Economic Aspects and Hydrogen Storage Techniques in Geological Structures

    Fikri Oğuzhan Şengül

Mevlüt Erhan Altun

Yasin Özkan

 Abstract

Underground hydrogen storage isn’t that different from underground natural gas storage. However, it is not currently available or physically possible as a means of storing energy, and it will not be in the foreseeable future. Underground hydrogen storage (UHS) is a promising method for safely, economically, and efficiently storing significant amounts of hydrogen in the subsurface. The selection of geological structures for underground hydrogen storage should be based on a thorough geological examination that considers both geological and engineering parameters. Underground hydrogen storage (UHS) has been proposed as a potentially promising technology for developing a large-scale hydrogen economy. In this study, economic aspects of underground storage and hydrogen storage techniques in geological structures are explained.

1.Introduction

Today, zero carbon emission energy which is hydrogen energy can be produced easily in terms of economical and technical but  it can not give enough energy to use for whatever.

Some countries will take on green energy instead of conventianal energy for environment in upcoming years. In fact, The Paris Agreement, also known as the Paris Accords or the Paris Climate Accords, is an international climate change treaty that was signed in 2015 by some countries. Climate change mitigation, adaptation, and financing are all covered. With this agreement, countries will use energy sources that will harm the environment as little as possible.

Firstly,underground hydrogen storage in geological structures will be explained in detailed. First part is divided into three: salt caverns, depleted oil and gas reservoirs, and aquifers. Second part is economic aspects of these underground storage techniques.

2.Underground hydrogen storage in geological structures

Salt Caverns

Salt caverns are a feasible option for hydrogen storage due to geological conditions like as tightness, excellent mechanical properties of salt, and chemical reaction resistance. Form and depth of the salt beds, correct composition and distribution of rocks in the reservoir, and rock solubility are all key factors to consider when choosing a location for underground storage in salt deposits. The significant thickness of salt deposits allows for the development of big underground storage facilities.

The injection-withdrawal process is adjustable and ideal for medium and short-term storage in salt cavern. Thanks to  high salinity of salt cavern, it prevents microorganisms from consuming hydrogen. Depth of caverns have influence in hydrogen storage capacity. That is, if we have lower depth cavern, we need lower amount of cushiong gas. Thus, cost of operation reduces. Salt cavern storage facilities are simple to handle, and gas can be injected and extracted lots of times each year. They’re one of the best options for preserving peak-time gas reserves.

Depleted Oil and Gas Reservoirs

Due to their well-identified geological structures, good tightness and integrity of their caprock, and pre-existence of requisite surface and subsurface facilities, depleted hydrocarbon reservoirs are the most appropriate options for underground hydrogen storage. There is a advantage of hydrogen storage in depleted reservoirs that we know all information about reservoir,formation, well characterization. This leads to reduce cost of storage.

Also, the tightness of depleted gas reservoir caprocks has been confirmed. The presence of residual gas in a depleted gas reservoir is considered a benefit since it can be used as cushion gas. On the other hand, if the residual gas can affect the purity of hydrogen, it can be considered as disadvantage.When planning and developing the facilities needed for  underground hydrogen storage (UHS) in a depleted gas deposit, it’s critical to stop gas extraction as soon as possible. This enables storage to be built in less time and at a cheaper price.

Aquifers

Aquifers are porous and permeable media in which fresh or saline water fills the pore spaces. Aquifers are present all across the world, making them an excellent UHS option. They’re found in all sedimentary basins across the world, and they could be a suitable option for underground hydrogen storage in locations where depleted hydrocarbon reserves or salt caverns aren’t accessible. As water fills the pore space of the aquifer chosen for storage, it must be moved downward and sideways to make room for storage. This activity is linked to a rise in pressure in the structure . When gas is injected into the storage space, it replaces water, which then returns when the gas is extracted. During the operation of the storage facility, the gas/water boundary shifts, and water seals the storage area, including at the bottom. There will be a considerable amount of gas left in the aquifer that will not be recoverable later. Many potential risks are associated with hydrogen migration in aquifers, including leaking along unsuspected faults, biological reactions, and hydrogen interactions with minerals in reservoir rock. In contrast to depleted oil and gas resources, the tightness of an aquifer is unknown at first and must be acknowledged. This is why aquifers necessitate the drilling of wells to conduct thorough, time-consuming, and expensive testing to evaluate the tightness of the entire storage site and the sealing rocks above. This raises the expense of constructing such a storage facility.

3.Economic Aspects of Underground Hydrogen Storage

The examination of capital expenditures for three hydrogen storage alternatives revealed that depleted hydrocarbon resources (1.23 USD/kg of stored hydrogen) are the most economically appealing, followed by aquifers (1.29 USD/kg). Salt caverns (1.61 USD/kg)  are far more expensive. A business case for hydrogen storage in salt caverns in the years 2025 and 2050 was analyzed, taking into account demand for hydrogen from diverse sectors such as mobility hydrogen-consuming industry, and “Power-to-Gas” technology. The results demonstrate that the overall cost of integrated production and underground hydrogen storage is dominated by electrolysis (> 80% of total cost), with electricity playing a significant role. Although the leaching of a salt cavern necessitates a large financial expenditure, it accounts for just a small portion of the total UHS cost. The mobility market is definitely the primary driver, both in terms of quantity and economics, with a lower target cost (€4/kgH2, ex-storage). To be profitable, elec-trolysers must be used at a high usage rate. For a 50% renewable penetration rate, there is a requirement for huge storage. The cost of hydrogen ranges from € 4.5/kg to € 6.6/kg H2, and the cost of underground mass storage is always less than 5% of the total cost.

• 1.5 kWh/kg system (4.5 wt.% hydrogen)
• 1.0 kWh/L system (0.030 kg hydrogen/L
• $10/kWh ($333/kg stored hydrogen capacity)

4.Conclusion

Energy storage is seen as a vital part of the energy supply chain in the twenty-first century. This is due to the fact that it can increase the use of renewable energy resources, improve grid stability, increase energy system efficiency, reduce fossil fuels, and minimize the environmental effect of energy output.

In this report, we first examined underground storage techniques and then we studied economic aspects of these techniques. Actually, we made a price comparison but these prices are changing constantly because of economy. Underground hydrogen storage is not yet, and will not be in the coming years, a practical and available method of storing energy. Lowering the cost of hydrogen production through electrolysis will be a critical component in implementing this technique of energy storage on a large scale in the future. The transformation of geological space into hydrogen-filled space will be a difficult task for both the public and private sectors. Before full-scale underground hydrogen storage can be implemented, geological, technological, economic, legal, and social difficulties must be overcome.

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