System efficiency is key to the development of standalone lighting systems as their overall cost is tied to the battery pack size and photovoltaic (PV) panel required to ensure system autonomy. Given the timing gap between energy production and consumption in standalone outdoor lighting systems, in this paper, we propose a single-stage solution using GaN-based transistors as main switching devices. When voltage levels are within certain requirements, this topology allows for the parallel connection of PV panel and LED load, eliminating the need for switching relays typically used in this type of converter, thus reducing system complexity and cost. During the daytime, the system operates as a synchronous buck converter, harvesting energy from a solar-powered panel to charge the battery. We use a maximum power point tracking (MPPT) algorithm to maximize harvested energy. At night, the circuit acts as a synchronous boost converter, draining the battery to supply the LED load. We developed a 100W prototype for experimental verification. In charging mode, the system presented an efficiency higher than 92% within the entire power range with 97.3% peak efficiency. In driver mode, 95.8% peak efficiency was achieved.