How the energy transition is transforming grid operation
In order to assess which actions the energy transition requires, it is first necessary to understand the basic structure of the electricity grid. Like a road network extending from a motorway to a country lane, the electricity grid also has routes that can be assigned to different hierarchical levels, depending on their function. While the largely lossless transmission grid (high-voltage level) transports the energy nationwide from the power stations to the major consumption centres, the distribution grid is responsible for carrying the electricity throughout the regions to the end users. At least this is the traditional division of labour; but it is changing gradually as the energy transition progresses. Extra-high-voltage wires achieve values of up to kilovolts (kV), but high, medium and low-voltage lines will not manage more than 110 kV and 35 kV, i.e. 400 V.
The electricity grid is changing from a distribution to a “collection grid”.
The distribution grid in particular is required to handle new tasks in order to accommodate increasing quantities produced using decentralised and renewable energy sources. In some cases, generation can even exceed consumption in a grid section when large numbers of decentralised power generation units are connected to the distribution grid, turning the distribution grid into a “collection grid”. The electricity grid must then compensate fluctuations and maintain reliable supply, even in peak load times. Flexibility, i.e. the capability of the grid to balance out local fluctuations in generation and load, is key here.
Broadly speaking there are two ways to make the electricity grid more flexible and therefore efficient, and fortunately they are complementary: the grid can be optimised both by expanding it, as well as by introducing changes to its operation. The latter method takes a flexible approach, for instance by integrating energy storage systems that withhold electricity in times of low demand and then release it when energy requirements increase. Moreover, application of a smart demand side management (DSM) system allows companies and private households to deactivate some of their electrical devices at certain times. This flexible load displacement is an effective method of easing the strain on the grid.
dena studies help build momentum
In its Grid Study II, dena analysed the integration of renewable energy sources in the German electricity supply system for 2015 to 2020, including a forecast for 2025. It found that an additional 1,700 to 3,600 km of extra-high-voltage lines will have to be built, depending on which transmission technology is used – while at the same time optimising the current integrated grid. Grid Study II focused on the transmission grid. In contrast, the dena Distribution Grid Study deals with high, medium and low-voltage grids. The results confirm a significant need for enlargement by 2030. The dena Ancillary Services Study indicates not only that there are changes in the required expansion of electricity grids, but also in their operation. It shows that decentralised energy plants and grid operating resources can and must accept greater responsibility for the electricity system, as conventional power stations, which primarily meet our need for ancillary services today, will have far shorter operating hours in future.
Grid expansion und ancillary services are necessary
In summary: A double-pronged strategy is recommended. This will require the expansion of the electricity grid wherever necessary, and secondly, the systematic exploitation of alternative, operational options. In other words, wherever possible the introduction of smart control to improve capacity utilisation of the existing grid.