# Selected Aspects of Designing Modular PEMFC Stacks as Power Sources for Unmanned Aerial Vehicles
## 1 Introduction
showed that when hybrid power sources are used in the propulsion system, the hydrogen consumption of the fuel cell can be reduced using an energy management system [25]. The number of completed and fully equipped drones powered by commercial hybrid electric propulsion systems (each of which consists of a PEMFC fuel cell and battery) has also gradually increased. A Hycopter powered by PEMFCs (HES Energy Systems, Horizon, Singapore) flew for over 4 h. Energyor, Technologies Inc., Montreal, Quebec, Canada) presented a multirotor vehicle in which the use of PEMFCs enabled a flight of over 2 h. Other successful tests include those conducted by MMC, a Chinese manufacturer of drones, and Intelligent Energy, incorporating fuel cells into UAV designs and extending flight times from 2 to more than 4 h [26; 27; 28; 29; 30]. The use of hydrogen-powered fuel cells in hybrid power systems, in addition to extending flight time compared to only battery-powered systems, has an additional advantage that increases their operability: hydrogen tanks can be refueled within a few minutes so that the UAV can perform its next mission; unlike in the case of electrochemical batteries, which must be recharged for several hours to be reused, or must be replaced with new extra battery cell packages [31]. With regard to the commercial solutions listed in papers [26; 27; 28; 29; 30], efforts undertaken in many aerospace or fuel cell research laboratories are also focused on conducting a series of modelling and simulations concerning optimization of PEMFC stack performance in hybrid power sources under UAV flight. Most of these are also confirmed by experimental investigations in stationary conditions by testing under variable electrical loads [32; 33; 34]. The increase in durability of PEMFC stacks under variable electrical loads in different conditions is one of the main strategical goals for developing the technology of hybrid propulsion systems for application in UAVs. The increase of durability of the PEMFC stack under variable electrical loads in different conditions is one of main strategical goals for the developing technology of hybrid propulsion systems for UAV applications. The main components of the energy system in an electrical hybrid propulsion system comprise an electrochemical battery, hydrogen-oxygen fuel cells, and DC-DC converters. In some cases the range of electrical voltage during PEMFC stack operation is not compatible with the electrical architecture of the current electrical engine system. Within this framework, multistack fuel cell (MCFC) systems may be possible solutions. Indeed, when associated with specific electrical flowing reagents and coolant architecture, MCFC systems may offer superior performance in terms of power output and system durability. In the case of inferior electrical operation due to the presence of degraded cells in the module, the system may still be reliable thanks to the redundancy of other PEMFC modules. Modular fuel cell stacks have been used in air-independent propulsion for submarine power supplies and for space exploration vehicles [35; 36; 37; 38]. The results of electrical properties and durability of a modular PEMFC stack designed as part of a hybrid source for use in a propulsion system designed to supply an electrical engine in a motor glider or Antares DLR-H\({}_{2}\) research aircraft [39; 40]. The goal of the paper is to present selected results concentrating on the construction and electrical performance of modular polymer membrane fuel cell stacks as components of hybrid power sources capable of application in drones. One power source is a device composed of two identical subunits, each consisting of a 1-kW fuel cell stack, intended to supply power to the main electric engine. The other power source is a 500-W PEMFC stack, consisting of three modules, intended to serve as a component of a hybrid power source designed to supply auxiliary on-board equipment.