StEnSea – Results from the pilot test at Lake Constance

• Development and field-testing of a novel pumped hydro energy storage system. • Detailed description of all development phases and evaluation of the field test. • Fully functional scaled prototype developed, installed and tested in Lake Constance. • Test operation has confirmed that ventilation is not required. Storing energy offshore by means of hollow concrete spheres placed at the bottom of the sea is a very attractive solution to combine technical features of conventional pumped hydro storage systems with a huge resource potential around the globe in an economic way. However, the design, construction and installation of large concrete spheres as well as the required electro-mechanical equipment such as pump turbines and controls require R&D at system and component level as well as for the offshore logistics and grid integration. In a first scaled test using a 3 m diameter sphere a fully functional automated system has been developed, installed and tested in about 100 m water depth in Lake Constance in the South of Germany through the winter period of 2016/2017. This paper addresses the experimental work and results as well as the design and logistics investigations towards full scale systems. A short outlook is provided for the next development phase currently under negotiation with funding agencies.