Siemens and its project partners involved in the IREN2 research project have succeeded in operating the isolated grid in the Allgäu municipality of Wildpoldsried in an uninterrupted and stable manner. They have thus created a regional, self-contained, intelligent electricity distribution network, a microgrid.

As the proportion of decentralized, renewable power generation units such as photovoltaic or biogas plants in the energy mix continues to rise, local stand-alone grids should be able to make an important contribution to maintaining a high level of supply security in the future. They will also step in in the event of disruptions such as storms, flooding or blackouts.

Depending on the amount of sunshine, the lithium-ion battery must either temporarily store surplus electricity or release it when required. It has a maximum output of 300 kilowatts and a capacity of 138 kilowatt hours.

© Siemens

"The growing share of decentralized energy generators such as photovoltaic systems and wind turbines in local grids require more intelligent control to maintain the stability and optimal operation of the grid," said Constantin Ginet, Head of Global Microgrid Solutions at the Siemens Energy Management Division. "We have now successfully demonstrated the capabilities of a microgrid in Wildpoldsried under real-life conditions. This is an important milestone in showing that microgrids will help contribute to the success of the energy transition in Germany and worldwide in the future."

The island grid test took place as part of the IREN2 research project. Siemens, Allgäuer Überlandwerk, AllgäuNetz, ID.KOM, RWTH Aachen and Kempten University of Applied Sciences have been working together since 2011 to set up and test a smart grid in the Allgäu region. The aim of the project is to technically and economically optimize an energy system with decentralized power generation. The municipality of Wildpoldsried, with around 2,500 inhabitants, is supplied entirely from renewable energy sources and generates seven times as much electricity as it consumes throughout the year.

Successful proof of islanding capability

The verification of the isolated grid capability of the low-voltage grid was carried out in four steps. First, the experts deliberately initiated a power outage. The power supply in the affected grid section was then restored locally as a stand-alone grid. According to Siemens, this isolated grid operation functioned smoothly when decoupled from the public power grid. In the next step, the partners synchronized the isolated grid with the public grid again without interruption, so that there was no impact on the 32 affected connections in several streets, including a school, a kindergarten, a commercial building and several private households. Finally, the experts demonstrated how the affected section of the grid could be switched to island operation and back again "at the touch of a button" without interrupting the power supply.

"As we suspected in advance, the affected connections of our customers did not notice the switch from normal operation to the island grid," says Guido Zeller, IREN2 project manager and employee at AllgäuNetz. "By participating in the research project today, we have once again taken the energy transition a step further," adds Michael Lucke, Managing Director of Allgäuer Überlandwerk.

The stand-alone grid trial in Wildpoldsried will also serve as a model for other low-voltage grids in the future. This is because island grids are becoming increasingly important in a fundamentally changing energy world. Electricity from renewable energy sources is becoming increasingly important. At the beginning of the 1990s, there were only around one hundred large power plants generating electricity in Germany. In the meantime, the number of small, decentralized power generation plants has risen to several million. Their number will continue to grow in the future. As the proportion of renewable energy sources increases, so do the fluctuations in electricity generation. Smart grids are one solution: thanks to intelligent control and energy storage, they can balance volatile generation and consumption and thus enable stable grid operation.