Technical and economic feasibility of applying fuel cells as the power source of unmanned aerial vehicles

This study aims to quantitatively compare the weight, cost, and flight endurance of small unmanned aerial vehicles (UAVs) powered by batteries and fuel cells. We compare the use of lithium-polymer (LiPo) batteries, proton exchange membrane fuel cells (PEMFCs), and direct methanol fuel cells (DMFCs) in powering two representative small UAVs: KHawk-Thermal (fixed-wing, 1.4 m wingspan) and KHawk-CarbonQuad (quadcopter, 0.7 m diagonal length). This study uses experimentally measured polarization curves of fuel cells and power consumption data of LiPo-powered UAVs during flight tests as input to obtain the minimum mass, power consumption, and life cycle costs (LCC) of these power systems. The analyses consider the voltage, efficiency, and power at each current density to find the optimal operating current density to obtain the minimum weight and cost of fuel cell systems to obtain the desired flight endurance. The LiPo battery is the most cost-effective option to power UAVs with an endurance of 0.7 hrs (42 min) or less. At medium flight endurance (e.g., 0.8 – 2.1 hrs), the PEMFC system has the lowest mass and LCC. While hydrogen is the most energy-dense fuel, hydrogen storage significantly increases the mass and cost of the system. For UAVs undergoing long endurance missions (>2.2 hrs for fixed-wing UAVs, > 4.3 hrs for quadcopter UAVs), a DMFC system has the lowest mass and power consumption due to the high energy density of methanol and its simple storage requirements. This study also analyzes the impact of key parameters, such as the specific energy and power of battery and fuel cells, the mass ratio of hydrogen storage, and the lift-to-drag ratio, on UAVs' mass and power consumption.