Metal hydride storage as a complete system

GKN Hydrogen has developed a complete containerized storage system which allows hydrogen to be stored in discs of metal hydride powder. The solution employs solid-state technology to store hydrogen safely for long periods. The pioneering company based in Pfalzen, northern Italy, became part of the British engineering corporation Langley in August 2024.

Admittedly, the many practical benefits of using metal hydrides for hydrogen storage are in no way a new revelation. Metal hydrides are compact and require neither high pressures nor low temperatures. Even in the event of a fire they are relatively safe since most of the hydrogen is firmly bonded in the metal. It’s why developers attempted to use them in hydrogen cars in the 1970s. And yet this technology is still not found in any automobile. One of the reasons for this, as tests showed, is the immense metal weight that had to be carried in relation to the amount of hydrogen stored. Not only that, the issue of on-board heat management proved tricky to handle.

On the other hand, what is relatively new is the use of metal hydride storage systems in stationary applications. Storage solutions for microgrids, neighborhood schemes and industrial units usually stay put. Such systems can also be used for hydrogen mobility, albeit essentially to store hydrogen at the refueling station.

If needs must, the hydrogen can also be moved around in shipping containers. These are best transported by boat or train, though road trains are also possible across the vast expanses of the prairies. “In the USA we are currently developing a mobile refueler. This will enable hydrogen to be transported to remote areas, thereby providing a truck-based refueling option in these locations,” says Dirk Bolz, head of marketing at GKN Hydrogen.

Dirk Bolz, head of marketing at GKN Hydrogen

In these applications, there will be little concern about using titanium-iron alloy as the material and the combined weight of the storage container for 250 kilograms of hydrogen and the associated equipment adding up to over 30 metric tons. It thus allows GKN Hydrogen to sidestep a key problem with this technology.

The company has also found solutions for other challenges: “Our specialist knowledge and intellectual property lie principally in two areas. One of those is production processes – in other words how you press a bonded material from metal powder,” says Bolz. In the early days the powder was formed into small pellets; today they are more like round, flat discs. “The other area is the charging and discharging of the storage system – in other words the thermal cycling of the storage system.”

The actual storage unit is designed as a pipe-in-pipe system (see fig. 1). In the inner pipe, the hydrogen flows around the discs made from compressed metal powder. A heat transfer medium flows through the outer pipe carrying away the heat which arises when hydrogen bonds to the metal. Adding heat reverses the process and the storage system is discharged.

Ten years of hydrogen storage research
GKN’s history can be traced back to the dawn of industrialization. The company started when an ironworks was founded in Dowlais, South Wales, in the 18th century. Since then, it has been involved in a wide range of industrial technologies, including the manufacture of steel, screws and drive shafts for cars. GKN Powder Metallurgy, headquartered in the German city of Bonn, is the specialist in powder metals within the international corporation. Its developers have been working on the application of metal hydrides for hydrogen storage for a good decade. The metal powder is made in the company’s factories spread across the world.

Up until 2023, the production of complete containerized systems was based at the GKN Sinter Metals factory in Bruneck in South Tyrol, Italy. This is where the first pilot applications originated. “Initially it was an off-grid solution for a vacation home and demonstrators at our sites. They were quickly followed by the first fully integrated power-to-power systems that incorporated everything from the electrolyzer and storage system down to the fuel cell,” explains Bolz. A year ago, GKN Hydrogen moved to Pfalzen, a 3,000-strong community located on the outskirts of Bruneck, where the systems are now produced and refined.

Levelized cost of storage rules
As an industrial enterprise, GKN knows full well that price is a key deciding factor for customers. According to Bolz, the current volume of production means the capital costs for a metal hydride storage system, depending on use, are around one and a half times that of a comparable pressurized tank. “Yet, depending on the application, the TCO – total cost of ownership – of our storage systems is on a par with or even below pressurized tanks. That’s due to the much lower maintenance costs.” He therefore recommends paying attention to the levelized cost of storage or LCOS for a specific project.

As the main components of the storage system are unmoving, the cost of maintenance is lower in comparison with high-pressure systems with a compressor unit and the storage system has a longer life expectancy. The efficiency is also greater. This is because once the hydrogen is bound in the metal, it stays there – in contrast with gas or even liquid storage tanks in which some of the molecules are discharged over time. Furthermore, the metal hydride storage system operates at low pressure, which can save considerably on energy costs, depending on the pressure level for production and application.

Batteries compared and contrasted
In addition to straight hydrogen storage systems, GKN Hydrogen also offers turnkey power-to-power solutions which come with the electrolyzer and fuel cell already installed. These are similar to commercial battery systems in terms of size and energy density. The HY2MEDI storage system includes a fuel cell and electrolyzer which are prefitted in a 20-foot (6-m) container. It holds 120 kg of hydrogen. This can then supply around 2 megawatt-hours of electricity using the in-built fuel cell. By comparison, the battery storage system of a well-known manufacturer in the same format has a capacity of 1.9 MWh.

However, metal hydrides and batteries each have their strengths in very different areas of application. Where a high number of short storage cycles are the order of the day, a battery solution comes out clearly on top. The battery manufacturer puts cycle efficiency at “up to 98 percent.” Looking purely at electrical efficiency, metal hydride systems are only 32 percent efficient. If a customer also requires heating, a significant proportion of losses can be used for heating purposes, which brings the overall efficiency to 70 percent. “Our systems are used in buildings or backup solutions for critical infrastructure for longer storage periods, from around two days to several weeks or months.”

GKN Hydrogen’s complete storage system is available as a containerized solution

“In industry, storage volumes and cycling dynamics tend to be the crucial factors,” stresses Bolz. If energy is not released for a long time, a battery’s losses will increase – but not in the case of metal hydride. The metal hydride storage system can also excel when it comes to cycle stability. According to GKN, after 3,500 cycles, the capacity remains at 99 percent of the starting value. Even beyond that, the storage systems have so far proved stable. “To date, we have put our storage solutions through about 6,000 cycles and we haven’t observed any mechanical wear or chemical degradation,” says Bolz.

Advantages for safety
The use of both hydrogen and batteries requires special safety precautions, particularly in relation to explosion and fire prevention. A great deal of experience has been acquired with regard to batteries which reduces anxiety about their use, including applications in residential properties. New battery materials will also greatly increase fire safety in the near future.

Hydrogen in pressurized tanks is, on the other hand, relatively new outside industrial uses. There is little experience of its application in homes or residential areas, in particular, and skepticism abounds. This is where metal hydride storage systems could come in.

“Only around 4 percent of the hydrogen stored in our system is present as gas. The rest is chemically bonded, in other words fixed,” explains Bolz. This minimizes the fire load and risk of explosion. What has been absent so far, compared with batteries, are well-honed practices within public authority approvals procedures. Authorities currently ask for the same evidence as required for high-pressure tanks, says Bolz. But he assumes this will soon change. “At the moment we are working to prove that our storage systems are the safest on the market by carrying out simulations and test installations.”

In fact it is the safety aspect which has recently opened the door to the Japanese market for GKN. In Japan, high-pressure tanks of 10 bar or higher are subject to strict safety regulations. That’s why Mitsubishi Corporation Technos, a Japanese trading company specializing in industrial machines, signed a memorandum of understanding with GKN Hydrogen just a few months ago.

Takeover by Langley Holdings
At the beginning of August, GKN Hydrogen had some big news: The company had joined British group Langley Holdings. This latest move followed several previous shifts at GKN. In 2018, the aerospace and holding company Melrose Industries bought GKN Group. At that time, GKN Hydrogen was still a business unit, becoming a stand-alone company within the group in 2021. In 2023, Melrose separated off several GKN companies into the Dowlais Group, among them GKN Hydrogen.

The new owner Langley is a family-run British corporation which started out in the 1970s as a supplier to the coal industry and has since grown into one of the UK’s biggest private companies. With 90 subsidiaries and a workforce of 5,000 staff, Langley estimates its turnover in 2024 will be about USD 1.5 billion. Around half of these earnings are expected to come from the Power Solutions Division, which will henceforth include GKN Hydrogen. Other companies in this division are Bergen Engines, a Norwegian manufacturer of medium-speed engines, the Italian Marelli Motori, which makes electric motors and generators, and the German Piller Group, which provides uninterruptible power supply systems.

Guido Degen, CEO of GKN Hydrogen, describes the takeover as an opportunity for the company to accelerate development. They are said to be excited about “potential synergies” with other companies in the division. Even before the takeover, GKN Hydrogen saw itself as ready to fly. “To date, we have built and installed 27 systems globally,” said Bolz in early summer. This equates to a storage capacity of 60 MWh around the world. “This is no longer lab status, it’s technology readiness level 9. The manufacturing processes are standardized. Scaled-up series production and the subsequent cost benefits are possible any time – we are, in a sense, prepared for the growth that has been forecast for the sector.”

Eva Augsten