Hydrogen energy storage-definition,working principle and key technology

Hydrogen mainly appears in the form of compound state on the earth, which constitutes 75% of the mass of the universe and is widely distributed. Compared with traditional energy, hydrogen energy storage is known as the cleanest energy in the 21st century and an important supplement to electric energy in the future secondary energy system.

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Under the background of low-carbon development and energy transformation, the hydrogen energy storage industry has ushered in new development opportunities. This article will introduce hydrogen energy storage from various aspects including definition, working principle and key technology.

What is hydrogen energy storage

Hydrogen energy storage is an energy storage technology applied in a specific environment. Its essence is hydrogen storage, that is, flammable and explosive hydrogen is stored in a stable form, and more energy is stored with less total mass.

Working principle and energy conversion process of hydrogen energy storage

Hydrogen energy storage technology makes use of electricity → hydrogen → electricity. The basic principle is to electrolyze water to obtain hydrogen and oxygen.

The schematic diagram is as follows:

In the renewable energy power generation system, the intermittent generation and transmission of electricity are often limited. The surplus, off peak or low-quality electricity is used to produce hydrogen on a large scale to convert electric energy into hydrogen energy for storage; When the power output is insufficient, hydrogen is used to convert into electric energy through fuel cells or other means for transmission to the Internet.

Advantages and disadvantages of hydrogen energy storage

As a clean, efficient and sustainable carbon free energy storage technology, hydrogen energy storage has advantages that other energy storage technologies cannot match:

● Simple raw materials, no resource anxiety

Hydrogen can be obtained by direct electrolysis of water on the earth through direct current;

● It can be an effective supplement to the new power system

Hydrogen energy can be used as an effective medium to store abandoned light or wind resources to solve the problem of waste caused by intermittent and random new energy power generation;

● Strong span of time and space dimensions

New energy sources such as photovoltaic and wind power have seasonal fluctuations and uneven spatial distribution. Hydrogen energy storage has a longer energy storage time and extremely high storage capacity, which is expected to become an effective solution for long-term, cross regional energy storage;

● Great energy density and calorific value

The energy density of hydrogen energy storage can reach 140 MJ/kg, more than 100 times that of lithium battery and other electrochemical energy storage. It can store more energy in a smaller volume, effectively avoiding energy waste. In terms of calorific value, the calorific value of hydrogen can reach 120 MJ/kg, 3-4 times that of coal, natural gas, oil and other traditional fossil fuels.

At the same time, its weaknesses cannot be ignored:

● The power system is still not completely decarbonized

At present, the process of hydrogen production is not completely zero carbon;

● High hydrogen production cost

In the process of electrolyzing water, the electricity charge usually accounts for about 80% of the preparation cost, and the investment cost is high;

● Low hydrogen production efficiency

At present, the overall electricity → hydrogen → electricity energy efficiency of hydrogen energy storage is only about 30%, and the energy loss is higher than other commonly used energy storage technologies.

The evaluation indexes of various energy storage technologies are different, and their application ranges are also different. Hydrogen energy storage has absolute advantages in terms of energy storage duration and storage capacity.

What are the key technologies of hydrogen energy storage system

The key technology of hydrogen energy storage system is hydrogen storage. Hydrogen storage technology can be divided into:

● Physical hydrogen storage (the most mature technology)
● Chemical hydrogen storage
● Underground hydrogen storage
● Other hydrogen storage

Physical hydrogen storage mainly includes high-pressure gaseous hydrogen storage and low-temperature liquid hydrogen storage; Chemical hydrogen storage mainly includes hydrogen storage by coordination hydride, inorganic compound, organic liquid, liquid ammonia and methanol.

High pressure gaseous hydrogen storage

High pressure gaseous hydrogen storage is the most mature and commonly used hydrogen storage technology. High pressure gaseous hydrogen storage technology refers to the storage of hydrogen in a high-density gaseous form by high-pressure compression above the critical temperature of hydrogen.

This hydrogen storage technology has the advantages of low cost, low energy consumption, easy dehydrogenation, etc., but the hydrogen storage density is greatly affected by the pressure, and the pressure is limited by the tank material. Therefore, looking for a light and high-pressure hydrogen storage tank has become the key to high-pressure gaseous hydrogen storage.

At present, high-pressure gaseous hydrogen storage containers are mainly divided into four types: pure steel metal bottles (Type I), steel liner fiber circumferential wound bottles (Type II), aluminum liner fiber full wound bottles (Type III) and plastic liner fiber wound bottles (Type IV). In addition, various countries have been developing Type V hydrogen storage bottles, that is, liner free filament winding.

Low temperature liquid hydrogen storage

Low temperature liquid hydrogen storage technology is a kind of cryogenic hydrogen storage technology. After being compressed, the hydrogen is cryogenic to below 21K (about – 253 ° C) to make it liquid hydrogen, and then stored in a special insulated vacuum container (Dewar).

Its advantage is that the volume energy of hydrogen is high, and the density of liquid hydrogen can reach 70.78kg/m3, which is about 850 times the density of hydrogen under standard conditions.

However, the boiling point of liquid hydrogen is extremely low, and the temperature difference between liquid hydrogen and the environment is great, so the thermal insulation requirements for hydrogen storage vessels are very high.

In China, cryogenic liquid hydrogen is still in its infancy and is mainly used in military and aerospace fields (the energy density of hydrogen is three times that of ordinary gasoline, which means that the fuel deadweight can be reduced by 2/3 and various performance parameters of aircraft can be greatly improved).

Organic liquid hydrogen storage

Organic liquid hydrogen storage technology is based on the hydrogenation of unsaturated liquid organics under the action of catalyst to generate stable compounds, which can be stored and transported in liquid form at room temperature and pressure, and the required amount of hydrogen can be extracted through dehydrogenation reaction.

Compared with high-pressure gaseous hydrogen storage and low-temperature liquid hydrogen storage, the reaction process of organic liquid hydrogen storage is reversible and the hydrogen storage density is high; The hydrogen carrier is safe and convenient for storage and transportation, and is suitable for long-distance transportation; Existing gasoline pipelines, gas stations and other infrastructure can be used.

However, there are still technical bottlenecks such as complex dehydrogenation technology, large energy consumption for dehydrogenation, and dehydrogenation catalyst technology that need to be broken through.

In the field of organic liquid hydrogen storage, American chemists have developed a B-N based liquid hydrogen storage material, which can work safely at room temperature. The breakthrough of this technology provides a solution to the problem of hydrogen energy storage and transportation.

Underground hydrogen storage

Underground hydrogen storage technology is to use underground geological structures for large-scale hydrogen energy storage, that is, use energy to electrolyze water to produce hydrogen, inject hydrogen into underground geological structures such as salt caverns, depleted oil and gas reservoirs and aquifers, and store hydrogen energy.

The main advantage of underground hydrogen storage technology is low energy storage cost. In addition, compared with the ground hydrogen storage, the hydrogen stored underground does not contact with the oxygen in the atmosphere, so it has no explosion risk and is safer.

Although compared with the surface hydrogen storage technology, the underground hydrogen storage efficiency is relatively low and the initial investment is large, because of its large storage capacity, the underground hydrogen storage can better reflect the economy.

Development status of global hydrogen energy storage

Up to now, there are about 60 fixed hydrogen storage facilities built or under construction in the world, mainly distributed in Germany, Canada, Italy, France, etc.

Japan is a world leader in the key technologies and commercial applications of fuel cells. It has comprehensive technologies in the field of hydrogen energy and fuel cells, and is expected to build a hydrogen society by 2050.

The United States has planned a complete development route from research and development to industrialization from 2000 to 2040, and has implemented a 30% – 50% tax credit for operating hydrogen energy infrastructure.

At present, the number of hydrogen refueling stations in operation in Europe ranks first in the world, and the effect of hydrogen technology and industrial development policy is remarkable.

In recent years, China has attached great importance to the development of the hydrogen energy industry, made key arrangements in science and technology projects, innovation projects, etc., and achieved certain results. Compared with other countries, China has a large gap in hydrogen fuel cell industry in general, but it is developing rapidly. Here are top 25 energy storage companies in China in 2022.

From now to the future, the hydrogen energy industry is on the fast track of development. In the long run, hydrogen energy storage in the future is the most suitable large-scale and long-period green power storage scheme, which can make up for the shortcomings of other energy storage forms.

It will store a large number of abandoned wind, light and electricity, becoming another mainstream energy storage method after pumped storage and lithium battery energy storage.