Thermodynamic analysis of energy storage with a liquid air Rankine cycle

Energy storage will be an important issue in a world where renewable energy will contribute a major part of the energy production. Liquefaction of gasses is being looked into as a means of energy storage. This liquid can then be expanded in a Rankine cycle in order to recover the stored energy when it is needed. If waste heat is used as input for the boiler, this can be an interesting technology to compactly store energy. In this paper an analysis is made of the efficiency of storing liquefied air. Starting from the thermodynamics of the basic cycle, a more complex combined cycle is studied. It is clear the ideal cycles have a high efficiency. Taking real expander efficiencies into account however considerably reduces the actual output. Furthermore, using combined cycles for liquefaction and energy production do not raise efficiency in a significant way, unless isothermal expansion can be well approached. Conversion efficiencies range from 20 to 50%, making these cycles comparable to hydrogen storage and compressed air storage. (C) 2012 Elsevier Ltd. All rights reserved.