Techno-economic and life cycle assessment of large energy storage systems

Abstract: Energy storage systems (ESSs) play a key role in the implementation of sustainable energy. However, the life cycle cost, energy use, and greenhouse gas (GHG) emissions, which are important decision factors for their implementation, has received limited attention. For this reason, the economic and environmental implications of implementing ESSs were explored in this thesis. In this study, life cycle assessment models were developed to determine the economic feasibility, net energy ratio (NER), and GHG impact of ESSs. ESSs here refer to pump hydro storage (PHS) and compressed air energy storage (CAES). The PHS stores energy in the form of gravitational potential energy of water by using height differential between two reservoirs whereas CAES stores energy in compressed air. The life cycle assessment (LCA) models were developed using data-intensive bottom-up methods for capacity ranges of 98–491 MW, 81–404 MW, and 60–298 MW for PHS, conventional CAES (C-CAES), and adiabatic CAES (A-CAES), respectively. For CAES systems, cost models were developed for storage in salt caverns, hard rock caverns, and porous formations. The NER was calculated as a ratio of net energy output to the total net energy input, while LCA was conducted based on the direct emissions factor (DEF) and total emissions factor (TEF) of the ESS. The DEF is the amount of emissions associated with the storage systems per kWh of electricity produced. DEF does not include upstream emissions from electricity generation whereas TEF incorporates the upstream emissions from electricity generation in addition to the direct GHG emissions. The results show that the levelised cost of electricity is $69–$121 for PHS, $58–$70 for C-CAES, and $96–$121 per MWh for A-CAES. C-CAES is economically attractive at all capacities, PHS is economically attractive at higher capacities, and A-CAES is not attractive compared to PHS and C-CAES. The NER for PHS, C-CAES, and A-CAES is 0.778, 0.543, and 0.702, respectively. The NER is highest for PHS, followed by A-CAES and then C-CAES. The DEF (gCO2e/KWh) for PHS, C-CAES, and A-CAES, was 7.79, 264.36, and 4.96, respectively. The DEF for C-CAES is significantly higher due to the consumption of natural gas during the production of electricity.