Life Cycle Assessment of Cryobattery Energy Storage

The United Nations Paris Agreement 2016 requires rapid decarbonisation of energy systems and this implies electricity grids that are increasingly made up of intermittent generators such as wind and solar photovoltaics and increased electrification of energy services (UNFCCC, 2015). This is likely to mean a greater demand for balancing and flexibility services in the electricity system. Currently these services are typically provided by natural gas generators, diesel electric generators (DEG) and pumped water storage. However these approaches are either direct emitters of greenhouse gases (GHG) or spatially constrained. New forms of energy storage will therefore be relied upon for short-term operating reserve capacity, frequency response, demand management and peaking services. Many new forms of energy storage do not have direct GHG emissions but do however entail upstream resource consumption and operational energy losses (with associated GHG emissions) (Denholm and Kulcinski, 2004, Hiremath et al., 2015). A life cycle assessment (LCA) approach is required therefore to determine the net contribution energy storage devices can have for decarbonising the electricity sector.

Cryobattery energy storage, also referred to as liquid air energy storage (LAES) is a form of thermo-mechanical energy storage for electricity grid scale applications. It is based on the liquefaction of air through cooling and compression for charging and a turbine powered by re-expansion during discharge and developed for large scale grid application. The goal of this study is to apply a LCA method to determine the life cycle impact of a 20MW/80MWh scale cryobattery system. A comparison is also made with equivalent DEG and natural gas turbine generator alternatives to determine the net GHG emissions savings potential of the cryobattery system. The study finds that for a range of use phase and end of life scenario assumptions GHG emissions per unit of electricity supplied to the electricity grid are between 30 kg CO2eq/MWh to 232 kg CO2eq/MWh. This compares favorably with equivalent GHG emisisions values for DEG and open cycle gas tubines of 955 kg CO2eq/MWh and 701 kg CO2eq/MWh respectively.