# Power Sources for Unmanned Aerial Vehicles: A State-of-the Art
## 2 Unmanned Aerial Vehicle (UAV)
### Fuel Cell Powered UAVs
For example, laser beams used for power transfer may have a limited range or be affected by obstructions, such as buildings or other objects that can block or interfere with the transmission. This can restrict the operational altitude and area of the UAV, requiring it to operate within a specific range from the GS to maintain a consistent power supply. Another concern with wireless refueling is the potential for UAV damage in case of tethering loss. In some cases, UAVs may be tethered to the power source or laser transmitter through physical connections, such as cables or beams. If the tethering connection is lost or severed, it can lead to a sudden loss of power or disruption in the energy transfer, which may result in the UAV losing control or experiencing a sudden shutdown. This can potentially lead to damage to the UAV or compromise the mission's success. To mitigate these limitations and concerns, careful planning, system redundancy, and safety measures need to be implemented. This may involve the use of backup power sources or redundant laser transmitters to ensure uninterrupted operation and minimize the risk of power loss. Additionally, thorough risk assessments and safety protocols should be in place to prevent or mitigate potential damage to the UAV in case of tethering loss or system failures. In a study [89], a comparison of various battery types (Li-ion, Ni-Cd, Ni-Mh) and fuel cells was conducted, considering criteria such as energy and power densities, discharging characteristics, temperature effects, efficiency, and endurance. However, it is important to note that flight tests were not conducted to evaluate the actual behavior, capabilities, and performance of these power sources in real flight conditions. Figure 6 in the study presents a comparison of specific power versus specific energy for batteries, fuel cells, and supercapacitors. It indicates that fuel cells demonstrate higher specific energy compared  
\begin{table} \begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Power Supplying Technique** & **Advantages** & **Limitations and Drawbacks** \\ \hline Wireless refueling using laser beams offers the potential for unlimited operating time for UAVs without the need to land. By utilizing a single energy source, such as a ground station equipped with a laser transmitter, the UAVs can receive a continuous and uninterrupted power supply while in flight. This eliminates the need for frequent battery changes or recharging, allowing for persistent operation and extended mission durations. & While wireless refueling offers the advantage of unlimited operating time and eliminates the need for landing or battery replacement, it comes with certain limitations. One of these limitations is the necessity of a ground station (GS) to provide the power supply or laser transmitter. The GS serves as the central hub for supplying power or transmitting the laser beam to the UAV in flight. \\ \hline \hline \end{tabular}   
In addition to providing power, wireless refueling also enables safe and effective data transfer between the UAV and the ground station. Along with power, the laser beam can be used to transmit data and communication signals, ensuring seamless connectivity and information exchange between the UAV and the ground control. \begin{table}
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**Power Supplying Technique** & **Advantages** & **Limitations and Drawbacks** \\ \hline \hline \end{tabular}  
Wireless refueling using laser beams offers the potential for unlimited operating time for UAVs without the need to land. By utilizing a single energy source, such as a ground station equipped with a laser transmitter, the UAVs can receive a continuous and uninterrupted power supply while in flight. This eliminates the need for frequent battery changes or recharging, allowing for persistent operation and extended mission durations.  
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