18 January 2023
Prof. Witthaut, there has been repeated talk of imminent blackouts in Germany – in other words, of nationwide power cuts – in recent months. So far, it has not come to that. Was there or is there a realistic risk of such scenarios in the future?
The risk of a blackout has been, still is and will remain very low. Parts of the media and some politicians, however, have painted a different picture. In my opinion, this results from the fact that terms have been used incorrectly – perhaps out of ignorance, perhaps out of political calculation.
Which terms do you mean?
Blackout and controlled shutdown. Experts define a blackout as an unplanned, uncontrolled, large-scale power failure. The last time such a large-scale outage occurred in Europe was in November 2006. Controlled, locally limited power cuts by grid operators, by contrast, are an emergency measure in the event of power shortages. The likelihood of such action is indeed much greater than in previous years.
For what reason?
There was a risk of a massive gas shortage because of the Ukraine war and the halt in Russian gas deliveries. Gas-fired power plants, however, contribute a considerable share to the German electricity mix. In addition, we purchase electricity from neighbouring countries in certain situations, including nuclear power from France. However, several nuclear power plants in France are at a standstill because they need to be checked or repaired. This standstill has slowly increased over the last few years so that this supply is therefore not necessarily reliable. There could be bottlenecks and, accordingly, the need to switch off consumers in a controlled manner.
What happens during a controlled shutdown of this kind?
First, some industries will have their electricity cut off – in a controlled manner and accompanied by financial compensation payments. Hospitals or other critical infrastructures will of course not be taken off the grid. The supply of food or medicine would not be at risk.
How massive does the deficiency have to be for electricity to be cut off?
That’s impossible to say exactly. In the event of a shortage, electricity prices will first rocket. This in itself will lead to industrial consumers saving or even ceasing operations. Only if this self-regulation is not sufficient will electricity be specifically switched off by the grid operators. This is nothing out of the ordinary, by the way. In France, in particular, this is routinely used in industry as there have been power shortages there from time to time in the past. Private households, however, are usually not affected.
Would this be different in the case of a blackout?
Yes, a blackout can affect everyone and everything, including medical care and the supply of food. There are emergency power generators available for such cases, but these only secure the critical infrastructure’s nationwide power supply for a few days. A blackout lasting two weeks would probably have devastating consequences. However, the likelihood of this happening is negligible because the European power grid is quite robust, and there are also a number of emergency measures that can be taken to avert such a scenario.
So if the power goes out at home, that has nothing to do with a blackout?
Power outages happen hundreds of times every week, but these only affect a small part of the distribution network, often just one street. The technicians go there and typically fix the problem quickly. There are many causes: an excavator has accidentally cut a cable, for example, or the street’s transformer is defective.
What would have to happen for a blackout to occur?
A look at the history of major power failures in Europe shows that the reasons were not a foreseeable lack of electricity. In 2003, for example, there was a short circuit in a high-voltage line crossing the Alps, which led to a prolonged blackout in a relatively large area. In 2006, a line across the Ems was taken out of service, and then a faulty switching action was carried out in a transformer station. In both cases, a domino effect followed: one line fails, the current flows a different way, a second line is overloaded and switched off in an emergency shutdown. The current flows another way again and the next line is switched off in an emergency shutdown. This goes on and on. By the way, such domino effects also occurred twice in 2021, but nothing really happened because the grid operators were able to compensate for the problem.
So the causes of blackouts have so far been exclusively in the grid and not the lack of electricity?
Right. In all cases, everything was fine on the part of the producers – it was the transmission grid that was overloaded or damaged. In 2005, for example, a snow chaos in the Münsterland region demolished several power lines, which resulted in widespread power failures. Sometimes even minor damage is enough, however. In January 2019, for example, a meter on a German-Austrian coupling line was defective. In the end, 1.5 gigawatts had to be taken off the grid in an emergency.
Can a blackout never be caused by power deficiency?
It can in principle, but in the past, the reasons were found in the transmission grid and not with the producers. Electricity generation and consumption must always be in balance in order for the grid to remain stable. You can think of it like a scale, with the amount of electricity generated on one side and the demand on the other. However, an imbalance doesn’t come out of the blue, and the network operators – as mentioned – have forecasts and a variety of possibilities to intervene. A sudden failure of a power plant would be much more problematic, but precautions are also being taken for this.
You conduct research into the stability of power grids. What factors influence this stability?
A number of different aspects play a role here. For example, the amount of electricity generated must meet the demand. Generation is therefore coordinated on the basis of forecasts on the electricity markets, and the quantities are made available accordingly. In operation as such, there are several control loops that permanently adjust the generation. In addition, the current on each line must not exceed a certain safety value, otherwise damage to lines or short circuits will occur. There is sometimes an emergency shutdown of lines to avoid this. Furthermore, the voltage must be kept stable. If power is generated primarily in northern Germany, but large consumers are located in Bavaria, then the voltage in the south drops over the set value – in principle, a voltage drop can also lead to a blackout. Such potentially dangerous situations are usually known several days in advance through simulations. Electricity providers react in these cases, for example by shutting down wind turbines in the north and ramping up power plants in the south.
Renewable energies such as wind power are increasingly being used in Germany. What challenges does this pose for the electricity grids?
Production and consumption are spatially separated. Wind power is much cheaper and more reliable on the North Sea coast than in Bavaria. In order to bring the energy from north to south, however, we need a much stronger grid. In addition, wind and solar energy are not controllable the way coal-fired power plants are. Instead, they are determined solely by the weather. We therefore need much greater flexibility by means of storage, backup generators and flexible consumers. What is more, renewable and fossil power plants differ massively in their grid connection. Power plants generate electricity in so-called synchronous machines, while wind turbines and photovoltaic systems do so in power electronic inverters. The two components behave differently when feeding electricity into the grid. Synchronous machines have some advantageous stabilizing properties, but inverters are incredibly flexible. Our main problem is that we have no empirical data on how best to build and operate a network of inverters. We can’t just try it out in a field experiment. A lot of research is still needed here.
What needs to be done now to improve the existing systems?
The most important thing is stop dawdling over grid expansion. We urgently need more transmission capacities, especially in order to bring wind power from the north to the industrial consumers in the south. This means more power lines in particular, but also more storage and backup solutions for failing lines and the like. Current flexible backup systems are specifically gas-fired power plants, but they are particularly affected by the gas crisis. In my opinion, the hesitant grid expansion is one of the biggest obstacles to energy transition. However, there are other technical things that could be improved as well, including optimized simulations and monitoring mechanisms.
How does your research help with this?
We primarily investigate line failures and their possible consequences: when can these lead to dangerous error cascades? Where is the network particularly vulnerable? We also do research into the control systems that ensure that generation and consumption remain balanced. For this purpose, we carry out mathematical and statistical analyses of data from power grids to see what we can learn from this about the systems and their stability. In fact, many characteristics of the grids are reflected in the power frequency data, for example, and they also show that the power grid is not only to be considered from a technical point of view.
Why is that?
Laws, regulations and markets also influence the stability and reliability of the grid. Frequency stability, for example, is to a large degree determined by trading on the European electricity market. That is to say energy is traded in blocks of time – typically 1-hour and 15-minute blocks. This means that during this period, the supplier must deliver a certain amount of electricity. So the power is ramped up at the beginning of the block to reach the agreed quantity, and it is abruptly ramped down at the end. This creates many erratic ramps in the generator network, while the load from the 300 million consumers in the European power grid changes only slowly and steadily. As a result, there is always an imbalance between generation and consumption, which has a negative effect on frequency stability. This is why, in the frequency data, we clearly see the fingerprints of legal regulations on electricity trading. They are the driving force behind frequency stability problems, not renewables, which have much less impact on frequency stability.
The interview was conducted by Janosch Deeg.