Feasibility analysis of underwater pumped-hydro energy storage in Maltese waters

Abstract

The dissertation focused on Underwater Pumped Hydro Storage (UPHS) Systems and their feasibility in the local scenario. In order to better understand such systems, an extensive literature review was carried out on energy storage technologies, namely batteries, flywheels, compressed air, underwater compressed air, thermal and pumped hydro storage. A comparison was carried out between a number of these storage types and it was found that Underwater Compressed Air Energy Storage (UWCAES) and PHS (which includes UPHS) were two leading technologies due to high power rating and a long discharge times. The objectives of this study were to : 1. Generate an analytical tool to analyse a UPH System at the local scenario and to determine the revenue and feasibility of the system ; 2. Obtain reliable data and cost estimates of componenets and parts to use in the system analysis for economic viability 3. Determine the revenues and feasibility of a UPHS system at the local level ; 4. Determine what conditions must be met in order to make such a system economically feasible Throughout this dissertation, the UPHS Systems that were considered for case studies were the MIT Energy Strage Spheres and Fraunhofer’s StEnSea Unit. These Units were described in detail and costs, expenses and the in-life cycle of a system were determined. A Microsoft Excel tool named the SubSea Analytical Tool was developed to work out the costings necessary to commission a System and to determine the profitability of such a System. The results showed that for the Systems presented, neither one was feasible to commission in a local scenario. The revenue generated after selling the energy stored as electricity was toolow compared to the capital and running costs. In the discussion, a sensitivity analysis was conducted to show he impact of modifying each variable with the Levelised System Profits over the System’s lifetime, and the critical cost-drivers were successfully identified.

The cost drivers were identified to be the electricity price margin, concrete costs, pump-turbine costs and the semi-submergible barge costs. The electrical interface only had an impact with a low number of Units in a System. Note that the term “Unit” refers to either a StEnSea Unit or an Energy Storage Sphere. Cost-cutting ideas were generated and applied to both Systems, and once these improvements were applied, both Systems turned to be economically viable. The set of conditions to have a feasible System were successfully determined as part of the conclusions to this study.