StEnSea

StEnSea - Stored Energy in the Sea

The project Stored Energy in the Sea (StEnSea) explored, for the first time, a new form of environmentally friendly large-scale electrical energy storage 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 engaged as partners to test the novel 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 hollow concrete body located on the seabed. In pumping mode, the hollow sphere is emptied using current and in discharge mode, it is refilled with water via a turbine to recover the stored energy. A detailed description of the operating principle and further information can be found on the StEnSea topic page.

System Analysis and Planning

The project consisted of a detailed system analysis covering design, construction, and logistics concept for the pressure vessel, development and detailed design of the pump/turbine, power grid integration 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) site analysis identified an installable global storage capacity of approximately 817 TWh, more than 1000 times the currently installed worldwide pumped storage capacity. In particular, the application of this technology in coastal sites, for example near 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 investigated the economic efficiency of the concept across a range of parameters, e.g., number of units 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 scale model of the offshore pumped storage system was built to demonstrate the operating principle in a model test for the first time worldwide. The functional model was successfully installed and tested in Lake Constance at a water depth of 100 m. In the process, detailed questions regarding design and construction, installation and logistics, as well as operation and maintenance concepts for the storage system were addressed. As part of the project, the Institute of Fluid Mechanics and Hydraulic Machines at the University of Stuttgart investigated the technical feasibility and provided an initial preliminary dimensioning for the pump turbine for both the functional model and the commercial full-scale system. The sphere for the model test was designed and manufactured by Hochtief Solutions AG.

The model test showed that operation of the system is feasible both with and without a pressure compensation 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 prior to the experiment with the Institute for Lake Research at Lake Constance and all other stakeholders. Although Lake Constance is one of Germany’s most important drinking water reservoirs y, permission 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 using diving robots to further investigate the actual effects. These confirmed the low impact on the underwater ecosystem.

Lowering of the StEnSea sphere into Lake Constance

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

Photo Documentation

Art Project Accompanying 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 entirely different perspective on the research project. Inspired by shapes, materials, and events, she highlighted the potential for an aesthetic interpretation of the project. As a result, the graduate of the State Academy of Fine Arts in Stuttgart designed the fabrics shown in the illustration.

Research Project StEnSea