The study, published in Nature Energy, analyzed the reliability of the electrical supply after splitting larger grids into smaller autonomous cells, called “micro-grids”.
A micro-grid would, for example, allow independent villages to utilize renewables set up in their own proximity, instead of relying on the nearest larger grid to draw their power.
The international team of scientists asked: Do renewables impact grid frequency as negatively as sometimes claimed by critics?; How likely are large and, therefore, risky deviations from the reference frequency?; and What would be the consequent challenges posed by renewables to the electrical power grid and its operators.
To answer these questions, data was collected from grids of different sizes in France, Germany, the U.K., Finland, Mallorca and the U.S.
European power grids operate at 50Hz. If additional power is drawn from the grid, then the frequency drops for a short time, until extra power is provided. The generators used by renewables can also bring about grid fluctuations, due to the unreliability of the sun shining, and the speed at which the wind blows, for instance.
It is these fluctuations from around 50Hz, which critics scrutinize, due to their ability to damage sensitive electronic devices.
Results from the German grid found that there were significant fluctuations every 15 minutes, which corresponded to the time period in which power plants would agree on a new power dispatch through an energy trade. So their first findings indicated that energy trading had a significant impact on power fluctuations. Similar results were found for the U.K. grid.
Furthermore, the random deviations from 50 Hz do not follow normal distribution. To understand the observations made, and plan a fully renewable power grid, the scientists created a mathematical model for the power grid that computed the size of fluctuations to be expected, dependent on the size of synchronous regions. The model enables the impact of renewables to be made clearer.
What they found was that smaller grids, particularly in Mallorca, but also in the U.K. grid, showed larger frequency deviation than bigger grids, like for example, the European continental grid.
Benjamin Schäfer, one of the study’s authors said, “Our study indicates that splitting a large grid, like the European grid, into small micro-grids will lead to larger frequency deviations. Micro-grids are therefore only an option if current frequency regulations are made less strict.”
When comparing different regions, research showed that a larger share of renewable generation resulted in larger frequency deviations. The U.S. for example has a far smaller share of wind and solar generation compared to the U.K., with frequency deviations being less stark in the U.S. as well.
In order to include additional renewable generators into the grid(s), the scientists conclude that smart adaptation from consumers and producers is required following grid frequency. When high, incentives should be made to consume more energy.
“The U.K. is somewhat special in that it has a much higher component of wind power contributing, and it also has an overall smaller grid than the rest of Europe. Still frequency fluctuations caused by trading seem to be at least as relevant as fluctuations caused by renewables,” said Professor Beck.