Blackout in Spain: “Our energy system was built to meet the requirements of 1880”

The power outage that paralyzed Spain and Portugal two weeks ago quickly sparked a debate about the extent to which the energy transition, and in particular wind and solar power, were to blame.

Engineers can provide answers to these questions. Until now, the generators of conventional power plants—whether hydroelectric, coal-fired, or nuclear—have kept the grid stable, explains Florian Dörfler, a professor in the Department of Information Technology and Electrical Engineering at ETH Zurich.

But that's changing when more wind and solar power is fed into the grid. These green power plants produce direct current, which must first be converted into alternating current via an inverter.

After the power outage, several observers quickly concluded that renewable energy sources were to blame. What is right and wrong with this argument?

What's true is that the major bottleneck when integrating large numbers of renewables isn't the variability of renewables, as the public generally believes. It's more about how to keep the grid stable. But that's not necessarily related to the renewable energy sources themselves, but rather to the power electronics that feed in the renewables.

Can you give an example of how renewable energy is fed into the grid?

For example, modern hydroelectric power plants are now built so that the generators no longer rotate at 50 hertz, but rather at the current water flow rate. The power electronics, with the help of so-called inverters, then regulate this up or down to 50 hertz. [Editor's note: This is the frequency at which the European grid is stable.]

Coal, gas, and nuclear power plants, on the other hand, feed alternating current directly into the grid. How does this work?

The way alternating current is generated goes back to a 120-year-old technology and to Mr. Nikola Tesla: A large iron core rotates in a magnetic field, thereby inducing currents and voltages.

What does this have to do with the stability of the network?

This large iron core is an inert mass. Even if there are fluctuations or disruptions in the grid, it would continue to rotate robustly at the same speed. Essentially, like a spin bike at the gym, whose pedals keep turning. This inertia doesn't exist with inverters.

But what role do these inverters play in the energy transition?

Sooner or later, the grid will be increasingly dominated by these inverters. All renewables, new hydropower, and even high-voltage and direct current lines are interconnected via inverters. And that's the current bottleneck: How do you make these inverters robust? How do you keep the grid stable, especially in the event of a fault?

We are in a transition phase, what does this mean for the way we manage the power grid?

This leads to absurd developments: Over ten years ago, the Biblis nuclear power plant in Germany was shut down. However, the generator, this inert mass, was allowed to continue running for several years using electricity from the grid to stabilize voltages and frequencies on the grid. Instead of supplying electricity, the generator only consumed electricity.

Is this a model that could be carried into the future?

You could. But of course, that's a very archaic technology and causes mechanical and electrical losses. I don't think it will be a long-term solution.

Which solution do you prefer?

The best, cheapest solution is always a software solution, and that's what it will all come down to sooner or later. Technologically, we have all the solutions in the drawer. We just need to implement them. There are also "grid-forming" inverters – inverters that automatically synchronize and can thus stabilize the grid. This is a technology that was developed ten or eleven years ago and is becoming increasingly robust. It simply needs to be introduced across the board.

Why is this not the case?

Currently, only a small percentage of all renewable energy sources are equipped with these inverters and the necessary software. People all over Europe, but also in the US, are writing regulations. The technology exists, but what doesn't exist yet are the standards.

In Spain, too, there were critics after the power outage, complaining about the lack of regulation. Why is this complicated?

There are hundreds of manufacturers of inverters, wind turbines, solar panels, and batteries. Everyone is cooking their own soup. Now we have to ensure that these systems are compatible. These standards simply don't exist yet; they're just being written. Of course, they should have been written a good five or six years earlier.

You say that the technical solutions exist. But at the same time, it has also been the case until now that the grid-forming inverters shut down in the event of a fault. Are there any solutions?

For a long time, there was a bottleneck with the inverter: How do you ensure that they can continue to synchronize even in the event of a fault, i.e., when there are large voltage drops? Now I believe we've found a good solution for that.

You've developed a new inverter algorithm that could allow wind turbines or photovoltaic systems to continue supplying electricity and contribute to stability. Why was finding a solution so difficult?

It's one of those problems that can't be solved with money or manpower. It simply requires a brilliant idea. In this case, it was a master's student who had six months to really get to grips with the idea.

However, as a result of the power outage in Spain, fundamental doubts have arisen about the stability of a green power grid. What do you say to this?

That's the burning question: Would a conventional grid, with many synchronous generators, have survived or not? We don't yet know the answer. It's possible that the inverters contributed to us simply not having enough inertia or that we weren't able to synchronize robustly enough in the event of a fault. But that's speculation at the moment.

Nevertheless, one thing is clear: the energy transition presents us with technical challenges. Our energy system was not designed to meet the requirements of renewable energy.

In principle, it was built to the requirements of 1880.

But we can't simply tear down the system and rebuild it. Where are the friction points?

People very aggressively integrated renewables and pushed forward energy and market liberalization before the technology was ready. For example, every power plant above a certain capacity was supposed to be able to form a grid and provide a kind of virtual inertia, emulating the mechanical inertia of conventional power plants. There are plenty of solutions for this. What's missing are the standards, the coercion, and the business case.

How do you turn this into a business?

There are energy markets for virtual inertia. For example, I could place a battery next to my solar farm that, in the event of a failure, would assume the role of a virtual inertia for the first few seconds, quickly absorbing energy or releasing it back into the grid. This could serve both as a grid-forming mechanism and as an inertia. But currently, there's neither the requirement nor the market for it.

Why do electricity producers have no incentive to take on this role in maintaining grid stability?

I get more money if I simply feed in energy and sell it.

Many critics of renewable energy say that a power outage like the one on the Iberian Peninsula would not have happened with conventional coal-fired or nuclear power plants. Is that true?

The chronology of the outage shows that, for unknown reasons, there were major fluctuations in the European system. However, there are enough synchronous generators in the European grid, so this has nothing to do with renewables. In Spain, two power plants failed within a few seconds. It's unknown exactly why. But no grid in the world could have withstood the failure of two power plants, not even a conventional one.

Why is the fact that two power plants went offline such a shock to the power grid?

Every grid is designed to withstand a worst-case failure. And that worst-case failure is usually the loss of a large power plant.

But in Spain it was not just the loss of these two power plants.

A few seconds later, approximately 15 gigawatts—a large portion of Spain's generation—quickly dropped off the grid. And this could be related to renewables. The frequencies dropped very quickly after the two power plants failed. And renewables are designed to simply disconnect from the grid when they see these types of signals.

Is this a protective mechanism to prevent them from being damaged in the event of a malfunction?

Exactly, to protect themselves. But a conventional power plant, with those large flywheels, with that inert mass, might have continued to rotate robustly for even longer and perhaps lasted a few seconds longer. Perhaps that would have been long enough to quickly bring the backup generation online. Who knows.

This buffer time is therefore needed to be able to react and prevent a power outage.

The inertial mass gives you four to five seconds more time to react. If there had been enough batteries in Spain that could have quickly ramped up within those four to five seconds and sent a few gigawatts of power into the system, it might have been possible to stabilize it. Fundamentally, we need fast storage, batteries, for example. But also flywheels. Various startups are building flywheels that serve both as storage and provide inertial mass. These are all possible solutions.

Nuclear power supporters, in particular, say this would certainly have been achieved with nuclear power plants. Is that true?

I keep reading: "Nuclear generators would have saved the situation." That's not true. Nuclear generators do have a lot of inert mass, but they can only be adjusted up and down very slowly. So they would never have been able to produce that power within three seconds; more likely within half an hour. In that case, you need energy sources that can be adjusted up and down very quickly, such as batteries and other storage devices. Gas-fired power plants would also be possible.

The events in Spain are a wake-up call, that much is clear. But are they also the first major power outage of the renewable energy era?

No. We already had a similar blackout in Australia in 2016. There, too, the share of electricity generated by renewables was very high. Then there was a major disruption, in this case a major storm that took down a few lines, and a blackout followed. So, that was the first truly major event where one could ask: Would a conventional grid have survived these disruptions? The conclusion in Australia is: Yes, a conventional grid would have survived.

There are many reasons for an energy transition. But the sequencing was clearly not done correctly. This also undermines public confidence in green energy alternatives. What went wrong?

Renewables were integrated very quickly and very aggressively without creating the necessary technological framework. For me, the conclusion is: create the standards first before integrating the technology.

So, should the energy transition have been delayed until standards had been formulated? Should the energy transition have been accepted, or at least not, at the cost of possibly slowing down?

No, of course not. Otherwise, nothing would have ever progressed. Many of the central problems, such as inertia and grid-forming inverters, were only recognized by experts about twelve years ago. But today, technology should be prioritized over markets. Currently, it's the other way around: A problem in the grid is identified, a corresponding energy market product is created, the technology follows, and standards come at the very end.