What is compressed air energy storage-the advantages and disadvantages

Introduction

At present, the existing energy storage technologies mainly include pumped storage, compressed air storage, flywheel storage, superconducting storage, lithium battery, flow battery, etc. Among them,compressed air energy storagetechnology has the characteristics of large energy storage capacity, long cycle and long service life. It is a large-scale energy storage technology with broad development prospects.

Compressed air energy storage is an energy storage technology based on the development of gas turbines. It stores energy in the form of compressed air and has been listed as a new energy storage technology by various countries. It has the characteristics of zero emission, zero pollution and high efficiency. The relevant technology is mature and has huge development space.

At present, the design efficiency of systems above 100 MW level can reach 70% – 75%, the annual cycle times exceed 500, the service life reaches 30 years, and the average kwh cost is 0.325 RMB, which is far lower than the lithium iron phosphate battery, sodium battery and vanadium battery with the kWh cost of about 0.6 RMB / kWh. With significant economic benefits, it has officially changed from a demonstration project to a large-scale commercialization.

What is compressed air energy storage

Compressed air energy storage technology (CAES) is considered as one of the most potential large-scale electric energy storage technologies. The traditional compressed air energy storage is based on the energy storage technology developed by gas turbine.

What’s the working principle of compressed air energy storage

During the operation of the gas turbine, after the air is compressed to high pressure by the compressor, it is heated by fuel combustion in the combustion chamber, and then the high-temperature and high-pressure gas drives the turbine to expand to do work. It can be simplified as four continuous processes: compression, heating, expansion and cooling.

The compressor and turbine do not work at the same time in the compressed air energy storage system. When storing energy, the compressed air energy storage system compresses air with electric energy and stores it in the air storage chamber. When the system releases energy, the high-pressure air is released from the air storage chamber, enters the combustion chamber, and is heated by fuel combustion, and then drives the turbine to generate electricity.

What’s the composition of compressed air system

Compressed air system is mainly composed of four core parts: compression system, expansion system, power generation system and air storage tank.

At present, the advanced liquid air energy storage mainly involves the following equipment: compressor unit, air purification unit, liquefaction unit, refrigeration expander, liquid storage unit, cryopump, expander electric unit, expander electromechanical unit, heat storage unit, cold storage unit, lithium bromide cold and heat dual supply unit.

The advantages and disadvantages of compressed air energy storage

The advantages of compressed air energy storage are long working time and service life (about 40-50 years), good efficiency, less site restrictions, good economic performance and high safety performance. The following are the advantages and disadvantages of compressed air energy storage.

Advantages	Large capacity (more than 100MW), suitable for building large-scale energy storage power stations, second only to pumped storage power stations
	Long working hours, which can last for hours or even days
	The construction cost and operation cost are relatively low, far lower than sodium sulfur battery or flow battery
	Long service life(40-50 years), can store or release energy for tens of thousands of times
Disadvantages(traditional CAES)	Rely on burning fossil fuels to provide heat source
	Large gas storage chambers need to be built according to specific geographical conditions, such as rock caves, Salt Caves, abandoned mines, etc
	Insufficient utilization of waste heat, no use of heat generated by air compression and exhaust heat of turbine

Table1. the advantages and disadvantages of compressed air energy storage

Compressed air energy storage vs pumped storage and lithium iron phosphate battery

The cost per kilowatt hour of compressed air is still slightly higher than that of pumped storage, but far lower than that of lithium iron phosphate battery. Although the energy storage efficiency of compressed air is lower than that of lithium-ion batteries, the comprehensive cost of compressed air energy storage is still significantly lower than that of lithium-ion energy storage based on the additional charging cost of 0.06 RMB / kwh per kWh.

The investment cycle is shorter than that of pumped storage, and the individual investment scale is limited. The construction period of compressed air energy storage is shorter than pumped storage, so as to facilitate the rapid production of the project.

In addition, pumped storage power stations generally have better economy only when they are more than 1 million kilowatts, while compressed air of more than 100000 kilowatts can have better commerciality. The individual investment of compressed air energy storage is small and can be flexibly configured.

Cost analysis and prediction of compressed air energy storage

The improvement of system efficiency and the reduction of cost are the foundation of the commercial development of compressed air energy storage.

At present, according to the completed and under construction projects, the system efficiency of megawatt level can reach 52.1%, the system efficiency of 10MW can reach 60.2%, the design efficiency of systems above 100MW level can reach 70%, and the efficiency of advanced compressed air energy storage system can approach 75%.

After the system scale increases, the unit investment cost also continues to decrease. Each time the system scale increases by an order of magnitude, the unit cost decreases by about 30%.

The development of compressed air energy storage in the world

The Huntorf in Germany built in 1978 and the Alabama commercial compressed air energy storage power station built in 1991 are commercial power stations. Additionally, China has successively carried out R & D and construction of compressed air, supercritical compressed air and liquid compressed air energy storage projects.

Huntorf compressed air energy storage power station in Germany is the first compressed air energy storage power station put into commercial operation in the world. The gas storage part of the system is two underground caves with a total volume of 310000m3. The power station can continuously store energy for 12 hours and output electric energy for 3 hours. The compressor power is 60MW, and the power generation can reach 290MW.

Since the system directly discharges the high-temperature exhaust gas generated by combustion to the atmosphere, resulting in waste of heat energy, its efficiency is about 40%. McIntosh power station in the United States was put into operation in 1991. A regenerator was added to recover heat energy from waste gas, increasing the system efficiency to 54%.

Most of the air compression projects are pilot demonstration projects. China’s compressed air energy storage projects started at the kilowatt level and gradually broke through the key technologies of 1-100mw compressed air energy storage systems. The first international 1.5MW and 10MW advanced compressed air energy storage demonstration projects were completed in Hebei, China, in 2013 and Guizhou, China, in 2016.

The first 100MW advanced compressed air energy storage demonstration project in Zhangjiakou, China was successfully connected to the grid at the end of 2021, The overall R & D process and system performance are at the leading level in the world.

In recent years, China has started the research and development of CAES technology, and has made significant progress and breakthroughs. In 2021, the Jiangsu Jintan salt cavern compressed air energy storage national test and demonstration project was successfully connected to the grid in China.

There are many gerat factories do well in the field of energy storage, which can be shown in top 20 energy storage system companies in China.

The first phase of the system has an installed power generation capacity of 60MW, an energy storage capacity of 300mwh, and a long-term construction scale of 1000MW. It is the world’s first non afterburning compressed air energy storage power station. This system can improve the electrical energy conversion efficiency to more than 60%, and there is no combustion and emission in the whole process.

The prediction of the future development of compressed air energy storage

The overall industrial scale of compressed air energy storage is still small, but it is expected to become an important supplement in the future.

By the end of 2021, compressed air energy storage accounted for 2.3% of the world’s new energy storage installed capacity, and in China, compressed air accounted for 3.2% of China’s new energy storage cumulative installed capacity.

At past compressed air energy storage was constrained by low energy storage efficiency and high power consumption cost. However, with the progress of technology, the energy storage efficiency of large-scale power stations has risen to 70% – 75%.

Although it is slightly lower than that of pumped storage power stations, it has the conditions for large-scale commercial application.In general, compressed air energy storage is expected to be an important supplement of pumped storage in the field of large-scale energy storage power stations after its energy efficiency is improved.