Large-scale solar thermal systems in Africa, offshore wind parks in the North Sea, photovoltaic power plants in the south, and many decentralized systems in central Europe are to produce a large percentage of our electricity in the future. But a number of challenges must still be overcome for the transition to renewable energy to be successful. How can we combine renewables and then transport electricity, without considerable loss, across thousands of kilometers? Can strongly fluctuating energy be effectively stored? How can we feed the electricity into our networks? In the Beyond Tomorrow project “Supergrid,” Fraunhofer researchers are developing components that will store and distribute electricity with minimal loss.

Innovative medium and high voltage direct current networks

“The planned, rapid development of renewable electricity generation not only necessitates the modification of existing power grids, but also an optimized energy-efficient integration of renewable energy and storage technologies that can cope with fluctuating demands for electricity. This calls for technological innovation that redefines the principles involved. Our goal is to develop key technologies at the interface between energy generation and feeding the power grid, and to optimize these in a holistic theoretical approach based on what the systems should be capable of,” explains Dr. Werner Platzer, who is based at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg and coordinates the “Supergrid” project. Scientists from the Fraunhofer Institute for Solar Energy Systems ISE, for Optronics, System Technologies and Image Exploitation IOSB, for Mechanics of Materials IWM, for Integrated Systems and Component Technology IISB are collaborating on the project.

One focus of the project is the development of components and systems for new forms of middle and high voltage DC networks, through which electricity from the sun and wind can be connected to DC-transport grid lines distances with minimal loss. High-voltage DC transmission is today used in point-to-point connections. Tomorrow’s underground DC networks will link together various separate energy sources – such as wind and solar power stations – across great distances without any significant loss of energy. This calls for new control procedures and system components that are currently under development by Fraunhofer scientists in the “Supergrid” project.

High-temperature storage systems: storing heat

Solar thermal power plants, such as in the Desertec project under construction in southern Europe and northern Africa, are set to play an important role in supplying tomorrow’s electricity. Here, solar energy is transformed into hot steamheat that is then used to generate electricity. The big advantage is that the heat can be stored in high temperature thermal energy storage systemsenabling power plants to deliver electricity round the clock.

Fraunhofer scientists want to reduce the costs of the efficient high-temperature storage devices by more than half in the long term. Heat can be very effectively stored in salt mixtures (nitrate and nitrite, among others). The disadvantage, however, is that these substances are highly corrosive. Fraunhofer researchers are thus investigating materials with long-term resistance to salt-melt corrosion, even at high temperatures. 

“Embedding networked generation and storage technology in a holistic strategy for the development of renewable energy, however, first requires a detailed analysis of the energy market,” says Platzer, explaining one of the key aspects of the project. On the basis of such an analysis, scientists plan to develop integrated and optimized grid structures.