Stadtwerke München, Germany (SWM) has jointly with Siemens’ Infrastructure & Cities division created a virtual power plant in which a number of small-scale, distributed energy sources are pooled and operated like a single installation. The main aim of SWM is to improve the reliability of planning and forecasting for decentralised power generation sources in the area which it supplies, by means of this virtual power plant which was devised jointly with Siemens.

In the first stage, unit cogenerating stations with a total rating of 8MW were integrated, along with renewable energy generating plants totalling 12 MW. The core component of this virtual interconnection is the distributed energy management system (DEMS) made by Siemens. It ensures that Stadtwerke München can not only optimally deploy and operate its decentralised energy sources and loads, but also add more value from greater marketing scope.

the central point of SWM’s virtual power plant, in which six unit-type cogeneration modules, five hydropower plants and a wind farm in the Munich area have been combined to form a virtual interconnection, is that it can be operated more efficiently than the decentralised plants separately. “We are in a position to create a virtual power plant as a key element of a Smart Grid in such a way as to provide maximum possible benefit for the operators of the integrated distributed energy sources and for the power supplier too. For municipal utilities, virtual power plants offer new potential”, commented Jan Mrosik, CEO of the Smart Grid division of the Siemens Infrastructure & Cities sector.

“The virtual power plant meets the demands encountered in both operation and marketing. It enables SWM to add more value, because it opens up further marketing alternatives, for example on the Leipzig Energy Exchange EEX or the market for regulated energy. Our initial positive experience is encouraging us to expand the virtual power plant by including further energy sources and switched loads. In the long term this will create prospects for counteracting the supply problems that arise when more of the infeed comes from renewable energy sources. That is precisely what a Smart Grid is all about”, said Stephan Schwarz, SWM director for Utilities and Technology.

The Siemens DEMS networks and pools the individual distributed energy sources, so as to be able to control them centrally as if they were one power plant. The system processes all the important information such as weather forecasts, current electricity prices and energy demand. Based on these data, a deployment schedule for all included plants is drawn up and monitored. For example, thermal loads are predicted depending on weather forecasts and day type in hourly time resolution. The anticipated level of generation from renewable energy sources is based on weather forecasts and on the respective plant characteristics. The calculated deployment schedule consequently minimises the costs of generation and operation in the interconnected plants of the virtual power station. The DEMS takes account of ecological as well as economic aspects.

In the context of real-time optimisation and on the basis of the deployment schedule, deviations from plan that occur in the course of system management are allocated to generation, storage and controllable loads, so that overall planned targets can be met. The software-based distributed energy management system is connected to the process via the Simatic WinCC HMI, also made by Siemens. For the exchange of individual values (and ranges thereof) between DEMS and the components involved, standardised TCP-IP data interfaces are used. As communication takes place via LAN or WAN, GPRS, bus systems or ISDN lines, the existing communications infrastructure of the operator of the virtual power plant can be utilised.