only a volage ncrease or decrease function to reduce the number of power semiconductor devices makes it impossible to perform the maximum power estimation(MPPT) in all areas in the battery charger. In addition a DC/DC converter for LED lighting has a limitation in the design of the lighting voltage since LED lighting only operates at voltages lower or higher than the battery voltage. Therefore, in this study, we propose a novel power conversion system using a single bi-directional buck-boost DC/DC converter which uses the features of stand-alone solar streetlight of not running DC/DC converters for battery charging and DC/DC converters for LED lighting at the same time.