Energy storage technology and industrial development under the background of energy internet

China Energy Storage Network News: In his book "The Third Industrial Revolution", the famous American scholar Jeremy Rifkin first proposed the vision of the Internet of Energy. As an important component of the Internet of Energy, energy storage technology is directly related to whether the Internet of Energy can be realized. It is a key supporting technology for the large-scale use of renewable energy and the basis for the widespread application of distributed energy and microgrids.

In the context of energy internet, energy storage technologies or equipment such as electrochemical energy storage, heat storage, hydrogen energy storage, and electric vehicles have realized the "interconnection" of power grids, transportation networks, natural gas pipeline networks, and heating and cooling networks around power supply. Energy storage and energy conversion equipment have jointly established a coupling relationship between multiple energy networks. In the future energy internet, some new energy power generation will be converted through hydrogen production, heat production, etc., or stored in bidirectional power storage equipment such as electrochemical energy storage and returned to the grid in a timely manner. Supported by various power storage technologies, new energy power generation and conversion equipment such as cogeneration units, fuel cells, and heat pumps operate in coordination, achieving the matching of multiple energy production and consumption with electricity as the core under the goal of efficient utilization of new energy.

As the research on energy Internet gradually advances, its application value will continue to be reflected and its scope of application will continue to expand. It is a technology and industry with great development prospects in the energy Internet.

Current status and trends of various energy storage technologies and industrial development

From a technical perspective, energy storage can be mainly divided into electrochemical energy storage, compressed air energy storage, molten salt thermal storage, hydrogen energy storage suitable for energy-type applications, and flywheel, superconducting and supercapacitor energy storage suitable for power-type short-term applications.

Pumped storage is the most mature and widely used large-scale energy storage technology, with the advantages of large scale, long life and low operating cost. The current efficiency can reach about 70%, and the construction cost is roughly 3500￥/kW~4000￥/kW. The main disadvantage is that the construction of power stations is limited by geographical resource conditions, and involves a series of environmental protection issues such as flooding of the upper and lower reservoirs, changes in water quality, and salinization of soil in the reservoir area.

Sodium-sulfur batteries have the advantages of high energy density, no self-discharge, and readily available raw materials such as sodium and sulfur. Their main disadvantages are poor rate performance, high cost, and potential safety hazards in high-temperature operation. Future development trends are mainly to improve rate performance, further reduce manufacturing costs, and improve long-term operating reliability and system safety.

At present, the main liquid flow battery systems include: sodium polysulfide/bromine, all-vanadium, zinc/bromine, iron/chromium and other systems. Among them, the all-vanadium system is relatively mature, and many MW-level engineering demonstration projects have been built. It has the advantages of long life, independent design of power and capacity, and good safety. The main disadvantages are low efficiency and energy density, and a narrow operating environment temperature window. The development trend is mainly to use highly selective, low-permeability ion membranes and high-conductivity electrodes to improve efficiency, increase working current density and electrolyte utilization to solve high cost problems, etc.

Lead-carbon battery is a new type of energy storage device formed by introducing carbon materials with capacitance characteristics into the lead negative electrode of traditional lead-acid battery in the form of "internal parallel" or "internal mixing". Compared with traditional lead-acid batteries, it has advantages such as high rate and long cycle life. However, the addition of carbon materials is prone to problems such as easy hydrogen evolution at the negative electrode and easy water loss in the battery. The development trend is mainly to further improve the battery specific energy density and cycle life, while developing cheap and high-performance carbon materials.

Lithium-ion batteries are made of a wide variety of materials, including lithium manganese oxide, lithium iron phosphate, and nickel cobalt manganese oxide, which are suitable for positive electrodes; graphite, hard (soft) carbon, and lithium titanate, which are suitable for negative electrodes. The main advantages of lithium-ion batteries are: high energy storage density and power density, high efficiency, and a wide range of applications; high attention, rapid technological progress, and great development potential. The main disadvantages are: the use of organic electrolytes, which poses a safety hazard; technical and economic indicators such as life and cost still need to be improved.

In recent years, developed countries represented by the United States and Japan have explored the development path of energy storage batteries and have made certain progress in achieving long battery life, low cost and high safety. Long-life battery materials represented by zero-strain materials, sodium-based battery systems that can break free from the constraints of lithium resources, and all-solid-state batteries based on solid-state electrolytes are currently the main research hotspots and development trends.

Compressed air energy storage has the advantages of large scale, long life, and low operation and maintenance costs. At present, the traditional compressed air energy storage using natural gas and underground caves is relatively mature, with an efficiency of up to 70%. In recent years, scholars at home and abroad have successively proposed a variety of new compressed air energy storage technologies such as adiabatic, liquid and supercritical, breaking away from the limitations of geographical and resource conditions, but it is still basically in the stage of technological breakthrough or small-scale demonstration, and the efficiency is basically less than 60%. The development trend is mainly to improve the overall efficiency by making full use of the heat release and cold release in the entire cycle process, and to achieve scale through modularization.

Molten salt heat storage utilizes the characteristics of molten salt, such as large temperature range, high specific heat capacity, and good heat transfer performance. The heat is heated by heat transfer medium and heat exchanger to store the molten salt. When the heat is needed, the stored heat is taken out through heat exchanger, heat transfer medium, power pump and other equipment for use. It has been applied in solar thermal power generation. Its advantages are mainly large scale and convenient use with conventional gas engines. However, it still has disadvantages such as high cost, low efficiency and reliability. The development trend is mainly to break through the selection of working fluids and key materials.

Hydrogen energy storage is to decompose water into hydrogen and oxygen through electrolysis to achieve the conversion of electrical energy into chemical energy. It is considered to be an important support for the future energy Internet and is increasingly becoming the focus of energy science and technology innovation and industrial support in many countries. The current problems are mainly low energy conversion efficiency (total efficiency is less than 50%) and high energy consumption in the production process, which requires the establishment of supporting infrastructure such as hydrogen transmission pipelines and hydrogen refueling stations. In all aspects of hydrogen energy storage, the main development trend of hydrogen production is to reduce energy consumption, reduce costs, and improve conversion efficiency. Hydrogen storage mainly focuses on the development of new and efficient hydrogen storage materials and the improvement of the pressure resistance of hydrogen storage containers. Hydrogen transmission mainly focuses on the development of hydrogen transmission pipeline materials that are resistant to hydrogen embrittlement and penetration, and the research on the technology of mixed transmission of hydrogen and natural gas, the construction and improvement of related supporting facilities. Hydrogen use mainly focuses on the development of low-cost gas reforming technology, the reduction of the cost of hydrogen fuel cells, and the improvement of performance stability.

Flywheel energy storage has the advantages of high power density, long service life and environmental friendliness. Its main disadvantages are low energy storage density and high self-discharge rate. It is currently mainly suitable for applications such as power quality improvement and uninterruptible power supply.

Superconducting energy storage and supercapacitor energy storage are essentially energy storage in electromagnetic fields. There is no energy form conversion process. They have the advantages of high efficiency, fast response speed and long cycle life, and are suitable for applications such as improving power quality. The disadvantages of superconducting energy storage are that it requires a low-temperature refrigeration system, complex system construction, and high cost. The main problem faced by supercapacitors in large-scale applications is low energy density. Its development trend is mainly to develop high-performance electrode and electrolyte key material technologies to increase energy storage density and reduce costs.