Researchers in China have proposed a novel method for storing surplus renewable energy by converting it into compressed air and integrating it into urban district heating pipelines. In this concept, existing infrastructure used to circulate hot water or steam for building heating is repurposed as an energy storage medium. The system operates on an adiabatic principle, in which the heat generated during air compression is captured and reused rather than dissipated, improving overall efficiency.
“This method does not require complex structural modifications and does not affect the original heating functionality,” the researchers said. “In addition, it enables gas storage during periods when the heating system is idle, thereby overcoming geographical constraints and allowing for widespread application in various urban heating networks. Furthermore, because the system can serve both heating and energy storage functions simultaneously, it does not require the heating pipeline to be abandoned.”
The heating pipeline compressed-air energy storage (HP-CAES) system was designed using thermodynamic modelling and simulations based on the central district heating infrastructure of Zhumadian City in Henan province, China.
The proposed HP-CAES system stores compressed air inside the heating pipeline network during non-heating seasons, allowing existing infrastructure to serve as an energy storage device. During periods of low electricity demand, surplus electricity powers multi-stage compressors that compress ambient air. The heat generated during compression is recovered through heat exchangers and stored in hot-water tanks, while the compressed air is injected into the heating pipelines.
Unlike conventional metal tanks, the insulated steel pipeline walls possess significant thermal inertia and absorb part of the compression heat, helping stabilize air temperature and pressure during storage. When electricity demand rises, compressed air is released from pipelines, reheated using stored thermal energy, and expanded through turbines to generate electricity.
In the simulations, the HP-CAES system had a total compressed-air storage volume of 38,334.69 m³, consisting of three pipeline sections: 7,792 m of 1,400 mm-diameter pipe, 13,622 m of 1,200 mm-diameter pipe, and 13,946 m of 1,000 mm-diameter pipe. They all had a baseline wall thickness of 15 mm and a 50 mm insulation layer. The system operated at a charging pressure of 10 MPa and a discharging pressure of 4 MPa. In further pressure sensitivity analyses, those were extended to 5-11 MPa end pressure of charging (EPC) and 1-6.5 MPa end pressure of discharging (EPD)
The model used three-stage compressors and three-stage expanders, each with rated isentropic efficiencies of 0.88 and 0.92, respectively. Compressor and expander mass flow rates were both 120 kg/s, while the cooling and preheating water flow rates were 36 kg/s each. Thermal storage consisted of 2,178 m³ hot-water and ambient-temperature storage tanks, and the resulting baseline system delivered an input power of 72.32 MW, an output power of 43.68 MW, and an energy storage capacity of 229.33 MWh.
This system was compared with a metal tank-compressed air energy storage (MT-CAES) system, which served as the reference case. In the MT-CAES configuration, compressed air was stored in conventional metal pressure vessels. At the same time, all other major system components and operating conditions were kept identical to those of the proposed system to isolate the effect of the storage method itself.
The analysis showed that air temperature within the storage system varies throughout operational cycles as a result of compression, heat losses, and subsequent expansion. In the case of a system operating between an EPC of 10.00 MPa and an EPD of 4.00 MPa, the metallic storage tank experiences a maximum temperature swing of 75.18 K. By contrast, the heating pipeline network shows only minor thermal variation of 14.52 K, attributed to its higher thermal inertia and effective insulation. At an equivalent storage volume of 38,334.46 m³, the heating pipeline configuration was found to achieve an energy storage density of 5.98 kWh/m³, outperforming the metal tank system by 34.68%.
The scientists also found that using the sliding pressure (SP) mode instead of constant pressure (CP) improved round-trip efficiency by 4.77% for HP-CAES and 3.29% for MT-CAES, mainly by reducing throttling losses. Under SP operation, the HP-CAES system achieved a higher initial expansion pressure and an efficiency 2.64% higher than MT-CAES. The analysis also showed that optimizing pressure ranges and stage numbers requires balancing energy efficiency, storage density, and ecological performance. Under SP operation, the HP-CAES system achieved a higher initial expansion pressure of 9.91 MPa, resulting in a higher expansion ratio during discharge and a 2.64% higher round-trip efficiency (RTE) than the MT-CAES system. The research team also ascertianed that optimizing pressure ranges and stage numbers requires balancing energy efficiency, storage density, and ecological performance.
“Under the conditions of EPC at 10 MPa and EPD at 4 MPa, the investment cost of the HP-CAES system is $29.61 million, accounting for only 56.58% of that of the MT-CAES system; its static payback period (SPP) is 4,324 days, which is only 40.65% of that of the MT-CAES system,” the group stated. “Further economic analysis under different combinations of EPC and EPD reveals that the HP-CAES system achieves the shortest SPP of 3,524 days when EPC and EPD are set at 5.0 MPa and 3.0 MPa, respectively. Under the conditions of EPC at 5.0 MPa and EPD at 3.0 MPa, a 1 MW HP-CAES system can be deployed per 2.90 km2 of urban heating district, indicating its favorable application potential in urban heating networks.”
The system was presented in “Research on adiabatic compressed air energy storage system using urban heating pipeline as storage device,” published in Applied Thermal Engineering. Scientists from China's Xi'an Jiaotong University, Zhengzhou University, and the Chinese Academy of Sciences have participated in the study.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.