StEnSEA

StEnSEA - Stored Energy in the Sea

The Stored Energy in the Sea (StEnSea) project was the first to explore a new form of environmentally friendly storage of large quantities of electrical energy in the sea. After the idea was developed by Prof. Horst Schmidt-Böcking and Dr. Gerhard Luther in 2011/2012, Fraunhofer IEE and Hochtief Engineering were contacted as suitable partners to test the new pumped storage concept in practice. Following a structural feasibility study by Hochtief Engineering, the concept of conventional pumped storage was transferred to the sea with funding from the BMWK.

The underwater pumped storage power plant uses the sea itself as the upper storage reservoir. The lower storage reservoir is formed by a spherical concrete hollow body on the seabed. In pumping mode, the hollow body is emptied using charging current and, in discharge mode, it is refilled with water via a turbine, thus recovering the stored energy. A detailed description of how it works and further information can be found on the StEnSea topic page.

System analysis and design

The project consisted of a detailed system analysis with design, construction, and logistics concept for the pressure vessel, development and detailed design of the pump/turbine, integration into the power grid based on load flow calculations, market analyses and economic feasibility studies for an international market, and the development of a market launch strategy and roadmap for technical implementation..

A GIS (geographic information system) location analysis revealed a globally installable storage capacity of around 817 TWh, which is more than 1000 times the pumped storage capacity currently installed worldwide. In particular, the application of this technology in coastal locations, for example off large densely populated regions such as Norway (Norwegian Trench), Spain, the USA, and Japan, shows great potential.

Potential and economic efficiency

A techno-economic analysis was used to examine the economic efficiency of the concept across a range of parameters, such as the number of plants installed in a park, and showed that this technology is competitive with existing storage technologies.

Model test in Lake Constance

In addition, a 1:10 model of the offshore pumped storage facility was built to demonstrate the operating principle for the first time worldwide in a model test. The functional model was successfully installed and tested in Lake Constance at a water depth of 100 m. In addition, detailed questions regarding the design and construction, installation and logistics, as well as operating modes and maintenance concepts for the storage system were investigated. As part of the project, the Institute of Fluid Mechanics and Hydraulic Machines at the University of Stuttgart investigated the technical feasibility and made an initial preliminary dimensioning for the pump turbine of the functional model and the commercial target size. The sphere for the model test was designed and manufactured by Hochtief Solutions AG.

In particular, the model test showed that the system can be operated with and without a pressure equalization line.

Parameters	StEnSea System 1:10 (Lake Constance)	StEnSea-System 1:1
Outer diameter/ m	3	30
Weight/ t	20	20.000
Water depth/ m	100	600 - 800
Capacity/ MWh	0,001 – 0,003	20
Power/ MW	0,002 - 0,004	5 - 7
Efficiency	0,40	0,80

Ecological aspects and safety measures

To assess the ecological risks, consultations were held with the Institute for Lake Research at Lake Constance and all other stakeholders prior to the start of the experiment. Although Lake Constance is one of the most important drinking water reservoirs in Germany, the application to conduct the experiment was approved because the ecological risks posed by the materials used in the concrete sphere (mainly steel and concrete) are minimal.
The suction of animals was prevented by a low flow velocity at the water inlet and a correspondingly fine-meshed grid. Before and during the experiment, additional analyses were carried out with diving robots in order to better investigate the actual effects. These confirmed the low impact on the underwater world.

Funding: Federal Ministry for Economic Affairs and Energy

Functional principle and follow-up project

Theme Page

Functional principle Ocean pumped storage power plants

Stensea

Project Page

StEnSEA 2.0

mehr info

Photographic Documentation

Art project accompanies research project

Ein Foto vom Kunstobjekt aus Stoff zum Forschungsprojekt StEnSEA — © Velia Dietz

Textile designer Velia Dietz provided artistic support for the StEnSea research project as part of her state graduate scholarship “textile,” thereby creating a completely different approach to the research project. She drew inspiration from forms and materials as well as events, highlighting the possibility of an aesthetic interpretation of the project. As a result, the graduate of the State Academy of Fine Arts in Stuttgart designed the fabrics shown here.

Research Project StEnSEA