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Herten: A town in the Ruhr region with a thousand years of history and once one of the largest mining towns in Europe serves as a model region for the research project.
© Arnoldius, CC BY-SA 3.0
Power grids – local management system

Follow-up workshop participants (from left to right): Dr Margret Waschbüsch (Project Management Jülich), Franz Gilles (Herten municipal utilities), Leander Grunwald (Fraunhofer UMSICHT), Dr Barbette Nieder (Town of Herten), Andreas Dietrich (University of Duisburg-Essen), Dr Annedore Kanngießer (Fraunhofer UMSICHT), Thorsten Rattmann (Managing Director of Herten municipal utilities), Dieter König (Project Management, Dortmund University of Applied Sciences), Prof. Dr Christoph Weber (University of Duisburg-Essen), Dr Jan Gall (Robert Bosch GmbH), Prof. Dr Christian Rehtanz (Dortmund University of Applied Sciences), Detlef Großjohann (Herten municipal utilities), Dr Stefan Kippelt (Dortmund University of Applied Sciences), Bernhard Dick (Dortmund University of Applied Sciences), Carsten Beier (Fraunhofer UMSICHT)
© TU Dortmund

The town as a virtual energy storage system

Scientists from industry, research and municipal companies have developed a management system as part of the “City as Storage System” project, bundling CHP plants, heat pumps, night storage heating infrastructures, PV batteries and other systems. Final field testing has shown how storage units, generators and loads in coordinated operation support the power grid as a virtual energy storage system.

Virtual storage systems in urban regions can already contribute to ensuring stable power grids. Researchers came to this conclusion having completed their theoretical and practical investigations. Considerable storage potential currently remains untapped, hidden away in various distribution grid systems. Bundling into a virtual energy storage system can exploit this potential for the further development of renewable energies. Simulation calculations for the model regions of Herten and Wunsiedel have revealed an exploitable storage potential of 5 and 3 MWh respectively on average. Projections for all of Germany indicate virtual storage systems could surpass the output of current existing pumped storage power plants.

The research project (as reported by BINE Information Service) shows how this can be implemented, though also what technical and regulatory hurdles remain. Field testing in the model region should reveal whether developed models and technical solutions prove successful in practice.

Heterogeneous system pool

Various energy converters, storage systems and consumers worked together in a grid-supportive manner in field testing. A specific concept had to be developed and implemented for CHP plants, heat pumps, night storage heating infrastructures, PV batteries and other systems respectively. This is technically feasible in a research project, though too costly for efficient use. Researchers recommend integrating a communication interface such as VHPREADY or EEBUS for future product developments in order to efficiently tap the flexibility potential of individual systems.

ICT infrastructure, protocols and interfaces

The principle job of the central computer involved data collection for the various types of system and passing plant timetables to the controller used. Operation of a virtual storage system is shown to be associated with relatively high data traffic and consequently demands efficiently designed databases, protocols with low overheads and standardised interfaces. New communication protocols and interfaces were implemented for this reason. Widgets were developed to visualise the data of the virtual storage systems.

Operational planning of virtual storage systems

The central optimisation approach has proven successful in practice. The framework software and modelling language developed demonstrated favourable performance and increasing dependability as field testing progressed. For very high numbers of participating systems, the extent, however, to which computation time keeps pace with the requirements of timetable operation would need to be looked at in practice. The performance of databases and interfaces in particular for accessing prognoses and measurement data should also be considered in this regard from field test experience.

Forecasting methods

The heating requirement forecast has proven to be a very important element of the overall optimisation concept. For plants with small heat storage systems in particular, incorrect forecasts can lead to large deviations from the scheduled timetable. In this performance class especially, detailed measurements of plant operation and heat demand are often lacking, meaning that annual consumption rates have to be partially relied on in field testing. A monitoring and measurement phase involving in particular the recording of heat demand at the various times of year should consequently precede integration in a virtual storage system.

Virtual storage in distribution grids

Field testing was able to show that the technical restrictions of distribution grids can be factored into the operational planning of virtual storage systems with relative ease. A prerequisite in this regard, however, is the availability of a sufficiently accurate forecast of grid load and the ability to pass this information to the storage operator.

Practical flexibility potential of various system types

Essentially, all technologies under review can be integrated into a virtual storage system, though with very different potentials. For smaller systems such as heat pumps, heat storage combined with lacking heat quantity measurements quickly becomes the limiting factor. Converting to a larger buffer storage system seems to make sense in this regard, yet presents considerable challenges around on-site regulation. Existing electric storage heaters can offer high flexibility in practice subject to certain constraints in relation to necessary conversion measures. For battery storage systems, in particular combined with a PV system, whether combined operation to include self-consumption is preferred over purely market-sourced optimisation must be looked at on a case-by-case basis.

Energy Storage research initiative

The research project was funded as part of the Energy Storage research initiative conducted by the German Federal Ministry for Economic Affairs and Energy. The final report will be published shortly.

For more details about the project, please see the project business card on the web portal of the Energy Storage Funding Initiative at forschung-energiespeicher.info.



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Project management
TU Dortmund, ie3

Project partner
Robert Bosch GmbH

Project partner
Fraunhofer UMSICHT

Project partner
SWW Wunsiedel GmbH

Project partner
Hertener Stadtwerke GmbH


City as Storage
Project presentation on the portal for the Energy Storage Funding Initiative

Energy storage systems
Recent reports on research, development and demonstration of energy storage systems

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