Unmanned Systems Technology 024 | Wingcopter 178 l 5G focus l UUVs insight l CES report l Stromkind KAT l Intelligent Energy fuel cell l Earthsense TerraSentia l Connectors focus l Advanced Engineering report

65 the behaviour of the UAV in the air were unchanged from when using only a battery (aside from the longer endurance). The next steps were to add and mature a range of ancillary systems to the fuel cell stack, to develop and mature a turnkey product. This, the company intended, would enable a level of energy density for UAVs to fly longer and further. “If you’re mapping a large area with battery- powered multi-copters, you need to come down every 20 minutes and replace your battery,” says Andy Kelly, IE’s head of UAV product development. “That determines how many stops you need on your journey, how long the overall operation takes, and how many UAVs you need. “With a fuel cell, you can travel three to four times longer, have far fewer stops, refill your fuel tank in minutes or even seconds and have greatly increased productivity. It also enables entirely new applications for small UAVs, such as offshore wind farm inspection, for which a UAV needs 30 minutes to get out to a wind farm, 15-20 minutes to inspect it, and 30 minutes to come back again.” Development history The company’s 800 W fuel cell power module is air-cooled, with an open- cathode design for drawing in air from the surrounding environment, and is hybridised with a small battery. It has a footprint of 196 x 140 x 100 mm, and a mass of 930 g. Even compared with IE’s previous (and first) production model, rated at 650 W (which weighs 800 g), this represents a small but important increase in power density. As Kelly explains, “For an extra 130 g you’re getting another 150 W of power. In real terms, you’re talking about being able to carry about 1.5 kg more mass at the price of that weight. So, with all that extra mass, you can either carry a larger cylinder of hydrogen to double your flight time, or a larger payload.” This higher power-to-weight ratio is achieved by increasing the number of cells in the stack, which in turn need more cooling – more power means more heat produced. Since PEM fuel cells are typically around 50% energy efficient, each extra kilowatt of electrical power means another kilowatt of heat is generated. The extra cooling required means the latest 800 W module has two cooling ducts, compared with just one on the 650 W module. The 800 W module uses two electric motors to power the fan in its two ducts, and they’re the same model as the one in the 650 W module. Possibly the most important change between IE’s initial prototype fuel cell modules and the productionised versions was to upgrade the cell technology. The 800 W (and 650 W) fuel modules integrate cells based on IE’s AC64 design, which stands for air- cooled and has about 64 cm 2 of cell area. By contrast, the prototype had 10 cm 2 of cell area. “That meant each fuel cell, and its active area for energy production, was much smaller,” Kelly explains. “The bare bones of the fuel cell were generally the same as what we have now, we just now use significantly fewer cells in each stack but with a bigger cell area.” That in turn meant the original prototype went from containing two fuel cell stacks and 74 cells each to a single stack with 34 cells in (28 cells in the 650 W unit). This has allowed significant increases in energy density and efficiency. Whereas the prototype was designed to power a modified DJI M100 quadcopter, which carried no payload, for an hour and 17 minutes, the latest system can produce similar or better results for larger Intelligent Energy fuel cell | Dossier Unmanned Systems Technology | February/March 2019 Intelligent Energy’s UAV power systems use about 64 cm 2 of active PEM area on each fuel cell, improving energy density and reducing the overall part count compared with the prototype