Daniel Murrant, Practice Manager – Networks and Energy Storage, at Energy Systems Catapult
Britain’s energy system is undergoing its most profound transformation since the Industrial Revolution. The drive to eliminate fossil fuels is essential for Net Zero, but it also brings new challenges. Chief among them is how we keep the electricity system balanced. As the role of coal and gas diminishes, the answer lies in developing new forms of ‘flexibility’ – and this concept is reshaping the way we power our lives.
Policymakers, regulators, and the system operator are all grappling with how best to deliver on flexibility. But what exactly is flexibility, and why has it become one of the most important concepts in energy policy?
Flexibility matters more than you think
In simple terms, flexibility is about ensuring the lights stay on when renewable generation does not line up with demand. Our recent report Enabling Distributed Flexibility for Net Zero defines it as “balancing energy demand and supply across all time and spatial scales, keeping within the physical constraints of the system.”
Put another way, at every moment of every day, at any location, the amount of electricity going into the grid must equal the amount being taken out, while accounting for storage, transmission, and conversion losses. Unlike gas networks, which can cope with hours of imbalance, electricity systems have no such tolerance. Even a small mismatch risks a system failure. This is why flexibility is not an optional extra: it is essential to a functioning, decarbonised energy system.
There are four broad ways of delivering flexibility:
- Supply-side flexibility: adjusting generation up or down. In the past, this often meant increasing or reducing output from coal or gas. In a low-carbon system, it may involve hydrogen-fired turbines. SSE Thermal and Siemens energy are collaborating on “Mission H2 Power” to develop gas turbines that can run entirely on hydrogen.
- Demand-side flexibility: shifting or reducing electricity use. A familiar example is charging electric vehicles (EVs) when supply is plentiful, often at lower prices. Companies such as Ohme are developing smart chargers that automate this process for drivers.
- Energy storage: adding or removing energy from storage technologies such as batteries, pumped hydro, or thermal storage. Much more of this will be needed in future, with companies like RheEnergise developing innovative storage approaches.
- Interconnection: importing or exporting electricity through cross-border interconnectors. These links allow energy to flow where it is most needed. National Grid Ventures is exploring hybrid interconnectors that also connect offshore wind farms directly into the system.
Why the old flex playbook no longer works
For decades, flexibility was almost entirely about supply. If demand rose, more coal or gas was burned. Stockpiles of fuel provided security, and costs were relatively predictable. That model is no longer viable. Renewables cannot be controlled in the same way, and volatile fossil fuel prices have exposed the risks of over-reliance on gas.
Instead, the system must diversify. Demand-side flexibility, storage, and interconnection must all play a much larger role, alongside new forms of clean supply-side flexibility. At the same time, electricity demand is rising sharply as cars, heating, and industrial processes switch away from fossil fuels. This combination of increasing demand and more variable supply makes flexibility more important than ever.
The transition is not only technical but behavioural. Consumers will increasingly interact with the energy system in new ways, whether through EV charging, smart appliances, or home energy storage. Real-time management of demand at scale will be just as critical as innovation in generation.
Innovating to Net Zero 2026
At Energy Systems Catapult, we are exploring how flexibility can be delivered through our Innovating to Net Zero 2026 programme (ITNZ 2026). Using our whole-system models such as ESME and ESME Flex, alongside market, consumer, and digital insights, we are analysing how different forms of flexibility can close the gaps between supply and demand – what we call “peak gaps.”
These peak gaps will define the shape of the future energy system. Our work is assessing not only the technical solutions available, but also the enabling conditions required to unlock them – from market signals and regulation to consumer engagement. We are also examining progress to date, including the impact of the Clean Power 2030 target, and what more is needed to secure a resilient and affordable low-carbon system.
A central part of ITNZ 2026 is engaging with innovators. From technology developers to service providers, their insights are essential to our analysis. By highlighting barriers and exploring how they can be overcome, we aim to help create the conditions for innovation to thrive. This collaboration is critical if we are to build a flexible system that is fit for Net Zero.
What’s next for flex?
The journey to Net Zero requires more than replacing fossil fuels with renewables. It requires a transformation in how we balance the system, manage demand, and design markets that reward flexibility. Britain has the expertise and the innovators to rise to this challenge. The task now is to create the right environment for them to succeed – so that the electricity system of the future is clean, reliable, resilient, and affordable.
For more information, visit: https://es.catapult.org.uk/
This article appeared in the September 2025 issue of Energy Manager magazine. Subscribe here.
