Application of Cryogenic Energy Storage (CES) in distributed renewable generation

Abstract

Application of energy storage becomes a common solution for improvement of renewable generation system performance. Nowadays thermal energy storage by water sensitive heat provides limited flexibility in operation of generation facilities. Storage capacity for this type of energy accumulation accounts only for 35-55 kWh•m -3 . For example, if a combined heat power (CHP) generator had the output of 100 MWe, then the heat energy for accumulation will be at least equal to this value. Waste heat will fill the tank with a volume of 2000 m3 in only one hour. Another limitation is low efficiency to convert heat energy from thermal storage to electrical energy. Due to that great interest is in liquid air energy storage (LAES). Cryogenic technologies nowadays represent widely used industrial tools. However, the first pilot plant operation demonstrates very low round trip efficiency. Intensive effort of many researches encourages further development of cryogenic energy storage (CES). Various simulations of the process and combination with another energy technology predict round trip efficiency up to 50% and more. Our research was focused on two aspects: firstly, to apply for process design in coordinate pressure-enthalpy widely used in refrigeration and secondly investigate the possible benefit of joint operation bioCHP and CES. The proposed process flowsheet employs Kapitza cycle for air liquefaction and single stage compression, and single stage expansion. As results of considerations the equation was developed for calculation of specific energy for air liquefaction. Calculation resulted in specific work value of 2223 kJ•kg -1 .The eEnergy recovery process from CES was based on liquid air pressure increase up to 60 bar and then superheating to 350 ºC with application of steam from turbine extraction. Since optimum combination of parameters was not investigated, the round trip efficiency was only 10%. Nevertheless, our research reveals that just 6% of total steam flow from extraction of the turbine with rated capacity 4 MW will ensure 1 MW output in the air turbine. 12 cubic meters of liquid air can generate electrical power of 1 MW during one hour.