A power engineer on the Iberian grid collapse: It makes me very afraid for Britain

Telegraph

01-05-2025

Last Monday, the Iberian grid suffered a disturbance in the south-west at 12:33. In 3.5 seconds this worsened and the interconnection to France disconnected. All renewable generation then went off-line, followed by disconnection of all rotating generation plant. The Iberian blackout was complete within a few seconds.
At the time the grid was producing 28.4 GW of power, of which 79 per cent was solar and wind. This was a problematic situation as solar and wind plants have another, not widely known, downside – one quite apart from their intermittency and expense.
This is the fact that they do not supply any inertia to the grid. Thermal powerplants – coal, gas, nuclear, for example – drive large spinning generators which are directly, synchronously connected to the grid. If there are changes which cause a difference between demand and supply, the generators will start to spin faster or slower: but their inertia resists this process, meaning that the frequency of the alternating current in the grid changes only slowly. There is time for the grid managers to act, matching supply to demand and keeping the grid frequency within limits.
This is vital because all grids must supply power at a steady frequency so that electrical appliances work properly and safely. Deviations from the standard grid frequency can cause damage to equipment and other problems: in practice what happens quite rapidly when frequency changes significantly is that grid machinery trips out to prevent these issues and grids go down.
When a grid has very little inertia in it – as with the Iberian one on Monday – a problem which a high-inertia grid would easily resist can cause a blackout within seconds. Lack of inertia was certainly the primary cause of the Iberian blackout, as Matt Oliver has opined in these pages. A grid with more inertia would not have collapsed as quickly, and its operators would have had time to keep it up and running.
Restoration of supplies was completed by early Tuesday morning, based on reconnection to France, which facilitated progressive area reconnections across Spain and Portugal.
Iberia is part of the Continental Europe Synchronous Area which stretches to 32 countries. It is interconnected as a phase-locked, 50 Hz grid with a generation capacity of 700 GW. To improve the stability of this grid, the EU aim is that all partners will extract 10 per cent of their power consumption from synchronous interconnectors – ones which transmit grid inertia – helping to make the whole system more resilient. France is at 10 per cent, but peninsula grids and those at the geographical fringe are the least interconnected. Spain has just 2 per cent from synchronous interconnectors.
But there are places where things are worse. The UK and Ireland are island grids. They do have undersea power interconnectors to Europe but these are non-synchronous DC links and transmit no grid inertia. There's little prospect that this will change.
Both the Irish and UK grid system operators have developed an array of grid protection services that can control grid frequency, loss of load or generation protection, grid phase angle and recovering from grid outages. Neither country has, to date, ever experienced a total system failure, even during WWII.
In 1974 construction started on Dinorwig Power Station. It is a pumped storage generation plant designed specifically for the provision of all the UK's grid protection services. Dinorwig can make huge changes to its output in a matter of seconds, compensating for sudden events. Operation began in 1984. In 1990 all the UK's generating stations could provide inertia.
Nowadays, 55 per cent of our generation mix (wind, solar, DC imports) cannot supply inertia to the grid. Are we approaching a system that compares with Spain and Portugal on Monday?
It certainly looks that way. In 2012 the National Grid produced a solar briefing note for the government which is still available online. In that note they imagine a system that has 22 GW of solar power attached to the grid. They demonstrate their concerns based on a sunny summer day when demand is low. The sun rises at 5 o'clock when little or no synchronous plant other than nuclear generation will be on line and at midday, solar is 60 per cent of all generation. The Grid's engineers then considered that situation 'difficult to manage' and concluded that wind+solar power must never exceed 60 per cent of generation.
We now have 17.7 GW of grid-connected solar farms to which we must add all rooftop solar installations. At midday on Tuesday according to Gridwatch the UK's asynchronous, no-inertia generation was at 66 per cent of total generation.
In 2024 National Grid produced a System Operability Framework document. Their objective was to outline how future scenarios of generation mixes would impact upon protection services for the grid. As more and more renewable generators are brought on-line, the difficulties of managing the grid have become more and more onerous. For example, one service titled 'primary response' in 1990 called for selected generation plants to increase generation within 10 seconds after a fault is detected: by 1,200 MW in winter and 1,500 MW in summer. In 2024 these increases are required in 1.2 seconds!
After nearly 50 years of operation, Dinorwig Power Station is currently shut down for major repairs and there has been no information on when it will re-open. Over the next five years all of our nuclear stations, bar Sizewell, will be closed. Over the same period our combined cycle gas generator fleet will halve from 30 GW to 15 GW. (It takes 5 years to build a new CCGT even using an existing site. The new ones are 66 per cent efficient and cost less than £1 billion to build a 1 GW plant – one third the cost of an offshore windmill.)
We will lose huge amounts of grid inertia. Low-inertia operation will become routine. It is hard to imagine that we won't start to suffer complete national blackouts like the Iberian one.
One last piece of doom: the recovery of Spain's grid in just one day is impressive. This speed is certainly due to the assistance of a large, stable grid reconnecting into the Iberian system thus allowing recovery in a series of stable steps as each grid area is recovered. We will not have that facility in the UK with our asynchronous interconnectors.