The scientists from the Institute of Engineering Thermophysics at the Chinese Academy of Sciences and Xi’an Jiaotong University have proposed to convert urban district heating mains into large-scale energy storage systems. In the summer, when heating systems are not in use, they propose to fill the pipelines with the compressed air generated using an excess electricity from solar and wind power plants. According to their calculations, this approach could prove cheaper and more efficient than traditional compressed air energy storage (CAES) systems.
CAES technology is considered one of the most promising ways to store large amounts of electricity. Its principle is relatively simple: when more electricity is generated than its consumers need, the electricity is used to compress the air. This air is then stored under high pressure and, when necessary, released through turbines for electricity generation.
Interest in such systems is steadily growing in China. This year, for example, Harbin Electric Corporation has announced launching of one of the world’s largest adiabatic CAES facilities, with a capacity of 2.4 GWh, in Jiangsu Province. It is located in a salt cavern and designed for a long-term electricity storage without fuel combustion or carbon dioxide emissions.
However, traditional CAES systems have a major limitation. They require either massive high-pressure metal tanks or geological structures, such as salt caverns. Both options entail significant costs.
This time, the Chinese scientists have proposed to use the available infrastructure – urban district heating mains. In the summer, when heating pipelines are idle, the mains can serve as a giant compressed air storage facility.
To test the idea, the researchers simulated operation of urban heating mains spanning nearly 35 km with the pipes ranging from 1 to 1.4 m in diameter. The total volume of such a storage facility exceeded 38,000 cubic meters. Calculations showed that the system is capable of storing about 229 MWh of energy at an output power of nearly 44 MW. This reserve is sufficient to supply electricity to tens of thousands of city apartments for several hours or to smooth out the load peaks in a large urban district.
When the new system was compared to a traditional compressed air storage facility based on metal tanks, it turned out that the heat pipelines are capable of storing approximately 35% more energy for the same volume.
Economic analyses have also demonstrated the new concept’s advantages. According to the researchers’ estimates, the construction cost of the system is only 57% of the cost of a traditional compressed air storage facility. Moreover, the new system can pay for itself in approximately 10 to 12 years, whereas the traditional compressed air storage facilities require about 30 years for it.
