# Power Sources for Unmanned Aerial Vehicles: A State-of-the Art
## 3 Conclusions
Hybrid systems, which combine multiple power sources, offer significant advantages over single-source systems. By leveraging the specific strengths of each power source, hybrid systems can address issues such as prolonged charging times, short flight durations, and limited peak power supply. Supercapacitors (SCs) are commonly used in hybrid systems due to their ability to overcome the drawbacks of other power sources. SCs have high energy density, short recharge periods, and virtually unlimited cycle life, making them a promising replacement for Li-Po batteries in hybrid systems. Hydrogen fuel cells, often incorporating Li-Po batteries, can be considered a type of hybrid system. However, Li-Po batteries present several disadvantages in drone applications, including low energy density, short flight times, long recharge times, environmental hazards, and limited lifespan compared to other power sources. SCs, with their high energy density, short recharge periods, and long cycle life, offer a potential solution as a replacement for Li-Po batteries in hybrid systems. Further research is necessary to evaluate the impact of SCs on the effectiveness of fuel cell systems in drone applications. Overall, the implementation of hybrid systems with SCs shows promise in improving the flight time and efficiency of UAVs. To truly advance current systems, hybrid systems need to be comparable in weight and size to existing drones while providing enhanced performance and addressing the limitations of single-source power systems. Further research and development are required to optimize the integration and performance of hybrid power systems in UAV applications. Conceptualization, Y.N.S. and W.G. ; writing--original draft preparation, Y.N.S. ; writing--review and editing, Y.N.S., M.T.H.S., F.S.S., M.N., W.G., S.S., A.L. and A.H.; visualization, Y.N.S. ; supervision, M.T.H.S. and A.L. ; project administration, F.S.S., M.N., W.G., A.L. and A.H.; funding acquisition, M.T.H.S., M.N, W.G. and A.L. All authors have read and agreed to the published version of the manuscript. The authors are grateful for the financial support given by The Ministry of Higher Education Malaysia (MOHE) under the Higher Institution Centre of Excellence (HICOE2.0/5210004) at the Institute of Tropical Forestry and Forest Products. The research was financially supported as a statutory work of the Poznan University of Technology (No. 0214/SBAD/0241). This research was partially financed by the Ministry of Science and Higher Education of Poland with allocation to the Faculty of Mechanical Engineering, Bialystok University of Technology, for the WZ/WM-IIM/5/2023 academic project in the mechanical engineering discipline. Not applicable. Data Availability Statement: Data sharing does not apply to this article as no new data were created or analyzed in this study. The authors would like to thank the Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia, and the Laboratory of Biocomposite Technology, the Institute of Tropical Forestry and Forest Product (INTROP), Universiti Putra Malaysia, for the close collaboration in this research. The authors declare no conflict of interest.