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71 the ‘fuel’ can fit the volume needed, rather than the other way around – a key advantage, particularly in the aerospace sector. Each gramme of it produces up to a litre of hydrogen gas, giving it a very high specific energy and making it ideal for mobile or portable applications where weight is crucial, such as in unmanned aerial or space vehicles. It can also be packaged into cartridges which, when combined with a fuel cell, have two to three times the specific energy of a lithium-ion battery. In comparison with an alternative hydrogen production plant using a pressure of up to 700 atmospheres, it produces the fuel but without the same safety concerns or cost of infrastructure. It can be moulded into pellets as well, to form a solid fuel but which has the properties of a fluid, making it far easier to transport it in large quantities and offering the prospect in the future of it being as easy to use as hydrocarbon fuels are now. The principal advantages of this pellet system are that it does not need high pressures such as those for storing gaseous hydrogen, does not need cryogenic temperatures for the storage of liquid fuel, has a high specific energy (energy per unit weight), is a stable solid at room temperature and the pellets are not the only forms this fuel can be shaped into. The process can allow solid fuel to be fitted into any potential spare volume in a vehicle, which can have benefits in systems such as UAVs. The future When paired, fuel cells and battery technology can be seen as symbiotic: an advance for one can encourage the development of the other. However, the use of batteries alone in unmanned systems can only go so far. Their capability in unmanned systems is ultimately limited, owing to the comparative difficulty of recharging them on or close to an unmanned vehicle. The advent of advanced fuel cells however is starting to remove these limitations, and there is a world full of chemicals waiting to be converted into zero-emissions hydrogen close to the vehicle, if not in it. However, it must be remembered that the ease of providing solar recharging may outweigh the requirements for faster hydrogen-based charging at this time. It is exciting to see that the structural design of UAVs is moving in the direction of highly optimised systems that blur the barriers between traditional functions. This has produced long-duration UAVs capable of gaseous storage, producing ever-longer flight durations and providing the unmanned systems industry with solutions that are not tied to traditional methods of refuelling. Granted, there are still technical challenges to overcome, such as the ability to generate hydrogen locally and/or to provide suitable methods of storage. However, history shows that where there is a technical challenge, there will be people to provide the solutions needed. Acknowledgements The author would like to thank Bob Byron at Infinity Fuels, Stephen Bennington at Cella Energy, Taras Wankewycz at Horizon Energy Systems and Chris D’Couto at Neah Power and Michel Bitton at Energyor for their help with researching this article. Unmanned Systems Technology | Dec 2015/Jan 2016 Canada Energyor Technologies +1 514 744 6122 www.energyor.com Germany DLR – German Aerospace Center +49 220 360 12474 www.dlr.de SFC Energy (EFOY) +49 896 735 920 www.efoy-pro.com Singapore Horizon Energy Systems +65 625 039 49 www.hes.sg UK Cella Energy +44 (0)1235 43 7740 www.cellaenergy.com USA AMI’s Ultra Electronics +1 734 302 7632 www.ultra-ami.com Hydrogenics – Fuel Cell Power Systems +1 905 361 3660 www.hydrogenics.com Infinity Fuel Cell & Hydrogen +1 860 688 6500 www.infinityfuel.com Neah Power Systems +1 425 424 3324 www.neahpower.com Oorja Fuel Cells +1 510 659 1899 www.oorjafuelcells.com Protonex Technology Corporation +1 508 490 9960 www.protonex.com UltraCell +1 925 455 9400 www.ultracell-llc.com Some examples of fuel cell manufacturers