Using life cycle assessment, metrics for calculation of the input energy requirements and greenhouse gas emissions from utility scale energy storage systems have been developed and applied to three storage technologies: pumped hydro storage (PHS), compressed air energy storage (CAES) and advanced battery energy storage (BES) using vanadium and sodium polysulphide electrolytes. In general, the use of energy storage with electricity generation increases the input energy required to produce electricity, as well as the total greenhouse gas emissions. Despite this increase, the life cycle GHG emission rate from storage systems when coupled with nuclear or renewable sources is substantially lower than from fossil fuel derived electricity sources. GHG emissions from PHS when coupled with nuclear and renewable energy systems are lower than those from BES or CAES. When coupled with fossil generation, CAES has significantly lower net GHG emissions than PHS or BES. (C) 2003 Elsevier Ltd. All rights reserved.