Green Hydrogen—Production and Storage Methods: Current Status and Future Directions

Abstract

Green hydrogen has become a central topic in discussions about the global energy transition, seen as a promising solution for decarbonizing economies and meeting climate goals. As part of the process of decarbonization, green hydrogen can replace fossil fuels currently in use, helping to reduce emissions in sectors vital to the global economy, such as industry and transport, as well as in the power and heat sectors. Whilst there is significant potential for green hydrogen, there are also challenges. The upfront costs for infrastructure and technology are high, and the availability and accessibility of the renewables needed for production varies by region. Green hydrogen production and storage technologies are continuously evolving and being promoted as the demand for hydrogen in many applications grows. Considering this, this paper presents the main methods for its production and storage, as well as its economic impact. Hence, the trend of governments and international organizations is to invest in research and development to make this technology more accessible and efficient, given the carbon reduction targets.

1. Introduction

Renewable energy plays a key role in the global decarbonization process by mitigating carbon emissions and combating climate change, and renewable energy sources such as solar, wind, and hydropower are vital for the energy transition, providing an alternative to fossil fuels and reducing carbon emissions in different sectors [1]

Of all industries, shipping dominates world trade and has a significant impact on the economies of the countries where it takes place. However, it is one of the most fossil fuel-intensive sectors and, therefore, a major source of carbon emissions. To support the development of maritime traffic, as has been investigated in several studies [2,3,4,5,6], it is essential to be aware of the climatic conditions and extreme events. Awareness of the wind and wave climate in this region has multiple benefits, including avoiding hazardous areas, preventing accidents, and exploiting resources for renewable energy production. The transition to renewable energy sources, such as wind and solar power, can significantly transform this sector through less polluting solutions, such as green energy vessels or alternative fuels.

Recent research [5] explores the integration of aquaculture with renewable energy sources, such as wind farms and wave farms, in multifunctional platforms and how they can generate cost savings and sustainable development. Although the use of wind turbines, floating solar farms, and wave energy capture systems on the same platforms can optimize available space and resources, contributing to decarbonization and transition to sustainable energy sources goals, to fully harness this potential, stringent environmental assessments and advanced technologies are needed to manage the challenges of environmental impacts [1,7]. Major advances have been achieved worldwide in offshore renewable technologies, such as floating photovoltaics, wind farms, and wave energy converters, used by countries such as Japan, the USA, Spain, and China [7], although there are challenges related to technological maturity, cost, environmental impact, and the necessary infrastructure, these solutions offer significant potential for cleaner and sustainable energy.

One of the main trends of our century is the decarbonization of the planet, and hydrogen is expected to play a major role in this process. According to the Global Hydrogen Review 2024 [8], in 2023, global demand for hydrogen reached a new record with an increase of 2.5% compared to 2022 and is foreseen to continue to grow in the following years.

Green hydrogen is hydrogen produced from renewable energy sources that is carbon-free compared to “gray” hydrogen from fossil fuels and is essential for a sustainable energy transition. The most advanced technology used to produce it is water electrolysis powered by renewable electricity [9,10,11]. It is powered by renewable electricity, which aligns with net-zero targets. This approach exploits synergies between sectors, reduces technological costs, and provides flexibility to the energy sector. Technological improvements and the low costs of renewable energy also reduce the production price of green hydrogen, attracting growing interest in this solution [12,13].

The market’s rapid growth for green hydrogen production comes mainly from hard-to-decarbonize industrial sectors [14], such as steel and chemicals industries, as well as transport and energy. Thus, creating a global market for green hydrogen is seen as an essential pillar for the success of this rising trend. The role of green hydrogen [15] in regional and global energy transition scenarios varies significantly due to several factors, such as reduced greenhouse gas emissions, limited technology, multipurpose uses of hydrogen in various fields, and the final cost of producing, storing, and distributing it. However, as zero or net-zero emission scenarios become more dominant, green hydrogen is increasingly prominent in public discussions and energy transition plans [16,17].

Green hydropower policy is crucial for creating a low-carbon economy, and according to the IRENA (2020) report [18], well-structured policies and favorable regulations are needed to encourage investment in hydropower technologies, lower production costs, and promote the necessary infrastructure. Furthermore, other studies [19,20] suggest that a well-defined national hydrogen strategy can help integrate hydrogen into other sectors, such as transportation and industry, thereby reducing dependence on fossil fuels. Safety issues also need to be addressed, such as regulating the storage and transport of hydrogen to ensure social acceptance and consumer confidence. It is also important to highlight the importance of an integrated approach, including technology standardization and harmonization of international regulations to support long-term green hydrogen development.

The global fossil fuel crisis has intensified interest in developing sustainable energy sources. Microalgae are seen as a potential source of hydrogen due to their ability to decompose water into H₂ and O₂ using solar energy [21]. Hydrogen production by photo-biological methods is considered more efficient and less energy-consuming than other production methods, such as electrolysis or steam methane reforming [22]. Focusing on the prospects of different environmentally friendly hydrogen production technologies, [23,24] based on a comparative analysis, the yield of biomass production is comparable to electrolysis technology, with the advantage of lower operating costs and higher energy efficiency. By selecting cost-effective polymeric materials for membrane synthesis, hydrogen production by adsorption may become economically feasible.

The green hydrogen value chain is a key solution for the transition to sustainable energy systems, including the production, storage, transportation, and end-use stages [25,26].

In this research, the economic impact of hydrogen, as well as production and storage modalities, were investigated. Major challenges include a lack of distribution infrastructure and high production costs. Supportive policies and pilot projects are essential to reduce these barriers and attract investment in green hydrogen infrastructure. In the long term, international collaboration and regions developing hydrogen clusters will be key to creating a global green economy.

The main aim of this paper was to build an overview of the status of green hydrogen, the current trends, and the drivers of the most popular methods of obtaining and storing it, combining statistical data with scientific literature. There are several significant aspects of hydrogen breakthroughs [27], including investment prospects, technological progress, industrial change, infrastructure development, exporting opportunities, government financial support, energy transition, and carbon reduction. The major issues [28,29,30] to be studied for the transition to green hydrogen are its production and storage due to its high costs and the need to develop efficient and environmentally friendly technologies. However, green hydrogen offers the potential to replace fossil fuels in various areas, including energy production, transportation, and industry, and researchers can innovate and develop technologies to improve its use, contributing significantly to the transition to a greener economy.

2. Economic Impact

As mentioned above, green hydrogen has the potential to significantly impact the global economy due to its ability to contribute to the transition to more sustainable energy sources. The direct ways in which it can contribute economically are numerous [14,31,32,33], but mainly, it can contribute to reducing carbon emissions, developing new industries, generating new workplaces, diversifying energy sources in different areas such as power generation, transportation, and other industries, reducing energy costs, international trade, and beyond.

According to data extracted from the online statistical data and market research platform Statista [34] and as can be seen in Figure 1, in 2021, China was the leading exporter of hydrogen globally, with exports worth 2.73 billion US dollars. China was followed by Germany and the United States, with a significant difference of 33% and 37%, respectively, in terms of hydrogen exports. Internal and external trade is influenced by several factors that drive the positioning of each region. For example, China’s potential is due to the domestic need and decarbonization goals of its industry, while the potential to produce green hydrogen from wind and solar energy allows Germany to export at competitive prices. Qatar, Canada, and Australia, too, due to their abundant resources, could become important exporters. European countries are steadily increasing green hydrogen production by investing in research and development to accelerate the transition to a low-carbon economy. Brazil could also play an important role in the green hydrogen industry but is struggling with challenges due to the necessary infrastructure.

The global demand for hydrogen is constantly growing, having a significant impact on different sectors of the economy. As we can see in Figure 2, according to Statista data [34], the application for hydrogen is shown, referring to the year 2019 and estimates up to the year 2070 when the estimated forecast global demand for hydrogen is expected to increase to over 500 million metric tons.

Green hydrogen has several applications that will progress with technological advances [35,36,37,38,39,40,41,42]. Its main uses are in the chemical industry for feedstock and fuel [37,39], in the industrial sectors as a heat source for high temperatures [40,41], and as a fuel in the transportation industry [42]. The recent tendency is for manufacturers to switch from conventional combustion, and therefore, the transportation sector is expected to become the largest consumer of hydrogen.

The maritime industry [43] is responsible for about 2.2% of global carbon emissions [44], but the uptake of hydrogen at a rate of even 5% [45] could contribute to a reduction in global emissions of up to 9%, and renewable energy has the potential to become an effective solution for decarbonization in the maritime sector. In the shipping industry, the use of green hydrogen could lead to a reduction of CO₂ emissions for this method of transportation, although there are numerous challenges due to international regulations and standards, storage technologies, and especially the cost of production. Despite all issues, green hydrogen could be a solution for coastal and short-sea transportation [46,47,48] due to short distances, numerous ports, and less tight regulations. The storage of green hydrogen on ships requires dedicated equipment and represents a challenge from a safety point of view, as the study of the technologies needed to implement this solution is in continuous research [48,49].

To support the growing demand in this industry, it is necessary to develop an adequate green hydrogen infrastructure [50], but there are several obstacles in the way. The production of green hydrogen requires specialized electrolysis [9,10,11] plants that convert electricity from renewable sources into hydrogen. These plants can require substantial investment, and the technology is still in its early [35] compared to conventional hydrogen production methods. In addition to production, hydrogen storage and transportation are critical issues that require innovative solutions [35,51]. Hydrogen’s low energy density makes the storage process complicated, and thus, safe and reliable containers and technological devices for handling hydrogen are needed to ensure its safe and efficient delivery [52]. The current infrastructure is mainly focused on natural gas transportation, which hinders the integration of hydrogen.

Although the cost of production for renewable technologies has decreased significantly in recent years, compared to the price of hydrogen from fossil fuels, green hydrogen remains expensive. Collaboration between government, industry, and research institutions is needed to develop policies and strategies to support innovation and investment in renewable energy. Therefore, a favorable legislative framework, together with subsidies and financial incentives [53], is essential to promote the development of the necessary infrastructure and reduce the costs associated with the production of green hydrogen, thus facilitating the transition to a hydrogen economy.

As can be seen in Figure 3, Australia is the country with the largest number of green hydropower plants in the world. As of 2022, the country had 96 facilities [30], and due to the abundance of solar and petroleum resources, solar energy is the main source of renewable energy production in Australia. By 2050, Australia is expected to have among the lowest costs for producing green hydrogen [54,55]. Regarding the US, in most states, there are green hydrogen production facilities [55] depending on local resources and needs despite the challenges of technology and infrastructure. In Europe, Germany, Spain, and the Netherlands have numerous green hydrogen production and transport networks, and there is continuous investment in renewable energy production linked to electrolysis facilities.

In terms of green hydrogen production at the European level, Figure 4 gives a comparison between production in 2022 and future projections for 2030 for the top 5 countries with the highest production, based on data provided by the International Renewable Energy Agency, IRENA [56]. By 2030, Italy is expected to increase its production by 80%, the Netherlands and Spain by 75%, France by 70%, and Germany by 60%. In line with the European strategy, Italy intends to become a major player in the field of green hydrogen based on solar energy by developing hydrogen production in disused industrial areas and by increasing the production of electrolyzers [57].

A comparative analysis in terms of the environmental impacts of green hydrogen on production, storage, and distribution is presented in

Table 1. The environmental impacts of green hydrogen.

Stage	Advantages	Disadvantages	Overall Impact
Production	Uses renewable energy	High consumption of water and rare metals	Reduced
Storage	Liquefaction is effective for high-volume	Energy consumption for pressurization and liquefaction	Moderate
Distribution	Pipelines have low long-term emissions	Transportation is energy-consuming	Reduce to moderate

. To minimize the environmental impact, on the production side, technologies need to be developed to reduce the consumption of rare metals, and on the long-term distribution side, the infrastructure needs to be expanded. Also, the development of new storage methods to reduce the loss of liquefied hydrogen can lead to minimizing environmental impacts.

3. Production

Nowadays, most of the hydrogen produced around the world comes from fossil fuels, namely gas and coal. Depending on how it is produced in current use, hydrogen is classified into the following categories [58,59]: green, blue, yellow, pink, turquoise, brown, black, white, and gray (Figure 5).

The color of hydrogen is influenced by the production methods as well as the manufacturing process, and in many applications, the color can indicate the level of quality and purity. Hydrogen gray, the most common type so far, is predominantly used for ammonia production, and 40% of its quantity comes from chemical processes, according to the literature [59]. White hydrogen is found in nature, in underground deposits, but there are currently no strategies in place to exploit it. Pink, green, and yellow hydrogen is produced by the electrolysis of different energy sources, while turquoise hydrogen is produced by the pyrolysis of methane, which can be by thermal, catalytic, or plasma deposition. The brown and black hydrogen is produced by gasification, and the color corresponds to the type of coal used; this production method is popular due to the availability of natural resources. Gray and blue hydrogen are produced by steam reforming. Blue hydrogen includes the use of carbon capture and storage, and being produced from fossil fuels, currently has lower costs than green hydrogen [59].

The main method currently used to produce hydrogen is through fossil fuels. Other methods to produce green hydrogen are water electrolysis, thermal reforming of methane, gasification of biomass, and others. Pyrolyzing methane is not a “green” process but integrating carbon capture technologies can significantly reduce carbon emissions [60]. The current trend is to produce green hydrogen through various processes involving the use of renewable energy, to be an environmentally friendly alternative to traditional hydrogen production methods, and to be carbon neutral.

The Water Electrolysis process to obtain green hydrogen is highlighted in Figure 6, wherein water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) using electricity that comes from renewable sources. It is called green hydrogen because it generates no carbon dioxide emissions during production, unlike “gray” hydrogen, which is made from fossil fuels.

Electrolysis can be alkaline, proton exchange membrane, or high temperature [60,61,62,63,64]. The first type is the most common today due to its low cost, although it is not as efficient and fast as the other methods. The development of the materials industry in terms of the electrodes and catalysts used has led to the development of the proton exchange membrane (PEM) electrolysis process to decrease costs and improve operational efficiency [60,61]. High-temperature electrolysis (HTE) stands out due to the possibility of utilizing the waste heat to reduce the electrical energy required to produce hydrogen.

Regarding alkaline electrolysis vs. proton exchange membranes, the most important factor in hydrogen production is price, followed by safety and energy consumption [61]. Energy consumption directly affects production costs, and although alkaline batteries currently offer a slight advantage, their performance will change as technology advances and the hydrogen industry develops. Each type of electrolysis, whether alkaline, solid polymer membrane, or solid oxide, has distinct advantages and limitations depending on their physical characteristics and energy efficiency. Solid oxide electrolyzers have the highest current density, but their energy efficiency depends on efficient heat management, whereas alkaline and polymer membrane electrolyzers are limited by issues of membrane strength and performance, and all technologies must improve membrane selectivity to reduce hydrogen losses at partial load [65].

Detailed analysis of the energy alignment and reaction kinetics can help to improve the efficiency of the electron transfer process and thus show why certain methods outperform others in terms of electron transfer efficiency and overall productivity. Among the important factors in electron transfer are the materials from which the electrodes are made and their mechanical properties; for example, high conductivity reduces resistance and energy losses.

High-temperature electrolysis is an advanced method of hydrogen production, operating at higher temperatures of 500–900 °C [66,67], based on solid oxide electrolyzers (SOEs) in which water (H₂O) is decomposed into hydrogen (H₂) and oxygen (O₂) by applying an electric current. The added heat helps to reduce the need for electricity, and a benefit of this method is the possibility of a renewable energy supply.

A comparison among alkaline, PEM, and HTE electrolysis is presented in

Table 2. Comparison between types of electrolysis.

Type of Electrolysis	Operating Cost	LCOH	Efficiency	Durability	Applicability
Alkaline	Average	4–6 $/kg H2	60–70%	High	Industrial applications
PEM	High	6–8 $/kg H2	65–80%	Average	Renewable energy
HTE	High	8–10 $/kg H2	80–90%	Low	Industrial applications

regarding efficiency metrics and cost implications. Despite HTE having the best efficiency, this method has a high price and, in the long term, has low durability. Although the choice of technology depends on the context of the application, alkaline electrolysis remains the most popular solution in terms of cost and scalability.

A recently developed green hydrogen production technology is Photoelectrochemical Hydrogen Production (PEC), which is based on the conversion of solar energy into chemical energy, but unfortunately, the technology required to use this method is not yet economically sustainable [60,68]. There are three main methods to produce solar hydrogen, as shown in Figure 7. The first method combines photovoltaic systems with electrolyzers, the second focuses on photoelectrochemical cells, and the third method involves photocatalytic systems with semiconductor particles. Although photoelectrochemical systems offer an excellent opportunity [69] to integrate renewable energy sources with hydrogen production methods, it is vital to fundamentally understand the processes, transport phenomena, thermodynamics, electrochemistry, engineering design, and performance evaluation.

Another popular type of hydrogen production is the biological mode, which can involve two pathways: water biophotolysis by algae and photofermentation by bacteria, generally using microorganisms [70], as indicated in Figure 8 [60]. The production of hydrogen by microorganisms has become of interest because of its potential as a renewable energy source, utilizing natural resources such as solar energy and water.

Dark fermentation [71,72], one of the most studied biological processes for hydrogen production, involves using anaerobic organisms to convert organic waste or wastewater into hydrogen. Although this method is promising for sustainable hydrogen production, it has limitations related to low yields. However, improving the technique by immobilizing microorganisms and carefully controlling operating conditions can increase production efficiency without depending on light [71].

Green microalgae and cyanobacteria are microorganisms that perform oxygenic photosynthesis, absorbing solar energy and converting it into chemical energy by decomposing water into molecular oxygen and protons [73]. Microalgae are considered a promising source of hydrogen-based energy; although this process is considered more efficient and less energy-intensive than traditional methods, high production costs currently limit its economic feasibility.

Consequently, there are numerous types of biological processes [74,75,76,77] for obtaining green hydrogen;

Table 3. Comparison of major biological methods to produce Green Hydrogen.

Production Methods	Efficiency	Advantages	Challenges
Dark fermentation	90%	Uses of organic waste	Requires product treatment
Microbial Electrolysis Cells	49.8%	Wastewater treatment integration	Dependence on an external energy source
Waste utilization	Positive net energy production	Reduced costs and waste management	Reactor complexity

gives an overview of the most relevant biological technologies in terms of yield, advantages, and main challenges encountered. To overcome potential factors, optimization of process parameters is necessary to scale up the technology. Although with technological advancement such challenges will eventually be overcome, for this method to be economically and environmentally feasible, a multidisciplinary approach is required. Production of green hydrogen by mass conversion, even though a sustainable method, is limited by high bioreactor costs, operating conditions, and toxicity of wastewater treatment effluents, and therefore, this method suffers from low yields and slow conversions [75].

The production of green hydrogen is under continuous development to make the transition to cleaner and more sustainable energy sources, and the current trend supports the implementation of innovative production methods to meet global carbon reduction targets.

For clearer insights into the relative benefits and drawbacks, using IEA data [8], a comparison of the main production techniques presented in this section in terms of energy consumption, efficiency, and current cost has been made in

Table 4. Comparison of production methods.

Production Methods	Energy Consumption	Efficiency	Cost
Electrolysis	High	60–80%	4–6 $/kg H2
PEC	Low	10–20%	10–15 $/kg H2
Biological	Very low	5–15%	10–25 $/kg H2

. The efficiency of electrolysis and PEC varies depending on the electrolyzer technology, and especially for PEC, it can be improved, while the biological method has a low efficiency, being still in the experimental stage of production. Although the cost of electrolysis is the lowest, it will continue to decrease with technological development. The costs for PEC and biological methods are high due to the complex technologies and the environmental control and maintenance requirements. Thus, although electrolysis has a high level of energy consumption, it remains the most efficient and lowest-cost method currently.

Recent technological advances in using renewable electricity to produce green hydrogen have opened new possibilities for reducing emissions and increasing the efficiency of this sustainable process. The main technological directions include advances in catalysts and electrode materials, optimization of electrolytes and electrolyzers, leading to cost reductions, and opening new perspectives for a wide range of industries.

The study of the environmental implications of green hydrogen production [78,79], including the use of water in electrolysis and the life cycle assessment of hydrogen systems, needs to be carefully evaluated, considering the water consumption required and energy efficiency as well as the indirect impact of production and recyclability of the materials used. Although the use of water in the electrolysis process does not directly emit greenhouse gases, this process requires a considerable amount of water, which is a pressure for more arid areas. The lifecycle of hydrogen systems is a defining parameter for impact analysis from the extraction of raw materials, production of equipment and facilities to the production and use of green hydrogen, and indirect emissions from the various processes associated with the electrolysis plant and the infrastructure need to be included, as well as the resulting waste and its recyclability.

4. Storage Methods

One challenge in the development of renewable energy technologies is the storage of green hydrogen, and the main methods of storing it are gas form, liquid form, solid form, methanol or ammonia, pumping, or others.

To better understand the advantages and disadvantages of the main hydrogen storage methods, a SWOT analysis (strengths, weaknesses, opportunities, and threats) was performed, illustrated in Figure 9.

Gas storage is the most common method of storing hydrogen. While this method has the advantage of existing infrastructure, it requires expensive equipment and has safety risks due to the flammability and explosibility of hydrogen [80].

Liquid storage allows the hydrogen to be compressed, which means more hydrogen can be stored in a smaller volume but requires higher cooling and storage costs, advanced technology, and increased security. The materials analyzed for liquid-phase hydrogen storage offer high hydrogen content, and although each material has advantages and disadvantages, they perform well at moderate temperatures, unlike other methods that require high temperatures to produce hydrogen [81].

Compared to gaseous or liquid hydrogen, storage in solids offers better safety and has a higher storage capacity per unit volume. However, materials are expensive to manufacture, and there are several limitations on operating temperatures and pressure. There are new solutions, such as complex metal hydrides and intermetallic compounds, which can absorb and release hydrogen through chemical or physical reactions. In addition, nanotechnology can improve material properties by manipulation at the atomic level [60,82].

Pumped storage is an indirect method of energy storage where excess renewable energy is used to produce hydrogen again. The main advantage is the use of excess renewable energy, but it has a lower energy efficiency compared to other direct storage methods. This method has also gained popularity due to its flexibility, long lifetime, and high efficiency [83].

Using IEA data [8], a comparison of the storage costs and the levelized cost of hydrogen (LCOH) in the storage methods presented above was performed, as in

Table 5. Comparison of storage methods.

Storage Methods	Storage Cost	LCOH	Safety Protocols
Liquid	3–6 $/kg H2	8–12 $/kg H2	Thermal insulation Pressure check Emergency equipment
Solid	4–7 $/kg H2	9–14 $/kg H2	Temperature check Material integrity check Safe protection against chemical reaction hazards
Gas	1–2 $/kg H2	5–8 $/kg H2	Pressure check Ventilation Verification Verification of the structural integrity of tanks
Pumped	≤1 $/kg H2	3–6 $/kg H2	Checking structural integrity Ventilation Verification Gas Detection

. Pumped storage is the most recommended method from the cost point of view for large quantities, while storage in gaseous form is the most suitable method for the short term, being an affordable option. Safety protocols for storage methods are essential to prevent fires, leaks, or even explosions [84,85] and depend on several international regulations concerning the operation and maintenance of equipment, as well as training of staff in emergency measures.

Around the world, projects are underway to develop hydrogen storage methods. As presented in [80], the project funded by the German Federal Ministry explores and demonstrates the large-scale production of hydrogen from renewable sources, while the project developed by Europa supports the energy transition and emission reduction by comparing the energy efficiency and carbon footprint of liquefied hydrogen and ammonia. Other projects in North America, the UK, and France are exploring green hydrogen storage, including salt caverns and the use of ammonia as a hydrogen carrier.

An example of a project investigating long-term underground storage and integration into energy grids is the HyUnder project for deployment in geologically prospective regions in Europe. It was based on four key elements, namely integration of hydrogen into the natural gas grid, early market, established market, and transportation. Referring to Spain, which has a high potential in terms of renewable energy sources [86], several locations suitable to produce green hydrogen have been identified in the project, and a financial analysis has been carried out, which showed that the cost for the construction of caverns is insignificant in addition to the price of the electrolyzers. With their technological development, this solution will become a viable solution both from a technological and environmental point of view, as well as economically.

Another example of a project related to storage in metallic hydrides is the HyCARE project implemented in European countries, which aimed to create a tank for the storage of green hydrogen. Within the project, it was concluded that this type of storage depends on the synthesis method [87] and that the use of qualitative raw materials will increase the production price. However, this method has a few advantages, among which are the safety of storage, energy efficiency, large storage quantity, recyclability, and long-term cost reduction.

Potential technological breakthroughs could overcome current storage limitations, such as advances in materials science or nanotechnology, from the viewpoint of cost, efficiency, and safety. A direction might be the study of metal oxides [88] that can store green hydrogen and represent a cheaper alternative to metal hydrides; the transportation can be performed in conditions of increased safety and efficiency and is easier to implement in industrial applications.

Thus, there are various options for hydrogen storage and development in cryogenic compression and liquefaction, and the use of functionalized adsorbent materials for hydrogen storage continues to emerge [80,83]. Even though hydrogen technology is a clean and renewable energy source, it has many advantages, but it also has some disadvantages in terms of cost and required technologies. Therefore, a hydrogen storage method that is suitable and safe must be sought.

5. Cost Impact

Hydrogen could play an important role in the coming years in decarbonizing the energy sector, but it requires significant investment in both the development of the necessary technologies and infrastructure. According to information released by The Energy Futures Initiative (EFI) and the King Abdullah Petroleum Studies and Research Center (KAPSARC) in the Global Hydrogen Future report, the hydrogen market could grow to $250 billion by 2030 and even $1 trillion by 2050 [89]. However, the green hydrogen industry is struggling with major challenges related to high costs and technology dependence.

Improving the sustainability of renewable hydrogen production systems [90] is thus crucial for cost reduction as it allows costs to be spread over a larger production volume, and technology and political support are essential in this process. Therefore, minimizing the use of rare materials and systems development are key directions for cost reduction.

Countries with good wind resources, as presented in [91], depend on good photovoltaic resources to achieve cost competitiveness, as photovoltaic potential remains a key component for cost reduction due to the possibility of direct use of energy for electrolysis instead of electricity storage and distribution, leading to cost reduction. Therefore, to facilitate the widespread adoption of hydrogen, infrastructure must be developed, production accelerated, and demand for green hydrogen will peak when it is competitively priced [92].

To be able to determine the final cost of green hydrogen, it is necessary to establish the cost of three main components, as shown in Figure 10, namely the cost of production, the cost of storage, and the cost of distribution. Another set of factors to be included in determining the cost is the market price and demand, investment costs, and supply costs. However, the price of producing energy from renewable sources is continuously decreasing, which is driving down the price of hydrogen from electrolysis [93,94,95,96,97].

Hydrogen is difficult to store because of its properties. There are three main methods of storing hydrogen: high pressure, low pressure, and cryogenic storage.

In the transportation industry, the size-related characteristic of the final product is one of the main factors, and in this direction, the volume-related problems imposed using hydrogen should be properly handled. The storage of hydrogen in liquid form reduces volumetric density issues as opposed to gaseous. However, storage in gaseous form presents price benefits [94,95].

One type of long-term, safe, and low-cost storage is geologic storage [98,99]. The barriers encountered in this method are limited experience, the necessary regulations, the presence of microorganisms, and possible problems with the interaction of hydrogen with the storage site.

Other viable solutions for storage are hydrogen storage in high-pressure tanks, chemical storage, or metal hydride [99,100], and although the cost of implementing the necessary systems varies due to the technologies and regulations required, according to the Energy Earth shots program, the price of green hydrogen is expected to drop to $1/kg in the future [101]. Chemical storage has many advantages, as it is compatible with fossil fuel infrastructure and is characterized by its recyclability [99]. The decreasing price of electrochemical technology is a key factor in the development of clean hydrogen systems [102]. For hydrogen storage, formic acid is a preferred material [103] due to its characteristics, but specific policies should be developed to improve its long-term stability and durability. Thus, each storage method has its advantages and disadvantages, and the choice of storage form depends on the destination.

The production costs of green hydrogen are also divided into three main branches, namely, the cost of electricity, the cost of electrolyzers or costs related to the production method, and the cost of the green hydrogen plant. By harnessing the production of hydrogen through electrolysis, oxygen can be sold to different industries due to its characteristics, and thus, the cost of producing green hydrogen will decrease. However, as presented [104], electricity prices need to decline below 22 USD/MWh for green hydrogen production to be able to compete with the rest of the combustible type.

A challenge for green hydrogen is to choose a production method that fulfills the end goal, meets safety requirements, and is cost-effective. The cost of electrolysis, one of the most widely used methods, varies depending on the type of electrolyzer and the installation costs, being one of the most expensive technologies [105,106,107,108]. Although the gasification process of biomass has lower energy compared to fermentation, the cost of this method is lower and the efficiency higher [106].

In a study by Kirchem and Schill [109], an analysis of the cost requirements for the energy sector related to green hydrogen in Germany is carried out, and an assessment of the production cost shows that average electricity prices play a key role in determining the cost of hydrogen production. Thus, the expansion of renewable energy is essential, but this depends on technological constraints and the potential for source expansion.

At the national level, the development of a large-scale hydrogen production and distribution network is preferred [93] due to the savings on the total price, although the storage costs would be higher due to the size of the tanks.

From an economic point of view, the transportation of hydrogen plays an important role and should be chosen according to the state of the hydrogen. For example, gaseous hydrogen transportation by pipelines and liquid hydrogen transportation by road is recommended [105].

For the moment [93,94], the transportation of green hydrogen by pipelines is the most economical solution; due to the long time needed to develop these networks, transportation by trailers would be a much more feasible solution. Related to transportation, the main advantage of using hydrogen is that existing infrastructure can be used.

The cost of hydrogen is also influenced by the renewable energy source [96,110,111,112,113]. For example, both photovoltaic and solar thermal systems require difficult spatial conditions, whereas hydroelectric, geothermal, and biomass energy sources are more efficient for this reason [96].

A study of a solar-powered building [111] in an energy-intensive city in Kuwait indicates that a system of photovoltaic panels and solar collectors could completely cover energy needs and contribute significantly to reducing carbon emissions. Optimization of electrolysis systems [112] according to the type of renewable energy can boost the economic efficiency of green hydrogen production by integrating systems in strategic locations and by conducting an analysis of the factors influencing production costs.

Another study related to wind energy in SUS [113] implies that by 2020, wind energy will account for almost 8% of the total energy produced [114] and that several areas that are not considered good wind resources can be revisited [115], and together with the development of technology, this percentage will increase substantially.

Furthermore, regarding the projection of green hydrogen produced from wind farms, a diagram is presented in Figure 11 for the year 2021, compared to 2020, at the European level, based on information provided by Statista [34] in which the cost for green hydrogen production and breakeven power price is evaluated. Green hydrogen could be sold for EUR 5.1 per kilogram by 2021, while by 2030 it could fall to as low as EUR 3.7 per kilogram.

In various locations [116,117,118], a feasible alternative to electricity infrastructure is wind energy conversion due to the expected cost savings for electrolyzers and the fact that hydrogen allows long-distance transportation. Results of a study [119] for energy systems in remote Japanese islands offer new perspectives for the development of seawater electrolysis technologies and show the efficiency and economic viability of this system, emphasizing that the use of surplus electricity can lead to significant reductions in total costs.

The deciding factors [120,121] for investing in green hydrogen are production, storage, and logistics, and their influence can affect the efficiency and success of this direction for reducing carbon emissions.

In this context, Figure 12, based on data provided by Statista [34], shows the investments needed for green hydrogen worldwide to mitigate the effects of climate change. The largest investment is needed for production and technology development. Also, investments need to be made in transportation methods and logistics needed to reach the destination, and thus, the final price will decrease, and this directive will be feasible. Although the initial investment will be large, the investment in this directive is profitable and can be recovered in a few years or, in some cases, 2 to 4 years [122].

Therefore, the cost of green hydrogen can be influenced by a number of technological, economic, and environmental factors, and as regulations and technological advances emerge, it will be an economically viable alternative for the transition to a sustainable energy economy.

6. Future Perspectives for Green Hydrogen

Overcoming economic and regulatory barriers can lead the hydrogen industry to a window of valuable opportunities in the fight against the climate and energy crisis and can play a crucial role in energy storage, helping to manage the challenges caused by intermittent renewables [123]. The future of hydrogen includes a wide range of industries, such as steel production, thermal industry, household, and energy conversion, and by 2050, the demand for hydrogen is expected to increase 7 times [124] in these industries.

The IEA report “The Future of Hydrogen” [125] sets out several recommendations for the long-term expansion of the clean hydrogen industry, including raising awareness of the risks, stimulating demand, tracking progress, removing barriers, and developing standards.

Hydrogen could be a step forward for a green society, but this requires technological development, low prices, and an expansion of the production, storage, and logistics network [96,126,127,128,129]. Although several countries have already invested in green hydrogen, more funding and government support are still needed to reach the goal of carbon zero by 2050 [127], and research needs to be accelerated to make hydrogen a viable alternative to traditional fuels.

Policies promoting green hydrogen have become a key pillar for the energy transition in many leading countries, such as Germany, China, Japan, South Korea, and the United States. As a result, well-defined national strategies have been adopted to develop green hydrogen production, transportation, and storage technologies and to attract funding from both public and private investors. These pilot projects outline the importance of developing clear strategies and financial support. Also, creating partnerships between the government, private sector, industry, and academia can accelerate research and deployment of new technologies.

Emerging technologies for green hydrogen are essential to improving the efficiency of its production, storage, and utilization. Improvements in electrolysis processes, the development of nanomaterials and catalysts, storage in metal hydrides, storage in ammonia, and the investigation of cryogenic storage are all contributing to the transition to green hydrogen in a much faster timeframe. Also, new technologies for the direct conversion of solar energy into hydrogen, as well as the use of artificial intelligence in hydrogen management, are under continuous investigation.

According to Hydrogen for Net-Zero [92], at the end of 2021, there were 522 large-scale projects announced to be implemented by 2030, but these are the only publicly announced projects. These projects are shown in Figure 13, and we can see that most projects are in European areas, succeeded by Asia and China.

Of the total number of projects, about 70% will be commissioned before 2030, and in Europe, of the total number of projects, 16 will be giga-scale, and it could be more because early-stage projects have not been announced and are not included in Figure 13 [92].

China has set the goal of becoming a carbon-neutral country by 2060 [130,131,132] and to achieve this goal, it is focused on implementing renewable energy projects that mainly involve hydrogen. Research conducted by Taghizadeh-Hesary F. et al. [131] has outlined that projects involving green hydrogen currently represent a financing risk and that finding solutions to reduce this risk is essential to achieve the goals of neutrality.

In terms of hydrogen storage and logistics, the United States has advanced facilities but faces challenges for long-term grid expansion due to renewable energy capacity. However, the drive governed by ambitious policies aims to reduce the cost of production [133].

A series of advances are yet to be made in manufacturing processes, but also in materials science [134,135], and together with integration into complex energy systems will maximize the potential of green hydrogen. Pilot, experimental, and commercial projects can help to overcome barriers and provide a pathway for the widespread use of these systems.

The study by Kopteva A. and all [136] shows that pilot projects, such as the one in the Magadan region of Russia, can produce green hydrogen, but the economic efficiency is limited due to high production and transportation costs, and the investment can be recovered only after a long period. The pilot project implemented in Russia can be a starting point for resource-based countries in energy transition processes and similar climate conditions.

A projection of green hydrogen production by the International Energy Agency (IEA), Hydrogen Council, International Renewable Energy Agency (IRENA), and Bloomberg New Energy Finance (BloombergNEF) for 2050 in million metric tons is presented in Figure 14. The highest estimate comes from BloombergNEF, which supports the idea that as the price of electrolysis falls, green hydrogen will become increasingly competitive. Although it is anticipated that production prices will decrease due to technological advances resulting from research conducted in this area [137], initial installation prices are currently high.

Furthermore, a technical, economic, and social analysis [138,139] shows that centralized production must be linked to distributed production. At the urban level, distributed generation can contribute to economic solutions for households and reduce the carbon footprint of urban services. Thus, these aspects must be considered in future energy policies to optimize the social utility of the hydrogen economy.

Figure 15 offers a perspective on the potential for green hydrogen production by 2050 for several regions using Statista data [4]. Sub-Saharan Africa and America are the regions with the greatest potential to produce cost-effective green hydrogen.

A multi-disciplinary approach [140,141], both technological advances, spatial analysis for land use, and water resource evaluation in Sub-Saharan Africa represents a viable pathway towards sustainable yield as it is a very promising region for green hydrogen production given its huge renewable energy resources.

In the transition to renewables, green hydrogen can create a bridge between Europe and Africa due to the potential for exports, especially from North Africa. Countries with abundant renewable resources present an advantage for hydrogen production, especially countries that already have an advanced natural gas offense that can also be used for hydrogen [142].

Even though many projects to accelerate the hydrogen industry have emerged in recent years, more and more countries are supporting this direction, and every hydrogen application can contribute to the carbon neutrality goal further, the industry still faces some challenges. The IEA proposes four value chains [125] to contribute to the 2030 targets, presented in Figure 16, such as opening doors to low-cost hydrogen hubs, expanding supply, achieving adequate scale for competitive fuel cell and refueling vehicles, and starting international hydrogen trade on the global market. Thus, the diversification of the application areas of green hydrogen will lead to an increase in offers, and the gas infrastructure will contribute to the short-term goal of expanding the network.

Currently, there are advances in the hydrogen vehicle industry [125,143,144], but there is a desire to expand production to increase demand and lower the price in the long term. In this direction, various national governments have ambitious 2030 targets for the vehicle industry that could lead to achieving these goals.

Hydrogen transportation between countries is an opportunity to be seized, and investments in infrastructure will have the greatest impact if they are in regions with the greatest potential for hydrogen imports and exports. Thus, the development of the hydrogen industry must be stepped up for the world to be fully decarbonized by 2050 [145], in which international and long-distance transport will be a necessary tool to facilitate hydrogen uptake.

The cost of hydrogen production varies between regions [104,125,146], with Europe and Japan having relatively high costs and hydrogen imports can help maintain energy security in a low-carbon future. In contrast, in China hydrogen production is much cheaper due to significant investments in renewable energy.

Although there are a number of ambitious plans to scale up hydrogen, it remains to be seen whether they will be implemented on time and the allocated budget will reach [147] due to the barriers that still exist. The development of electrolyzers and the reduction of their price is a possible solution for a rapid decrease in the producer price and in increasing the competitiveness of green hydrogen.

7. Conclusions

Concerns about climate change have grown in recent times, and together with concerns about the sustainability of fossil fuel use, have led to the need to invest in and develop low-carbon technologies to maintain global security.

The advantages of green hydrogen production support global trends regarding reducing carbon emissions and energy dependence, although it faces disadvantages related to the lack of adequate infrastructure for production, storage, and distribution, as well as climate change that may affect the availability of renewable energy sources.

Green hydrogen is a promising solution to current energy challenges; although it faces many difficulties, future forecasts predict a significant increase in demand and production. In addition, investment in innovative technologies and continued research, together with government support, can transform the green hydrogen industry, contributing to a more sustainable energy future.

Predictions and trends for green hydrogen point to a significant increase in its production and use in the coming decades, supported by technological innovation, increased demand, and supportive policies, and this transition is essential to achieve decarbonization and a sustainable energy economy.

One of the main factors limiting the expansion of the clean hydrogen industry is the costs associated with its use in the depletion of fossil fuels, but it is expected that as the benefits of hydrogen use become more widely recognized and more economically viable, advanced technologies emerge, more countries will invest in using this technology.

In the context of the circular economy, the role of hydrogen can provide a solution for waste reduction and resource recovery, contributing to a more sustainable and efficient economic system. The circular nature of the economy based on the principle of waste reduction and resource recovery can minimize environmental impacts and support sustainable development, such as recycling organic waste to produce green hydrogen through anaerobic fermentation or producing hydrogen from biomass through gasification or steam reforming processes.

Linking regions with high renewable potential with those with lower potential through a hydrogen transportation infrastructure, as well as investing in advanced energy storage technologies such as high-capacity batteries or storing hydrogen in liquid or chemical compound form, are solutions to the problems of regional disparity. Consequently, some regions will have to depend on advanced technological solutions and infrastructure to overcome these limitations and ensure more equitable access to this clean form of energy.

Thus, green hydrogen is being promoted as a solution to decarbonize the economy (transport, heating, and industry), being presented as the clean replacement for fossil gases, but there are limitations to hydrogen, as presented in this paper, due to the technologies and infrastructure required.