Energy transition: Stress test for grid stability 

Power transmission line in Germany

What the decarbonization of the energy system means for transmission system operators.

By 2030, Germany aims to source at least 80 percent of its electricity from renewables. The fundamental transformation of the energy supply system creates major challenges for grid operators, at least in part because the expansion of the transmission infrastructure is progressing sluggishly. TransnetBW, one of Germany’s four national transmission system operators, is turning to innovative technology to continue to ensure grid stability.

In Germany, the transformation of the energy supply system is in full swing: In the past ten years, the proportion of electricity generated using renewables has roughly doubled. In 2021, just under 42 percent of gross electricity consumption was derived from renewables. By 2030, that figure will be at least 80 percent, based on the German government’s stated target.


Wind power is already the country’s most important source of energy, accounting for about 23 percent of generation in 2021, and that proportion will continue increasing. In summer of 2022, Germany ratcheted up its expansion goals for photovoltaics (PV) and onshore wind power another step: The overall target figure for installed PV capacity by 2030 is 215 gigawatts and 115 gigawatts for onshore wind capacity.

Energy transition changes the whole situation 

The result is a fundamental change in the overall conditions for Germany’s transmission system operators (TSOs), because electricity production from wind and solar power fluctuates significantly, depending on the weather. The more renewable power that’s connected to the grid, the more challenging it will be for grid operators to forecast electricity generation and keep it in balance with demand.


And that’s not all: Large-scale wind turbine systems are concentrated on Germany’s northern coast, where there’s plenty of wind. But the electricity is also needed in the industrial centers in southern and western Germany, where large numbers of conventional power stations are being decommissioned. This means that more and more electricity has to be transported across great distances.

For a number of years we’ve had to work with a generation structure that the grid can’t handle.
Michael Jesberger, Managing Director of TransnetBW GmbH

That is causing increasing bottlenecks in electricity transmission – in other words, situations where there’s not enough grid capacity to transport the electricity being produced. “Our grids weren’t built for north-south transportation,” says Michael Jesberger, Managing Director of TransnetBW GmbH. His company is one of the four transmission system operators in Germany, and it’s tasked with ensuring grid stability in the Baden-Wuerttemberg control area. “For a number of years we’ve had to work with a generation structure that the grid can’t handle,” he adds.


And there’s no sign of the situation easing anytime soon, because electricity demand is likely to continue rising. The main driver is the efforts being made by consumers to reduce carbon emissions: the switch to electromobility, the increasing popularity of heat pumps to heat buildings, and the electrification of industrial processes.


In the long term, the only way to solve the problem is to develop the grid to the point where it can manage the changed conditions. But that requires time-consuming planning and approval processes, and so the result is very slow progress on the work of expanding the grid.

Costly redispatch

TSOs are resorting to “redispatch” to prevent electricity outages despite the bottlenecks in the transmission system. This involves strategies like shutting down power stations upstream of the bottleneck in order to reduce the volume of electricity being generated in the northern German grid. In parallel, power stations downstream of the bottleneck are powered up to cover the increased demand in the south.


To make redispatch work, power station operators need to keep the appropriate capacity available every day to draw on when required, while grid operators lease power station capacity on a long-term basis to cover unusual situations: what’s known as grid reserve capacity.


Managing bottlenecks this way comes at a price, though: The German Federal Network Agency reports that redispatch costs in 2020 amounted to €1.4 billion. This is paid for by consumers via grid fees. 

Improving grid capacity utilization

Grid operators are therefore looking for opportunities to improve capacity utilization of the existing grid. One method introduced by TransnetBW is what’s known as dynamic line rating. This approach takes advantage of the fact that overhead lines can transport up to 50 percent more electricity when it’s windy and in cooler ambient temperatures.


To make the most of this potential, TransnetBW measures parameters like wind speed and ambient temperature right at the power poles. This data is then used to calculate the maximum possible load flows in the various weather situations in order to maintain the amount of slack in the overhead lines within the specified technical limits. 

Measures like dynamic line rating help us save some of the costs of redispatch.
Michael Jesberger, Managing Director of TransnetBW GmbH

TransnetBW is also integrating phase-shifting transformers into its grid. They allow operators to better control the flow of electricity and distribute them more evenly, which also contributes to improved grid capacity utilization.


“Measures like dynamic line rating and integrating elements that control load flows help us save some of the costs of redispatch,” says Jesberger. “But that doesn’t solve the fundamental problem of grid bottlenecks.”

Innovative grid boosters

For the future, TransnetBW is working with other distribution system operators to trial other new and innovative concepts to better utilize the capacity of the existing grid. Transmission systems have traditionally been operated preventively. This means that the power flow situation in the transmission system is forecast in order to ensure security of operation – which involves keeping redundant equipment available for use only in the event of a fault in the grid. In other words, part of the available capacity is reserved for emergency situations.


Grid boosters – battery storage systems that are placed at strategically favorable nodes in the grid – are also intended to allow this reserve capacity to be used during normal operation in the future. If a fault occurs, they can ease the load in the short term until fixes can be put in place: for example, turning on power stations downstream of the bottleneck, using switching options, or feed-in management.


“Grid boosters help us raise the capacity limits on the lines and therefore increase the capacity utilization of the existing network, while leaving the security level unchanged,” Jesberger explains. In addition, in 2023 TransnetBW will put a 300-MW gas turbine into operation as “special technical equipment” for when fixes are needed, so there will be a flexible resource at its disposal to help stabilize the electricity grid.

Collaboration in Europe is the key

With the increasing importance of renewables, the role of TransnetBW in Europe is changing. “We’ve had energy exchanges in Europe for decades,” Jesberger says. But he notes that this exchange has intensified due to the new challenges. One reason is that concepts like the grid booster can be implemented only between control zones, and another is that much more electricity is being traded across national borders than used to be the case. “European transmission system operators are becoming more and more European,” Jesberger observes. 

In Europe, we need optimized processes and standards to make collaboration easier at all levels.
Michael Jesberger, Managing Director of TransnetBW GmbH

One example of this intensified collaboration is the PICASSO project, which involves eight European TSOs. The goal is to build a platform that enables collective access to secondary operating reserve. The platform is hosted by TransnetBW. “There’s an increasing need to optimize balancing energy across the board, for both technical and economic reasons,” Jesberger says. The project is especially important from the perspective of future high-voltage DC (HVDC) lines. “In Europe, we need optimized processes and standards to make collaboration easier at all levels,” Jesberger adds. 

Growing complexity – and the grid control system has to keep pace

Increased capacity utilization, larger fluctuations, and more electricity transfers along with more unplanned interventions, new equipment, and more collaboration with grid and power station operators are making grid management increasingly complex. Guaranteeing secure grid operation in the face of this complexity is the task of the switching engineers at the Wendlingen main control center. The Spectrum Power energy management system from Siemens supports them in this difficult task.


Getting prepared for the future involves a little upheaval: “Previously, we trained our switching engineers to be generalists,” says Jesberger. Now, however, the trend is toward giving new employees a more specialized training. But grid management hasn’t just become more technically demanding. “Pressure is constantly rising at the control desk,” Jesberger notes. “We need well-trained employees with strong nerves and stress tolerance who’re capable of doing the right thing in extreme situations.”

We need a grid control system with a modular structure that’s designed with an eye to the future.
Michael Jesberger, Managing Director of TransnetBW GmbH

The switching engineers need to be able to rely on a powerful grid control system that can manage future challenges. “We need a grid control system with a modular structure that’s designed with an eye to the future,” Jesberger says. “It has to be able to support the switching engineer in the best possible way.”


The challenges that transmission system operators like TransnetBW are facing make it clear: For the decarbonization of the energy system to succeed, a lot more is needed than just PV systems and wind turbines. Regulators are being called on to facilitate the necessary adjustments to infrastructure simultaneous with rapid grid expansion. Players in the energy industry need to work together more intensively, and the industry needs smart solutions in order to overcome increasing grid complexity. 

August 24, 2022

Picture credits: TransnetBW, Siemens AG