The temporal and spatial characteristics of seasonal hydrogen storage will play a very important role in the coupling of multi-energy systems. This essay believes that there are several key issues worth noting in the seasonal hydrogen storage coupled multi-energy system, namely, hydrogen storage methods, coupling models, and benefit evaluation. Through research, this article innovatively divides seasonal hydrogen storage into two types: space transfer hydrogen storage technology and time transfer physical property conversion hydrogen storage technology. Then sort out the two most typical seasonal hydrogen storage multi-energy system application scenarios and their hydrogen storage unit models. Finally, it is shown that hydrogen storage methods should be selected according to different periods of time and regions, and the benefits should be evaluated before they can be used in practice. This review study is applicable to the process of coupling seasonal hydrogen storage in multi-energy systems. Hydrogen energy is used as an intermediate energy link for the selection, evaluation and modeling of the optimal selection and rational utilization.
The energy transition problem based on renewable energy and the realization of large-scale decarbonization and temperature control goals mentioned in the Paris Agreement are the two major challenges facing China’s energy industry. Therefore, hydrogen energy storage, which has the advantages of clean, flexible, sustainable, and diverse storage methods, has emerged. People have made technological breakthroughs in hydrogen production, storage, transportation and other links, so that hydrogen energy has become an important form of supplementary energy. As an energy carrier or raw material, hydrogen energy not only has significant advantages in dealing with the problem of mismatch between wind/photovoltaic power generation and electricity load, but also has a wide range of uses, either directly entering the hydrogen industry chain, or entering hydrogen refueling stations through transportation to supply fuel cell vehicles, or converted into electricity and heat for users [
On the one hand, the energy storage methods involved in the current power system mainly solve short-term-scale problems, such as intra-day peak regulation, frequency modulation, and grade climbing, but it is difficult to overcome long-term power fluctuations and maximize the use of renewable energy. On the other hand, as the installed capacity of renewable energy increases, the imbalance between load and renewable energy output has become increasingly prominent.
Multi-energy System refers to a new energy system view formed by coupling multiple energy systems such as cold, heat, electricity, and gas in the links of energy production, transmission, and use. From the perspective of operational planning, the interaction between energy departments is currently becoming more frequent. For example, in most cases, electricity, cooling/heating, and natural gas networks interact through various distributed technologies. Similarly, the interaction between the electricity, fuel chain, and transportation sectors has also been carried out through the transportation of electric vehicles, biofuels, and hydrogen. Based on these, the key to the study of a multi-energy system for cross-season hydrogen storage is to start with hydrogen storage methods, coupling models, and benefit evaluation. Combine seasonal hydrogen storage with multi-energy systems to realize a regional-scale energy management system, and create new value for improving the coupling and reliability of the energy system, reducing carbon emissions and improving economy.
Regarding the hydrogen storage technology coupled in the multi-energy system, scholars at home and abroad have carried out relevant research, but the advantages of long-term storage of hydrogen energy have not been well utilized. For multi-energy systems containing hydrogen storage units, domestic scholars have made a lot of research results. In the technical field, Liu et al. [
Research on hydrogen storage technology is more advanced in Japan, the United States and Europe, especially the research on seasonal time scale hydrogen storage systems, which have relatively mature research results abroad. In view of the differences in resource conditions and grid structures in different regions, seasonal hydrogen storage is generally based on specific regions for research. Vogt et al. [
For multi-energy systems, seasonal hydrogen storage will actually achieve good results. However, judging from a large amount of literature, people have not classified them according to the characteristics of hydrogen energy, so that they can be better coupled to the energy system and give play to the greatest advantages of hydrogen storage units. Therefore, this article innovatively believes that seasonal hydrogen storage should be classified according to two key characteristics of space transfer and time transfer, and then used in different regions and scenarios.
Seasonal energy storage needs to solve the following problems: suppress the imbalance of power supply and demand on a long-term scale; when coordinated with short-term energy storage, it can make up for the limited scale of short-term energy storage capacity, peak shaving and energy transfer capabilities; and when renewable energy is coordinated with each other, it can cooperate to achieve efficient consumption of renewable energy and enhance system flexibility. Therefore, based on the two storage characteristics of hydrogen energy that are transferable in space and transferable in time, this paper proposes that seasonal hydrogen storage is more appropriate for long-term energy storage in a multi-energy system.
On the one hand, seasonal hydrogen storage is based on the phenomenon that the electricity and heat load in spring and autumn are less than that in winter and summer. It can achieve long-term energy translation, smooth power fluctuations, and solve the imbalance between renewable energy output and seasonal load. Therefore, the hydrogen storage technology has high requirements on the time scale, which not only requires low self-loss rate of energy storage equipment when it is not used for a long time, but also requires high energy round-trip efficiency. Compared with short-term energy storage, its efficiency characteristic curve is shown in
On the other hand, current technology cannot directly store the electricity converted from renewable energy for a long time, and usually needs to be converted into other forms of energy. Through the establishment of electricity-heat, electricity-gas or electricity-hydrogen conversion forms, the power system can be coupled with other energy systems, and the supply and demand balance and energy translation of renewable energy can be realized in a wider range of energy systems. So in order to meet the above characteristics, it is necessary to select an appropriate hydrogen storage method, and to make reasonable planning and optimization in energy system planning.
The hydrogen energy described in this article comes from the technology of water electrolysis. The surplus electricity from wind power, photovoltaic power or part of nuclear power is electrolyzed into hydrogen gas, and then the hydrogen is stored through advanced storage technology. When electricity is needed, the stored hydrogen is converted into electrical energy and sent to the Internet through different methods; or carbon dioxide is methanated for use in the gas system. The latter uses hydrogen as the medium to bridge the gap between the traditional power system and the natural gas system, making the bidirectional flow of power and natural gas energy a possibility, which is the energy complementation and interoperability advocated by the multi-energy system. It not only promotes the deep integration of gas and electricity networks, but also provides a good way to solve the volatility of renewable energy development. The following innovatively divide hydrogen storage technology into two types: space transfer and time transfer hydrogen storage technology. Then select suitable hydrogen storage methods based on the above-mentioned long-term, cross-energy form seasonal characteristics.
The space transfer type hydrogen storage technology described in this article includes three types: underground salt cavern hydrogen storage, physical adsorption hydrogen storage, and glass microsphere hydrogen storage, mainly storing hydrogen through different physical spaces. Hydrogen storage in underground salt caverns is mostly suitable for on-site consumption due to its special geological conditions. Physical adsorption and hydrogen storage in glass microspheres can be used for spatial scheduling, but due to capacity limitations, they are temporarily not used in multi-energy systems. Therefore, only a brief introduction is given. Further development requires further breakthroughs in cost and technology.
Underground hydrogen storage (UHS) technology was proposed by Gregory [
On the one hand, the development of underground hydrogen storage technology is related to the large-scale use of hydrogen energy and the volatility of hydrogen demand; on the other hand, it can convert excess renewable energy into hydrogen energy for storage. The salt cavern storage technology and operating conditions of hydrogen are similar to those of natural gas underground storage, and the volumetric energy density of hydrogen is almost one third of that of natural gas. So gaseous hydrogen storage is more expensive than natural gas storage [
The characteristics of underground storage in different regions are different. In response to this situation, domestic and foreign researchers have made preliminary explorations on underground hydrogen storage technologies in different regions. Bai et al. [
The principle of physical adsorption hydrogen storage is to use the van der Waals force of different materials to adsorb hydrogen on a porous structure with a high specific surface area. Its characteristics are simple storage method, fast hydrogen absorption and desorption speed, and low activation energy. The main materials are carbon-based materials, metal organic framework materials, mineral porous materials and microporous polymer materials.
Carbon-based hydrogen storage materials include activated carbon (AC), graphite nanofiber (GNF), carbon nanotube (CNT) and carbon nanofiber (CNF) [
Name of the material | Fahrenheit/K | Pressure/MPa | Mass density | Economy |
---|---|---|---|---|
Activated carbon | 77 | 2–4 | 5.3–7.4 | Compared with compressed hydrogen storage, it saves hydrogen compression cost.Compared with liquid hydrogen, the cost of liquefaction is saved. Activated carbon has a long life, and based on current technology, super activated carbon can be produced on a large scale. |
93 | 6 | 9.8 | ||
Graphite nanofiber | indoor temperature | 7.04 | 3.8 | |
25 | 12 | 67 | ||
Carbon nanotube | indoor temperature | 11 | 12 | |
indoor temperature | 10/12 | 10 | ||
298 | 10–12 | 4.2 | ||
Carbon nanofiber | 80 | 12 | 8.25 | |
indoor temperature | 0.05 | 6.5 |
The metal-organic framework is a 3D framework structure formed by the coordination of metal ions through rigid organic ligands. The material has the advantages of strong structural design, low density, large specific surface area and pore volume, and high spatial regularity. Sagara et al. [
Inorganic porous materials refer to porous materials with nano-pores in the structure, and representative materials are zeolite, sepiolite, etc. The results of Jhung et al. [
Hollow glass microspheres are non-permeable under low temperature, but are porous under high temperature. Hydrogen can enter the glass body under certain temperature and pressure conditions. As the temperature drops to room temperature or below, the hydrogen stays in the glass sphere. Similarly, hydrogen can be released as the temperature rises. The outer diameter of the hollow glass microsphere (HGM) is generally on the order of millimeters or sub-millimeters, and the wall thickness is from a few microns to tens of microns. The main component of the spherical shell is SO2, which also contains elements such as K, Na and B, and its hydrogen storage capacity is above 15 wt%. The material has the special properties of hollow structure and pore wall structure, so it provides some possibilities for preparing materials with different functions. Rapp et al. [
The focus of long-term physical property conversion hydrogen storage technology is to change the physical state or chemical properties of hydrogen through compression, liquefaction, or complex hydride, so that it can be stored for a long time for cross-season applications. This article focuses on hydrogen storage technologies such as high-pressure gaseous, low-temperature liquefaction, complex hydrides, and organic hydrides.
The main advantages of high-pressure gaseous hydrogen storage are low storage energy consumption, low cost, fast hydrogen charging and discharging speed, and relatively mature technology; the disadvantages are low volumetric hydrogen storage density, small volumetric capacity, and potential leakage risks. The current technological breakthrough lies in the improvement of the material of the storage tank, and development in the direction of lighter weight, higher pressure, and further improvement of the mass density of hydrogen storage under the premise of ensuring safety performance. Of course, when considering economic issues, it’s not that the higher the pressure, the better. For example, under the condition of 70 MPa, the hydrogen storage tank and the pressure are no longer in a linear relationship, and doubling the pressure can only increase the hydrogen storage capacity by 40%−50%. Furthermore, as the pressure increases, the requirements for the wall thickness and pressure-bearing capacity of the tank also increase, resulting in an increase in the weight of the container and a reduction in the efficiency of hydrogen storage. Through calculation, it is most in line with economic benefits when it is around 55–60 MPa [
At present, the materials for high-pressure gaseous hydrogen storage tanks are mainly aluminum liner fiber winding and plastic liner fiber winding. A typical domestic company is Sinoma Technology (Chengdu), which mainly produces three-type hydrogen storage tanks with aluminum inner tank and carbon fiber winding. The product has high safety performance, and the inner tank adopts the aluminum sheet stretching forming process. Compared with aluminum tube forming, the inner and outer surfaces of the sheet-formed inner liner are smoother, the inner liner fibers are tighter, the fatigue performance of the product is greatly improved, and the consistency is good, and it is expected to reach 70 MPa working pressure. The 70 MPa high-pressure hydrogen storage tank of Toyota of Japan is used in commercial fuel cell models, as shown in
The main advantages of liquefied hydrogen storage are high density, high purity, large volumetric capacity, simple storage and transportation, etc.; the disadvantages are high energy consumption, volatility, and high cost in the liquefaction process. The liquid hydrogen storage tank is generally divided into two layers inside and outside. The inner tank contains pure liquid hydrogen cooled to 20 K, and a support made of glass fiber tape is placed in the center of the outer shell. The support has good thermal insulation, and the multilayer aluminized polyester film in the middle of the sandwich is used to reduce heat radiation. The tank liner is generally made of aluminum alloy, stainless steel and other materials, and the outer shell is generally made of low-carbon steel, stainless steel and other materials, and aluminum alloy materials can also be used to reduce the weight of the container [
Liquid hydrogen storage and transportation has always been a research hotspot in various countries. In recent years, Japan, the United States, Germany and other countries have reduced the transportation cost of liquid hydrogen to about one-eighth of high-pressure hydrogen. At present, the world’s largest cryogenic liquefied hydrogen storage tank is located at the Kennedy Space Center in the United States, with a volume of 112 × 104 L. However, in order to ensure low temperature and high-pressure conditions, liquid hydrogen storage not only has requirements on the tank material, but also needs to have a strict insulation scheme and cooling equipment. Therefore, the volume of storage tank for cryogenic liquefied hydrogen storage is generally small, and the mass density of hydrogen is about 10% [
With the development of chemical and physical technology, people not only use the transformation between gas, liquid and solid, but also use complexes and organic hydrides to store hydrogen energy. The hydrogen storage of complex hydrides originated from the high hydrogen content of boron hydride complexes. Japanese researchers first developed complex hydrogen storage materials such as sodium borohydride and potassium borohydride, which can produce hydrogen storage materials that are higher than their own through hydrolysis reactions. Hydrogen with a lot of hydrogen. Lin et al. [
Liquid organic hydride hydrogen storage technology is realized by a pair of reversible reactions between some alkenes, alkynes or aromatic hydrocarbons and hydrogen. At present, there are more hydrogen storage media reported in the literature: C6H12 [
Hydrogen storage technology | Volumetric capacity | Cost | Security | Transportation convenience | Technical maturity | Application |
---|---|---|---|---|---|---|
Low temperature liquid hydrogen storage | Large | high | poor | convenient | immature | Aerospace, electronics, transportation, etc. |
High pressure gaseous hydrogen storage | small | low | poor | more convenient | mature | Most hydrogen industries, such as automotive, chemical, transportation |
Metal hydride | large | low | safety | most convenient | mature | Military (submarine, ship, etc.) |
Organic liquid hydrogen storage | large | high | safety | most convenient | immature | Automotive sector, transportation, etc. |
Cost is one of the key factors in choosing hydrogen storage technology. The research report “Hydrogen: The Economics of Storage” released by Bloomberg New Energy Finance gives the storage costs of various hydrogen storage technologies in different cycles, the specific comparison results are shown in
Combining the above hydrogen storage technologies and screening the key factors of seasonal hydrogen storage, this paper sorts out two typical scenarios of seasonal hydrogen storage multi-energy systems. The first is to use salt cavern hydrogen storage as a seasonal hydrogen storage method for multi-energy systems when geological conditions permit. The schematic diagram of the structure is shown in
In recent years, salt caverns have been researched and applied as natural gas storage. When the cave is storing natural gas, the state of the surrounding salt rock has also been analyzed in detail by many researchers [ 1) The mass balance in the cave describes the dynamics of hydrogen in the cave: 2) The mass balance of the salt rock, described as a porous medium: 3) Momentum balance of salt rock:
In order to simplify the numerical solution and lay the foundation for the optimization model, after using the continuous equation, the dimensionless parameters are introduced. According to different constant parameters, three different types of hydrogen storage areas are obtained. The salt cave (Zone 1) is characterized by a linear distribution of pressure in the cave, and similar pressure changes are found throughout the rock area, similar to a sealed tank; On the contrary, the reservoir (Zone 2) is affected by the obvious penetration of H2 through the rock formation, forming a nonlinear profile at all stages of the entire cycle. In addition, due to the relatively large porosity and permeability, the pressure change in the reservoir area with time is limited, and the maximum change is less than 1 bar, which has no effect at the end of the area. Zone 3 ignores the rocky area and treats the cave as an impermeable storage tank.
Different from underground hydrogen storage modeling, the P2H model needs to consider the mutual conversion of multiple energy forms while meeting long-term storage. The P2H model established by Gabrielli et al. [
When
Ivalin et al. [
The existing analysis methods of seasonal hydrogen storage are mostly based on traditional short-term energy storage mathematical models. For example, extend the time scale of energy storage to monthly or quarterly, and then establish a coupling relationship between adjacent periods to reflect long-term energy storage behavior. Jiang et al. [
In order to combine other key components and equipment for hydrogen production and hydrogen storage, the mathematical linear models described in the previous section need to be combined with the schematic diagrams of the multi-energy system shown in
As of the previous section, the system has been described as considering an hourly resolution optimization problem with a one-year time interval, namely T = 8760 h. However, the traditional MILP mentioned above cannot include seasonal storage, and when choosing different technical equipment, a large number of variables and constraints will be generated, making comprehensive optimization almost impossible. Pfenninger [
Based on this, Gabrielli et al. [
where
Due to the difference in seasonal load demand of multi-energy systems, as well as the randomness and indirectness of renewable energy, the demand for seasonal hydrogen storage capacity is very large. The investment and planning of seasonal hydrogen storage requires detailed demand analysis and benefit evaluation to balance the sufficiency of system capacity and investment economy, and to achieve a reasonable allocation of seasonal hydrogen storage. According to different resource conditions, installed capacity, and load requirements in different regions, the size of energy storage capacity is also different. Therefore, scholars usually conduct seasonal hydrogen storage research on multi-energy systems for specific regions or design parameters. Gabrielli et al. [
The key driving force of hydrogen storage is the excess of renewable energy generation. Therefore, in the context of the rapid development of renewable energy, the conversion of excess energy into hydrogen has been recognized by many countries in the world. On the one hand, the seasonal hydrogen storage multi-energy system can coordinate multiple energy forms and utilize the complex coupling relationship between various links to make electricity, heat, natural gas and other systems interconnected and develop into an organic whole, thereby making the energy system more flexible; On the other hand, it can also promote the stable operation of multiple energy systems and achieve large-scale decarbonization and temperature control goals.
This article analyzes the characteristics of multi-energy systems and hydrogen storage through literature reading, and proposes two seasonal hydrogen storage modes suitable for multi-energy systems: One is underground hydrogen storage. Its advantage is not only the convenience of large-scale long-term storage, but also the potential for zero carbon emissions when renewable energy power generation and energy demand have the same seasonal dynamics; The other is the P2H system, which has the advantage of a wide range of applications, especially suitable for smooth wind power generation [
Seasonal hydrogen storage provides a viable option for solving the intermittent problem of renewable energy, and the wider the scope of implementation, the more significant the effect of reducing carbon emissions and balancing energy supply and demand throughout the year. At present, more and more large-scale hydrogen-based energy storage demonstration projects are planned, promoted and implemented globally, including Germany, Denmark, and Japan. As the proportion of renewable energy sources increases, hydrogen energy as a long-term energy storage method is expected to accelerate its development and implementation. It is speculated that the cost of hydrogen storage in salt caverns is expected to drop to 140 Euro/MWh in 2030, which is even lower than the predicted cost of pumped storage. This article is suitable for the study of seasonal hydrogen storage multi-energy systems, and provides references for optimal selection and rational utilization of hydrogen energy as an intermediate energy link in the selection, evaluation and modeling.
All authors contributed equally to this work.