Power to heat to power. Underwater energy storage solution.

A successful energy transition requires grid-scale electric energy storage and Carnot batteries represent a potential solution. BattMarines is a Carnot battery concept relying on storing large quantities of high-pressure steam ready to be expanded in a conventional steam power plant. The key idea is to take advantage of high pressure ambient at large sea depths, so that a thin shell vessel can be utilized to store high quality steam at low cost. Power plant is built on a platform/ship with steam pipeline connection to the vessel on the sea floor. The thesis considers the general concept including a rough description of plant configuration, thermodynamic efficiency, insulation requirements and potential materials. Several parameters studies have been carried out to quantify performance. In particular, granular glass and the mullite mineral foam have been identified as suitable insulation materials. Storing time strongly depends on the selection (days to weeks), while roundtrip efficiency is weakly influenced by the choice and lays between 41-44 %. The present conceptual study supports initial assumptions of an energetically feasible and economic competitive energy storage solution. Moreover, a suitable solution for the main challenge of sufficient thermal insulation in a high-pressure environment could be identified.