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36 F ive years ago, the use of solar cells in autonomous vehicles was limited largely to spacecraft, rovers bound for the Moon or Mars, and large HALE pseudosatellite UAVs. These days though there is an enormous range of unmanned vehicles in every realm of operation, whose engineers have chosen to incorporate photovoltaic (PV) modules as a primary or secondary source of power; they are also now a feature in charging stations for extending the range and endurance of automotive and multi-rotor systems. The solar panels used most widely among unmanned systems fall broadly into one of two categories – single- junction products made mainly from crystalline silicon, and thin-film modules as well as higher efficiency multi-junction products (tandem cells) made from a range of other semiconductors. In both cases, manufacturers understand that for solar cells to be considered a viable alternative power source for battery-electric vehicles – compared with simply adding more battery packs or cells – many key performance specifications need to be optimised. These include how well the cells absorb sunlight, the conversion efficiency to electrical power (in kW, A and V), the weight and size of solar modules relative to the power they can supply, the cost to manufacture them, and their life expectancy before they have to be replaced. All types of cell for the unmanned space are made as thin and flexible as possible, to conform to the aerodynamics of the vehicles and to make them easier to work with. Cells for unmanned vehicles typically consist of several layers. The solar material is embedded in a protective encapsulant, with layers of weatherable material on top. In stationary solar farm-type modules, this is a glass sheet with the encapsulant beneath; in thin-film modules for vehicle installations, it is a thin polymer. … there’s power, and as Rory Jackson explains, advances in capturing sunlight to power unmanned systems are making the technology a real contender Where there’s light… October/November 2020 | Unmanned Systems Technology