Assessment of the round-trip efficiency of gravity energy storage system: Analytical and numerical analysis of energy loss mechanisms

Abstract

Emerging large-scale energy storage systems (ESS), such as gravity energy storage (GES), are required in the current energy transition to facilitate the integration of renewable energy systems. The main role of ESS is to reduce the intermittency of renewable energy production and balance energy supply and demand. Efficiency considerations are critical when developing energy storage systems. In this paper, a novel multi-domain simulation tool is employed to determine the round-trip energy efficiency (RTE) of gravity energy storage system. The study considers analytical and numerical simulations to investigate the effect of the flow rate and the pressure on the energy losses i.e., hydraulic losses, mechanical equipment losses, and particularly friction and leakage induced energy losses. Different designs are compared to determine the most efficient storage scenario and to assess the scaling up effect on GES' efficiency of storage. The effect of the internal and external positioning of GES return pipe on the system's round-trip efficiency was also compared. Finally, the overall round-trip efficiency of GES system was calculated and compared to other energy storage technologies. The results obtained from the analytical and numerical models show that the round-trip energy efficiency depends on the pressure inside GES chambers, consequently, the operating scale. The obtained round-trip efficiency of GES system ranges between 65 % and 90 %. The amount of energy lost due to the sealing friction represents the largest share in comparison with other loss mechanisms, with a percentage of 21.1 % and 0.9 % for small-scale and large-scale operations, respectively. This study demonstrates that GES operates more effectively in large-scale applications.