Solutions for Offshore Renewable Energy Storage: PowerBundle and Repurpose Pipeline Energy Storage (ROPES)
Authors: De Klerk Kevin , Hazim Azril Syazwan , Kloster Ernst , Buhagiar Daniel , Gray Alasdair 
Published: October 2022

Abstract
There is a significant drive to decarbonise the energy system resulting in a need to integrate large quantities of intermittent renewable power into both onshore consumer grids and offshore isolated grids. This brings significant technical challenges that can be addressed using the right energy storage technology for future times of intermittency and peak power demands.
The PowerBundle is a full-scale subsea hydro-pneumatic energy storage (HPES) system. Electricity is used to pump seawater into a closed pipeline bundle to compress a volume of pre-charged air and is then recovered by allowing the compressed air to push the water back out through a hydraulic turbine generator. The surrounding seawater acts as a natural heatsink, avoiding thermal losses and making the solution highly energy efficient. At the heart of the development is an established supply-chain, developed over 40 years, which will deliver a reliable system with an up to 40-year service lifetime, independent of the charging-discharging regime. The system avoids any harmful chemicals and embodies the core principles of safety, reliability, sustainability and cost-effectiveness. This HPES solution will be attractive for offshore projects requiring an interface to provide power balancing and scheduling, which will benefit stakeholders in the oil-and-gas and renewable energy sectors seeking to deliver intermittent power to their end customer. This development will lead to a significant reduction of greenhouse gas (GHG) emissions due to more holistic renewable infrastructure. The PowerBundle provides a scalable storage solution which can be placed in waters close to land, supporting the scale-up, resilience and economies of renewable electricity.
However, as a first step, the innovative Repurposed Offshore Pipelines as Energy Storage (ROPES) solution repurposes existing, aged offshore installations into energy storage systems based on proven hydro-pneumatic principles, towards a cost-competitive, highly reliable system. Findings from a recent Concept Assess study prove the cost competitiveness of the solution, thanks to a low Levelised Cost of Storage (LCOS), paired with the value of deferring full decommissioning of existing assets. The study scope covers aspects of market recognition, technical feasibility, risk and opportunity assessment, cost estimates and value delivery to potential clients. Four case studies covering potential prospects offshore Australia and in the North Sea illustrate the diverse architectural application of the solution. The resultant cost estimates form the Net Present Value (NPV) analysis, and eventually derive the solution LCOS, which shows cost superiority over marinised Li-ion batteries and is comparable to onshore battery systems. The solution shows clear benefits over a typical battery storage system, including reduced safety risks, less topside constraints along with a longer and predictable operating lifetime. The ROPES solution enables the storage of renewable power whilst allowing to optimise time and expenditure for decommissioning of existing infrastructure, therefore represents a unique opportunity to unlock a new market segment within the offshore energy sector while the PowerBundle technology reaches maturity.