The City as a Storage Facility: Virtual storage of electricity

Virtual energy storage in cities as a contribution to the integration of renewable energies

Virtual Energy Storage

The principle of virtual energy storage includes various systems.

Central optimization platform

Virtual storage may be visualized as updated forecasts, measuring data, and roadmaps via a graphical user interface.

Project aims

When electricity producers and consumers in a city work together via a central system, a virtual storage facility is created for the energy system. The joint project The City as a Storage Facility has investigated how virtual energy storage facilities can be implemented in practice and which technical and regulatory hurdles have to be overcome to achieve this. Particular attention was paid to the development of existing but unused storage facilities in cities. These include, for example, combined heat and power plants and heat pumps with heat storage, but also electric storage heaters and small battery storage units.


The change towards fluctuating renewable power generation requires flexible energy systems so that the power grids can be operated in a stable way in the future. From an economic and technical point of view, it is, therefore, necessary to expand electrical storage capacities. Great storage potential is currently hidden unused in local distribution networks. Both in municipal locations (swimming pools, local heating networks) and in private households, there are a large number of systems with flexibility that has not yet been actively used. The distributed storage facilities in urban areas were identified in the joint project The City as a Storage Facility and then bundled into a virtual large storage facility. In this way, the hidden storage potential can be used to further expand renewable energies.  

Virtual storage demonstrated in field test for one year

The feasibility of a virtual energy storage system was the focus of the project and was investigated for one year in the model regions of Herten and Wunsiedel. As part of the field test, the systems bundled into a virtual storage facility were controlled according to an optimized schedule. The schedules were determined using a specially developed modeling, optimization, and forecasting environment and updated several times a day. The system restrictions, the condition of the local distribution network, and the requirements of the energy market, as well as the customers’ own forecast heat demand, were taken into account.



A central management system was developed in the The City as a Storage Facility project that virtually bundles and optimizes the storage capacities of CHP plants, heat pumps, electric storage heaters, PV battery storage systems, and other systems. The established ICT infrastructure ensured secure and reliable communication with the individual systems. The one-year field test of the system by the public utility companies in Herten and Wunsiedel showed that storage facilities, producers and loads in coordinated operation as virtual energy storage facilities can compensate for fluctuating generation from renewable energy sources. A large number of practical findings were gained as to which systems should preferably be integrated and how the technical connection and control can be realized. This represents an important basis for an economical use of the connection by the public utility companies. Simulation calculations for the model regions Herten and Wunsiedel also revealed a shift potential of up to ten megawatt-hours (MWh) per day. Projected over the entire federal territory, virtual storage facilities could exceed the capacity of the pumped-storage plants currently available.

Project partners

  • TU Dortmund, Institut für Energiesysteme, Energieeffizienz und Energiewirtschaft
  • Universität Duisburg-Essen, Lehrstuhl für Energiewirtschaft
  • Robert Bosch GmbH
  • Bittner+Krull Softwaresysteme GmbH
  • SWW Wunsiedel GmbH
  • Hertener Stadtwerke

Funding information

Federal Ministry for economic affairs and climate action


Duration: December 2013 to February 2018