German energy policy has set itself a clear goal: to see to it that by the year 2050, at least 80 percent of electricity in Germany will come from renewable sources – wind and solar energy foremost among them. While this sounds good, it also poses a challenge for the operation of the power grid: the supply of green power rises and falls with wind and lulls, sunshine and cloudy skies. For power grids, the added transport of current also poses an enormous strain because they were not designed to accommodate thousands of wind turbines in Germany’s north, nor millions of solar modules, all feeding their current into the transmission or distribution grid.

To help accommodate more and more renewable energy in the grid, researchers in the Fraunhofer Network on "Smart Grids" are developing a variety of new technical solutions. Prof. Dr. Jürgen Schmid, director of the Fraunhofer Institute for Wind Energy and Energy System Technology IWES in Kassel, describes the tasks that lie ahead for scientists: "To keep the power grid in functioning order, it has to be equipped for the new age of green power. Grid operators also need new control instruments such as wind and solar output forecasts for mission planning at their plants."

One thing is certain - a paradigm shift is underway: existing grid structures oriented toward large, conventional power plants need to be redesigned. In the future, power will be fed into the grid decentrally by a large number of energy producers. To offset the fluctuations that this involves, large consumers such as cold-room operators or swimming pools can step into the breach whenever the grid is rich in green power, to actively relieve grid load. The scenario would function something like this: a cooling house starts up its cooling equipment and drops the thermostat temperature further – as a way of storing cold for periods in which the wind turbines are standing still. These potentials, among other things, are demonstrated in the "eTelligence" project in Cuxhaven, which is sponsored by the E-Energy Initiative of the Federal Ministry of Economics and Technology.

Operated intelligently, the inverters on photovoltaic and wind plants that convert direct current from the plants to alternating current for the power grid can also help maintain grid stability. Currently, every inverter in use feeds current into the low-voltage grids in cities and towns, regardless of other current. In the future, sensors in the transformers in these local grids will coordinate the activity of these inverters. This stabilizes the power grid.

"This approach is particularly interesting in regions with a very high photovoltaic share because low-voltage grids still lack the high-resolution measurement technology found in high-voltage grids and will thus play a decisive role in creating the smart grid of the future," explains Dr. Peter Bretschneider of the Fraunhofer Application Center System Technology AST in Ilmenau. He is one of the coordinators of the Fraunhofer Network on "Smart Grids."

In the future, the principles that work for large consumers will also work for private users: the specialists in the Fraunhofer Network have developed the right software applications for the job. With these software solutions, depending on the current supply, household appliances can automatically be switched on and off, with energy storage equipment and micro-block-type thermal power stations involved as well. If the sun is shining or when lots of wind is blowing, current is cheap. This is when it makes sense to activate clothes dryers and freezers. "Smart energy systems at the end consumer’s grid level are the key to a sustainable and reliable energy supply," explains Dr. Christof Wittwer of the Fraunhofer Institute for Solar Energy Systems ISE. Solutions such as the openMUC and OGEMA software are available free of charge as open-source programs. "In the future, they will provide the basis for mass application of decentralised energy management with automatic communication between households or small businesses and the energy market," Dr. Philipp Strauss at IWES adds.

Along with large consumers and private households, the Network is also studying the use of electric cars and small storage batteries in homes and businesses that can provide intermediate storage of solar energy for use during the night or cloudy periods of the day. At the Fraunhofer trade fair stand in Hall 13, Stand C41, the scientists are also presenting charging-management solutions for electric vehicles, as well as mobile and stationary intelligent electricity meters: Smart Meters. Visitors are welcome to use the "Smart-Grid Demonstrator" to slip into the role of an energy manager and attempt to harmonize fluctuations in power generation and consumption.