Unmanned Systems Technology 008 | Alti Transition UAS | Ground control systems | Xponential 2016 report | Insitu Orbital N20 | UAVs | Solar power | Oceanology International 2016 report

84 Focus | Solar power 22 V multiplied by 1 A, that makes 22 W. Specifying a solar technology is simply a matter of studying the requirements of the vehicle – how much power and at what voltage it needs, and by dividing power by voltage to fnd how much current is required to charge the battery and run the load. Then you make a rectangular arrangement of solar cells to give you that voltage and that current. The future It is clear that in the future the solar industry will focus on pushing the boundaries of effciency. One way to achieve that will be to study the different band gaps in the sunlight for the junctions to collect more light. One industry player is already working on a six-junction device in the inverted metaphoric platform that will collect different levels of light at a specifc energy. The inverted metamorphic multi-junction solar cell design is grown inverted, upside down compared with conventional multi- junction solar cells. This process offers improved conversion effciency through a better performing lattice-matched top cell, and allows more junctions (sub-cells) to be grown in the stack. Such developments are already pushing effciency levels up to 37% cent for space applications. There is a huge and growing commercial market for sustainable power, with major data providers such as Google looking at putting an internet in the sky and making the internet available for everyone. They may use satellites for that, or airships or high-altitude long-endurance UAVs, but whichever they choose they will all need electrical power of some sort. Then there are military applications. For the military market, the ability to have higher performance solar cells for increased duration for drones to look over the horizon, to be sent out for longer missions and loiter over targets or areas being reconnoitred for longer periods of time, has a great value to the military. For this the solar power industry is looking to develop enhanced performance using space-grade cells of two to three times as high effciency as can be had with the commercial terrestrial cells. With the ability to extend UAV durations to two, three or even up to eight hours by recharging the onboard battery with solar it opens up a whole new set of missions. That applies not just to hand-launched craft but also to some of the high-altitude, long-duration vehicles that provide a lot of reconnaissance and intelligence gathering. That interests the military, and with the military willing to pay a bit more for those capabilities, that may well drive the rest of the industry forward. Acknowledgements The author would like to thank Ken Steele at Alliance Spacesystems, Ted Stern at SolAero, Ray Chan and Noren Pan at ML Devices, and Rich Kapusta and Robert Parenti at Alta Devices for their help with researching this article. June/July 2016 | Unmanned Systems Technology USA Alta Devices +1 408 988 8600 www.altadevices.com Ascent Solar Technologies +1 720 872 5000 www.ascentsolar.com MicroLink Devices +1 847 588 3001 www.mldevices.com SolAero Technologies +1 505-332-5000 www.solaerotech.com Some examples of solar power-related suppliers The formation of a four-junction cell (Courtesy of SolAero Technologies)