Commercial energy storage overview

Renewable energy is an essential part of the long-term plan for carbon neutrality. Regardless of the controllable nuclear fusion, space mining, and large-scale mature development of hydropower resources that do not have a commercial route in the short term, wind energy, and solar energy are currently the most promising renewable energy sources. Still, they are limited by wind and light resources. Energy storage will be an essential part of future energy utilization. This article and subsequent articles will include large-scale commercial energy storage technologies, mainly focusing on implementation cases.

In recent years, the rapid construction of energy storage systems has made some past data no longer helpful, such as "compressed air energy storage ranked second with a total installed capacity of 440MW, and sodium-sulfur batteries ranked third, with a total capacity scale of 440 MW. 316MW" etc. In addition, the news that Huawei has signed the world's "largest" energy storage project with 1300MWh is overwhelming. However, according to the existing data, 1300MWh is not the most significant energy storage project globally. The central largest energy storage project belongs to pumped storage. For physical energy storage technologies such as salt energy storage, in the case of electrochemical energy storage, 1300MWh is not the most significant project (it may also be a matter of statistical caliber). The current capacity of Moss Landing Energy Storage Center has reached 1600MWh (including 1200MWh in the second phase, 400MWh in the second phase). Still, Huawei's entry has spotlighted the energy storage industry on the stage.

Currently, commercialized and potential energy storage technologies can classify into mechanical energy storage, thermal energy storage, electrical energy storage, chemical energy storage, and electrochemical energy storage. Physics and chemistry are essentially the same, so let's classify them according to the thinking of our predecessors for the time being.

1. Mechanical energy storage / thermal storage and cold storage

Pumped storage:

There are two upper and lower reservoirs, pumping water to the upper reservoir during energy storage and draining water to the lower reservoir during power generation. The technology is mature. By the end of 2020, the global installed capacity of pumped storage capacity was 159 million kilowatts, accounting for 94% of the total energy storage capacity. At present, my country has put into operation a total of 32.49 million kilowatts of pumped storage power stations; the full scale of pumped storage power stations under construction is 55.13 million kilowatts. The scale of both built and under construction ranks first in the world. An energy storage power station's installed capacity can reach thousands of MW, the annual power generation can reach several billion kWh, and the black start speed can be on the order of a few minutes. At present, the largest energy storage power station in operation in China, Hebei Fengning Pumped Storage Power Station, has an installed capacity of 3.6 million kilowatts and an annual power generation capacity of 6.6 billion kWh (which can absorb 8.8 billion kWh of excess power, with an efficiency of about 75%). Black start time 3-5 minutes. Although pumped storage is generally considered to have the disadvantages of limited site selection, long investment cycle, and significant investment, it is still the most mature technology, the safest operation, and the lowest cost energy storage means. The National Energy Administration has released the Medium and Long-Term Development Plan for Pumped Storage (2021-2035).

By 2025, the total production scale of pumped storage will be more than 62 million kilowatts; by 2030, the full production scale will be about 120 million kilowatts; by 2035, a modern pumped storage industry that meets the needs of high-proportion and large-scale development of new energy will be formed.

Hebei Fengning Pumped Storage Power Station - Lower Reservoir

Compressed air energy storage:

When the electricity load is low, the air is compressed and stored by electricity (usually held in underground salt caves, natural caves, etc.). When the electricity consumption peaks, the high-pressure air is released to drive the generator to generate electricity.

compressed air energy storage

Compressed air energy storage is generally considered the second most suitable technology for GW-scale large-scale energy storage after pumped storage. Still, it is limited by its more stringent site selection conditions, high investment cost, and energy storage efficiency than pumped storage. Low, the commercial progress of compressed air energy storage is slow. Until September of this year (2021), my country's first large-scale compressed air energy storage project - Jiangsu Jintan Salt Cave Compressed Air Energy Storage National Test Demonstration Project, has just been connected to the grid. The installed capacity of the first phase of the project is 60MW, and the power conversion efficiency is about 60%; the long-term construction scale of the project will reach 1000MW. In October 2021, the first 10 MW advanced compressed air energy storage system independently developed by my country was connected to the grid in Bijie, Guizhou. It can say that the commercial road of compact air energy storage has just begun, but the future is promising.

Jintan compressed air energy storage project.

Molten salt energy storage:

Molten salt energy storage, generally combined with solar thermal power generation, concentrates sunlight and stores heat in molten salt. When generating electricity, molten salt heat is used to generate electricity, and most of them generate steam to drive a turbine generator.

molten salt heat storage

They shouted Hi-Tech Dunhuang 100MW molten salt tower solar thermal power station in China's largest solar thermal power station. The Delingha 135 MW CSP project with a larger installed capacity has started construction. Its energy storage time can reach 11 hours. The total investment of the project is 3.126 billion yuan. It is planned to be officially connected to the grid before September 30, 2022, and it can generate about 435 million kWh of electricity every year.

Dunhuang CSP Station

Physical energy storage technologies include flywheel energy storage, cold storage energy storage, etc.

2. Electrical energy storage:

Supercapacitor: Limited by its low energy density (refer to below) and severe self-discharge, it is currently only used in a small range of vehicle energy recovery, instantaneous peak shaving, and valley filling. Typical applications are Shanghai Yangshan Deepwater Port, where 23 cranes significantly impact the power grid. To reduce the impact of cranes on the power grid, a 3MW/17.2KWh supercapacitor energy storage system is installed as a backup source, which can continuously provide a 20s electricity supply.

Superconducting energy storage: omitted

3. Electrochemical energy storage:

This article classifies commercial electrochemical energy storage into the following categories:

Lead-acid, lead-carbon batteries

flow battery

Metal-ion batteries, including lithium-ion batteries, sodium-ion batteries, etc.

Rechargeable Metal-Sulfur/Oxygen/Air Batteries

other

Lead-acid and lead-carbon batteries: As a mature energy storage technology, lead-acid batteries are widely used in car startups, backup power supply for communication base station power plants, etc. After the Pb negative electrode of the lead-acid battery is doped with carbon materials, the lead-carbon battery can effectively improve the over-discharge problem. According to Tianneng's 2020 annual report, the State Grid Zhicheng (Jinling Substation) 12MW/48MWh lead-carbon energy storage project completed by the company is the first super-large lead-carbon energy storage power station in Zhejiang Province and even the whole country.

Flow battery: The flow battery usually consists of liquid stored in a container flowing through the electrodes. The charge and discharge are completed through the ion exchange membrane; refer to the figure below.

Flow battery schematic

In the direction of the more representative all-vanadium flow battery, the Guodian Longyuan, 5MW/10MWh project, completed by the Dalian Institute of Chemical Physics and Dalian Rongke Energy Storage, was the most extensive all-vanadium flow battery energy storage system in the world at that time, which is currently under construction The larger-scale all-vanadium redox flow battery energy storage system reaches 200MW/800MWh.

Metal-ion battery: the fastest-growing and most widely used electrochemical energy storage technology. Among them, lithium-ion batteries are commonly used in consumer electronics, power batteries, and other fields, and their applications in energy storage are also increasing. Including the previous Huawei projects under construction that use lithium-ion battery energy storage, the largest lithium-ion battery energy storage project built so far is the Moss Landing energy storage station consisting of Phase I 300MW/1200MWh and Phase II 100MW/400MWh, a total of 400MW/1600MWh.

Lithium-Ion Battery

Due to the limitation of lithium production capacity and cost, replacing sodium ions with relatively low energy density but abundant reserves are expected to reduce the price has become a development path for lithium-ion batteries. Its principle and primary materials are similar to lithium-ion batteries, but it has not yet been industrialized on a large scale. , the sodium-ion battery energy storage system put into operation in existing reports has only seen a scale of 1MWh.

Aluminum-ion batteries have the characteristics of high theoretical capacity and abundant reserves. It is also a research direction to replace lithium-ion batteries, but there is no clear commercialization route. An Indian company that has become popular recently announced that it will commercialize the production of aluminum-ion batteries next year and will build a 10MW energy storage unit. Let us wait and see.

wait and see

Rechargeable metal-sulfur/oxygen/air batteries: including lithium-sulfur, lithium-oxygen/air, sodium-sulfur, rechargeable aluminum-air batteries, etc., with higher energy density than ion batteries. The current representative of commercialization is sodium-sulfur batteries. NGK is currently the leading supplier of sodium-sulfur battery systems. The enormous scale that has been put into operation is a 108MW/648MWh sodium-sulfur battery energy storage system in the United Arab Emirates.

4. Chemical energy storage: Decades ago, Schrödinger wrote that life depends on acquiring negative entropy. But if you don't rely on external energy, entropy will increase, so life must take in power. Life finds its way, and to store energy, plants convert solar energy into chemical energy in organic matter through photosynthesis. Chemical energy storage has been a natural choice from the very beginning. Chemical energy storage has been a robust energy storage method for human beings since It made volts into electric stacks. Still, the commercial utilization of large-scale energy storage has just begun.

Hydrogen storage, methanol, etc.: Hydrogen energy has the outstanding advantages of high energy density, cleanliness, and environmental protection and is widely regarded as an ideal energy source in the future. The route of hydrogen production→hydrogen storage→fuel cell is already on the way. At present, more than 100 hydrogen refueling stations have been built in my country, ranking among the top in the world, including the world's largest hydrogen refueling station in Beijing. However, due to the limitations of hydrogen storage technology and the risk of a hydrogen explosion, indirect hydrogen storage represented by methanol may also be an essential path for future energy, such as the "liquid sunlight" technology of Li Can's team at the Dalian Institute of Chemistry, Chinese Academy of Sciences.

Metal-air primary batteries: represented by aluminum-air batteries with high theoretical energy density, but there is little progress in commercialization. Phinergy, a representative company mentioned in many reports, used aluminum-air batteries for its vehicles. One thousand miles, the leading solution in energy storage is rechargeable zinc-air batteries.