Net energy balance and greenhouse gas emissions from renewable energy storage systems

Abstract

Using life-cycle assessment, metrics for the calculation of input energy requirements and greenhouse gas emissions from utility 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 systems (BESS). Methodology for evaluating dispatchable renewable systems that combine renewable energy generation and energy storage is also introduced. In general, the use of energy storage with renewable generation substantially increases the input energy required to produce electricity, as well as the total greenhouse gas emissions. The change in input energy is reflected in an overall reduction in the system energy payback ratio (EPR). The change in EPR and emissions rate is relatively small when PHS is used, but is significant when CAES or BESS is utilized. CAES produces substantial emissions from the combustion of natural gas during operation, while BESS systems are highly energy- intensive in the construction phase. Coupling storage and renewable energy systems can increase the per unit GHG emission rate by a factor of 2-5 times over the base rate. Even so, this emission rate is still substantially lower than fossil fuel derived electricity sources. iii