Abstract
Renewable energy (wind and solar power, etc.) are developing rapidly around the world. However, compared to traditional power (coal or hydro), renewable energy has the drawbacks of intermittence and instability. Energy storage is the key to solving the above problems. The present study focuses on the compressed air energy storage (CAES) system, which is one of the large-scale energy storage methods. As a lot of underground coal mines are going to be closed in China in the coming years, a novel CAES system is proposed for application in roadways of the closing coal mines. The new system combines pumped-hydro and compressed-air methods, and features constant air pressure and temperature. Another specific character of the system is the usage of flexible bags to store the compressed air, which can effectively reduce air leakage. The governing equations of the system are derived, and the response of the system is analyzed. According to the equations, for a roadway with depth of 500 m and volume of 10,000 cubic meters, the power generation capacity of the CAES system is approximately 18 MW and the generating time is 1.76 h. The results show that the new CAES system proposed is reasonable, and provides a suitable way to utilize the underground space of coal mines.
Highlights
Renewable energy are developing rapidly in China and around the world
pumped-hydro storage (PHS) and compressed air energy storage (CAES) are suitable for large-scale energy storage
The results show that smaller cross sections of the water and air pipes will induce larger pressure loss of the final air pressure, especially when the diameter of water pipe (D) is less than 0.8 m and that of air pipe (d) is less than 0.5 m for the roadway with 500 m depth
Summary
Renewable energy (wind and solar power, etc.) are developing rapidly in China and around the world. The newly installed capacity of wind power in China in 2017 is 188.4 GW, which is. 35% of the newly installed wind power in the world [1,2]. There are many methods of energy storage, such as pumped-hydro storage (PHS), compressed air energy storage (CAES), flywheel energy storage, superconducting magnetic energy storage, and battery and super capacitor energy storage [3,4]. Among these methods, PHS and CAES are suitable for large-scale energy storage. The PHS plant has critical requirements of the geoconditions, Energies 2019, 12, 4188; doi:10.3390/en12214188 www.mdpi.com/journal/energies
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