Grid frequency collapse and blackouts in GB, Europe, and Australia explained

Energy has been capturing headlines across the globe in the last week, following a total blackout in Spain and Portugal. 

Thankfully power is now restored across the peninsula, a detailed dive into what triggered the blackouts will take some time including identifying the causes of the event. In this blog we’re going to take a look at what we know so far, more broadly why blackouts happen, a look at similar events in the UK and Australia and finally explore what this means for distributed flexibility and increasingly renewable grids. 

Why do blackouts happen?

Blackouts can be triggered by a number of factors, from power station trips, loss of loads, and faulty equipment all which ultimately result in a severe imbalance between supply and demand.

Most grids operate at 50Hz, this means that frequency oscillates 50 times per second. A delta between supply (power generation) and demand (power consumption) causes frequency to rise and fall; if a large generator trips frequency will fall. Typically a safe range for frequency sits between 49.8Hz and 50.2Hz, but it is not uncommon to see frequency fall to 49.7Hz in the event of a very large trip - such as losing the IFA interconnector that connects the GB Energy Market to France. In GB the statutory frequency limits are 49.5Hz-50.5Hz.

It’s important to note that large generators and interconnectors trip very often - Transmission System Operators (TSOs) will procure enough fast acting frequency and reserve to cover an N-1 situation, this means that the system can lose it’s largest generator and no blackouts will occur. Battery storage is an excellent solution to providing frequency stabilisation services as batteries can react within milliseconds. 

A blackout is typically a result of a more severe set of circumstances, such as two generators tripping within seconds, such that there is not sufficient frequency or reserve to prevent frequency plummeting. In these events load shedding will often be triggered via an automatic protection scheme such as Low Frequency Demand Disconnection (LFDD) in the UK. This is where substations that detect a change in frequency automatically disconnect demand in a series of 9 stages - this was what helped to contain the partial blackout in the UK in August 2019 (more on that later). 

What is inertia?

Inertia is the property of an object to resist changes to its present state. In the context of the electricity grid this refers to the property of the grid to return to its intended frequency when there is a disturbance due to a sudden change of supply or demand that impacts frequency. A by-product of synchronous AC generators (CCGTs, nuclear and coal) is that they provide inertia intrinsically due to the rotating mass of spinning generators and automatic governors making them excellent at providing inertia thus keeping the grid stable whenever there is a sudden change in supply or demand. Grids with high inertia can reduce the Rate of Change of Frequency (RoCoF) more effectively, lowering the risk of blackouts.

Whereas grids operating with low inertia, frequency can fall so fast that it goes into an emergency state before assets and mechanisms such as LFDD can respond. It is not just the absolute frequency that matters, but the RoCoF. Every generator will have a relay mechanism to automatically shut-down if RoCoF is high and frequency falls past a certain level (i.e. there is a blackout). If inertia is low or relays are triggered too early this can accelerate the RoCoF and cause frequency to plummet further. 

Renewable generators don’t typically provide inertia because their inverters read grid frequency rather than forming it. However, with grid forming inverters renewable assets can provide synthetic inertia. There has to date been little incentive for generators to install grid forming inverters as inertia markets are not yet commonplace. With high PV and wind generation and few grid forming inverters the Spanish grid operates at lower inertia levels than it would have with previous generation mixes. This means that there were fewer synchronous generators to help arrest frequency and the RoCoF would have been very high.

‍What happened in the Iberian Peninsula last week? 

We don’t yet know all of the details, this will be a long and detailed process led by Red Eléctrica - the Spanish TSO. What we do know is that at 12:33pm on Monday 28 April multiple trips occurred causing frequency to fall, 3.5 seconds later the Iberian Peninsula (Spain and Portugal) disconnected from the rest of Europe due to the French interconnectors tripping. Frequency then went into freefall accelerated by inertia being relatively low, a high RoCoF would have meant relays would have been triggered on generators and some loads. Total generation quickly fell to 0GW in Spain, a total blackout, with the Portuguese grid experiencing a blackout as well.   

Remarkably power was restored across the peninsula within hours, with 99% of national demand restored by 06:00 on 30 April. Restoring a grid from a total blackout, known as a black start, is a delicate act and one that is very hard to practise, as supply and demand must be kept in balance throughout the repowering process. 

While we await the outcome of Red Eléctrica (Spanish TSO) and Rede Eléctrica Nacional’s (Portuguese TSO) reviews into the events of 29 April. Until then, it’s worth taking a look at similar events across the globe and exploring how those events altered the direction of energy markets and the generation fleet. 

‍Partial Blackout in the UK

On the 9th of August 2019 a lightning strike hit transmission lines.  Following this there was a near instant loss of two main power stations (Little Barford CCGT and Hornsea One Offshore windfarm) - a generation loss of over 2.1GW which caused frequency to drop to 48.8Hz followed by a loss of a number of smaller generators in the distribution network that came off when LFDD was triggered.

This event disrupted power supply to over 1 million electricity customers and power was restored 45mins though rail services remained impacted until 11 August. In its scale this event is much less severe than last week’s events in Spain. 

On the 9th of August batteries accounted for 472MW of the 1GW of reserves that NESO had at their disposal, these batteries were predominantly delivering Firm Frequency Response (FFR). Almost 6 years later the UK grid has over 4.8GW/6.6GWh of utility scale batteries and procures significantly more fast acting frequency response services across Dynamic Containment, Dynamic Moderation and Dynamic Regulation (Dx services) - these services all include a much more stringent metering requirement than FFR. In the early days of the Dx services demand from NESO outstripped battery capacity driving a 12 to 18month period of incredibly high battery revenues for those who had assets on the ground. 

Blackout in South Australia 

On 26 September 2016 a large storm took out a number of high voltage pylons in South Australia. The drop in voltage led to automatic protection mechanisms being triggered across a number of windfarms, creating a generation loss of 456MW this was followed by the loss of the interconnector that joins South Australia to Victoria resulting in a further loss of 613MW. This resulted in a total blackout (with the exception of a small island) in South Australia. 

Official reports on the blackout point to a low inertia system as a result of too fewer synchronous generators that resulted in frequency falling faster than it would if there was more inertia. Frequency quickly breached the 47Hz limit and generation disconnected across the state. 

What played out after that event has become part of energy transition folklore. In a late night Twitter exchange in March 2017 Australian Tech Billionaire Mike Cannon-Brookes and Tesla boss Elon Musk coaxed each other into offering the then South-Australian premier a 100MW battery in 100 days (from contract signing). 

That battery did indeed get built and was first energised in December 2017 as a 100MW/129MWh asset, the world’s first “Big Battery”. Now operated by Neoen, the asset has subsequently been expanded to 150MW. By any measure the project has been a huge success, delivering $150 million in value in its first two years alone, and regularly providing key support to the South Australian market, and making its owners a tidy profit along the way.

What does this mean for flex and grids of the future?

In both the UK and Australian events, and likely the Iberian event, high renewable grids were in an operation with less synchronous thermal generation than in previous years. More renewable generation is a good thing and not to blame for blackouts. However, an increasingly renewable grid is requiring TSOs, markets and market participants to invest heavily in flexible generation assets, such as battery storage, EV fleets and flexible loads. 

As evidenced by the response to the UK and Australian blackouts battery storage has proven to be a large part of the answer here, providing sub second frequency response in GW quantities to help provide security of supply. 

Flexibility is required at a fundamental market level to balance an increasingly renewable energy system (storing cheap solar or wind power and discharging it into more scarce supply periods). However, with faster acting flexibility technology such as battery storage there are crucial added benefits via the provision of ancillary services. 

It will be interesting to see how this plays out in Spain, with the the Spanish battery market currently much smaller than many of it’s European neighbours. Much of this is a consequence of the regulatory and energy market environment in Spain, such as not having a market based FCR ancillary service like many countries in Europe.  

‍How about inertia? 

An emerging and important topic is inertia, historically grids received this for free as a by-product of synchronous thermal generation. There have been great advances in grid forming inverter technology which means renewable assets can provide synthetic inertia however there is not yet a market for this in Europe so there is little monetary incentive for asset owners to install these more expensive devices. In Australia, the Dalrymple and Hornsdale batteries provide synthetic inertia and in the GB energy Market NESO has awarded some Stability Pathfinder contracts to battery storage, however that market is currently dominated by synchronous condensers. 

It looks likely that the topic of inertia markets and synthetic inertia will continue to gain momentum in light of our increasingly decarbonised grids and following high RoCoF in all three blackouts we’ve referenced in this blog. 

Shift to distributed assets - does this help?

In the two blackouts we know lots about it was the loss of numerous large generators or interconnectors that triggered frequency to drop suddenly. The continual shift to an energy system with more distributed and decentralised assets may help to mitigate the risk of the largest generator falling and can ensure that response services are delivered in the local area that is impacted by a frequency disturbance. However, in most grids especially across highly interconnected markets such as Europe this large risk asset is increasingly interconnectors. 

Looking forward

Along with the energy community we’re looking forward to hearing more about the specifics of the Iberian blackout in due course. Until then, looking at previous events, what is abundantly clear is the need for more flexible generation assets. Power stations and interconnectors tripping is a common phenomenon, the key is ensuring that the TSOs have the right tools and assets at their disposal to manage them with as little impact on the power system and customers as possible. Gridcog has been built to allow our clients to simulate even the most complicated flexibility projects. Get in touch with the team if you’d like to learn more.   

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