Today's electricity grids are kept stable by the inertia of spinning masses — mostly fossil fuel generators. But what happens when those spinning masses are replaced by inverter-based resources like wind, solar, and batteries? The answer is that inverters must take over the stabilizing job, becoming "grid-forming" rather than merely “grid-following.” I chat with two experts about how grid-forming inverters work, how many are out there, and what the future holds for them.
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David Roberts
Hello everyone, this is Volts for September 5, 2025. How inverters can stabilize a renewables-heavy grid. I'm your host, David Roberts. If you have paid any attention to power grids at all, you've probably heard that the reason modern electricity grids are such a miraculous achievement is that they have to remain in perfect balance at all times. The amount of electricity entering the grid must precisely match the amount leaving, or else frequency fluctuates, problems cascade, and eventually there are blackouts.
You may have heard this fact and thought, "Well, that can't literally be true, can it? It can't be the case that every time I turn on my stove, some power plant operator turns up the output of their power plant by a stove's amount at that exact second. That's fantastical. There must be some buffer."
And you're right, there is. In the seconds or milliseconds between when demand rises or falls on a grid and a grid operator is able to respond by adding or subtracting supply, the energy to buffer that transition and keep frequency and voltage under control is provided by inertia.
Specifically, almost every electricity generator involves a large spinning mass, rotating coils through a magnetic field. And there is kinetic energy in that spinning mass. Like a flywheel, that inertial energy can be tweaked very quickly. The mass can spin more quickly, thereby absorbing energy, or spin more slowly, thereby releasing energy, keeping the grid in balance in those key seconds. Collectively, spinning masses constitute a kind of shock absorber for the grid.
Now here's the first: solar panels, batteries, and most wind turbines, the building blocks of tomorrow's energy system, do not connect to the grid via large spinning masses. Rather, they connect through inverters, which are all electronics. No moving parts, nothing spinning, no kinetic energy. Lacking inertia, inverter-based resources have not, to date, actively contributed to grid stability.
In fact, there are widespread worries that replacing (primarily fossil fuel-based) spinning masses with clean inverter-based resources will leave grids with too little inertia, too little buffer, prone to accidents and breakdowns like what happened in Spain and Portugal recently.
But here's the second twist. A modern inverter, properly programmed, can effectively mimic a spinning mass, adding or subtracting tiny increments of energy to the grid in milliseconds. This ersatz spinning mass provides what is called in the business "synthetic inertia." Inverters attached to batteries are best at this, for reasons we'll get into. But inverters on solar panels and wind turbines can contribute as well.
So the problem is solved and we can all go home? Haha, of course not. It is never that simple. To get into the details, I have with me today two experts: Daniel Duckwitz works on grid stability products for SMA Solar Technology, a large power conversion company based in Germany; Catarina Augusto is a renewable energy engineer who works on grids and flexibility for the nonprofit SolarPower Europe.
As you could probably tell from the lengthier-than-usual intro, this subject can get somewhat technical. But the larger issue we're circling around here could not be more simple and profoundly important: can we or can we not run a stable electricity grid on renewable energy?
All right then, with no further ado, Daniel Duckwitz, Catarina Augusto, welcome to Volts. Thank you so much for coming.
Daniel Duckwitz
Thank you for having us.
David Roberts
Very excited to get into this. I think this is a technical area that is hugely important and I think largely invisible to a lot of people. So I'm excited to get into it. I want to start, Daniel, with you just for people who are not familiar with this area and this stuff. You know, I touched on it in the introduction, but these spinning masses, maybe you could just briefly describe what services they are providing to the grid, the kind of services that we are going to have to get from somewhere else if we retire these spinning masses. What are sort of the main categories of services they provide?
Daniel Duckwitz
Yeah, so I think your introduction was really, really good. So turning on the stove is probably not the reference scenario for planning the security of supply of a larger interconnection, but instead it would be scenarios like a sudden loss of a really large generator, like a gigawatt-scale power plant, or like a transmission failure that suddenly disconnects a really, really large load center. And in these cases it's not, sorry to say that, as insignificant as your stove is to the power system.
But it is really getting the system into trouble. And what happens if there is such a sudden unbalance is that this instantly missing power will be taken from the rotational masses, from the energy of these flywheels in the synchronous generators. And this will buffer the system so that the operators of the power system, but also of the individual power plants, have time to adjust the output of their plants or an automatic control system in the plants can adjust automatically the output.
David Roberts
And can you say just quickly, how long is that interval between sort of a big event, say some other power plant trips off, there's a big hole in supply, the grid operators are going to respond by turning some other power plant up. How long does that take? Is that milliseconds, is that seconds, 30 seconds, what's the range?
Daniel Duckwitz
It would take around 1 to 30 seconds to adjust the output of the other plants. So they would use frequency control to detect that frequency in the system is falling or rising, and then they would automatically adjust. And there is a service: it's frequency containment reserve or fast frequency response services. There are different names for it, but they all do the same. They measure frequency in the power system and then they increase or decrease the output of a power plant or of a battery. And in that way they help the system to find back to a balanced state.
But that is what happens after 1 second, 5 seconds, even up to 30 seconds. And then for the grid to get to that balanced state again, what it needs is some instant buffer. And that would be the power from the inertia and the energy from the inertia, that will be instantly available within less than a few milliseconds. And then up to the point where the power plants can adjust their output according to the needs. And that is the role of the inertia.
David Roberts
When we talk about these services, these grid services, there's inertia. Is frequency control separate from that somehow? Is voltage control separate from that? Are there distinct services here, or is there just the one? The injecting?
Daniel Duckwitz
Yeah, there are active power-related services that aim at balancing frequency. And to have frequency imbalance, you need generation and load imbalance. That is the one, let's say one part of the grid services world where traditional frequency control services would be part of. The inertia is also part of that, but in the past it has always been a byproduct of the rotating machines. Now it will be a service that needs to be defined regarding how much power, how much energy should be reserved from the batteries and how fast and in what relation to others should they have the reaction.
So this would be the frequency control active power-related services. And then on the other hand, there are voltage-related services which balance the voltage in the grid to make sure that the voltage is very, very close to the nominal voltage in all locations.
David Roberts
And that is also provided by the spinning masses?
Daniel Duckwitz
It can be provided by synchronous generators, it can be provided by STATCOMs (static synchronous compensators), it can be provided by big capacitors or inductors in the system and of course also by renewable power plants. So when we talk about voltage control services, it's once again a bit similar. You have instant imbalance that needs to be balanced. So that would be some inherent reaction or a very fast control scheme. And then there is more — the steady-state balancing of the grid, so to say, to balance within five minutes, to readjust the voltages to get closer to nominal again after some event.
And this is like similar to the frequency and active power, but it is usually treated as two separate categories. And also the stability, there is voltage stability and there is frequency stability. And there are in some big real-world events, they can also interact, voltage and frequency stability. But in the theory in the textbook, it is separated.
David Roberts
Got it. And all of these services are at their root small injections or withdrawals of energy from the grid, right? I mean, that's whether you're talking about frequency control or inertia, one way or another, you're talking about something very quickly injecting or removing energy from the grid.
Daniel Duckwitz
Yes, exactly.
David Roberts
This problem of low inertia leading to problems, is that a purely modern problem? Is that something that's new to us with the retirement of fossil fuel plants? Or do we have historical experience with low inertia on grids?
Daniel Duckwitz
It is now at the moment we are dealing with a specific transition where rotating machines are being removed. But also in the past there have been events where low inertia power systems were operated, and that is systems that focus on hydro energy. Because the turbines in hydro, they have a higher power density because the water will have a higher power density compared to steam. And that means the turbine has less mass, less inertia. And let's say the power systems that have focused on hydro, like parts of Canada, maybe parts of the US, for example, Norway, they always had their engineering to do regarding frequency control.
But of course, today we're talking about something different compared to these, let's say, older versions of the engineering problem.
David Roberts
So in terms of just a bunch of spinning masses disappearing from the grid and us needing to compensate for that, this is a new thing that's confronting us, basically.
Daniel Duckwitz
Yeah. I mean, the big difference is that today solar plants, but also wind plants, they are interfaced through power electronic converters to the grid. And these don't have any rotating mass. So it's not like they have low inertia, but no inertia. And that is a new quality, of course, but also something that can be solved as an engineering problem.
David Roberts
I mean, when it finally sank into me that all these different grid services we're talking about are some version of injecting or withdrawing energy from the grid, it sort of clicked to me: why wouldn't batteries be able to do that? I mean, it seems like, indeed it seems like batteries are much more purpose-designed to do that than a giant spinning mass. I'll just put it this way, if all you wanted was those services and you had a blank sheet of paper, you wouldn't build a giant spinning mass to provide it.
Right. I mean, it just seems like batteries are more natural in this role. Seems to me anyway. But, so, Daniel, an inverter, this piece of electronics, briefly describe the difference — inverters to date traditionally have been what are called "grid-following" inverters. And what we're discussing today, inverters that are taking an active role in shaping and stabilizing the grid, are called "grid-forming" inverters. Maybe just briefly explain what's the difference there? What was a grid-following inverter and what do grid-forming inverters do that's different?
Daniel Duckwitz
Yeah. So when connecting an inverter, the control system of that inverter needs to make sure that the current of the inverter is synchronous to the grid voltage so that it will have the right AC waveform, so that it has the right synchronous waveform to feed the power to the grid. And to do that, the grid-following inverters, what they do is they observe the voltage, they also calculate the frequency based on the observed voltage, and then they follow the grid with their current. So they are basically observing what is happening out there and then synchronize according to what they observed.
David Roberts
So, they match the grid's conditions?
Daniel Duckwitz
Yes, they match it and then they can feed power. But then when it comes to the inertia we discussed, it has to be activated within milliseconds — it's not really, it doesn't have to be activated, but it has to be provided within a millisecond, maybe even without the inverter noticing that it is already providing the response. And that is the difference. Instead of observing the grid and following the external frequency in the grid, these grid-forming control schemes, they make the frequency and they make the voltage. And that means that if you switch on your stove or anything larger happens out there, the voltage will remain a stiff voltage source, and then the current needed by your stove will just begin to flow according to the needs.
And that in turn will then have an impact on the frequency that the grid-forming inverter makes or the internal state of frequency that it has in its control system. So that's the fundamental difference. It's not observing and following, but it is making it. And if it notices there is some higher load, it will adjust its internal frequency. And that is the fundamental difference between grid-following and grid-forming.
David Roberts
Right. So maybe like a good way to think about this is active versus passive. Grid-following inverters are just sort of passively matching grid conditions, whereas grid-forming inverters are purposefully shaping them. Now, let me ask this, and this is also something that I've had a time wrapping my mind around: the difference between a grid-following inverter and a grid-forming inverter — is there a physical difference or is it just software?
Daniel Duckwitz
I mean, to make the fundamental shift in principle of control, the hardware does not need to change. But then once you look closer, what is the actual stability need of the power system? You can adapt the design of the inverters to be optimized for applications with inertia. Like, for example, to have a defined power and energy reserve built into the battery system and the inverter to really have the reserve for your stove or for some larger incident. So maybe I stop using the stove example, but if you think about a loss of a large generator, like maybe a 3 gigawatt power plant, that is a few percent of the overall system generation and the overall load.
So you need a significant amount of power reserve in these inverters to really provide this additional power and energy instantly. And that is where design adaptations come into play. But then the very fundamental difference is not in hardware.
David Roberts
I see, but there is some difference in hardware. Because what I've been wondering is, could you just go to an existing old-fashioned inverter and update the software on it and make it grid-forming? Or do you have to purpose-build it to be grid-forming from the beginning?
Daniel Duckwitz
It is possible to change the operation in the field. So, it can be done.
David Roberts
Really?
Daniel Duckwitz
Yeah, yeah, it can be done. But then once you start thinking about what you want to achieve, often you come to the conclusion that the benefits are not as big as if you build a new one. And then also when we look at how much battery storage is being built at the moment and how much has been built like five years ago, it makes sense to consider it. But then it also makes sense to focus on the new projects and really design them in the first place for providing inertia with a defined performance. This is, let's say, we can go both ways.
David Roberts
I'll tell you why I'm asking. Because all these things are connected to the Internet in some way or another. And if this is software-controlled, shouldn't you be able to update the software over the Internet? And if that's the case, that's basically free. I mean not free, but it's cheap. Like, so if you could just over-the-air update all existing inverters to have new software that allows them to be grid-forming, why wouldn't you just do that? Like, why not make them all grid-forming, I guess is what I'm asking.
Daniel Duckwitz
Yeah, it's a good question. Yeah, yeah. And also a good idea. No, really, really. I mean we should really not forget that it can be retrofitted. But then, I mean it's not like we can dial into the larger battery storage plants and just install a new firmware.
David Roberts
I'm sure it's not simple, but it is. But there are no moving parts, right? I mean, it's pretty cheap to do it if you can arrange it.
Daniel Duckwitz
Yeah, I mean there is one part, you would basically have to renew the grid connection approval. So you would do, let's say, all the engineering that you have done regarding grid connection, grid code compliance, that you would repeat for doing the retrofit to get the permission from the network operator to do it. It is feasible, and we have done it, so it's not impossible.
David Roberts
I mean, I guess from a network operator's perspective though, a grid-forming inverter is always going to play better with the rest of the grid than a grid-following inverter, isn't it? I mean, it's always an upgrade from a grid operator's perspective, isn't it? It's just more intelligence out there to make use of.
Daniel Duckwitz
Yeah, there are also some concerns like losing control over the transmission network or of the distribution network. That is because the grid-forming inverters, they would allow the system to keep operating autonomously without all the other stuff that is needed today, like rotating machines. So usually when all the rotating machines are shut down — I mean that's not happening in the real world — but for maintenance works in the grid, for example, the network operator and their service personnel, they really, really want to be sure it is shut down if they isolate it. But with grid-forming it could actually continue to operate.
And then there is a safety concern, and I mean it sounds weird when you hear it first, but then on the other hand, it's really about the safety of the lives of the personnel out there that operate the switches and build the equipment for the networks. And this has to be ensured. And that is why it's not like — I mean usually, let's say the high-level transmission operator staff, they want it, they want it really, really quickly.
David Roberts
Oh yeah, because it just gives them more control over their, I mean pretty straightforwardly gives them more control over their network, doesn't it?
Daniel Duckwitz
Yeah.
David Roberts
So let me ask this. Mostly what we're talking about here, I think, are inverters on batteries. So, like, an inverter on a battery could set aside, I don't know, 1% of the battery's power in a little reserve that you could set aside for these grid faults or grid events when you need a little reserve power to bridge that millisecond gap that we're talking about. What about inverters on solar panels and wind turbines? They can't store power, obviously. Can they, though, offer other grid services?
Daniel Duckwitz
Yeah.
David Roberts
Like, do they count as grid-forming if they're attached to a solar panel?
Daniel Duckwitz
It is hard to get grid-forming with active power-based inertia with a solar panel because there is no storage in the, neither in the panel nor in the inverter. So this wouldn't be possible at the same level of quality, like for a battery. But then what the PV can do is really, really quickly reduce the power because for reducing you don't need storage. And it can also instantly, or almost instantly, balance the voltage, which would be the reactive power part of the services. But then, for really providing inertia that is reliable and has a defined performance, is really, really hard with solar plants.
David Roberts
Right, so grid-forming inverters on solar panels and wind turbines can offer some services.
Daniel Duckwitz
The thing is we would probably not call them grid-forming, but this would be some advanced—
David Roberts
Advanced inverters. Inverters plus?
Daniel Duckwitz
We call it transient voltage control for PV inverters. That means they will behave like a voltage source, but only regarding reactive power and not regarding inertia. So there is some middle ground between grid-following and grid-forming. And this would be what a PV-only plant can do. But then there is also another trend, and that is hybrid plants, which means many, many plants have a battery and solar. And even for wind, there is a tendency to do more batteries combined with wind. So there are options.
David Roberts
Right. So you can do some with inverters on wind turbines and solar panels. But to be fully grid-forming the way we're talking about, to really substitute for spinning masses, we're talking about batteries here for the most part. Are there things, things that grid-forming inverters can do for the grid that spinning masses cannot do? Are we getting anything extra here with this substitution?
Daniel Duckwitz
There are some advantages because you can program the behavior, and for the synchronous machines with their turbines, there is a tendency for oscillations between the turbines and the generator and the grid. There can be oscillations, and then you need additional damping controllers in the power plants, and these can only be tuned to be so good. But then when you do it as an emulation, you can tune the control system to avoid these oscillations in the first place, to provide damping for existing oscillations between other generators in the system. So this is a degree of freedom that conventional power plants don't have. And then there is another advantage, and that is for a thermal power plant to adjust the output, you would have to adjust the amount of steam or the amount of fuel that you put into the turbine.
And this takes some time. And that is why frequency control services, according to, let's say, the synchronous machine-based world, these will have response times in 10 to 30 seconds, which is absolutely not necessary for a battery. The battery can adjust its steady-state output within half a second. So, there are options to improve the overall system behavior to get back to the steady state much more quickly than before.
David Roberts
I see. So in some ways these inverters do what spinning masses do better than the spinning masses do?
Daniel Duckwitz
Yeah, they can do better. I mean, we are working with existing systems and an existing system will have varying amounts of rotating generators in it. So if it's a sunny day, there will be almost no rotating machines. If it's a cloudy day, there will be some, and at night, and if there is wind, or there is no wind. So we're dealing really with percentages of rotating machines versus inverters in the range of 10 to 100%, I would say, which means you can do better with the batteries, but still you need to be compatible with the old system, which means it shouldn't be too different.
David Roberts
One of the things you mentioned when we were exchanging emails beforehand is that one of the things maybe that batteries with inverters can do, that spinning masses can't do, has to do with sort of bolstering weak areas of the grid. Can you talk just briefly about what you mean by that?
Daniel Duckwitz
Yeah, when we talk about weak areas, that is usually coming up in an area that has a lot of land, a lot of renewables will be built, but there is not much else, no loads, and also not a lot of other generation. So in Australia, this happens. I'm sure there are areas in the US in California and Texas, all around probably where there are these really, really high renewable generation areas. I mean, you wouldn't build as a system operator, ISO, utility, you wouldn't build any more transmission lines than you absolutely need to build to feed the power.
David Roberts
We don't even build the transmission lines that we do need.
Daniel Duckwitz
Yeah, I mean, so you will operate the transmission line really very close to the limits, and that means it will become a weak grid area. That means the voltage has a tendency to not be very stable, not be very firm. And this is where the grid-forming will improve the voltage stability a lot. And that is actually what is happening in these systems. For example, in Australia, there is a system strength assessment framework. So if you want to connect in such a grid area, you have to find a way to either reinforce or to make the voltage stronger by, for example, building a grid-forming battery instead of a grid-following one.
David Roberts
Interesting.
Daniel Duckwitz
Or you would have to pay a fee to the system operator, and the system operator will then use that money to do something else to reinforce the system.
David Roberts
Well, I think people, especially listeners of this pod, are familiar with the interconnection process where you sort of apply, "I want to join this grid." Then the ISO assesses the grid and decides whether you can join on. And one of the big things that's slowing things down here is your power plant might be the one that triggers the need for additional infrastructure. And if that additional infrastructure is transmission, that's a huge increment of cost. But if you could put a battery with a grid-forming inverter as an alternative to building new transmission, that's much, much cheaper and faster, is it not?
Daniel Duckwitz
Yeah, yeah, sure. And that's the approach.
David Roberts
So this could speed up interconnection, in other words?
Daniel Duckwitz
Yeah, grid-forming is the key to speed up interconnections within some boundaries, of course, because you still want to transport the power from there to there, and you need a transmission line for that. But it is really, really the big and quick win for speeding up the connection process.
David Roberts
Interesting. Okay, I got one more technical question and then I want to talk to you, Catarina, about some policy questions. But just so listeners can wrap their head around this, what is the scale here? Like how much grid-forming battery would we need to replace all or the vast majority of spinning masses? Like is that a reasonable, realistic thing to think that there are enough batteries to do that?
Daniel Duckwitz
I think we are, I mean not halfway there, but I think the amount of batteries that is needed for operating a system independent of the generation mix, so that it can work with any generation mix, it would be around the same installed capacity or installed power of the peak load of the system, and then you can operate it completely without any spinning masses, and you would have all the reserves you need. And on the way there, I think even having half the peak load installed as batteries is already really a big step. And in some power systems, I think we are getting close to that point where half the peak load is already installed as storage.
David Roberts
Yeah, there are grids in the world now where this has penetrated to the point where these problems are present-day problems in some places, not in the US yet. So Catarina, let me turn to you then. From a policymaker's perspective, how much of this is out in the field? How much do we know about the performance of these things in the field? Do we know enough that policymakers are familiar with this, confident in it? Do they know about it at all yet? Where's the sort of like policymakers' level of familiarity with this option?
Catarina Augusto
So in terms of familiarity, there's already a lot of — especially with the situation of the blackout. Now I think grid-forming became more popular than grid investments. Everyone is speaking about grid-forming and everyone got an expert on grid-forming. That's what I feel. I was listening, very attentive to Daniel and I'm always learning with our technical members, giving all the insights and I feel that's the problem. So it's already there. So there is one thing that all the grids need. It's a set of rules, so requirements to connect to the grids. And these requirements are, let's say, the base rules that you need to fulfill to be able to maintain the stability.
And the current ones in EU already include grid-forming as part of this. They don't really define grid-forming. So that's the problem. What Daniel said, if PV as a standalone, it's part of it or not.
David Roberts
Yeah. Well, does it? I mean, if I'm a PV power plant and I don't have a battery, but I do have smart inverters, can I then satisfy that requirement? Can I call it a grid-forming inverter? Legally?
Catarina Augusto
Yeah. So legally it seems that's going in that direction, but it's not the reality and that's what the industry is trying to clarify. So I think that's the part, the knowledge that's not really clear.
David Roberts
Interesting.
Catarina Augusto
Not just for the policymakers, but I think also for the system operators. Because in the end of the day, when it comes to sustainability, policymakers will look at transmission system operators, at distribution, and ask especially to transmission, "What do you need?" And they will say, "Well, I need more grid-forming, so I need that." Now renewables know how to answer to grid-forming. And that's the part that Daniel explained very well, that we need to have a bit of clarity. What is grid-forming coming from batteries and what is the stability services that renewables, when they don't have batteries, can do?
David Roberts
So just to clarify what you're saying, interconnection rules in place in the EU already have something about grid-forming in them. It's just not super clear what it means?
Catarina Augusto
Exactly. So they are at the moment in a revision of the European Commission. So there is a process, it usually starts with a regulator where it kind of assesses because these codes already existed. So you need to kind of assess what kind of changes you need from time to time. Usually it's around 10 years. So let's say if we mess up now, we have to wait 10 years to correct.
David Roberts
Yeah, right.
Catarina Augusto
And now it's on the moment, it's on commission and it's at standby. What is also a concern because it's not really progressing and we need to look at requirements for stability and we need to put the right technologies entering to it. So that's a bit of a concern now that it's on a standby.
David Roberts
So is one of the possibilities here that all — I mean you could imagine interconnection rules that just say, "No matter what kind of generator you are, you also have to have a battery with a grid-forming inverter attached to it." Right, I mean you could imagine just because I mean the, like, relative to the cost of a power plant, I can't imagine a few batteries and a grid-forming inverter would be that much more expensive. Like, is that in the realm of possibility that just everyone could be required to do this?
Catarina Augusto
So ideally yes. And let's say the strength of — Daniel said about hybrid systems. So connecting PV or wind with any other energy, in this case would be with storage. It's something that we are seeing more and more. And I think it's also something that you want to do by yourself without any kind of rule, because you already want to optimize the way you use that connection point. It's going to be better for your business.
David Roberts
Why not do it? And I was sort of wondering along those lines, like if I'm a natural gas plant. I could stick a battery next to the plant and put a grid-forming inverter on it, and then I could be a grid-forming natural gas plant, couldn't I? I mean, is that something anyone's trying to do?
Catarina Augusto
I think a gas plant doesn't need the battery. But maybe Daniel can correct me on that. But yes, you can.
David Roberts
Well, if it's a requirement. If it becomes a requirement, you know, maybe they'll have to.
Catarina Augusto
For bigger plants it will be the case. So what happened now is that the requirements are mostly for transmission system. Everything is distribution. They are allowed to design a kind of a roadmap. So how they see progressing the need of grid-forming at distribution level. But the request for now is at transmission level. So every kind of plant on transmission level will need to be capable of providing grid-forming and to firm a certain, more higher value, will need to be able to give inertia. So the storage is already implicit that you have to add storage to a PV power plant.
David Roberts
In terms of policy, in terms of how you encourage this, I mean it is somewhat of an extra expense. So I'm wondering, are there markets in place? Like in the US, you know, we have these ancillary service markets where people can get paid for voltage stability and stuff like that. Are there markets to compensate grid-forming inverters for the services they're providing to grids?
Catarina Augusto
Yeah, so that's the big problem of hybridizing PV plants. It's that there is not sufficient revenue for storage in general. And when it comes to stability services, when we speak about grid-form inertia, there's nothing there. There's a requirement that you need to have, but nobody's going to tell you how they're going to be activated or procured. And that's the law missing is that we're looking at flexibility services. We are looking into expanding that section of storage. But then when it comes to stability, that's another field. There is not really a market for that. So we are not at the same level as the UK. That is a bit closer to us where they have grid-forming pretty clear already for some years on market.
David Roberts
Can we talk about that for a minute? I wanted to ask about sort of markets that are ahead on this or doing better on this. And the UK is an example that gets brought up frequently. So what's the UK situation with grid-forming inverters?
Catarina Augusto
So UK, they also have the situation where they have rules, requirements that need to be designed by law, and it comes more technical understanding how you proceed and how you define grid-forming. And then they have a market. So it means that you procure through market. So you need to comply if you have grid-forming. So you are not obliged to have it. But if you have it and you want to provide that service, you need to comply with certain requirements, and then you can provide it through a market. So that's the difference of two realities.
So let's say they're more forward-looking on a sustainable development of storage and grid-forming. Because that's also another concern: if you don't have a market, you are not really reacting to needs. So you said before, "And what about if we turn all the storage into grid-forming?" I don't think people really know the impact that will bring to it, and if there is really the need for these services for all storage. So what Daniel also said in the beginning, maybe we don't need to retrofit the existing plants with grid-forming inverters and we can continue with grid-following. So that's another concern.
David Roberts
One great advantage of markets is that they reveal that information.
Catarina Augusto
Exactly.
David Roberts
They reveal how much you need, how much it is worth to do this and that kind of thing. So is it the case now that every battery that's being installed in the UK has grid-forming inverters on it and they are active and working on the UK grid?
Catarina Augusto
I'm not saying maybe every battery, to be honest, I don't know. Because as a developer of a power plant, PV plus battery, you need to decide what is your ideal business case, and maybe not everywhere it makes sense.
Daniel Duckwitz
Yeah, maybe to add on that. So what we see in the UK is there is a market for inertia services, and basically everyone at least is evaluating if they can participate, and they need to do some technical qualification process with their plant, and then often the grid connection is not available within the next five years. So there are a lot of other obstacles for developing a storage asset. But then recently what we see is that really most of the batteries will be grid-forming ready in the UK, and also the developers prepare them from the technical design perspective for providing the service with a high amount of inertia later.
So basically, if there is a market, the more inertia power and energy the BESS (battery energy storage system) can deliver, the more revenue it will make. So there is an incentive to optimize the design for having more performance available. And this is something that is good. If you need a lot of inertia, it's good to have the batteries optimized to do as much as they can and then also, in contrast, to they are forced to do it. But then everyone would try to keep the extra cost as low as possible and probably not deliver the highest quality of the service.
David Roberts
Actually, this gets back to a slightly technical question, which is if I'm a battery and I'm in a particular region and I want a grid-forming inverter, to what extent is that grid-forming inverter just something I buy off the shelf versus something that has to be specifically programmed based on the conditions in the region where I'm located. How bespoke, I guess, is a grid-forming inverter?
Catarina Augusto
So when it comes to requirements, there is a set of requirements that you need to comply with to have that certification later. So at the moment if you don't have this European set of rules, it may happen that in the EU you will have 27 versions at least of inverters. If you have one TSO per country and if we go to this distribution level, you may have more. So that's a problem. But I don't know if you want to add something, Daniel, in terms of more details on the technical requirements.
Daniel Duckwitz
Yeah, I think basically what we can tune for, I mean not for the individual inverter necessarily, but for the overall BESS plant, is the amount of inertia it can provide regarding power and energy. Also the amount of short circuit current, which would be the short-term voltage support amount. And this can be tuned, it also reflects the hardware design. But then there are also some country-specific parameters. But what we would aim for is as an OEM and engineering partner for our customers, is that we are not starting from scratch in every market and especially not in every single state of the European Union or every state in the US, but that we have a defined standard, probably one for Europe, one for US, one for Australia, and then we only do minor adjustments depending on the location.
That would be an ideal target. And also, we do aim for getting as close as possible to that situation because it is just more efficient, and we have a lot of work to do anyways.
David Roberts
What about Australia? Is there something interesting to say about what Australia is doing here? Because Australia is really far down the road on renewables. I guess their goal is 82% renewables. I don't know where they came up with that number and are getting close and regularly have periods where 100% or more than 100% of their energy is coming from renewables. So it seems like if anybody's under the gun and really needs to solve this problem, it's Australia. Are they ahead on grid-forming inverters?
Daniel Duckwitz
They do have a system strength assessment framework. So they basically have an incentive. Even though it's not like you add revenues if you do grid-forming, but you avoid paying a fee. Or you could also say you avoid paying a penalty if you want. So there is an incentive for installing grid-forming already, but it's not very standardized yet. And also the defined quantities of how much inertia is required in which region, this is not, let's say, it is addressed, but it will be addressed probably even more accurately in the future. And this is something that is really, really, it really helps to speed up the installation.
And also this stability transition, if you define the target amounts of inertia, target amounts of short circuit level for each region or each larger state, that really helps to know where do you aim for and not just say "We need grid-forming." Because that could mean a lot of different things and it doesn't mean that you know what to do.
David Roberts
Well, again, that would be a great role for a market to play. Right. Like the whole point of markets is kind of to define those things and give you a sense of those things.
Catarina Augusto
Yeah, I believe we still lack transparency on the grid needs when it comes to — now, for example, in Europe it's mandatory for you to do flexibility assessments on grids and to make that part of the network planning. I think maybe we are missing something like this for when it comes to inertia and stability. It's not really clear when you asked before how much grid-forming we can substitute it better, as we don't even know how much grid-forming we need at the moment and how it's going to grow progressively.
David Roberts
That seems a little crazy to me that grid operators are not regularly assessing.
Catarina Augusto
I think they're assessing, but there's not really — if I ask, I never receive an answer.
David Roberts
I see. So they're treating the information as proprietary. One question I'd like to ask both of you is what policies would you like to see here? I don't know if we have enough experience with these things to do any sort of comparative — what policies work and what don't — but sort of like what are the policy instruments here that could speed up the sort of standardizing and spread of the market for these things?
Catarina Augusto
So first of all, the clear understanding of what is grid-forming and the recognition of TRL of technologies, I think that's not yet there. So there is a need for policy on piloting, also experimenting a bit and gaining the trust of system operators regarding storage. And then I think this network code, what we call it here, the rules to comply with the grid, need to have more harmonization for just the purpose that also Daniel met. And despite the fact that you have this clarity at European level on requirements, then you need a market to support the deployment of these services.
Otherwise, you will not be able to maintain systems sustainably and for storage to grow. So I think these are the main key areas.
David Roberts
And is there an EU-wide market for those services? Is that on the table? Is that something people are talking about? Is there a bill, is there a discussion at the EU level about this?
Catarina Augusto
Yeah, there is now a demand response, what we call it demand response network code. So it's a market code. So it's the code that then stipulates how services are procured and which kind of services. And some time ago now the Commission is assessing this code at the same time. And there was this question in the air from the regulation also, should we open this market from just flexibility to stability and bring the discussion of inertia? And I think that could be the place also. So take the chance that we are already working on flexibility services and start doing the same for stability.
Daniel Duckwitz
How about you, Daniel, are there particular policies that you advocate for?
I think, yeah, the UK approach, I do like it a lot because what the UK has done is they have given a technical specification in their grid code, so there is a clear understanding of what grid-forming is doing, how do I quantify inertia, what tests have to be passed, and so on. So the connection process is really well defined, and also the performance metrics are in the grid code. But then you decide how much of the quantity you want to provide, which can also relate to the CapEx of your project. For example, if you want to overbuild the batteries a bit more or something, and then you decide based on the market, how much you actually provide.
And this is a really good approach of the technical specification in a, let's say, rule for a wider area like the UK and then also the market design. And Europe could just do the same like the UK, because in principle the regulation in Europe says "There should be a market for inertia if it is efficient." And then so far only Germany came to the conclusion that it would be efficient and they are starting such a market next year. So I think where we do have these options of doing it, similar to the UK, I think Australia also has the inertia shortfall declaration part where they declare a lack of inertia in a certain area and then tender for filling up the levels that are missing.
And for US I can see some technical specification drafts, but there is no market incentive as of now, as far as I know. But we'd love to do a demonstration project in the US, of course.
David Roberts
Catarina, maybe this is a question for you, but on the politics, one thing I think I don't totally have my head wrapped around: like this grid-forming seems like an obviously good thing. It seems obviously good for the grid operators, seems good for ratepayers. It seems like it's helpful to generators, helpful to everyone. Is there an organized opposition? Is anyone against this stuff? Do you know what I mean? Like usually when you, in any market you can identify in the US you can find someone who hates it and is trying to kill it. Is anyone opposing this or is it just a matter of the slowness of trying to work it into regulation?
Catarina Augusto
I think, I think there's not really opposition, at least from our industry. There's a concern of not having the market and the right remuneration for it. But there is no opposition in that sense. But I don't know if the synchronous machines will be so happy.
David Roberts
Well, I'm sure they don't want to retire for a lot of reasons.
Catarina Augusto
But we have to work on decarbonization. So, well, what can we do regarding that? But regarding the technology and progressing on grid-forming, I don't think there is opposition. I think what is missing is the market and the knowledge when it comes to the right technology.
David Roberts
Well, sort of the inverse question then is, is there a particular industry that is lobbying for this? Like who, who is actually throwing money around and lobbying and pushing on this? Anyone? Or is it just something that wonks love? You know what I mean? Policy people love. Is there an actual industry that's committed to pushing this forward?
Catarina Augusto
Yeah, I think the transmission system operator. And then of course it's a good service that storage can bring. So of course it's something that also the storage industry is wanting to make more clear and that's why it's important also to understand the added value that they have. But I think it comes also as a request from the transmission system operator. There is just the need for a bit less, I understand for the stability part they need to be more conservative on the ideas and be cautious. But at the same time innovation is progressing a lot on storage. So I think that's the part that is still mismatching a bit.
David Roberts
Yeah, this is a fast-moving technology in a slow-moving industry. Well, Daniel, we're running out of time, but I just wanted to conclude by trying to press a little bit on this question. You know, a lot of times on this show we cover clean energy, we cover the energy transition. And I get excited, I get excited about new things, new technologies, and new ways of doing things. But I don't want to, I don't want to inadvertently sort of oversell this. So I guess I just push a little bit on — are grid-forming inverters at a level of technology readiness that actual technical nuts and bolts grid operators and utilities feel comfortable with them?
Like, do we really know for a technical certainty that these can step in and do all the work spinning masses were doing? And are we confident? Like, what is our general level of sort of industry and technical confidence in this?
Daniel Duckwitz
Yeah. So, personally and also as a company, we are fully convinced that we can do this.
David Roberts
Well, you sell them. I mean, you have to be convinced, right?
Daniel Duckwitz
Well, I mean, I could just argue for selling the grid-following stuff.
David Roberts
That's true.
Daniel Duckwitz
Yeah, but, but then no, we are really, really committed to not only selling the grid-forming technology, but we are also committed to making the power systems of today and tomorrow stable. Because without stability, the energy transition is not going to happen. So this is really, really, really important also for our business, it's important to have stable systems, and this is why we also focus on this kind of technology. But then when I talk to transmission system operators, I think maybe 10 years ago, 15 years ago, when I had the first talks with TSOs about — it wasn't even called grid-forming back then, it was virtual synchronous machine or whatever.
And they were like, "It does work, does it?" And I was like — I was in research back then — and I was, "I think it could work, let's do some research." And then we did some research and so on. And I think nowadays, like I would say 8 out of 10 engineers in the transmission companies are convinced it is going to work. But then we need, of course, to convince the other two. And the most important part is to really prove the technology in the field and do these demonstration projects, gain the experience even in an exchange.
And it is sometimes really causing a lot of extra effort to do this. But then it is worth it because only with proving the technology out there in the field in demonstration projects, but also the first commercial projects are out there online, really gives the confidence to move onward and do the right thing.
David Roberts
I mean there are grid-forming inverters on the grid doing grid-forming. Like, this is not theoretical, it's out there happening. So we can, there is performance in the field to assess here. We're not speculating.
Daniel Duckwitz
So we are in the UK, we provided support to the commissioning of the Blackhillock project, which is a 200-megawatt battery providing inertia to the system since February of this year.
David Roberts
And this is where again — is this the one in Sweden?
Daniel Duckwitz
It's in Scotland in the UK, Scotland. And the location is called Blackhillock, but I guess a Scotsman would pronounce it completely differently. I don't know how they would say. "Blackhillock," that's how I say it. And that's the first plant that is online since February. And in March there was this trip of a large gigawatt-scale power station and it has already provided inertia in that scenario. So it has proven its contribution to stabilizing the system one month after commissioning. So this is really giving us some confidence in the real world performance. And it's not the only plant out there.
We have also some smaller scale demonstration plants out there which have also been operated for between years and several months, and they have also responded to grid events of that scale, and we can see it works, and we're really, really looking forward to doing this in more and more markets and countries.
David Roberts
I saw the little demonstration project in Germany where the one region islanded, cut itself off from the national grid, and ran purely on renewables and grid-forming batteries for I don't know, like an hour or something. I mean, I don't know how seriously to take that as a demonstration, but like does seem like—
Daniel Duckwitz
Yeah, it was back in 2019, it was the first demonstration of the feasibility on the — I think it was a 15-megawatt plant and this small town was isolated from the transmission grid. So it was back then the first larger demonstration of the feasibility. But yeah, I mean it was operated for an hour off-grid and then resynchronized. And then since then I think it is resynchronized. But there are other projects where we prove the technology every day. And I mean the whole purpose is not to operate as a microgrid, but to operate as part of the interconnected system.
And we are getting more and more experience with that kind of operation.
David Roberts
Right. And I didn't mention this before though, I guess I'll just throw it out now. But like SMA, your company, you guys kind of got started with these inverters on microgrids. So like these things sort of grew out of "How can we have an islanded microgrid freestanding, operating on its own?" That's what sort of spurred the development of these things. And now the idea, I guess, is just to sort of like expand that out so that the macrogrid basically becomes —
Daniel Duckwitz
Yeah, so it started with the 5-kilowatt Sunny Island Inverter, which has been operating in many remote areas for I don't know what kind of energy supply situations, like a really small village out there where there is no distribution grid or no grid at all. And then they got a bit larger and larger. But then since around 10 years we have been working on bringing this to the interconnected systems. And during the past three to four years it has really gotten bigger. And we have now commissioned the first 100–200 megawatt scale projects. And yeah, so it's really evolving since more than 20 years from the very small units to the bigger units.
But the aim was the same back then: to operate these microgrids without diesel genset or to be able to operate them without diesel genset throughout the night in summer, but maybe not in winter at first, and then increase it. And that is really like a small energy transition. And now we are doing the big thing. I hope that we will all do it together now.
David Roberts
Yeah, it's moving so quickly. So interesting. Catarina, which grid do you think is going to get there first? If you're betting on a horse, who do you think is going to get rid of their spinning masses?
Catarina Augusto
The country, you mean?
David Roberts
Yeah. Well, any region. I don't know. A grid. Any grid.
Catarina Augusto
It doesn't count. UK, I imagine.
David Roberts
Well, if the UK could. I mean, they still have lots of gas, right? I mean, or some gas. You think they're going to get closer first?
Catarina Augusto
I wanted to say yes, but I don't know because to be honest, Germany tested a lot of solar deployed, but I also know that some policies are still very oriented on fossil fuels, so I'm a bit skeptical there. However, maybe this inertia market will do the job and make things go faster.
David Roberts
Well, let's hope so. Thank you two so much. This is super fascinating. Like I said at the beginning, it's technical, but this is like if you're trying to get from a grid with some renewable energy on it to a renewable energy grid, this is a step you have to take. This is a technology we have to master. So thank you two for coming on and walking us through it. This is fascinating.
Catarina Augusto
Thank you for the invite, David.
Daniel Duckwitz
It was great. It was a pleasure.
David Roberts
Thank you for listening to Volts. It takes a village to make this podcast work. Shout out, especially, to my super producer, Kyle McDonald, who makes me and my guests sound smart every week. And it is all supported entirely by listeners like you. So, if you value conversations like this, please consider joining our community of paid subscribers at volts.wtf. Or, leaving a nice review, or telling a friend about Volts. Or all three. Thanks so much, and I'll see you next time.
