Uncrewed Systems Technology 048 | Kodiak Driver | 5G focus | Tiburon USV | Skypersonic Skycopter and Skyrover | CES 2023 | Limbach L 2400 DX and L 550 EFG | NXInnovation NX 100 Enviro | Solar power focus | Protegimus Protection

101 multiple layers in a solar panel, including outer layers of highly transparent glasses, encapsulant polymers andmetallic back sheets – and the adhesives used in between – at the centre of all of them is the PV semiconductor cell, which carries most of the specifications that will define an end-user’s decision on whether to mount solar cells. The materials at the top end provide the highest commercially available solar conversion efficiency. Continuing to lead the way are multi-junction materials, which incorporate different semiconductors that are individually optimised for conversion efficiency at different wavelengths of solar energy. The most prominent productionised example for UAVs remains a triple- junction cell combining indium gallium phosphide (InGaP) with gallium arsenide (GaAs) and indium gallium arsenide (InGaAs). Collectively these materials provide more than 90% external quantum efficiency (the ratio of the number of charge carriers collected by the solar cell to the number of photons of a given energy shining on the solar cell from outside) over wavelengths of 450-1200 nm, and a typical power conversion efficiency of 28.5% in AM0 (zero atmosphere) and 30% in AM1.5 (terrestrial atmosphere). This solution also comes with a mass density of 250 g/m 2 , a power density of 390 W/m 2 and a specific power of 2200 W/kg in AM0, and is highly encapsulated for ruggedisation against UV light, ozone and very low temperatures. Other multi-junction cells are of course available, particularly among those used by spacecraft, but they are often many times heavier. Multi-junction panels are however among themost expensive, given that addingmore semiconductors to a panel increases development andmanufacturing costs, but interest in themnonetheless extends beyond their use in the stratosphere. For instance, somemilitary users are expressing interest in integrating multi-junction solar onto their low-altitude small UAVs for amore persistent power supply and range extension during border patrols and similar work. Elsewhere, the imminent boom in small satellites for applications such as telecoms, navigation and mapping will drive demand for highly efficient solar panels to power their dense electronics. Of course, these will mean changing their protection systems, doping systems and material thicknesses to account for issues such as outgassing or high levels of radiation in outer space. But as their extensive hardware will come with a minimum power requirement, the ability to install more solar power for less weight will reduce the cost of launching them into orbit, which remains the major expense for this new space industry. Solar power | Focus light Uncrewed Systems Technology | February/March 2023 Multi-junction solar cells power a wide range of UAVs across defence as well as commercial markets, from high-altitude pseudosatellite platforms... (Courtesy of Airbus) ...to smaller UAVs whose users want range extension as well as a recharging capability in remote areas (Courtesy of Microlink Devices)