A Novel Combined Electricity-Gas Storage System by Synthesizing Natural Gas Liquefaction and Regasification Processes in Pressure Reduction Stations

Daily fluctuations in natural gas and electricity load profiles call for an urgent need for adequate storage infrastructure. However, building isolated electricity and gas storage systems suffers from low efficiency and high investment. In this paper, an innovative combined electricity-gas storage (CEGS) concept is proposed by smartly synthesizing natural gas liquefaction and regasification processes. Excessive natural gas and electricity are stored simultaneously in the form of liquefied natural gas (LNG) during the off-peak period. When the on-peak period occurs, LNG is regasified and its retrievable energy is utilized to generate electricity in the regasification system. Through the process simulation, the mathematical model of the CEGS system is established and the energy storage performance of the specific CGES system is evaluated with an optimization procedure. In-depth thermodynamic analysis with highlights on energy flow and heat transfer composite curve is conducted. Results show that under the rated electricity capacity, the CEGS system possesses good energy density (60.35 kWh/m(3)) as well as high equivalent round-trip efficiency (127.1%), outperforming standalone energy storage systems and conventional power-to-gas. Moreover, with the optimal parameters, 26.7% of total thermal energy is excessive which can assist the heating supply in the urban industrial area or the district heating sector. Therefore, the CEGS offers a very promising solution to peak shaving issues of power and natural gas, and has a good application prospect in the multi-energy network.