Why the grid is turning to long-duration energy storage
As wind and solar supply more of Britain's electricity, storing energy for hours or days at a time is becoming as important as generating it in the first place.
The problem with intermittent power
Renewable electricity is now the backbone of the UK’s power system, but wind and sunshine do not arrive on demand. A calm winter week or a cloudy month can leave a grid heavily reliant on renewables short of supply, while a particularly windy period can produce more electricity than the system can use. Batteries have become a familiar fix for short-term wobbles, smoothing out fluctuations that last minutes or a few hours. But they are far less suited to bridging gaps that stretch across days, weeks or even seasons. That is the gap long-duration energy storage, often shortened to LDES, is designed to fill.
There is no single agreed threshold, but the term generally refers to technologies that can store energy and discharge it steadily for periods well beyond the four to six hours typical of lithium-ion batteries, sometimes for many days. The distinction matters because the economics and engineering of storing energy for an afternoon are very different from storing it for a fortnight.
Why batteries alone are not enough
Lithium-ion batteries are excellent at short, sharp bursts of charging and discharging, which is why they dominate applications like smoothing solar output over a day or responding instantly to sudden grid faults. But building enough lithium-ion capacity to cover a prolonged lull in wind generation would require vast numbers of cells, much of which would sit idle most of the time. That pushes up costs and raises questions about resource use, since lithium-ion production depends on materials such as lithium and cobalt that are subject to their own supply constraints.
Longer-duration technologies tend to use cheaper, more abundant materials and are built around physical processes rather than chemical cells, which can make them better suited to storing large amounts of energy economically, even if they are slower to charge and discharge.
The main technologies in play
Pumped hydro storage is the most established form of long-duration storage worldwide, including in the UK, where water is pumped uphill when electricity is abundant and released downhill through turbines when it is needed. It is proven and reliable but depends on suitable geography, limiting where new schemes can be built.
Compressed air and liquid air energy storage work on a similar principle of storing energy in a physical medium: air is compressed or cooled to a liquid state when power is plentiful, then expanded through turbines to generate electricity later. These systems can, in principle, be sited more flexibly than pumped hydro.
Flow batteries use liquid electrolytes stored in tanks, with the size of the tanks determining how much energy can be stored, independent of the power output. This makes them naturally suited to longer durations than conventional batteries.
Thermal storage, which heats materials such as molten salt, rock or even sand to very high temperatures, offers another route, storing energy as heat that can later generate electricity or supply heat directly to industry or homes.
Hydrogen, produced by using surplus renewable electricity to split water, is often discussed as a longer-term storage option too, since it can be stored for extended periods and converted back into electricity or used directly as a fuel, although efficiency losses in the conversion process remain a challenge.
Why the grid increasingly needs it
As the UK adds more offshore wind and solar capacity, the pattern of electricity supply is becoming less predictable and more seasonal, with surpluses at some times and shortfalls at others. Without adequate storage, this can mean renewable generation being curtailed, or turned down, because the grid has nowhere to put the excess power, while fossil fuel plants are kept running as a backstop for calmer periods. Long-duration storage offers a way to capture that surplus and release it when needed, reducing both waste and reliance on gas-fired generation for balancing.
Government and industry bodies have identified a lack of investment certainty as one of the main barriers to building more long-duration storage, since many of these technologies involve significant upfront costs and long asset lifespans, making revenue support mechanisms and clear market rules important to unlocking new projects. As the share of variable renewables on the grid continues to grow, the case for storage that can bridge not just hours but days and seasons is expected to become progressively stronger.