Hybrid energy storage system adjusts grid fluctuations

March 08, 2018 // By Christoph Hammerschmidt
With the implementation of the "energy turnaround", the switchover from carbon-based to renewable energy, the proportion of electricity generated from fluctuating renewable sources such as wind and sun increases. This requires the expansion of electricity storage capacities and flexible energy management. Researchers at the Fraunhofer Institute for Solar Energy Systems ISE and partners have developed a hybrid energy storage system consisting of a lithium-ion battery and a super capacitor for short-term performance requirements.

The hybrid storage is coupled to the medium-voltage grid by means of a novel modular inverter. During a one-year field test on the North Sea island of Borkum, the researchers are testing and comparing different control approaches in the energy management system.

As part of the EU project NETfficient, the electricity distribution network is equipped with a high proportion of renewable energies and various storage technologies. The developed solutions for energy autonomy will be tested under real conditions in order to transfer them later on to other regions. The spatially distributed storage facilities and generators are integrated into a smart grid and controlled by an intelligent energy and network management system. 40 home storage units, five commercial storage units, a thermal storage unit and a hybrid energy storage unit are integrated into the medium-voltage network. "In addition to the 500 kWh lithium-ion battery, one of the most important components in the system is the battery inverter developed at Fraunhofer ISE. It has a total output of one megawatt and consists of highly compact and particularly dynamic subunits with an output of 125 kW each. This allows us to realize all system sizes down to the multi-megawatt range," explains Olivier Stalter, head of the Power Electronics, Networks and Intelligent Systems division at Fraunhofer ISE. In addition to the lithium-ion battery, a supercapacitor is integrated as short-term storage. This absorbs power peaks and thus extends the service life of the battery.