Comparing the Pressure Containment Requirements of Three Subsea Hydro-Pneumatic Energy Storage Concepts

Abstract Hydro-pneumatic energy storage has significant potential for being deployed subsea and co-located with offshore wind farms. The pressure containment storing the compressed air is the bulkiest and most expensive component of such a storage technology. This paper evaluates three different subsea hydro-pneumatic energy storage concepts, comparing their volumetric storage densities, the steel and concrete anchoring requirements and cost of the pressure containment. The pressure variation experienced by the pressure containment across the storage cycle for the three variants, which would impact the efficiency of energy conversion machinery, is also compared. It is shown that having separate accumulators, each designed for a different operating pressure, offers the potential of reducing the cost of the pressure containment by up to 40% as compared to that for the simple concept having a single accumulator. A novel approach is presented to achieve such cost reduction without constraining the energy conversion machinery to operate over a wider operating pressure range.