Comment by Daniel Murrant, Practice Manager – Networks and Energy Storage, at Energy Systems Catapult. 

Britain’s energy system is facing its biggest challenge since the Industrial Revolution. As we race to ditch fossil fuels, we’re discovering that keeping the lights on isn’t as simple as flicking a switch. The solution? New forms of something called ‘flexibility’ – and it’s about to change how we power our lives.

Everyone from the UK government to the National Energy System Operator is scrambling to figure this out. But what exactly is flexibility, and why is it suddenly the most important word in energy?

What is flexibility (and why should you care)?

We’ve done the research, and here’s what energy flexibility means: keeping Britain’s lights on when renewables don’t cooperate.

In our Enabling Distributed Flexibility for Net Zero report we defined it as “balancing energy demand and supply across all time and spatial scales, keeping within the physical constraints of the system.” Translation? Making sure the at any point on the grid the energy flowing into the grid exactly matches what’s flowing out, every single second, while also taking into account any energy which is added to or released from storage and energy transmission and conversion losses.

Here’s why that matters: electricity grids are perfectionists. One tiny imbalance and everything crashes. Gas networks can coast for hours, but electricity? Zero tolerance. That’s why flexibility isn’t optional – and there are four ways to deliver it:

1. Supply-side flexibility; adjusting energy generation up or down. For example, this could be using flexible plant such as gas turbines or, in a future decarbonised system, potentially hydrogen-fired turbines. Innovation in this area includes “Mission H2 power” a collaboration between SSE Thermal and Siemens Energy aiming to deliver gas turbine technology capable of running on 100% hydrogen.

1. Demand-side flexibility; adjusting demand up or down. This involves changing a consumer’s pattern of demand. For example, charging electric vehicles (EV) at times when energy supply is high compared to demand, to make use of lower electricity prices. Innovation to support EV charging includes the development of smart EV chargers such as those developed by Ohme which can automatically schedule vehicle charge times.

3. Adding or removing energy from energy storage. Energy storage such as batteries, thermal storage, and pumped hydro storage are already used in the UK to help balance supply and demand. In the future we will see much more energy storage deployed and used, with some of this coming from innovative technologies such as that developed by RheEnergise.
4. Importing or exporting energy to or from other systems. This is through interconnectors to other countries. These interconnectors can allow energy to flow in either direction based on the balance of supply and demand between countries. Innovation focused around interconnection includes the work by National Grid Ventures to develop hybrid multi-purpose interconnectors, connecting not only electricity networks but also offshore wind farms.

Why the old flexibility playbook is dead

Historically, most flexibility has been provided through supply-side flexibility. Flexibility meant one thing: burn more coal, and later gas, when you need more power, burn less when you don’t. Keeping massive fuel stockpiles made it easy. That era is behind us. Renewables march to their own beat – no amount of shouting will make the wind blow harder at 6pm. And with volatile gas prices and North Sea resources drying up, the old approach isn’t just dirty – it’s expensive and unreliable. The harsh truth? You can’t command renewable energy like fossil fuels. So instead of relying on one trick (crank up the generators), we need to master the flexibility strategies 2-4 in the above list as well as changing the way supply-side flexibility is provided.

But wait, we’re not just changing how we make energy – we’re changing our consumption habits and the technologies that are dependent on clean energy. Cars, heating, industrial processes – they’re all making the switch to electricity. So, as we pile more demand onto the electricity grid, we need more flexibility and laser-precise, real-time flexibility at massive scale.

Innovating to Net Zero and flexibility

For Innovating to Net Zero 2026 (ITNZ 2026) we’re using our whole-energy system models (ESME and ESME Flex) and system maps, alongside insights from various system lenses (including markets, consumers and digitalisation), to explore how flexibility can meet the shifting gaps between supply and demand (referred to as “peak gaps”).  These four peak gap types, will drive the shape of the future system – more detail on why this is the case can be found here in the previous blog in this series. We will also explore the progress made so far in delivering a secure, affordable and flexible low-carbon energy system including the impact of measures such as the Clean Power 2030 target, and additional measures needed.

As the name suggests, innovation and innovators are at the heart of Innovating to Net Zero 2026. Throughout this process we are engaging with a range innovators building their input into our analysis, sharing how innovation can support meeting peak gaps, and highlighting the barriers to this innovation and the enabling conditions needed to overcome these barriers. This will be critical to supporting the innovation that we need to deliver the transition to a resilient and affordable low-carbon energy system.

These findings will be presented at our flagship Net Zero Event in February 2026 with an accompanying report but the story has already begun. In the coming months we’ll continue to publish this series of blogs that dive into the questions keeping energy experts awake, spotlight the pioneers rewriting the rules, and challenge the assumptions that have guided us so far.