Hydrogen is the most abundant substance in the universe and it could help to pave the way towards net zero within agriculture. However, this means generating it in a sustainable and affordable way which isn’t as accessible as it might seem. CPM investigates.
“When producing hydrogen from coal, it’d better to burn the coal for electricity in the first place.”
By Melanie Jenkins
The potential for green hydrogen to change energy and fertiliser production as we know it is boundless, with one quick Google search resulting in a myriad of results – many likely to be from well-known firms as they seek to get ahead of the game. But what can it bring to agriculture?
Despite its apparently unlimited nature, accessing hydrogen in a usable form isn’t that straightforward, but even so, it’s widely used across different industries, explains Cenex’s Nick McCarthy. “Hydrogen is essential to our civilisation; from its use in the manufacture of fertiliser to the de-sulphurisation of fuel for vehicles, it’s used in food production, glass making and a range of other chemical applications.”
However, there’s an issue with this. Although hydrogen itself can provide a clean and green source of energy, in the majority of cases it’s produced using natural gas or coal, he highlights. “How hydrogen is produced is often categorised using a colour code but green is the only one that’s produced entirely using renewable energy. When producing hydrogen from coal, it’d better to burn the coal for electricity in the first place.”
One of the key advantages of adopting hydrogen as a fuel is that the experience of operating with it is similar to what currently exists in liquid fuelled vehicles, says Nick. “As far as it potential to replace diesel internal combustion engines in agriculture goes, there are two options available or in development, depending on the machine and manufacturer in question.
“Hydrogen can either be used in a fuel cell or in an adapted internal combustion engine. In a fuel cell, an electrochemical process similar to that of a battery takes place, where the discharging of electrons produces energy.
“Where the internal combustion engine is concerned, JCB has been at the forefront of developing this technology. Unlike in fuel cells, the hydrogen used in adapted internal combustion engines doesn’t have to be as clean and because these are already the standard engines produced, it’s a much easier adaption to make than creating a new engine because the infrastructure already exists.”
But one of the biggest barriers to adopting this technology may be a lack of accessible locations for refuelling. “In the UK we have around 12 hydrogen refuelling stations, many of which are located on universities or behind security gates. And while there are firms producing mobile refuelling units, these are expensive and there are a number of legal and regulatory hurdles still to overcome.
“It’s not yet clear whether it’d be possible to take a hydrogen bowser onto a farm because the farm will count as an industrial zone. Or it might be possible to have it on farm but not to drive with it on public roads to access the farm, based on current laws.”
Nevertheless, the EU is working to overcome this with its Ten-T corridor policy which sets out road and other transport networks surrounding and adjacent to towns that are critical to the economics of the EU. “To allow for the integration of hydrogen as an accessible fuel across the EU, it’s been agreed that a hydrogen refuelling station will be built at each node of this network as well as one every 200km (124m).
“Before Brexit the UK was included in this policy, and although we aren’t now, the overall economic gravity it has hasn’t changed. So it’s essential that the UK aims to provide a similar frequency of refuelling stations to allow for the rollout of the technology and continued economic cohesion.”
The refuelling process itself is simple and would be very similar to adding a liquid fuel to a vehicle, says Nick. “The connectors would lock into place and would likely be cooled to ensure there’s no overheating and the process is quick – all-in-all it’s about a five-minute task for a passenger car sized fuel tank.”
But how does hydrogen’s work performance compare with diesel? In terms of energy density comparative to mass, hydrogen is fantastic, says Nick. “Hydrogen is lighter than air and even when it’s compressed and contained it doesn’t weigh much, however, it has a very low volumetric energy density meaning it’s the storage of the fuel which takes up space.”
According to the University of Michigan’s Center for Sustainable Systems, its volumetric energy density is 8MJ/L for liquid hydrogen, 5.6MJ/L for compressed hydrogen gas at 700bar (10,152psi) pressure, compared with 32MJ/L for gasoline at ambient conditions.
“In essence, this means that the number of hectares you can plough in a day is good, but the volume of hydrogen you can take with you to that field is limited, explains Nick. “I estimate 20kg of hydrogen would be required to achieves a day’s work from a tractor. It’s likely this would be stored on the roof of the cab but there’s then the challenge of maintaining balance.”
In addition to this, hydrogen has to be held at high pressures, with most non-road hydrogen prototypes storing the gas at 350bar, while on road this is 700bar to be able to store enough to operate. “That’s a lot of pressure to contain which means the thickness of the walls of the cylinders has to be considerable to store it safely.”
But safety is of utmost importance to manufacturers, with cylinders undergoing incredibly stringent testing, says Nick. “Tests include placing a cylinder in a bonfire for eight hours to see if it explodes, dragging them behind a truck on a 20ft chain, and firing rifles at them. Hydrogen cylinders are built to pass these tests and there’re UK firms installing them which expect their cylinders to outlast the vehicles they’re designed to go in.”
Access to green hydrogen is a further obstacle but in theory, the UK is one of the places in the world where there’s potential to produce cheap hydrogen, suggests Nick. “The UK has an incredible wind resource available and if this was pursued – privately or via government incentivisation – the UK could potentially produce hydrogen cheaply and be able to transport it domestically in a cost-effective manner.”
This article was taken from the latest issue of CPM. Read the article in full here.
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