A hybrid electric power system for high-endurance unmanned aerial vehicles is tested on the ground, alternating between fuel and solar cell power. A fuel cell system is constructed using a micro-processed controller, micro-pump, hydrogen generator using 20 wt% liquid sodium borohydride (NaBH4) solution, and proton exchange membrane fuel cell stack connected with a battery in parallel. The solar cell system consisted of a DC-DC converter, a battery, and solar modules. These two power sources are integrated via a power switching strategy using two solid-state relays connected to the controller, which turn on the fuel cell system to provide the power necessary to satisfy the load while the solar power system is on standby, charging the solar cell battery, or vice versa. In this way, not only is the operational period increased with high reliability by making one power source be on standby while the other is in use, but also the control logic of the system is simplified. Moreover, the fuel cell power could be adjusted by flowing different amounts of NaBH4 solutions using a controller to save liquid fuel, thereby extending the operational time.