Surprising findings on renewable energies and disturbances in power grids
Frequency fluctuations in the power grid are the order of the day. The more renewable energies are fed into the grid, the greater the load on the grid. It not only has to cope with large fluctuations, but also with increasingly small-scale, heterogeneous and decentralized power generation. These fluctuations have now been investigated in a research project at Jacobs University Bremen under the direction of Stefan Kettemann. The results show that the increasing supply of renewable energy leads to the spread of disturbances.
The researchers investigated at what speed and in what way disturbances spread in the network. One of the results: Even the slightest fluctuations, caused, for example, by a brief increase in electricity supplies in Bremen, can be measured over long distances, even in Munich, which is almost 600 kilometres away as the crow flies. But above all: certain networks are more robust than others. “We were particularly surprised that tree-like distribution networks leading from the generator to the consumer are more stable to such disturbances than close-meshed interconnected networks in which the power lines are connected in many loops in a circle,” says Kettemann. “The opposite would have been much more likely. After all, a tree structure has much more hierarchical connecting lines than a circular network with its multitude of meshes and loops”.
The researchers found the cause for this extraordinary phenomenon in the different oscillations, the wave modes, of both networks. Similar to organ pipes, whose deepest resonance tone gets deeper with the length, it can be seen that the resonance frequencies of close-meshed composite networks get lower with the size of the network. However, this does not apply to tree-like nets. Their resonance frequency remains the same as their size increases, making them less susceptible to interference.