Comment by Tom Luff, Practice Manager (Electricity Markets & Policy) and Charmalee Jayamaha, Practice Manager (Power Systems) at Energy Systems Catapult.

Monday 28 April, one of Europe’s most significant blackouts hit the Iberian Peninsula. This wasn’t a failure of renewables, but a wake-up call: Net Zero won’t deliver resilience by default – we must design it in.

The Iberian blackout: a warning

At 12:33pm local time, voltage instability in southwest Spain triggered a cascading collapse across the Spanish and Portuguese grids. Over 30GW of supply (more than 85% of total electricity demand) was lost as generators tripped, solar inverters disconnected, and the interconnector to France disconnected to protect the wider continental electricity network. The disruption brought transport, hospitals, telecommunications, and other essential services to a standstill. Most power was restored within two hours, but the full restoration across the entire system took more than 20 hours.

The Spanish grid was operating with more than 70% inverter-based generation at the time of the incident, mainly from solar and wind. While this reflects progress toward a low-carbon energy mix, the event has prompted valuable system wide learnings about how to evolve grid design and operability services – like reactive power (which helps control voltage) and inertia (which helps keep frequency steady) – to maintain stability and resilience as we incorporate more renewable generation into power systems worldwide.

What caused the blackout?

According to Spain’s Transmission System Operator, Red Eléctrica de España (REE), the system collapse began with voltage instability in Badajoz, Seville, and Granada. Synchronous generators – traditional power plants that spin in sync with the grid and help keep the system stable – disconnected, triggering a chain reaction: 2.2GW of generation was lost, frequency dropped rapidly with limited inertia to dampen the fall, and under-frequency load shedding failed to stabilise the system. The interconnector to France tripped, isolating Iberia and spreading instability to Portugal.

While renewables weren’t to blame, Spain’s blackout showed how a grid with high inverter-based generation can struggle without enough inertia or reactive power. It wasn’t a failure of clean energy, but of system design. As we move towards Net Zero, we must rethink how grids detect, respond to, and communicate during faults—because system resilience will matter as much as the energy sources themselves.

GB is better prepared but we can’t be complacent

In theory, a similar collapse could happen here – but the GB grid is better positioned to prevent and contain such failures. A nationwide blackout has never occurred in Great Britain in the 75-year history of having a National Grid.

The GB grid operator acted promptly on the lessons from the August 2019 partial blackout, introducing key safeguards: it now actively procures system inertia through the Stability Pathfinder project (see below) – to make sure there’s always enough “shock absorber” in the system to keep it stable; and GB’s suite of interconnectors to its neighbouring countries give access to diverse generation mixes and provides resilience benefits. Grid code reforms – such as the Accelerated Loss of Mains Change Programme – have reduced the risk of unnecessary generator disconnections.

But risks remain. The pace of electrification and decentralisation is challenging traditional system design. Rooftop solar and behind-the-meter assets are still largely invisible to operators. And extreme weather, cyber threats, and rising system complexity demand constant vigilance. Past performance is no guarantee of future resilience.

Net Zero can make the system more resilient

Net Zero is often framed as a source of new risk. Variable renewables reduce system inertia and the phase-out of fossil fuels removes traditional spinning reserves. Digitalisation introduces potential cybersecurity threats. And electrification of heat and transport shifts and sharpens electricity demand patterns.

But this transformation also unlocks powerful new tools to manage risk and strengthen resilience, the need for which is explored further in Energy Systems Catapult’s report, Resilience in our Net Zero Energy System. Local generation – such as rooftop solar – reduces dependence on national networks and can support communities during major system failures. Demand-side flexibility, from homes and businesses, offers instant response to stabilise the grid. Battery storage and smart inverters can provide synthetic inertia and fast frequency response. And data-driven forecasting, enabled by AI and real-time monitoring, enhances fault detection and operational awareness.

These aren’t just Net Zero technologies – they’re tools for resilience and energy security. By moving away from fossil fuels, we reduce our reliance on international supplies of gas and petrol. Smarter homes and responsive appliances can help flatten peaks and recover faster from shocks. If we can do it right, Net Zero, won’t just minimise carbon, it can strengthen the backbone of our economy.

Work is underway but more is needed

The National Energy System Operator (NESO) is taking a whole-system approach: planning generation, networks, and flexibility together. Flexibility markets are expanding, rewarding households and businesses for reducing or shifting demand when the grid needs it most.

Stability Pathfinder programmes are already delivering critical services – including voltage control, inertia, and fault-level support – using technologies like batteries, synchronous condensers, and grid-forming inverters. Black start trials using renewables and storage are underway, exploring faster and cleaner ways to restore power after major faults.

And many of the reforms now being considered by REE – such as improved voltage control, enhanced monitoring, and new inverter standards – have already been introduced in GB, particularly following the 2019 event.

Yet action must go further. Real-time visibility of distributed assets remains patchy. NESO and industry must accelerate deployment of phasor measurement units (sensors that monitor grid conditions in real time) and modern monitoring tools. Planning frameworks and market signals must go beyond traditional generation and better reflect the value of flexibility and local resilience. And crucially, investment in cybersecurity, data-sharing infrastructure, and digital coordination must keep pace with rising system complexity.

A resilient Net Zero future won’t build itself

Net Zero is a once-in-a-generation opportunity to redesign our energy system to be cleaner, cheaper, and more resilient. But resilience won’t emerge by accident. It must be designed in – through market reform, smart digital infrastructure, and strong local institutions.

Infrastructure investment is crucial, but it must be complemented by flexibility that is properly valued and embedded into planning and regulation. The Review of Electricity Market Arrangements is an opportunity to take a big step forward by introducing stronger locational signals in the electricity system; and the establishment of NESO and Great British Energy is an opportunity to tailor decarbonisation efforts to the characteristics of communities through Local Area Energy Planning. And as the system digitalises, cybersecurity and data resilience must be treated as core infrastructure, not afterthoughts.

If we can get it right, Net Zero won’t just help us avoid the shocks of the past, it will give us an energy system that’s ready for whatever comes next.