The role of compressed air energy storage and its development status

The composition and working principle of the compressed air system

Compressed air energy storage technology is regarded as another potential large-scale energy storage technology besides pumped storage power plant. The compressed-air energy storage system is mainly composed of compressor, gas storage, heat recovery system, heat storage system, expander and generator.

When storing energy, use low-valley electricity or renewable energy to drive the compressor to compress the air to a high-pressure state and store it in the air storage chamber, and at the same time recover and store the compression heat generated during the compression process through the regenerative system;

When releasing energy, the high-pressure air is released from the air storage chamber to drive the expander to generate electricity, and at the same time, the stored compression heat is used to heat the high-pressure air entering the expander, without fuel supplementary combustion, and the whole process has no combustion and zero emissions.

The role and significance of compressed air energy storage

In February this year, compressed-air energy storage was mentioned 9 times in the new energy storage development implementation plan released by the National Development and Reform Commission and the National Energy Administration.

It is pointed out that by 2025, the new energy storage has entered the stage of large-scale development from the initial stage of commercialization, and has the conditions for large-scale commercial application, and the 100-megawatt compressed air energy storage technology will realize engineering application; Actively explore the commercial development model, gradually reduce the cost of energy storage, and carry out pilot demonstrations of large-scale energy storage.

In the construction of new power systems, compressed air energy storage has a wide range of uses on the power supply side, the grid side, and the user side. In the application scenario of energy storage on the power supply side, the compressed air energy storage power station takes participation in auxiliary services such as peak regulation and frequency regulation as the main application scenario.

In the grid-side energy storage application scenario, the uses of compressed-air energy storage power station mainly include peak regulation and frequency regulation, black start, alleviation of transmission and distribution congestion, delaying investment in transmission and distribution equipment, and improving power supply reliability, etc., and play a role in ensuring the bottom grid.

In the user-side energy storage application scenario, the compressed air energy storage power station is based on meeting the needs of users to reduce electricity costs and improve electricity reliability. It can include electricity cost management scenarios based on peak and valley electricity prices, and participate in power ancillary service market scenarios etc.

Development status of compressed air energy storage

In 2014, Tsinghua University and other units built a 500-kilowatt non-supplementary combustion compressed air energy storage demonstration project in Wuhu, Anhui, with a system efficiency of about 40%. The Institute of Engineering Thermophysics, Chinese Academy of Sciences has built a 1.5-megawatt non-supplementary combustion supercritical compressed air energy storage system demonstration project in Langfang, Hebei. The energy storage system efficiency is about 52%. In 2016, a 10-megawatt compressed-air energy storage demonstration platform was built in Bijie, Guizhou, with a rated operating efficiency of 60.2%.

In the commercialization of compressed air energy storage power plants

At present, the projects that have been connected to the grid mainly include the Jiangsu Jintan Salt Cave Compressed Air Energy Storage Power Station National Demonstration Project Phase I 60MW/300MWh Project, Shandong Feicheng Salt Cave Advanced Compressed Air Energy Storage Peak Shaving Power Station Phase I 10 MW Demonstration Power Station, Hebei Zhangjiakou International’s first 100 MW/400 MWh advanced compressed air energy storage national demonstration project, etc.

Among them, the system efficiency of the 100 MW/400 MWh advanced compressed air energy storage project in Zhangjiakou, Hebei reached 70.4%, reaching the highest international level. At present, China’s compressed-air energy storage power station is still in the early stage of commercial development, and the main constraints include:

● The suitable location of gas storage is limited

Natural salt-cavern gas storage is the first choice for underground high-pressure gas storage in the world due to its remarkable advantages such as sealing and good economy. Some areas in Guangdong, and the “Three North” areas with huge installed capacity of photovoltaic and wind power and urgent demand for large-scale energy storage, lack rock-salt strata suitable for the construction of salt cavern underground gas storage.

● Artificial gas storage costs are high

In addition to natural underground spaces such as salt caverns, artificial excavation of hard rock cavern gas storage is an ideal alternative to gas storage. Its comprehensive construction cost is relatively high, and it is still in the commercial demonstration stage.

● Electricity pricing policy is unclear

At present, China has not issued a supporting policy document for the on-grid price of compressed air energy storage power stations, and the pricing mechanism of compressed-air energy storage power stations is still in the exploratory stage, which also affects the willingness to invest to a certain extent.

Compressed air energy storage underground gas storage site selection

The selection and location of underground gas storage is the primary issue and prerequisite for the planning and design of large-scale compressed air energy storage power plants. The compressed air energy storage underground gas storage needs to meet the technical requirements of high pressure resistance (10 MPa level), good air tightness, good geological stability, and resistance to alternating fatigue stress.

Underground salt caverns have the natural advantages of large volume, good airtightness and high stability, which can provide excellent gas storage conditions for compressed air energy storage, and are the first choice for compressed air energy storage underground gas storage. In addition, other underground spaces such as abandoned mines and artificial underground gas storage are also viable options for underground gas storage.

For abandoned mines, abandoned mines and roadways have the potential to be used as underground gas storage after transformation. However, taking the widely existing abandoned coal mine shafts and roadways as an example, there is a lack of spatial stability in their utilization. There are a series of problems such as the risk of roadway collapse and ground subsidence, the difficulty of groundwater treatment caused by the large burial depth, and the disposal of harmful gases such as coal mine gas.