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Energy Storage System

When it comes to energy storage, it is easy to think of batteries, but the existing battery technology is difficult to meet the requirements of grid-level energy storage. In fact, the market potential of energy storage is huge. According to the forecast of market research firm Pike Research, from 2011 to 2021, 122 billion US dollars will be invested in global energy storage projects. In large-scale energy storage systems, the most widely used traditional energy storage methods such as pumped hydro energy storage and compressed air energy storage are also undergoing continuous improvement and innovation. Today, Caixinenergy recommends an article that analyzes the current global energy storage technology and its impact and role on the grid.

Existing energy storage systems are mainly divided into five categories: mechanical energy storage, electrical energy storage, electrochemical energy storage, thermal energy storage and chemical energy storage. At present, the world’s highest proportion is pumped hydro storage, with a total installed capacity of 127GW, accounting for 99% of the total energy storage capacity, followed by compressed air energy storage, with a total installed capacity of 440MW, and sodium-sulfur batteries ranking third. , with a total capacity of 316MW.

Existing energy storage systems around the world:

1. Mechanical energy storage

Mechanical energy storage mainly includes pumped hydro energy storage, compressed air energy storage and flywheel energy storage.

(1) Pumped hydro storage: the water that uses excess power as a liquid energy medium when the power grid is low is pumped from the low-lying reservoir to the high-lying reservoir, and when the power grid peaks, the water in the high-lying reservoir flows back to the lower reservoir to drive the turbine generator. Power generation, the efficiency is generally about 75%, commonly known as in 4 out 3, with daily adjustment capacity, used for peak regulation and backup.

Disadvantages: Difficulty in site selection, and its dependence on terrain; large investment cycle and high losses, including pumping and storage loss + line loss; at this stage, it is also restricted by China’s electricity price policy. Last year, more than 80% of China’s pumping and storage were exposed to the sun, in August last year, the National Development and Reform Commission issued a policy on the price of pumped storage electricity. It may be better in the future, but it is definitely not the development trend of energy storage.

(2) Compressed air energy storage (CAES): Compressed air energy storage is to use the residual power when the load of the power system is at a low valley. When the power generation is insufficient, the compressed air is mixed with oil or natural gas through a heat exchanger, and then introduced into a gas turbine for power generation. There are many foreign studies and the technology is mature, and my country started a little later. It seems that Academician Lu Qiang has done more research in this area, such as cogeneration of cold and power.

Compressed air storage also has a peak shaving function, which is suitable for large-scale wind farms, because the mechanical work generated by wind energy can directly drive the compressor to rotate, reducing the intermediate conversion into electricity, thereby improving efficiency.

(3) Flywheel energy storage: It uses a high-speed rotating flywheel to store energy in the form of kinetic energy. When energy is needed, the flywheel slows down to release the stored energy. The single technology of flywheel energy storage is basically available in China (but the gap with foreign countries is more than 10 years). The difficulty lies in developing new products with different functions according to different purposes. Therefore, the flywheel energy storage power supply is a high-tech product but original innovation. It is not enough, which makes it more difficult to obtain national scientific research funding support.

2. Electrical energy storage

(1) Super capacitor energy storage: The electric double layer structure composed of activated carbon porous electrodes and electrolytes is used to obtain super-large capacitance. Unlike batteries, which utilize chemical reactions, the charging and discharging process of super capacitors is always a physical process. Short charging time, long service life, good temperature characteristics, energy saving and green environmental protection. There is nothing too complicated about super capacitors, which is the charging of the capacitor, and the rest is the problem of materials. The current research direction is whether it can achieve a small area and a larger capacitance. The development of super capacitors is still very fast. At present, new types of super capacitors based on graphene materials are very popular.

(2) Superconducting energy storage (SMES): a device for storing electrical energy made with the zero resistance of superconductors. The superconducting energy storage system roughly includes four major parts: superconducting coil, low-temperature system, power regulation system, and monitoring system. The development of superconducting material technology is the top priority of superconducting energy storage technology. Superconducting materials can be roughly divided into low-temperature superconducting materials, high-temperature superconducting materials, and room-temperature superconducting materials.

3. Electrochemical energy storage

(1) Lead-acid battery: It is a battery whose electrodes are mainly made of lead and its oxides, and the electrolyte is sulfuric acid solution. At present, it is widely used in the world, the cycle life can reach about 1000 times, the efficiency can reach 80%-90%, and the cost performance is high.

(2) Lithium-ion battery: It is a type of battery that uses lithium metal or lithium alloy as the negative electrode material and uses a non-aqueous electrolyte solution. Mainly used in portable mobile devices, its efficiency can reach more than 95%, the discharge time can reach several hours, the number of cycles can reach 5000 times or more, and the response is fast. It is the practical battery with the highest energy in the battery. most used. In recent years, technology has been continuously upgraded, and positive and negative electrode materials also have a variety of applications.

(3) Sodium-sulfur battery: It is a secondary battery with metal sodium as the negative electrode, sulfur as the positive electrode, and ceramic tube as the electrolyte diaphragm. The cycle cycle can reach 4500 times, the discharge time is 6-7 hours, the cycle round-trip efficiency is 75%, the energy density is high, and the response time is fast. At present, more than 200 such energy storage power stations have been built in Japan, Germany, France, the United States and other places, which are mainly used for load leveling, peak shifting and improving power quality.

(4) Flow battery: a high-performance battery that separates the positive and negative electrolytes and circulates them separately. The power and energy of the battery are not related, the energy stored depends on the size of the storage tank, so it can store energy for hours to days, and the capacity can reach the MW level. This battery has multiple systems, such as iron-chromium system, zinc-bromine system, sodium-bromine polysulfide system and all-vanadium system, among which vanadium battery is the most popular.

4. Thermal energy storage

Thermal energy storage: In a thermal energy storage system, thermal energy is stored in the medium of an insulated container and converted back to electrical energy when needed, or can be directly used without being converted back into electrical energy. Thermal energy storage is divided into sensible heat energy storage and latent heat energy storage. Thermal energy storage can store a lot of heat, so it can be used to generate electricity from renewable energy sources.

5. Chemical energy storage

Chemical energy storage: use hydrogen or synthetic natural gas as the carrier of secondary energy, use excess electricity to produce hydrogen, either directly use hydrogen as the energy carrier, or react with carbon dioxide to become synthetic natural gas (methane), hydrogen or synthetic In addition to being used for power generation, natural gas can also be used in other ways such as transportation. Germany is keen to promote this technology and has demonstration projects in operation.

What will the grid look like after reliable energy storage?

1. Support the realization of energy Internet and smart grid

Energy storage is an important device for smart grid to realize two-way energy interaction. Without energy storage, a complete smart grid would be impossible.

2. Use energy storage technology to face the test of new energy

It is mainly to stabilize and stabilize the output power of intermittent renewable energy power generation such as wind energy and solar energy, and to improve the ability of the grid to accept intermittent renewable energy.

3. Reduce peak-to-valley difference and improve equipment utilization

Power grid companies can obtain more peak load benefits while the peak load regulation and power supply pressure are relieved.

4. Improve the safety and reliability of power grid and power quality

Provide emergency power supply; reduce losses due to various transient power quality problems.

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