How blowing hot air propelled Chinese scientists to energy storage breakthrough

A team of Chinese researchers has made a breakthrough in improving the storage efficiency of renewable energy. The technological achievement was made at the world’s largest advanced compressed air energy storage (CAES) system, located in Hebei province.

The 100-megawatt facility achieved a record in efficiency during a recent test run, and will be put into commercial operation by the end of this year, according to an announcement on Tuesday on the website of the Institute of Engineering Thermophysics (IET), Chinese Academy of Sciences.

The project is being led by the same team that designed the world’s first 1.5MW and 10MW national CAES demonstration systems.

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Energy storage systems are widely used to collect energy generated from solar panels and wind farms, or to balance the loads of an electrical grid. The systems store energy during periods of low demand and release it during peak load periods.

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Typical energy storage systems have included mainstream pumped hydroelectric energy storage (PHES), which use water, and the popular battery energy storage (BESS) system, which rely on various types of batteries. The CAES system uses compressed air as a working medium.

Pump storage has a relatively long lifespan and a conversion efficiency rate of 75 per cent, but it has highly specific site requirements and necessitates long construction periods. Battery storage boasts a higher conversion efficiency rate of 90 per cent, but the life cycle of the systems is limited and battery costs remain high.

By comparison, the CAES system has certain advantages – long lifespans, low costs, easy to construct and an environmentally friendly conversion process that offers an overall conversion efficiency of 70 per cent, according to a report by the Global Energy Interconnection Development and Cooperation Organization in March 2020.

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CAES works by storing compressed air in hard rock formations underground. High performance electric centrifugal pumps compress the air to 140 atmospheres. When the high pressure air is released, it pushes generator blades to make electricity.

The core component of the system is a heat collection device. It collects the heat generated in the compression process and then stores it. The device later uses that heat to raise the temperature of the compressed air during its release to increase the output power.

The efficiency of the device is directly related to the overall conversion efficiency of the system.

Scientists from IET designed their own heat collection device. According to their statement, “test results show that the heat storage efficiency remains 98.95 per cent after eight hours and 98.73 per cent after 16 hours, which is the highest record of current CAES heat storage devices”.

The world’s first utility-scale CAES project was built in Germany in 1978. It is still operational, producing output power of 290MW. But without a heat collection device, it burns fossil fuel in the reheat process. As a result, the overall efficiency of the German facility is only 40 per cent.

According to statistics data from Zhiyan Consulting, an industry research institute in Beijing, by the end of 2020, CAES accounted for only 0.2 per cent of the global energy storage market, and only 0.03 per cent in China. However, energy storage systems totalling 4,000MW were installed in 2021, according to a March report in People’s Daily.

A 100MW energy storage system based on vanadium flow batteries is under construction in Dalian, Liaoning province. Lithium-ion battery energy storage, flywheel energy storage and other energy storage projects are also under way in Inner Mongolia, Ningxia and elsewhere.

“Although China’s installed capacity of energy storage ranks first in the world, the ratio of energy storage to new energy (wind and photovoltaic) installed capacity is less than 7 per cent,” the People’s Daily report said.

According to a development plan released in March, China intends to take the global lead in advanced energy storage systems and start mass construction by 2025.

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