Aconglomerate of many smaller power plants can replace traditional power plants. A research project known as Combined Power Plant 2 (Kombikraftwerk 2) has shown how it is possible to provide power using renewable energies, both today and in the future, without increased risk of a blackout.

German researchers from the Fraunhofer Institute for Wind Energy and Energy System Technology, or IWES, in Kassel, introduced the project at the Hannover Trade Fair earlier this month.

“Each source of energy – be it wind, sun or biogas – has its strengths and weaknesses. If we manage to skillfully combine the different characteristics of the regenerative energies, we can ensure the power supply for Germany,” predicts IWES deputy director Dr Kurt Rohrig.

The combined power plant shows it is technologically possible to let each individual producer feed electricity into the grid and have the grid remain stable during this process. To ensure that this will work, the IWES scientists and colleagues from the Siemens group have developed a software platform as part of the E-Energy Initiative of the German federal government under the motto ‘Together we are strong’, in which many small power plant operators can act together as a ‘virtual power plant’.

Since January 2011, the scientists have had such a power plant on trial in the Harz regene- rative model region (RegModHarz) – with very good results. Here, they have linked together, through the Internet, 25 plants with a nominal power output of 120 MW and, as simulated storage, a pumped storage plant and electric vehicles.

A central control ensures that the disadvantages of the renewable energies are reduced – because the sun does not always shine and the wind does not blow continuously. However, when many small producers work together, then the regional differences regarding wind and sunshine can be balanced out by the power grid or controllable biogas facilities.

In addition, surplus power can be stored or turned into thermal energy. A powerful network that has been decentralised can act as a larger entity. For this to work, the control room takes on two roles simultaneously. In its function as the ‘power plant facility manager’, it monitors the facilities that are interconnected within the virtual power plant. And, acting as the ‘pool coordinator’, it simultaneously markets the energy that is produced.

The software of the virtual power plant in the Harz region is being partially adopted for the Combined Power Plant 2 and expanded with grid stabilisation functions.

Renewable energies can stabilise the grid in Germany – on some days of the year, the electricity generated from the sun, wind, biomass, water and geothermal sources already accounts for more than half the required load.

“Ensuring that the electricity continues to reach the consumer reliably at 230 V and at a frequency of 50 Hertz . . . is a challenge that the regenerative energies will have to meet in the future,” says Kaspar Knorr, project manager of the Combined Power Plant 2 research project at the IWES.

The renewable-energy sources will also have to increasingly make contributions to the ancillary services. In the current system that is geared towards a few central producers, primarily traditional power plants ensure that these requirements are met. In their project, the scientists are modelling in detail what the power supply system of the future will look like and how the individual facilities might be distributed across Germany. They also determine the requirements for ancillary services such as frequency and voltage stabilisation, black start capability and inertia reserve, so that the renewable electricity will stably reach the consumer.

Thanks to their decentralised character and innovative developments, the renewables can already contribute to stabilising the power supply system. “With the Combined Power Plant 2, we are able to show what changes are in store for our power supply. And we demon- strate how the renewables master this task and how they can ensure the stable supply of electricity in the future,” emphasises Knorr.