Sizable Energy is developing an offshore gravity-based energy storage system that uses seawater depths and high-density brine to store and return renewable electricity to the grid. The technology applies the principle of pumped hydro storage at sea, using flexible reservoirs on the seabed and at the surface instead of conventional water reservoirs at different elevations.

When surplus electricity is available, pumps move brine from a flexible reservoir on the seabed to a floating reservoir at the surface. When electricity is needed, the brine flows back down through a turbine to generate power. The company describes the system as a closed-loop design that uses commonly available materials, requires no lithium and consumes no land.

Sizable Energy co-founder Simone Biondi told pv magazine Italia that the company had completed its demonstration and concept-validation phase and moved into project development over the past year. It completed offshore tests in Reggio Calabria with the University of Reggio Calabria, following earlier tank testing at the Dutch marine research institute Marin. The tests validated key components under real conditions and demonstrated that deployment operations could be completed without specialized vessels.

The company has also received the European Commission’s STEP Seal and secured additional funding for an integrated demonstrator with a data center in Naples, scheduled for the first half of 2027. Pre-front-end engineering design (pre-FEED) and front-end engineering design (FEED) activities are underway for an initial project in Calabria and a second in Sicily.

Biondi said Sizable Energy has built an international pipeline comprising more than 10 GWh of potential projects in the Mediterranean and Middle East, with advanced discussions also taking place in the Caribbean.

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