[ Episode #74 // Addiction Thinking ]

[00:05:28] Chris Nelder: Welcome Julian to the Energy Transition Show.

[00:05:30] Julian Leslie: Hi. Great to be here.

[00:05:32] Chris Nelder: Today, we're going to talk about how the UK plans to achieve its objectives for decarbonizing grid power, including some really interesting innovations in its wholesale market and the operational codes of its grid. But first, just for the avoidance of any potential confusion, why don't you explain for our listeners how National Grid ESO is organized and regulated, and what is the relationship that it has with National Grid, the utility company?

[00:05:55] Julian Leslie: Yes. So National Grid ESO here in Great Britain is the electricity system operator for all of GB. So that includes the countries of England, Wales and Scotland. And in terms of how we're regulated, we're regulated by the national regulator Ofgem. And they give us our license to operate and make sure that we have the wherewithal, the resources to do it, what it is that we need to do. So we do operate the Great Britain's transmission network. What we don't do, though, is we don't own the assets. So we operate the market and we do the real time operation and the planning of the network. But we don't actually own the assets so much like the ISOs and the RTOs that you see in the US.

[00:06:33] Chris Nelder: Okay, great.

[00:06:34] Julian Leslie: And as the ESO, we have sort of been on this journey now since, since the early 2000s where we've been looking to decarbonize the grid in GB and we're one of the fastest decarbonizing grid systems in the world with a 66% reduction in our carbon intensity of electricity produced since 2014 to where we are today. And what we're talking about today, I guess, is the activities that we're doing that's going to push that even further so that by 2025 we can operate for a few hours at totally zero carbon. And then to meet the government objectives in 2035, to operate a system at 100% zero carbon 100% of the time.

[00:07:11] Chris Nelder: Okay. So National Grid ESO has no direct commercial interest in this stuff and it basically functions as a government regulatory body. Is that fair?

[00:07:21] Julian Leslie: Yeah. Well, today we are still part of National Grid, although we are a legally separate entity within the National Grid Group. So as part of that, we are on the stock market and therefore investors can invest in National Grid, of which the ESO the electricity system operator is part of that. Although just the other week that is changing. So in the next 18 months to two years, we will be a public corporation, so owned by government, but at an arm's length.

[00:07:46] Chris Nelder: Oh, interesting.

[00:07:47] Julian Leslie: So we will have the right to operate under the government's control. But our regulatory structure, our ability to do work and our accountabilities will all be set by Ofgem, by the regulator, pretty much as they are today.

[00:08:00] Chris Nelder: Gotcha. Okay. Well, as the energy transition progresses and more variable renewable power generation is introduced to the system and displaces conventional thermal generators that churn out power with certain characteristics. Grid operators like National Grid ESO need to take care to provision what are sometimes called stability services to maintain the very strict operational limits of the grid. And so that's what we're going to talk about today, how you're providing those services in a system that is increasingly powered by variable renewables. So maybe you could just start by explaining to our audience what stability services are and what's needed to accommodate more variable renewable generation.

[00:08:40] Julian Leslie: Sure. So stability services are some things that the system operators around the world haven't had to think about because the way that power is being produced until today, using large rotating machines, whether they be gas or coal or nuclear, then they provide certain physical characteristics such as short circuit in feed, fault level contributions and also inertia. As we move to these more renewable sources which are connected to the grid system via some power electronics through something called an inverter, then we lose those sort of natural physical characteristics of the conventional power plant. So the system operates as we need to ensure that as we decarbonize the systems and as we get more and more renewables connected using these black boxes, these inverters that actually we find ways in which we can replace the loss of that synchronous generation, providing those services and replace that with other alternative solutions. And that's the work that we are doing and what we have done over the last year, 18 months within the ESO here in GB.

[00:09:44] Chris Nelder: Okay. So for those of our listeners who may have not listened to Episode #55, which is our super geeky show on voltage stability or Episode #126 about how the grid works, which is part of our Energy Basics mini series. Would you give us a brief refresher on what exactly inertia is?

[00:10:03] Julian Leslie: Yeah, there's two ways to think of it. I mean, physically what it is, it's a rotating mass. So in a conventional power plants, you've got the turbines, you have the generation itself all spinning synchronous speed with the grid system. And when you get a disturbance on the grid system, that rotating mass continues to operate. So if you think of a child's spinning top, which I'm not sure is so popular in the US, but certainly back in my day here in GB, a spinning top, you press this thing up and down and you get this spinning top up to speed and it makes a bit of a musical sound. And as you take your hand away from that toy, it continues to spin and it continues to make this musical sound for a few seconds until the inertia declines and then it topples over and the thing stops. The other way to think about inertia is to think about a system with lots of inertia. It's a bit like a steam train on a railway track that once a thing is moving it, it withstands a lot of shocks and a lot of disturbances and it just keeps plowing on through. Whereas your heavily inverter based renewable system, it's much more like a motorbike. It can be up and running and it can run straight and be safe and secure. But as it gets buffeted by the wind from the side or whatever, then you get those bit of a wobbles. And what we're trying to do with inertia on the system is trying to make sure that we have enough strength in the system, a bit like the steam train, to sort of make sure that we get some of those products and some of those services, such that the system can withstand those side winds, those generation trips, the lightning faults and the transmission system. And the system remains robust and secure.

[00:11:39] Chris Nelder: That's an interesting analogy. I hadn't heard the motorbike analogy before. I like it. Well, okay. So how do you measure and maintain system stability on the National Grid ESO system?

[00:11:50] Julian Leslie: Again, this is something that system operators around the world have not had to worry about measuring it because as long as your generation was running to meet demand, you inevitably got inertia and short circuit in feet. However, a couple of years ago, we recognized that the need to measure this, to understand how close to the cliff edge we really are on managing inertia on the system to drive down costs for the consumer, that if we can identify where the cliff edge is, then we can operate much more closely to it. So to date, what we've been doing, we use data that we feed into spreadsheets, we run some algorithms sort of offline almost to sort of understand where we see the inertia going and what are the machines or the devices we need to procure in order to manage that in real time. What we've done over the last 12-18 months is we've worked with two providers, one of which is a company called Reactive Technology, and they have built the largest ultra capacitor in the world up in the north east of England. And what that does, it pulses power across the grid. And they have these very high accuracy, what they call XMU measurement units dotted around the networks that measure the frequency up to 48,000 times a second. And because, you know, the disturbance is being placed on the system, you can use these XMU units to measure the impact. And by looking at those two things, then as a complex algorithm then works out what your real time inertia must be at that very millisecond on the grid system. So it's a bit like using if you think about a submarine, an underwater sonar on a fishing boat or whatever, it's a bit like that. It's sending out a pulse. And then by seeing what it receives across the network, it's able to calculate and get a vision or a view as to what is going on.

[00:13:34] Chris Nelder: That's fascinating. Is this something that's been done before to inject a signal like this and then try to sense it on the grid?

[00:13:41] Julian Leslie: No. This is the first time anywhere in the world that this has been done. And we've worked very closely with Reactive Technology as a partner to understand their technology, how it works, both for them also to understand how we operate the system today, but also how we can operate the system into the future.

[00:13:56] Chris Nelder: Okay.

[00:13:56] Julian Leslie: So as I say, bits of this kit has been commissioned and we're working through this summer to bring all of the bits of kit together, to start to get the first bits of data and information out of this process. As soon we get into this coming winter, we should have a very, very clear view as to what is the real inertia on the system in real time. But because it is the first in the world, we've also developed a second tool working with GE and what they have been doing is working to take data from our systems in pretty much real time. And this measures frequency and power flow changes between regions across Britain and it does about 50 times a second and again, so it's not pulsing electrical charge into the system like the Reactive Technologies one is, but it is looking at changes on the system, understanding therefore what the impacts of that should be and measuring those impacts and therefore using machine learning. And then it then tells us what our inertia is now. But more importantly, using that machine learning piece, it also talks about it and forecasts what it might be in the hours to come, in the 24 hours to come. So again, we can much better plan for bringing on conventional power plants. If we're short on inertia, we've got the time to identify which is the best one and in the best location. So what we hope to do by having these two tools, because both of them are first in the world sort of developments and comparing that with our sort of offline Excel spreadsheet almost that we use today, between those three pieces of information, we will get a real deep understanding and all three of those tools working together will help improve the data, the analysis and the information that each of them can provide us.

[00:15:36] Chris Nelder: Gotcha. Okay. So on January 31st, Ofgem, the UK grid regulator, updated its grid code concerning converter connected technologies, including renewables and interconnectors, to allow them to provide stability services. And I guess in this sense converter is equivalent to what we normally hear as inverter, is that right?

[00:15:58] Julian Leslie: Yeah, that's correct.

[00:15:59] Chris Nelder: Okay. So previously those services were only provided by synchronous generators, as you've mentioned earlier, like conventional thermal power plants with a big spinning mechanical mass. And we discussed grid forming inverters in Episode #153. So our listeners who listen to that are certainly aware of the technical challenges involved in integrating these resources and transitioning from a grid where system inertia is provided by synchronous generators to one where it's provided by grid forming inverters that produce what is sometimes called synthetic inertia. But perhaps you could explain the significance of this change to the grid code?

[00:16:37] Julian Leslie: I mean, this is a real significant world first achievement in defining the minimum viable products for a grid forming inverter. Before we had done this earlier this year, there was always the challenge of we didn't really know what the equipment providers could provide and they really didn't know what we wanted. And therefore, it's really hard to define what was required for a synchronous generator through a grid forming inverter, because there was this chicken and egg situation going on where we didn't know what the opportunities were and neither did the OEMs and the suppliers understand what it was that we needed. So through a lot of hard work working with the key suppliers in this sector, looking at what it is that they thought the capability of their devices could be, it was looking at what does it mean to have a synthetic replication of a conventional power plant? And by working together in that way, we've been able to define, as I say, for the first time anywhere in the world, this grid code requirement that that anybody now can pick up and go, well, if that is the minimum viable product, I can now invest in my supply chain. I can invest in my technology developments such that we can bring forward new and innovative grid forming inverter type of technologies. Hopefully drive down the costs because anybody can develop this. It's not just stuck with the original sort of OEMs and new people could come into the market. So it's really exciting that we've got this minimum technical requirements which is now defined that anybody can pick up. And what we hope to do and what we've seen as I know will come on to later is is through our stability pathfinders, we are now seeing these devices becoming commercially available and bidding into our markets and bringing those to the system in the next few years.

[00:18:16] Chris Nelder: So what are the implications of this change to the grid codes? How will they help Britain decarbonize its grid power?

[00:18:22] Julian Leslie: So having this change in the grid code is a real step forward in terms of now it's clearly laid out there to anybody that's interested developers, equipment manufacturers, what it is that we require as electricity system operator in GB for a grid forming inverter to do and what it's basically doing as we said earlier this is looking to artificially replicate inertia and short circuit in feed that you conventionally get from a power station. So by having this now in code, it is very clear, as we said a moment ago, anybody in the world can go and have a look at what this requirements are. Therefore, if you want to participate in the GB markets to provide short circuit in feed inertia using a grid forming inverter, then it is very clear for everybody to see what is the minimum requirement that that grid forming inverter needs to do. Now participating in the markets obviously is down today to the developer and the equipment manufacturer, they can make the grid forming inverter more responsive or deliver a larger range of the performance. Whatever the what the grid code has done, it has said as a minimum, if you want to put a grid forming inverter on the system in Great Britain, then this is what the grid forming inverter must comply with.

[00:19:36] Chris Nelder: Okay, so having this specification out there and actually using these new tools now to to sense inertia characteristics and to monitor in very, very active ways the performance of the grid. This is helping you to understand where inertia is needed on the system as the variable renewables are sort of coming and going from the system. Is that basically the idea?

[00:20:03] Julian Leslie: Absolutely that's the idea and there's two different characteristics these grid forming inverters can provide. One is the short circuit in feed, which is quite locational actually probably more regional or more locational than we perhaps thought a couple of years ago. And therefore, we are targeting specific regions where we need the short circuit in feed.

[00:20:21] Chris Nelder: Why don't you go ahead and just explain briefly what short circuit in feed means?

[00:20:25] Julian Leslie: So short circuit in feed is when you get a fault on the system, a system to earth fault, then current flows through the system to feed that fault. So it goes to earth. If you have a very lightly loaded short circuit in feed, then the system becomes unstable - it doesn't have anything robust to hold on to. But also, and probably more importantly, the protection systems that the transmission owners are operating possibly won't work either because they are looking for a change in current flowing across the circuit. And normally when you get the faults there's a big in rush of current that's feeding this fault down through earth and it recognizes out there opens the breaker and it protects the asset and obviously wherever this fault has occurred on the system. So very lightly loaded short circuit in feed networks are inoperable because they're unstable, but also they're inoperable because you don't get that short circuit in feed that you would need in order to secure the system.

[00:21:22] Chris Nelder: Okay. So your ability to accurately estimate inertia and then to sense it and then to essentially activate grid forming inverters to provide inertia when it's missing is sort of the core idea here.

[00:21:35] Julian Leslie: Yes. And it's doing that in a zero carbon way because we can provide inertia and short circuit in feed today. But that requires the continued running of gas or coal fired power plants, which is obviously not at zero carbon and not on the path to 100% zero carbon by 2035. So the beauty about the grid forming inverters is generally connected to a battery, or they could be connected to a wind farms. Again, they are zero carbon. But we're also through the same sort of market processes. We are also procuring anything that provides the need at zero carbon. So we do see more traditional synchronous compensators and condensers also and flywheels also connecting to the system through that process.

[00:22:19] Chris Nelder: Right. So that brings us to this stability pathfinder project that you've had ongoing under your network options assessment or in a way, initiative. What is the objective of the stability pathfinder project and what's involved in that?

[00:22:33] Julian Leslie: So we have been forecasting the decline in inertia and short circuit in feed for a number of years now. And we were debating on what is the right approach in order to provide and replace the decline in short circuit in feed and inertia. And if you look around the world, there's various ways to do this. So in Australia, AEMO if you're connecting a renewable farm, whether it be wind or solar in Australia, you as a developer need to make sure that you are not making the situation any worse. So therefore you as the wind farm developer are also building a flywheel or a grid forming inverter or something else alongside your particular connection. We decided in GB that actually we would let the developers develop a wind farm and do that in the most economic and low cost way possible. But what we would do as the system operater, we would see regionally and cumulatively when we were going to hit these various sort of key points in the decline of these particular services and then run a commercial market based process in order to replace that decline in short circuit and feed inertia. But we didn't define the solution. What we have defined is the need. So what is it that the system needs and when do they need it? Then we go to market. We do a request for information and say, look, by 2025 or whatever, this is the amount of inertia we need in this region. What are your options? Give us your technical data and your commercial data, and we run an assessment process and a full commercial tender. And then at the end of that, we procure the technologies that provide the need in the locations where it's needed. So that allows, therefore, all of the developers and the equipment manufacturers to really innovate, to think about how do we build and make a device that provides that particular service in the most cost effective and economic way possible.

[00:24:28] Chris Nelder: So this is really interesting. I think what's fascinating to me about this is that in the Australian system, as you mentioned, in the AEMO system, and we've covered that in previous episodes, they've put the responsibility, the onus for system stability essentially on each generator. And so they're basically forcing a wind farm or a solar farm to act as if it were a synchronous generator from the perspective of the grid where it's connecting to it. And that's something that I think a lot of people who are skeptical or maybe just not knowledgeable about the energy transition have assumed the way that things should work. For example, I've seen a lot of people over the years who don't believe in the energy transition or who think that nuclear plants are the only solution, who insist that every single asset on the grid has to have 100% backup that's firm and reliable because wind farms and solar plants are variable in their output. And that's always just seemed confused to me because system stability is a system property, it's not a generator property. And all generators, no matter what type they are, no matter how they act, are subject to their own faults. They all have the ability to go offline or their own reasons for being unreliable at different times and in different ways. And so it's the responsibility of the system operator to sort of orchestrate the way that all of these assets are acting together on the system to amount to system stability. It's not the responsibility of each individual generator to provide system stability. And so you've basically baked that concept into your approach to this.

[00:26:12] Julian Leslie: We have, indeed. And our view is, is that building one synchronous condenser, one grid forming inverter sites that provides the short circuit in feed, inertia for several wind farms or solar farms or whatever it might be, there must be a more efficient way to do it, because you're building a device once providing something that a system really needs, rather than every individual wind farm and solar farm having to build their own flywheel or whatever individually across the network. So we believe this is the right way. Obviously, there's many ways to to solve this particular problem. But this we are very much market led in Great Britain. And certainly one of our ambitions as the electricity system operators is that where there's value for the consumer, we should absolutely go to market and use competition to drive down costs for consumers. And as has been demonstrated through the pathfinders, also drive innovation, which again ultimately drives down costs for consumers.

[00:27:04] Chris Nelder: Yeah, I like that market based approach. And I think it's interesting that essentially what you're operating here is a transmission system. And so you're particularly paying attention to the decline in synchronous generation connected to the transmission system and looking for solutions to that with inverter based resources. But by taking that approach, you're also including distribution system level solutions and market based solutions, as well as just traditional transmission based solutions.

[00:27:36] Julian Leslie: Yes, absolutely. And again, it comes down to we describe the need on the system, which is likely to be at transmission level. But if there's somebody connected to the distribution system or comes up with some other innovative solution, then that is absolutely open to participate. And so they're not so much for stability and inertia, but certainly for voltage. Some of the pathfinders for voltage that we've run, we have absolutely had solutions at a distribution level that solve the voltage issue at source, which then solves the transmission level. So again, you can use much smaller devices capturing it near where the issue is created on the distribution system that avoids then having to build something even bigger on the transmission system. So all of our pathfinders are open to anybody and everybody. The incumbent transmission owners can participate, the incumbent distribution network operators and owners can participate as well as existing players in the market that have an asset that they can tweak and provide a different service as well as as what we've already talking about brand new innovative technologies, whether it be through grid forming inverters or there's another GE Grid Stability machine which is just being built for the GB market to build and providers inertia and short circuit in feed.

[00:28:51] Chris Nelder: Does this also imply that I mean, I'm going to use some of the terms of art that I've heard here in the US that if you had aggregations of DERs that could be coordinated and responding to grid signals to provide what's sometimes called non-wires alternatives that those essentially demand side resources could also participate here.

[00:29:13] Julian Leslie: Not so much for short circuit in feed or inertia. But certainly for frequency response. That is something that we are actively pursuing. And just today I was talking around if you have a million electric vehicles in a million households, actually, by the very nature of how they're just slightly different in timing and how they come onto the system in aggregate, they look like a high accuracy meter and they perform and you get the signals every second or whatever it is, because you're not getting a signal from every car every second, but you getting a signal every second from 20% of the cars or whatever. So that means that over the 5 seconds you're getting the granularity of data that you need to. We are absolutely in that space of ensuring that anybody and everybody can participate in whatever market their particular device is suitable for. But as I say, that aggregation is much more around either constraint management and shifting of load to meet generation or it's going to be frequency response very fast acting frequency response.

[00:30:14] Chris Nelder: I spent much of the last six years studying the grid integration aspects of electric vehicles. And, god, we could spend an hour talking about the challenges there. I mean, I know things are better in Europe, but here in the US we have yet, as far as I know, to have a single distribution utility, for example, offer a tariff that actually compensates vehicle owners for participating in some sort of a V2G type situation. Many of the vehicle manufacturers will just invalidate your warranty if you even try to use your vehicle that way. There's all sorts of issues that we still have to overcome, but the vision is beautiful. I mean, it is certainly a massive resource. And if you have either what we call smart chargers sometimes that have that intelligence and communications capability to actually talk to a grid and understand what the need is at a given millisecond. There's a real powerful resource there if we could figure out how to get out of our own way and harness that, I think.

[00:31:12] Julian Leslie: Yeah. And, and in GB just on that point, we don't have vehicle to grid yet on a large scale. There's obviously been trials or whatever, but we certainly have tariffs now which people will get paid to charge their vehicle on a sunny and windy Sunday afternoon because they are being incentivized to take power off the grid for that hour, 2 hours when the demand is low and the sun and the wind is high. So there's a couple hundred thousand people signed up to that right now. But this is the beginning of actually really shifting the load to meet the generation rather than what is historically been done the other way around.

[00:31:43] Chris Nelder: Exactly. So that would be what I would call a passive approach to manage charging using a TOU rate... All right. Well, as part of phase one of the NOA Stability Pathfinder project you launched and as you said, an RFI for Stability Services in July 2019. So I think that was the first RFI under this project in which you requested inertia solutions across Great Britain for delivery starting in April 2020, and you got nearly 50 responses to that RFI, but only accepted about a dozen of them. So how did you evaluate those tenders and decide which ones to accept?

[00:32:21] Julian Leslie: So the RFI we sent out in 2019 was, as you said, it was very much the first one, and we weren't sure what the market would do with with the information that we sent out there. And we were hugely impressed and surprised and pleased with the amount of interest that the market put forward. Obviously, we'd set out our technical requirements, the location elements of what it was we were looking for, and therefore the combination of looking at the technical capability of these 50 responses compared with their commercial offering that allowed us to run this tender process that sort of matched the biggest bang for your buck with the lowest cost solution in the right location, providing the services that we looked for. Obviously from that it was phase one and we learned a huge amount about the information that we needed to provide to the market in order for them to bid successfully. But also the market learned a lot also in terms of what it was that we were looking for and how to structure their technical and commercial bids to be successful. And the key about phase one is that it had to be we launched it in the summer of 2019, but it had to be operational at that point by April of 2021. COVID and things got in the way. So we had a bit of flexibility around that. But everything in phase one is now operational and the grid system today is running 24/7 and it's providing those critical services to the grid.

[00:33:44] Chris Nelder: Interesting. So what distinguished a winning tender from one that didn't make the cut.

[00:33:50] Julian Leslie: Either in the wrong location. It didn't provide us the service that we needed or was too expensive.

[00:33:56] Chris Nelder: So you had multiple tests that you were applying to figure out exactly which ones are going to fit? Yes. Again, highly locational requirements.

[00:34:03] Julian Leslie: Yeah. Well, the phase one was more for inertia, it's a less locational specific. But and because it was a trial as well, we didn't want to go and put all of our requirements out in one fell swoop. We wanted it to very much a trial by doing basis. These are called pathfinders. For that very reason that we weren't sure that what regulatory changes might need to be made the commercial construct of the contracts we were going to let, what types of technical data that the developers were going to send back to us. So we wanted to sort of test the water almost by doing a smaller request in phase one for inertia on a national basis, just to see what sort of response we would get and what type of solutions would come out of that. And as I say, we were hugely impressed and pleased with the response that we got and we believe we got some really good value solutions at zero carbon for the consumer.

[00:34:55] Chris Nelder: And how have those various assets performed so far?

[00:34:59] Julian Leslie: Well, really well. So we have pumped storage units in Scotland, which has just changed the way that it operates. So it spins in water or in air and provides that inertia and short circuit in feed. And we've got this old combined cycle gas turbine in Deeside in North Wales which is sort of disconnected so that the boiler and the gas turbine from the process, but it is now able to synchronize with its generator as a motor, but spin up that whole mass of the motor and the turbine stick on the back of that. Plus, we've had some of these brand new innovative solutions through Statcraft, and they worked with General Electric to build this rotating grid stabilizing machine. And there's two of those commissioned on the east coast of Scotland, which run 24 seven, providing the equivalent of two 500 megawatt coal fired power units. For these things, they fitted what I would call a barn where you might keep a few cows. I mean, it's not a big building, but it's providing the same inertia as a as a 500 megawatt coal fired power unit. It's hugely impressive.

[00:36:00] Chris Nelder: Fascinating. Alright, so then after that, you came to phase two of the NOA Stability Pathfinder project and you launched another RFI in June 2020 asking commercial and network operators to submit their stability solutions. And that RFI got several hundred responses, which I saw listed in the tender outcome that you published on April 6th of this year. But again, it looks like only a fraction of them passed the financial, health and economic assessment tests. So how would you characterize the winning submissions from phase two and what they'll do on the British power grid?

[00:36:35] Julian Leslie: So phase two was very locational specific. It is looking primarily for short circuit in feed. Most of these devices are providing short circuit in feed. You do get inertia as well. But the primary focus was short circuit in feed. And therefore in our commercial assessment, the more short circuit in feed you could provide gave you more points through that sort of tender selection process. Also, as I said earlier, short circuit in feed doesn't really travel very far across the electricity system either. So if you're a bit further away on your grid connection from where the actual need is, then your percentage effectiveness starts to decrease. So as we worked with the over 1500 sort of projects that were proposed to provide the solutions for Phase Two, we were able to sort of whittle some of those down because they weren't in the right locations. They weren't providing the volume of inertia on short circuit in feed that we needed, but also working with the developers through that process. Then quite quickly they could withdraw some of the options because they could see that actually it wasn't meeting the need, it wasn't in the right location or being delivered within the right timescales. So we gradually whittled all of that down and really got to sort of around 200 options that met and went all the way through to the final commercial stage. And it was at that point where you can then look at the technical performance, look at its percentage effectiveness, and then look at the commercial angle also. And then the combination of those aspects, you're able and through any like any normal commercial tender, you're able to score the submissions and those with the least cost. But the most effective solutions were the ones that made it through to the final cut.

[00:38:12] Chris Nelder: Hmm. So this is another world first, isn't it?

[00:38:15] Julian Leslie: Well, it's a world first, because it's different to Phase One, because world first in Phase Two is that (a) is probably focused on short circuit level and short circuit in feed, but (b) 50% of the solutions that were successful were using these grid forming inverters. So this is the first time anywhere in the world we believe that multiple grid forming inverters have been procured together to provide a system wide solution. So we know there's grid forming inverters, which have proven the fact that they can be a synchronous generator, but they are one of a kind on a system somewhere that has been hugely helpful and and has really helped to define what a grid forming inverter could and should do. What we've done here there in Phase Two is by procuring five of these devices in a relatively small geographical location. I mean, Scotland in GB terms is pretty big, but compared to America, Scotland is not big at all geographically, but to have five of these devices by 2024 connecting to the system and working together to provide that system strength. Is absolutely the world first and something that we're really proud to have been able to facilitate.

[00:39:21] Chris Nelder: It's very cool. So half of these new resources procured under Phase Two are grid forming inverters at multiple locations across the region, and they're specifically aimed at improving short circuit levels and improving the inertia and being able to address disturbances in the electricity system. And the other five solutions are essentially synchronous condensers. They're green, quote unquote, motors with free spinning flywheels that are just providing that kind of constant inertia on the system, did I get that right?

[00:39:53] Julian Leslie: Yeah, that's absolutely right.

[00:39:55] Chris Nelder: Okay.

[00:39:55] Julian Leslie: And I'm really pleased. Being an engineer at heart, if it was all the new technology and all ten sites were performing, grid forming inverters, I'd go, well, that's a bit of a risk there. What if it doesn't quite work in the way that we planned it to, but actually having that real mix across the selection, which wasn't a criteria, we didn't set out to have a 50/50 mix of conventional sort of traditional solutions and 50% of the new innovative solutions. That's just how it worked out in terms of, I say, the criteria, the assessment process that we went through so that deep down engineer that that sits within me is pleased that we've got a diversity of solutions and not putting all of our eggs in one basket, as it were.

[00:40:32] Chris Nelder: Yeah. I mean, it's got to give you some comfort just to know that those synchronous condensers are out there. So does this imply that there's some sort of an aftermarket or a second life, I guess, for the synchronous condenser portion of coal fired power plants, for example?

[00:40:47] Julian Leslie: I think potentially as we've seen with Deeside, this old combined cycle gas turbine is absolutely repurposed it's turbine hull in the generator in order to do this. As we look to Phase Three, which is more of an England wide, so much bigger geographical patch, again, regionally sensitive because short circuit in feed is the primary sort of driver for that. Maybe some of the coal fired power plant that has recently closed some of the older gas plant, which is about to close, maybe they will have a new lease of life and run themselves as a zero carbon motor and providing these services to the grid.

[00:41:21] Chris Nelder: Well, what makes a synchronous condenser in this solution set green? I mean, don't you have to have some way to ensure that they'll only get energy injected from renewable sources, for example, to be qualified as green.

[00:41:36] Julian Leslie: By 2035, 100% electricity on the system will be zero carbon. So, yes so today you're right to say that the megawatt that it's using to spin the machine up to synchronous speed will have a carbon intensity associated with it because we're not running yet at zero carbon, but it enables us to run at zero carbon and therefore the carbon is consuming its whatever the grid level of carbon is. And as we move, we've got a transition at some point and we are on that transition in 2025, we will have the first few hours where we will be operating at zero carbon and that'll likely be on a as I say, a sunny, windy Sunday afternoon in August maybe. But then as we get to 2035 here in GB, we'll be running this system 100% of the time with 100% zero carbon.

[00:42:20] Chris Nelder: Hmm. Okay, fair enough. So for those of our audience who are interested in the engineering side of this integration, but maybe haven't listened yet to our Episode #153 on how grid forming inverters work. How would you describe how these inverter based assets improve inertia and short circuit in feed on your system? Like what exactly on a technical level are they doing?

[00:42:41] Julian Leslie: There's papers and papers of really techie stuff to understand this, but.

[00:42:46] Chris Nelder: I know it's a tough question, especially in an audio only format.

[00:42:50] Julian Leslie: Exactly. I mean, I'd love to have a whiteboard and draw it all out. But anyway. But the grid forming converter or grid forming inverter is using power electronics to mimic what the synchronous machine would do. So it maintains its internal voltage at approximately constant and therefore as it receives a system disturbance it is working hard to keep the voltage sort of profile within the inverter pretty stable. And this behavior is the key thing that ensures the provision of inertia and short circuit levels, because if the disturbance happens, holding this voltage has the effect of withstanding the change on the system. And also as a fault occurs, then the inverters are able to inject short circuit and feed into the system. That lessens the disturbance on the system. And it also, as I say, provides that in feed in rush so that the protection systems work also. But it's a really smart, quick acting black box of power electronics. I mean, fundamentally, that's what it is.

[00:43:52] Chris Nelder: So the way that this actually works, you can see from an engineering standpoint how the system could operate completely with just grid forming inverters, like without any conventional thermal generators at all.

[00:44:06] Julian Leslie: I guess the theory that would be the case, there's yet to be a system anywhere in the world which is progressing in that way or has achieved that. But yes, I mean, the textbooks would tell you that that is absolutely possible.

[00:44:18] Chris Nelder: Well, from what we heard in Episode #153, I think there are some islands in Hawaii that are getting close to that level. Well, since you're bidding process clearly included a number of financial tests, could you explain how National Grid ESO evaluates the cost of provisioning these stability services in the sort of all a carte fashion, as contrasted with simply getting them as part of procuring power from a conventional thermal generator with a spinning mass. I mean, in other words, is building up a grid based on variable wind and solar and then buying these stability services to maintain system strength. Is that a good deal for consumers relative to just buying power from conventional generators and getting all the system strength as part of the package?

[00:45:00] Julian Leslie: I mean, our analysis here in GB is that it is a great deal because you won't decarbonize, which is a global challenge. You can't decarbonize if you're running coal and gas the whole time. And the way we've done the cost benefit assessment here in GB is that because we have the market operating, we can see very clearly the costs of running conventional power plant just to provide these services. And on the days when we need to do that, those are the high renewable output days. So the conventional plant isn't running through the market anyway. So in order to get the headroom and space to bring on the gas fired power plants, we are having to curtail renewable energy. And because gas fired power plant maybe has a minimum stable generation of 200 megawatts. So we have to buy off 200 megawatts of renewable wind in the market and then buy on 200 megawatts of gas just to provide inertia and short circuit in feed. Whereas through our Pathfinder projects, we don't need to do any of that because there's zero MWs. So the maybe absorbing a megawatt or two, but really the market will deliver a zero carbon solution that we then don't need to interfere with. So the cost to the consumer at that moment in time is zero because the market will say, here's all this wind, here's all the demand, the two match. That's great. And then we're saying and we can manage the system because we have these zero carbon solutions providing the inertia and the stability that we need and these contracts, so each one of these devices so far through the two contracts that we've let, there are roughly sort of 2 to £3 million a year to have one of these devices running for a full year. If you think about constraining 200 megawatts of wind in the job market, that's probably 60, 70, maybe £80 a megawatt hour plus then you've got to buy the gas on the system at 60, 70, £80 a megawatt hour also. So within a few hours, these devices have paid for themselves year round.

[00:46:55] Chris Nelder: Wow. Well, that's a pretty compelling case, economically speaking. Okay. So what sorts of technical challenges does National Grid ESO anticipate once the integration is well underway and renewables start becoming like a large share of overall supply, like 80% or so?

[00:47:14] Julian Leslie: So I mean, in GB we're a little fortunate in that we have a nuclear fleet of generation today and we're investing or the nation is investing in a new nuclear fleet as well. Plus, we do have some run of river hydro and some pumped storage hydro as well. So we never need to get to 100% purely renewable system because we're always going to have some of this generation running on the system which provides inertia and short circuit in feed. But that's not to say, though, when you end up with an array of ten, 12 gigawatts of nuclear and then 50, 60 gigawatts of offshore wind, managing that system is not going to be easy. And that's why preparing for that moment now, by understanding the Pathfinder processes, the types of technologies and the commercial arrangements that we can put in place to ensure that we are ready and prepared for that particular day when we do get the 80%, 85% of zero carbon. And in fact, on January the 6th, I think it was of this year, we had 86% zero carbon generation on the GB system. So we've been at these very, very low levels or high levels of zero carbon, whichever way you want to characterize that and what that allows us to do, we know exactly why that 14% of non-zero carbon generation was running. Some of it was decided by the market, but some of it was because we'd had to intervene in the market to provide the inertia and stability services. So that gives us great confidence that as we analyze these days with a very high penetration of zero carbon, that actually we can look at each and every individual machine that we ran, understand why we run that, and then we can, as we go forward with pathfinder and this stability procurement processes, we can then be procured exactly what it is that we need. So where the market then delivers as a fully zero carbon solution, we can sit back hands off the market and the market will deliver. And because of these Pathfinder projects which are running across the network, that the network will remain stable and operable.