When the grid fails, what does resilience really mean?

Power cuts were once considered rare, isolated events in Europe. In the last few years, they have become a strategic risk.

Last year, outages at Heathrow and across the Iberian Peninsula made headlines when they showcased how exposed modern infrastructure has become. At Heathrow, a local switchover failure disturbed operations. In Spain and Portugal, a widespread power outage left the regions without power. While the causes differed, the outcome was the same: systems that depend on a stable grid struggle to cope when it fails.  

This matters more as we move toward net zero. Electricity underpins how we heat, cool, move, and operate, with transport, communications, and critical infrastructure all dependent on a stable supply.  

To manage this growing risk, we must assess how well our systems are prepared to respond to failures. A more holistic approach, one that anticipates failure, its causes, and its wide-ranging commercial and social consequences, is essential. Without it, the fallout from power cuts becomes unacceptable.

Why classic approaches regarding resilience fall short

Resilience is often reduced to a simple concept: redundancy. A second grid connection, a backup generator, or another layer of capacity. But the events of last year show that this isn’t enough.  

If backup supply fails to transfer, as at Heathrow, or both supplies are lost entirely, as in Iberia, redundancy alone cannot guarantee continuity.  

Diesel generators are the default backup for many buildings. However, they have limited runtime, poor environmental performance, and rely on a successful switchover. At the same time, regulatory pressure is mounting to reduce reliance on said fossil fuels.  

Alternative fuels are being researched. Lower-carbon fuels like hydrotreated vegetable oil and hydrogen-ready generators can offer slight improvements. That being said, renewables are in the best position as a long-term solution, but their role concerning resilience is often misunderstood.  

The majority of renewable systems, including solar, wind, and battery energy storage systems, are intended to work alongside the main grid, not independently. They rely on grid-following inverters, which match their output to the grid’s voltage and frequency. When the grid fails, these systems disconnect for their safety.  

This pattern was clear in the Iberian outage. A system dominated by grid-following inverters, without self-supporting generation, struggled to recover from a disturbance leading to a widespread outage.  

Grid-forming inverters, which generate their own reliable voltage and frequency, offer a different approach. Capable of operating independently and stabilising the local grid, they are becoming a requirement in parts of the UK and Europe. However, large-scale deployment is still in its early stages, with cost, integration, and control complexity yet to be addressed.  

The overlooked vulnerability in buildings and infrastructure

As buildings become more energy-efficient, they commonly rely more on active systems. Mechanical cooling, ventilation, digital controls and tightly managed internal environments are now standard in many sectors.  

Under normal conditions, this delivers effectiveness and efficiency. Under failure conditions, it introduces risk.  

Take a prolonged outage that occurs during a heatwave. Cooling and ventilation fail, leading to rising internal temperatures. This leads to greater risks of failure for IT or medical equipment, air quality, and most importantly, occupant safety.  

These scenarios are rarely modelled in detail. Most design focuses on normal conditions, not prolonged grid failure, though maintaining building safety and function during outages is critical.  

Microgrids are often presented as a solution, but their application at scale continues to be challenging. While domestic systems can operate independently, extending this functionality to large buildings or critical infrastructure introduces high cost and technical complexity. In many cases, fully independent systems are not yet commercially viable.  

Rethinking resilience as part of system design

To meet the challenge, the industry needs to redefine resilience. It shouldn’t mean relying solely on disconnected backup measures; it should be a core design principle of the system.  

To do so requires exploring solutions such as private substations equipped with independent switching capability. This allows them to isolate from the main grid in case of a failure. Alternatively, integrating battery storage devices and synchronous condensers would help maintain local stability and provide power on demand. Another option is developing microgrid architectures that can operate independently when required. Blended approaches combining renewables, smart controls and lower-carbon backup systems are also becoming increasingly important.  

At the same time, there is a need to move beyond usual resilience standards such as N+1. Designing for practical situations means grasping not just the likelihood of failure, but its duration and consequences.  

This raises more fundamental questions. How long can a facility operate without power? What are the truly critical loads? How quickly can systems recover? And can resilience strategies be delivered in a way that complies with decarbonisation goals, rather than relying on high-emission fallback options?  

Resilience is more than a technical issue; it is a strategic requirement. As the grid grows greener, volatility and complexity will rise, driven by extreme weather, cyber risks, and system-wide events. Handling these challenges at the strategic level is key to guaranteeing reliability and commercial viability.  

The industry must embed uncertainty and disruption into its designs. Success means not only achieving maximum performance in ideal conditions, but guaranteeing safety, reliability, and functionality when those conditions fail.  

To strengthen resilience in your projects, consider outage scenarios from the outset. Contact our team to consider low-risk, effective design solutions.