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There are may ways to store energy. You can convert it into electricity and store it in batteries. You can make a tower of 12 ton concrete blocks and move them up and down like the weights of a grandfather clock. You can pump water uphill and then make it spin turbines on the way back down. You can store it chemically, heat sand or silicon up to extreme temperatures, or harness the power of rusting iron. You can even use compressed air. No matter what method you choose, there will always be losses associated with the conversion process. How big those losses are will be a major factor in determining whether any process is commercially viable.
In April, the Huaneng Group completed a 300 MW/1500 MWh compressed air energy storage (CAES) project in Hubei, China, which took two years to build and cost $270 million. The compressed air is contained in abandoned salt mines in the Yingcheng area of Hubei, China’s sixth most populous province. When activated, it was the largest grid-connected CAES project of its size in the world, according to the China Energy Engineering Corporation, which claims an equivalent pumped hydro energy storage system would have taken six to eight years to complete.
The project is designed to store 498 GWh of energy and output 319 GWh of energy a year with a round-trip efficiency of 64 percent. Up to 70 percent efficiency is possible, which would make it equal to that of the flow batteries available today, while pumped hydro energy storage can achieve closer to 80 percent efficiency, China Energy said according to Energy Storage News. The project will help balance the regional electrical grid during peak demand hours and assist in the integration of more renewable energy sources like wind and solar as they become available.
Pilot Project Uses Tech From Tsimghua University
While that was going on, a separate 60 MW project was underway nearby that also made use of salt caves to store compressed air. It represented a “proof of concept” opportunity for new technology developed by the electrical engineering department at Tsinghua University. The systems pioneered by the engineers at the university have now been awarded more than 100 new patents and will form the basis for more CAES systems in China and other nations that have the requisite geological requirements suitable for compressed air energy storage.
The facility incorporates groundbreaking non-fuel supplementary technology which eliminates the need for external fuel sources by storing and reusing the heat generated during air compression. This approach achieves zero carbon emissions and an energy conversion efficiency exceeding 60 percent. The engineering team developed new equipment essential to the operation of the CAES system, including high-load centrifugal compressors, high-parameter heat exchangers, and large-scale air turbines, which are fully designed and made in China.
The Jintan project stands out because of its state-of-the-art system and because of its streamlined flows and enhanced equipment configurations. Key technological highlights include a one-click start system that simplifies operations and reduces startup times from 20 minutes to just 5 minutes. The machine efficiency has been boosted by 0.5%, enhancing overall performance. The quick-start air turbine enables rapid response during peak shaving operations, which improve grid stability.
Compressed Air Energy Storage — Phase Two
With the new technology now proven, the Huaneng Group is launching phase two of its Jintan Salt Cavern Compressed Air Energy Storage project. When completed, it will be the largest CAES facility in the world. It will integrate the latest technologies to enhance power output, storage capacity, and efficiency, while setting a benchmark for sustainable energy solutions. According to Yahoo, Li Yaoqiang, chairman of China Salt Group, the project is the world’s first industrial-level project of clean compressed air energy storage and it is an important milestone in the utilization of salt cavern resources to explore the development of China’s salt industry.
The second phase of the Jintan project will feature two 350 MW non-fuel supplementary CAES units with a combined storage capacity of 1.2 million cubic meters. This will enable up to 2.8 GWh of electricity storage per full charge — larger than any other CAES facility in the world. Designed to operate for 330 charge-discharge cycles annually, the project outpaces existing technologies in both single-unit power generation and overall system efficiency.
The Jintan project is a collaboration between three entities. Huaneng International Power Jiangsu Energy Development Company is a subsidiary of Huaneng Group, which plays a central role in the investment, construction, and operation of the project. China National Salt Industry Group, through its subsidiary China Salt Cavern Comprehensive Utilization Company, provides underground gas storage capabilities that are key to the project’s feasibility. Tsinghua University is a key research and development partner on the project.
Once completed, the Jintan project will demonstrate the potential of CAES technology to contribute to a low-carbon energy grid. By leveraging existing salt caverns for energy storage and integrating innovative designs, the project will demonstrate how compressed air energy storage can be part of a sustainable solution to the intermittency of renewable energy sources. CAES is not applicable to all energy storage situations, as it requires underground caverns of salt or rock that are able to contain air under pressure for substantial periods of time. It is another tool that can be used to address the intermittency of renewable energy resources.
Other CAES News
Toronto-based Hydrostor is building two compressed air storage facilities, one in Australia and one in California. What makes its technology unique is that it actually uses the compressed air to push water uphill. That water gives the system a little bit more efficiency because the weight of the water above pushes down on the compressed air below more than ambient air pressure. The primary advantage of the Hydrostor process is that it may make compressed air storage possible in some areas that lack the salt caves or rock domes the Chinese system relies on. In any event, my colleague Michael Barnard has looked into Hydrostor and come away rather underwhelmed by it all.
Tina Casey recently wrote that underground compressed air energy storage is getting attention these days because it may be able to generate electricity for as long as eight hours whereas most grid-scale batteries have exhausted their power after three to four hours. The upshot of all this is that there are more forms of energy storage than just batteries. There is no one solution that is appropriate for every situation, and more options mean the transition to a cleaner, more sustainable grid will happen sooner than anyone expected just a few years ago. It’s good to have options.
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