Hydrogen Fuel Cells – Overcoming the Limitations of Traditional Drone Propulsion Methods?

By Ben Gross | April 19th, 2023

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While small UAVs (unmanned aerial vehicle) are now commonly used in a variety of civil and commercial applications, many of these platforms suffer from a bottleneck that limits their efficiency – short flight times. Unlike larger unmanned aircraft such as those used by the military, these small commercial models cannot be outfitted with internal combustion engines and other fuel-burning propulsion methods, and are thus limited in endurance.

The most common propulsion method for small drones is battery power. Even the most energy-dense battery technologies such as lithium-polymer (LiPo) pale in comparison to the output from combustible fuels, and it is rare to find a commercial battery-powered drone with a flight endurance of over an hour, with many unable even to break the half-hour mark.

A newer option for drone propulsion

In recent years, another drone propulsion technology has begun to emerge. Hydrogen fuel cells typically provide several times the endurance of a battery system of comparable weight, and provide a number of additional advantages as well. Commercial hydrogen fuel cell systems have only been available for less than a decade, and extensive research and development is being undertaken to help advance the technology further.

In addition to the energy density advantage, hydrogen fuel cells can also increase the efficiency of drone operations. Batteries take time to recharge, with charge cycles often being on the order of hours. Hydrogen fuel cells only require swapping out of a fuel cylinder, a process that takes mere minutes. Given sufficient availability of hydrogen, the use of fuel cells can thus significantly reduce the downtime of drone operations.

Hydrogen fuel cells also produce water as the sole emission. In a world where environmental impact and carbon footprint are considerations of ever-increasing importance, this gives them an advantage over combustion engines. Fuel cells are also quieter than engines, meaning that they will be less of a nuisance when operating in urban and populated areas.  The lack of noise and vibration is also beneficial to drones carrying exceptionally sensitive sensors and payloads.

With fewer moving parts, fuel cells also require less maintenance and overhaul than combustion engines, with a higher MTBF (Mean Time Between Failures). This again contributes to the overall efficiency of the operation and lowers manpower and spare parts costs.

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How do drone hydrogen fuel cells work?

Fuel cells are electrochemical systems that take advantage of the oxidation of a fuel source to create electrical energy that can be harnessed and used to power other devices and systems. Drone fuel cells use hydrogen as the fuel source and typically take in oxygen from the air, thus doing away with the need to carry a separate oxidizer.

A number of different fuel cell technologies have been developed for drone propulsion, with one of the most mature being the proton-exchange membrane (PEM). PEM fuel cells separate their positive and negative terminals with a solid polymer membrane.

Hydrogen fuel is fed in at the negative terminal, and the hydrogen atoms are stripped of their electrons to become protons. These protons permeate through the membrane to the positive terminal. The electrons travel to the positive terminal via an external route, and this flow of electrons translates to a usable electric current. At the positive terminal, the protons and electrons recombine with the addition of oxygen to form water.

The challenges of drone fuel cell technology

While hydrogen is the most abundant element in the universe, harnessing it to power vehicles is not entirely straightforward. Although it has an excellent energy density per unit mass, this mass is spread out over a large volume in hydrogen’s natural state. Hydrogen gas therefore has to be compressed in order to be useful, and these high pressures complicate both transportation and storage.

Many fuel cells also have a poor specific power, which means that they are unable to handle applications requiring very high peak output power. With future iterations of the technology, this may be improved, and in the meantime the shortfall can be made up by using a hybrid system that combines the fuel cell with a small battery. This battery can be used to provide extra power during phases of peak demand, and recharged during periods of low demand.

Fuel cells can also reach very high operating temperatures, and may require additional cooling capabilities in order to avoid disrupting other onboard systems or melting components.

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Applications of fuel cells for drones

The ability of hydrogen fuel cells to revolutionize both the range and flight time of drones potentially makes them an excellent match for BVLOS (beyond visual line of sight) platforms. With fewer landings required and greater areas covered, the enhanced efficiency translates into increased profitability for commercial drone applications.

Almost any unmanned aircraft use case could be enhanced with the combination of BVLOS operation and hydrogen fuel cell technology. Some of these applications include:

-Inspection of long stretches of road, railway, powerline and other critical infrastructure

-Offshore operations such as flights to oil rigs, vessels and wind farms

-Coverage of large areas of farmland for precision agriculture data collection

-Disaster relief and humanitarian aid to remote communities

A reliable communications solution for long-range drones

If you are looking to develop a long-range or BVLOS drone platform with the aid of hydrogen fuel cell power, you will need a robust communications solution to go with it. Aviation regulators apply highly strict safety criteria to drones flying beyond the visual line of sight of the operator, and with the addition of pressurized hydrogen gas, your road to certification will be even more arduous.

Elsight’s Halo platform can significantly boost your chances of gaining regulatory approval, providing the critical redundancy required for maximum safety and uptime. The carrier-agnostic system utilizes up to four datalinks from different cellular providers, and in addition to seamlessly utilizing these as backup links, it can also aggregate them together to maximize the available bandwidth for data-intensive applications such as streaming video and payload data.

The Halo hardware is also extremely lightweight and highly compact, making it ideal for hydrogen-powered platforms whose SWaP budgets will already be strained to the limit by complex fuel cells and bulky gas cylinders.

Please get in touch to find out more about how the proven Halo platform enables long-range drone operations and drone connectivity solutions around the world, opening up a wide variety of commercial applications.

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