First solid hydrogen drone takes to skies

Drone flying

25 July 2016 by Tom Marshall

The first drone powered by solid hydrogen made its maiden flight in February - the fruit of a long-term collaboration between the private sector and scientists at the Scottish Association for Marine Science (SAMS).

It flew for just ten minutes and didn't climb above a height of around 80 metres, but it proved the new power system works. The team are now planning another flight this summer that'll last an hour or two.

The hydrogen engine emits nothing but water, bringing both environmental and scientific benefits - particularly if you're trying to sample the atmosphere without picking up your own exhaust gases.

There have been many attempts to build aircraft that run on hydrogen. But if it's stored as a gas, to carry enough to be a useful fuel source you have to keep it at very high pressures. This means the piping and containment systems have to be strong and heavy, limiting how much the aircraft can carry and how long it can stay aloft.

"The problem with storing hydrogen is that it's a gas unless cooled below -238°C," says Dr Phil Anderson, head of the Marine Technology group at SAMS. "To get enough on board, one method is pressure, but you need to crank it up to around 700 atmospheres. That needs some heavy-duty engineering and it's a challenge just to build something light enough to fly." And if something goes wrong, it goes very wrong indeed - a high-pressure system has the potential to explode.

The system on the new drone operates at low pressure by using a solid form of hydrogen. This gets round the pressure problem, though it poses challenges of its own. The drone uses a system developed by UK firm Cella Energy - a spin-out of the Science & Technology Facilities Council - external link - which stores hydrogen as solid pellets that are gently heated to release it as a gas. A fuel cell devised by Arcola Energy then turns this hydrogen stream into electricity, which powers an electric motor. The partners were initially brought together by Innovate UK - then known as the Technology Strategy Board - to help accelerate the development of this exciting new technology.

The power system is light, powerful and clean. What's the catch? At the moment the pellets are expensive. The developers hope that economies of scale will mean costs fall as the system becomes more widely used.

Once that happens, it could start being used in all kinds of situations. One clear target is the inner city electric car; hydrogen would replace the batteries and eliminate the need for lengthy recharging. In this context the solid fuel system is inherently safer than one using high-pressure hydrogen.

For scientists, Anderson says hydrogen-fuelled drones' lack of gaseous emissions will create new possibilities. "It opens up a whole new style of atmospheric observation," he says. "With a large piloted plane you generally fly in quickly, taking measurements and leaving your pollution behind, but with a hydrogen-powered drone you can loiter over a small area for up to an hour, taking repeated measurements without ending up in a cloud of your own pollution. So you can get much better data on the composition of the atmosphere."

Unlike internal combustion engines, the electric motors on most UAVs are unfazed by a dunking in the sea, lending themselves to operations over the oceans. Hydrogen storage also copes better with cold temperatures than equivalent battery-powered systems or even internal combustion engines, which would make life easier for scientists working with drones at the poles.

In the meantime, this shows that collaboration between scientists and business is good for everyone. The researchers get to be involved with the development of next-generation technology that can help them with their work; the companies get practical input from expert users who can test their work in demanding situations and suggest possible improvements.

Anderson's now focused on cutting the drone's weight ahead of the next test flight. This should let the team do some real science along the way - perhaps examining the way the water leaving a sea loch as the tide goes out mixes with the open water.