On April 30th, the world's first 300-megawatt advanced compressed air energy storage national demonstration power station successfully connected to the grid in Feicheng, Shandong Province. This signifies that China now possesses the largest, most efficient, highest-performing, and lowest-cost new type of compressed air energy storage power station in the world.
Panorama of the 300-megawatt advanced compressed air energy storage national demonstration project in Feicheng, Shandong Province
Energy storage is like saving extra electricity for later use, acting as a large "power bank" for the grid. It enables solar and wind power, which rely on weather conditions, to smoothly integrate into the grid and store backup power.
Compressed air energy storage functions as an "air power bank," charging and discharging air as the medium. With excellent performance, large scale, long lifespan, and low cost, it is rapidly gaining momentum.
Compared to other energy storage technologies like lithium batteries and pumped hydro, compressed air energy storage is relatively "young." It has only been developed for just over a decade in China but has grown rapidly, becoming a rising star in the industry, surprising many insiders.
The concept of compressed air energy storage dates back to the late 1940s, with the first patent appearing in the US. Germany and the US built compressed air energy storage plants in 1978 and 1991, respectively, which are still operational today. While many countries have plans for compressed air energy storage, it is not as popular globally as in China.
In 2004, Dr. Chen Haisheng, who had just started working at the Institute of Engineering Thermophysics of the Chinese Academy of Sciences, began contemplating his research direction. He set three criteria for himself: sunrise industry, innovative field, and relevance to engineering thermophysics. But what technology met these criteria?
After over three months of research and analysis, Dr. Chen identified energy storage technology as his focus. At that time, it was an extremely niche area.
Back then, China was heavily reliant on thermal power, with renewable energy accounting for less than 1% of installed capacity, making it a minor player with no grid integration challenges. It was hard to imagine a future where solar and wind energy would challenge the dominance of thermal power generation, and energy storage would transition from "cold" to "hot."
Dr. Chen created a chart with various energy storage technologies on the y-axis and indicators like innovation, technological maturity, and relevance on the x-axis. Compressed air energy storage emerged as the top performer with five stars compared to other technologies.
At that time, compressed air energy storage in China was purely theoretical, lacking technological breakthroughs, presenting Dr. Chen with a blank canvas.
"The mission of the Chinese Academy of Sciences is innovation for the people." Dr. Chen believed that anticipating and addressing the country's future needs required proactive thinking, research, and practice.
He decided to take on the challenge. That's how he chose what he wanted to do in his lifetime.
Looking back now, over the past decade, wind and solar power capacity in China has grown eightfold. By 2023, wind and solar capacity surpassed thermal power in a historic milestone, accounting for 50.4% of total capacity, making China the world's most energy storage-demanding country. Energy storage has not only taken center stage in energy development history but will also play a crucial role.
In 2005, Dr. Chen was sent to the University of Leeds in the UK for a study visit, providing an excellent opportunity for technical exploration.
During his time in the UK, he and his mentor proposed the concept of liquid air energy storage, quickly securing £6 million in funding from the UK government and investment institutions. Originally planned for a one-year visit, the project extended to four years of formal work. Ultimately, in 2009, they completed the world's first megawatt-scale liquid air energy storage system. Due to the significantly higher density of liquid air compared to gaseous air, this system addressed the reliance on large gas storage caverns, making it more advanced than traditional technologies.
Chen Haisheng developed a liquid air energy storage device in the UK.
After returning to China in 2009, Chen Haisheng was determined to develop a more advanced compressed air energy storage technology than liquid air.
At that time, traditional compressed air energy storage technology suffered from low efficiency. The efficiency of energy storage plants in Germany and the United States was only 42% and 54%, respectively. This means that for every unit of electricity stored, only about half could be released, with the other half being consumed during the storage and release process. Additionally, traditional compressed air energy storage systems relied on natural gas for heat sources.
These two drawbacks were somewhat acceptable in countries rich in oil and gas resources, but in China, which faced shortages of oil and gas, they were undoubtedly fatal weaknesses.
To fundamentally overcome these two technological bottlenecks and promote compressed air energy storage in China, it was clear that mere tracking, imitation, and improvement were not enough. A thorough technological innovation was necessary. The confidence for innovation stemmed from the years of accumulation by Chinese scientists in the fields of power engineering and engineering thermophysics.
Traditional compressed air energy storage systems were based on gas turbine technology. During off-peak electricity periods, surplus electricity was used to compress air and store it in reservoirs. During peak electricity periods, high-pressure air was released into the combustion chamber, where it burned with fuel to drive a turbine for power generation. This approach allowed the gas turbine to work intermittently, with energy storage and release processes being independent, ultimately helping to smooth out peak and off-peak electricity demands.
The key to this system lay in the efficient operation of the turbine machinery. Since its establishment in 1956, the Institute of Engineering Thermophysics had a strong foundation in turbine machinery research, with its founder, Mr. Wu Zhonghua, being internationally recognized as a pioneer in turbine machinery.
Drawing on its expertise, in 2009, the Institute of Engineering Thermophysics proposed an advanced compressed air energy storage technology with independent intellectual property rights: during off-peak electricity periods, a compressor was used instead of a gas turbine to compress air, while recovering compression heat; during peak electricity periods, stored heat was released to heat high-pressure air, driving an expander to generate electricity.
In 2010, a 15-kilowatt advanced compressed energy storage system was constructed.
This improvement not only eliminates the need for additional fuel, achieving zero emissions, but also utilizes previously wasted compression heat energy, significantly increasing energy storage efficiency, theoretically reaching over 70%. This localized approach was established according to local conditions.
However, this change also means that there is no mature experience to draw upon, from basic research to key technologies, and even to engineering development.
Dare to be the "first crab eater"? Chen Haisheng did not hesitate: "We must master independent intellectual property rights. Even if it takes a few more years, we must grasp core technologies. We cannot always imitate or follow others, nor can we be constrained by them."
Persistently "nailing down nails" to break through "a wall"
Since the concept of compressed air energy storage was proposed, countries around the world have been using the technology route of gas turbine power generation. It wasn't until Chinese scientists proposed replacing core components that the industry saw a new path. However, China had no technical reserves in this technology, let alone an industrial foundation. Chen Haisheng described the difficulties faced at the time as hitting a wall.
"Banging your head against a wall with your eyes closed, even if you break your head and bleed, is useless. To make a breakthrough, you must focus limited time and resources on limited goals, increase the intensity of tackling key problems, just like nailing nails on a wall," he said.
In 2010, Chen Haisheng led a newly formed small team and set up a "nailing nails" timetable: completing a 1.5-megawatt demonstration project in 3 years, building a 10-megawatt demonstration project in 4 years, and constructing a 100-megawatt demonstration project in 5 years.
The 1.5-megawatt advanced compressed air energy storage system, completed in 2013.
The key challenge to overcome is the internal flow and heat transfer mechanisms of the core components, the compressor, and the expander.
Li Wen, Deputy Director of the Energy Storage Research and Development Center at the Institute of Engineering Thermophysics, explains that the air expander of the advanced compressed air energy storage system has a high load, with an expansion ratio exceeding conventional gas expanders by more than 2 times. It has a large flow rate and high speed, requiring not only efficient operation under high pressure, high load, and high speed but also solving the coupling issues with other turbine machinery. To address this, the team has established a series of experimental platforms, combined with computer simulations, for repeated testing, optimization, and improvement.
Thermal storage and cold storage technology are crucial factors determining the success of the technology.
Traditional compressed air energy storage technology requires combustion, consuming a large amount of natural gas. Through efforts, the Energy Storage Team at the Institute of Engineering Thermophysics has compensated for this drawback using advanced thermal storage and cold storage technology. Moreover, they use water as the lowest-cost thermal storage and cold storage medium.
"This is a solution that has never been seen anywhere in the world," says Wang Liang, a researcher at the Institute of Engineering Thermophysics.
To tackle such cutting-edge technology, one must possess sufficient technical prowess. Scaling up from 1.5 megawatts to 10 megawatts and then to 100 megawatts is not merely a matter of technological accumulation but a redesign of principles and key components.
The gas storage tank of the 10-megawatt compressed air energy storage demonstration project in Bijie, Guizhou, completed in 2016, was gradually filled with "nails" one after another, breaking through the thick wall as they formed a line and then a surface.
In 2021, the world's first 100-megawatt advanced compressed air energy storage national demonstration project in Zhangjiakou, Hebei, was successfully connected to the grid, achieving a power generation efficiency of 70.4%. It can generate over 132 million kilowatt-hours annually, saving 42,000 tons of standard coal and reducing carbon dioxide emissions by 109,000 tons.
Looking back at the timeline set years ago, everyone marvels at how they have truly followed this path step by step. However, this journey is far from over.
Through further technological innovation, the design efficiency of the Feicheng 300-megawatt demonstration power station in Shandong has reached 72.1%, comparable to the "big brother" of energy storage technology - pumped hydro storage. The station generates about 600 million kilowatt-hours per year, providing power security for around 200,000 to 300,000 households during peak electricity demand. It saves about 189,000 tons of standard coal annually and reduces carbon dioxide emissions by around 490,000 tons. In the future, this will be the mainstream technological route more suitable for China's power generation industry.
"The cost must come down for large-scale promotion, no matter what, it must be reduced," said Chen Haisheng. Since the first day of research and development investment, their goal has been to implement this technology in China for the benefit of the people.
Always the "first to eat the crab"
From the first test bench to the first demonstration project, to the first grid-connected power generation... along the way, the Institute of Engineering Thermophysics has been the "first to eat the crab" in China's compressed air energy storage.
Wang Liang still remembers that when they built the first 15-kilowatt test bench, due to the lack of a suitable site, they set up a canopy between two buildings and installed a fan door to create a laboratory. It was inconvenient inside because there was a thick tree, and everyone had to maneuver around it during the installation of the test bench.
For a team that was just starting out, the test bench was a necessity but also a "luxury." Due to the huge investment, funds were very tight when constructing the 1.5-megawatt pilot platform in 2012, requiring the concentration of all available resources.
In addition to financial constraints, lack of experience was also a hurdle for these young people.
"At that time, several just-graduated PhDs led a few PhD students who hadn't graduated yet, and they often stayed on-site for a month," said Li Wen. It was the first time everyone worked hard to turn scientific ideas into design drawings and then into instrument equipment. With no precedents to refer to domestically or internationally, every step had to be figured out through trial and error.
Li Wen gained insight from that period of progress and growth through trial and error: "There are no shortcuts in technology development; it must be step by step. But the fact is, as long as you are willing to explore, you can solve problems."
Following the development strategy of "developing a generation, demonstrating a generation, and applying a generation," the compressed air energy storage technology at the Institute of Engineering Thermophysics continues to evolve. While the previous generation technology is being demonstrated and applied, the next generation technology has already begun to be developed without stopping. Over the years, the team has traveled across the country with the projects. At the year-end summary meeting in 2023, they found that more than half of the staff had traveled for over 100 days, with some even exceeding 300 days.
They have been "living by the wind" all year round, enduring the elements. Taking the national renewable energy demonstration area in Zhangjiakou as an example, it has abundant wind and solar energy resources. However, due to strong winds, the winter temperature can feel like minus 40 degrees Celsius when it is actually around minus 20 degrees Celsius. Team members wearing two layers of down jackets would feel frozen after just a few minutes outdoors.
The Zhangjiakou 100-megawatt advanced compressed air energy storage national demonstration project was the first to use artificial caverns, which are artificially developed underground gas storage caves. Because this was a pioneering technological route, many unprecedented challenges were encountered during construction, leading to the team joking that "always being the first to eat the crab" was a bit hard to bear.
The panoramic view of the international first 100-megawatt advanced compressed air energy storage demonstration power station. All images in this article are provided by the Institute of Engineering Thermophysics.
On December 31, 2021, when the project finally successfully connected to the grid, the team members present couldn't help but cheer. Excitedly, they took a group photo, unanimously nominating the only woman on site - test engineer Fu Wenxiu - to stand in the center.
As a mother of a one-year-old child, she had been working on site for 103 days. She said, "Although the pressure was great, the happiness of success is something others cannot experience."
Unexpected yet inevitable
For today's compressed air energy storage, many people have expressed, "We didn't expect this."
Some elderly gentlemen had kindly reminded Chen Haisheng, "You put in 4 degrees of electricity and get out 3 degrees of electricity. Think carefully about whether this research direction is right for you."
A domestic peer sighed, "We used to be skeptical because the technology was too difficult, but we didn't expect it to succeed."
Xu Yujie, director of the energy storage research center, recalled the team's early days, saying that at that time, there were not even test benches in China, so they had to start from basic theoretical research. No one could have imagined that this technology has now reached an international leading level.
In Chen Haisheng's view, the birth and development of advanced compressed air energy storage technology at the Chinese Academy of Sciences was not accidental.
He said, "First, the Chinese Academy of Sciences encourages innovation and supports scientists in conducting forward-looking, long-term exploratory technical research."
After returning to China in 2009, the Institute of Engineering Thermophysics supported the establishment of an energy storage laboratory to carry out controversial energy storage research at the time. Chen Haisheng, then 32 years old, became the director of the laboratory. The institute's director at the time, Qin Wei, took him to the former High-Tech Research and Development Bureau of the Chinese Academy of Sciences to report on the research direction, which was recognized and affirmed. Later, the Chinese Academy of Sciences provided valuable initial funding, allowing the team to start from scratch in technical research.
"Second, the Chinese Academy of Sciences has a tradition of encouraging the transfer and transformation of scientific and technological achievements, which can support a technology from research and development to demonstration and application," Chen Haisheng said.
The process of industrializing innovative achievements from the laboratory is often referred to as the "valley of death," with a very high failure rate. The Institute of Engineering Thermophysics also encountered many obstacles in the industrialization process, but they persisted in conducting engineering demonstrations independently. With the support of relevant policies from the Chinese Academy of Sciences and the country, multiple projects have successfully demonstrated applications.
"Third, the Chinese Academy of Sciences can form large teams to carry out large-scale operations," Chen Haisheng explained. Compressed air energy storage is a multidisciplinary system engineering that requires building a large platform to provide long-term, high-intensity stable support.
"To overcome such hard technological challenges, there must be an institutionalized team," Xu Yujie said. "Even if we tackle the three key technologies of compressors, expanders, and heat storage exchangers separately, each individual technology also requires a large team to break through."
The Energy Storage Research Center currently has more than 200 staff and students. With the introduction of the national "dual carbon" goal, the energy storage industry has ushered in development opportunities, and energy storage talents have become a sought-after commodity in the job market. However, since its establishment, not a single core member of the team has left.
Wang Liang said that working diligently in the team allows him to focus on one thing and look forward to a hopeful future. "Having such a platform that allows me to persist in doing one thing and realizing my ideals makes me very happy."
In the movie "American Dreams in China," there is a classic line: "What is a dream? A dream is something that makes you feel that persistence is happiness." For the researchers at the Energy Storage Research Center, the dream of bringing clean energy into thousands of households calls them to overcome obstacles on the road to advancing key technologies in compressed air energy storage. Today, as this path widens, they will continue to move forward, pursuing even greater happiness.
