Analysis and design of an inverted oscillating water column for energy storage under choked flow conditions

Abstract

A novel idealised system based on an inverted, oscillating water column (iOWC) immersed in a mass of water as a potential mechanism for energy storage has been investigated. The system consists of a cylindrical tube separated by a moving disc, dividing the device into two chambers. One chamber contains air and the other water. During the discharge, water enters and contributes to the compression of the air enclosed in the lower chamber. Simultaneously, the compressed air exits the iOWC, ideally at atmospheric choked conditions. The device has been conceived for the energy storage during low-price periods, and for the recovery (e.g. through a low-pressure gas turbine) during peak-pricing hours. The performance the iOWC has been examined for two main design parameters, namely the aspect ratio Λ and of the nondimensional size of the outlet orifice δ. It has been concluded that Λ=16.5 and δ=0.0044 might be a realistic configuration for the practical implementation because (i) the gas is choked at the exit orifice, and (ii) the iOWC’s performance is stable (with relatively small oscillations). Additionally, a thermal study analysing the gas temperature has been conducted. Approximate theoretical solutions for the variables in study have been provided.