Liquid air energy storage: Potential and challenges of hybrid power plants

The current increase in the deployment of new renewable electricity generation systems is creating new challenges in balancing electric grids. Solutions including energy storage at small and large scales are becoming of paramount importance to guarantee and secure a stable supply of electricity. This paper presents a study about a hybrid solution including a large scale energy storage system coupled with power generation and fast responding energy storage systems. The hybrid plant is able to deliver the energy previously stored by using an air liquefaction process either with or without the contribution of additional energy from combustion. The paper also highlights how such hybrid plants may offer the chance of providing the grid with fast control services. An ideal energy storage technology should have a high power rating, a large storage capacity, high efficiency, low costs and no geographic constraints. The use of air as energy carrier has been studied since the 20th century with the first compressed air energy storage (CAES) systems. This technology is still considered to have a potential but it is geographically constrained, where suitable geological reservoirs are available, unless compressed air is stored in pressurized tanks with significant costs. Liquid Air Energy Storage (LAES) represents an interesting solution due to its relatively large volumetric energy density and ease of storage. Different process schemes for hybrid plants were modeled in this study with Aspen HYSYS® simulation software and the results were compared in terms of equivalent round-trip and fuel efficiencies. Equivalent round-trip efficiencies, higher than 80%, have been calculated showing that the proposed configurations might play an important role for power systems balancing in the near future.