Long duration hydrogen storage could be a missing link in the global energy transition. So far, we’ve struggled to find a way to decarbonise hard to abate industries. These include sectors long-haul transport, iron and steel production and chemical production — and are some of the world’s biggest polluters. These sectors have extensive energy requirements, which makes them notoriously difficult to decarbonise through conventional electrification alone. It is essential that we find a way to power energy intensive industries without fossil fuel reliance. If we don’t, we will fail to meet international net zero targets.
The solution could be hydrogen power.
Hydrogen: A high-density energy carrier
Hydrogen is a high-density energy carrier. This means it can store a significant amount of energy in a relatively small volume. Also, when combusted for fuel, its only byproduct is water. Hydrogens high energy density paired with its clean burning properties position it as a front runner for tackling these hard to abate sectors. Hydrogen can produce a huge amount of power without harmful emissions. Whilst hydrogen integration would require some infrastructure updates (as with every other renewable energy source) we could start using it without major structural overhauls.
We currently produce the majority of our current hydrogen supply is through carbon-intensive methods. However, we can produce hydrogen through electrolysis without greenhouse gas emissions. This process produces green hydrogen. A barrier of green hydrogen production is the cost. Though, as we have seen with renewable generation roll out, the more we use green hydrogen becomes, the more economically viable producing it will be.
For hydrogen power to be viable, we need to implement an effective long duration hydrogen storage framework . By 2050, demand is projected to rise to between 125 and 585 million tonnes of H2 per annum (Mtpa). Currently we do not have functional storage duration to manage growth at this scale. As new hydrogen technology becomes operational, so must hydrogen storage.
The need for hydrogen storage
The successful deployment of hydrogen power hinges on our ability to store it effectively. We don’t yet have the large-scale long duration storage infrastructure in place to manage the projected hydrogen demand. However, there are a number of storage models in development which will fit the future energy landscape. A holistic storage framework would best support hydrogen energy. This would see with different methods used locally to accommodate budgets, geographical makeup, grid demands and response times. We group these methods into the following categories: material, physical and adsorption-based storage.
Method 1: Material hydrogen storage methods
Material based storage is the process of chemically bonding hydrogen with other materials, creating compounds called hydrides. Common examples of hydrides are:
Methanol (CH3OH): Hydrogen bonds with carbon dioxide.
Ammonia (NH3): Hydrogen binds with nitrogen.
Metal Hydrides: Such as aluminium hydride (AlH3) and magnesium hydride (MgH2).
These compounds carry hydrogen, allowing us to store it at high densities without the need for specialised storage conditions. This makes material storage efficient and at this stage, cost effective. However, the process of extracting hydrogen raises questions about its economic viability. Breaking chemical bonds is very energy intensive, which makes the process costly. Typically, this is done through heating or a reacting with water (hydrolysis).
When selecting a hydride for hydrogen storage, each compound has different properties to consider. These include:
- Bond strength: Stronger bonds can store more energy, but require more energy to release hydrogen
- Pressure tolerance: This affects overall storage costs
- Hydrogen storage density: How much hydrogen can be stored in a given volume
- Facility suitability: Availability of appropriate storage facilities
Method 2: Physical hydrogen storage methods
Think of a library where the bookshelves are set up very spaciously. If we set the shelves 10 meters apart, there’s plenty of empty floor space, but limited room for actual book storage. This setup is inefficient. If we push the shelves closer together, the library would have the capacity to store considerably more books.
The concept of physical hydrogen storage is similar. The inefficient use of space in this hypothetical library is like storing hydrogen in its untreated form. Pure hydrogen gas has one of the lowest densities of all chemical elements. This just means there is a lot of space between one hydrogen atom and the next. At room temperature and 1 bar atmospheric pressure, hydrogen has a very low density, with less than 0.1kg hydrogen per m3. Storing hydrogen gas in this untreated form is difficult and not very cost efficient. Compressing or liquefying hydrogen is like pushing the bookshelves together, making more room for storage. The space between atoms reduces, increasing the hydrogen density significantly. This makes storage easier, more practicable and enables higher concentrations of storage in one vessel.
Why aren’t we using physical hydrogen storage already?
The technology for physical hydrogen storage exists, is proven to work effectively and is in active use. However, the mass roll out of these models are limited by their current cost. Treating and maintaining the gas at high pressure uses a lot of power, making the process energy intensive. There are also safety concerns with the storage of gas at high pressure. However, the storage of any reactive compound, including natural gas requires stringent safety measures to avoid hazards. Which have stored natural gas at pressure for close to a century. The safety standards of Hydrogen storage is no different the fossil fuel storage we’ve confidently operated since the 1960’s.
The main methods of physical hydrogen storage are compression and liquefaction.
Compressed Gas
Hydrogen molecules are small, meaning they are much more compressible than other elements. Just as you could squeeze more paperbacks than hard covers into a bookshelf, you can fit considerably more hydrogen than oxygen into the same space.
First, hydrogen is compressed. The most common method for this is mechanically increasing the pressure within a tank using pistons or diaphragms. This process, whilst effective, requires a significant amount of energy and generates a lot of wasted heat. Storelectric’s Green CAES™ has a solution to this. Our patent captures and reuses wasted heat from the compression cycle. This is then stored as thermal energy to improve efficiency and reduce emissions. This in turn enables sustainable, more cost-effective energy storage. There is an alternative compression method which is still in early stages of development called the electrochemical model. Here, hydrogen ions are driven through a membrane to compress them, however this is not in widespread use
Once the gas is compressed, there are several options for storage.
Storage Tanks
Currently, we most commonly store hydrogen in high-strength gas cylinders and tanks. These can withstand up to 100 bar pressure aboveground and 200 bar underground. This allowsfor storage of about 7.8kg of hydrogen per cubic metre at room temperature. This method is 99% efficient and has high discharge rates. The downside of storage tanks is their scale. Since they can only store a small amount of hydrogen, they are only useful for short-term small-scale storage. Since such a massive volume of hydrogen is required to decarbonise hard to abate sectors, we need to store it on a much greater scale.
Geological Storage
Geological storage offers this scale. Deep underground there are vast salt caverns and depleted gas reservoirs. For over a century, these successfully stored natural gas at pressure. These natural formations are huge, some as deep as the Eiffel Tower is tall. They can store massive amounts of hydrogen at high pressure (up to 200 bar!) for extended durations. Many of these assets are currently lying empty, left unused natural gas use has decreased.
These caverns present an opportunity for fossil fuel assets to be repurposed for the green economy. We can utilise them as facilities for long duration hydrogen storage. Caverns differ in size, offering medium and long storage durations. There are enough of them that we could store energy at the scale we need in to decarbonise the nation.
Storelectric’s ‘Compressed Air Energy Storage (CAES) with Long-Duration Hydrogen Storage’ patent demonstrates the potential of geological hydrogen storage. With low leakage and contamination rates, efficiencies of up to 98% and rapid energy discharge, geological long duration hydrogen storage could be the key to decarbonising hard to abate sectors. Salt caverns are already present both across the UK and internationally. Where they aren’t already naturally occurring, caverns, we can quickly create them in areas with suitable geology through solution mining.
We can also use natural gas fields for subterranean hydrogen storage – these generally have a greater capacity than salt caverns. However, these are more prone to leakages. Also due to their previous use storing hydrocarbons, hydrogen stored there would require treatment to prevent reactivity.
Liquefaction
Liquefaction involves converting hydrogen gas into a liquid form, substantially increasing its density. Here, we cool hydrogen down to its boiling point, –253°C, condensing the gas into liquid hydrogen. In its liquid form, we can store hydrogen at much higher densities than when compressed. We store it in double-walled vacuum vessels, like huge thermos flasks. As a gas under normal conditions we can store hydrogen at 0.1kg/m3. When stored as a liquid, we can stored it at a whopping 70kg/m3.
The most high-profile example of liquid hydrogen storage is the NASA plant at Cape Canaveral. Upon completion, it plans to supply up to 3.5 million litres of hydrogen to the Kennedy Space Centre.
While liquefaction allows us to store more hydrogen in any given vessel, the cooling process and temperature maintenance are incredibly energy-intensive. Additionally, if we don’t condense the gas quickly enough, a significant percentage of hydrogen boils and evaporates, leading to considerable loss. This means large scale liquefaction is logistically challenging and lacks economic viability.
Method 3: Adsorbent Hydrogen Storage
Adsorption based hydrogen storage is still largely in the research phase, despite being studied since the 1960s. This technique involves forming weak bonds between hydrogen molecules and the surface of porous materials such as Metal-Organic Frameworks (MOFs), activated carbons, zeolites and other porous materials.
The adsorption process is similar to a microfibre cloth picking up dust. Whilst the dust sticks to the surface, it can be removed with minimal effort since there’s no strong bond binding them together. This technology is promising, and there are efforts currently being made to realise its potential. However, there are a number of hurdles still to overcome, namely high energy intensity for limited storage capacity (the weak bonds only allow low density storage) and safety concerns.
A notable advancement in adsorption-based hydrogen storage has been brought forward by H2MOF, a California based company focused on developing a novel MOF using nanotechnology. Their approach aims to increase the surface area of the storage material. This would enable higher hydrogen storage densities at lower pressures (around 20 bar) and ambient temperatures, making the storage process both safer and more cost-effective.
H2MOF
To tackle this problem, a Californian company, is developing a new type of MOF, using nanotechnology. This technology gives the MOF a higher surface area increasing the number of hydrogen atoms that will bind to the metal.
The company claims the technology facilitates storage at much higher densities and allows hydrogen storage at low 20 bar pressures and ambient temperatures, making the technology safer and cheaper than traditional adsorption.
This is not yet an established technology, but it will be fascinating to see how it develops.
Hydrogen Transportation
Whilst hydrogen storage is a critical element of the hydrogen economy, we must also consider hydrogen transportation on an industrial scale. Hydrogen must be safely and efficiently moved from storage locations to the industrial sites it will power.
We can transport hydrogen as a hydride, utilising our already well-established ammonia and methanol transportation infrastructure. However, this process is costly and very energy-intensive. We must keep the compounds under pressure during transport and then break the chemical bonds to use the hydrogen.
Alternatively, we can transport hydrogen through our existing gas pipelines. These can accommodate approximately up to 15% hydrogen without major infrastructure modifications. Since hydrogen molecules are so small, they can pass through the materials used in our gas pipeline infrastructure. If we were to transport a mix higher than 15% hydrogen gas pipes and seals would need overhauled to prevent leakage.
To convert the gas grid to include hydrogen transportation, we should gradually increase the gas blend to 15%. After reaching this level, we should shift focus to industrial hubs which utilise pure hydrogen. These hubs will have their own pipeline infrastructure carrying 100% hydrogen. As hydrogen demand and supply grow, we can extend these pure hydrogen pipelines. Eventually, these hydrogen hubs will expand and connect, forming larger regional or national networks.
You can read more on this in our hydrogen transportation and storage blog.
The Future of Hydrogen Fuel
Hydrogen fuel has the potential to have the same impact on our energy system that coal did in the 19th century and oil did in the 20th. The hydrogen economy would see in a new era of energy generation and consumption, facilitating an international green re-industrialisation. By enabling clean energy to power traditionally hard-to-abate sectors, green hydrogen production will form the bedrock of our energy transition. This will be impossible without the deployment of large-scale, long-duration hydrogen storage. We need novel clean technology to facilitate this.
Innovations like Storelectric’s green CAES, and our hybrid project which utilises heat from Compressed Air Energy Storage (CAES) to catalyse electrolysis, represent exciting advancements in green hydrogen production. These developments will be pivotal in decarbonising heavy industries and paving the way for a sustainable, green energy future.
