Great Britain has built one of the world’s great offshore wind fleets, but it has not yet built anywhere to put the power. On windy days we pay wind farms to switch off. On still days we pay gas plants to switch on. Consumers pay twice and the bill is growing every year.

LDES is the key missing piece. Storing surplus energy when it is abundant and releasing it when the country needs it most is the only way a renewables-led grid can be affordable, secure and low-carbon at the same time. Analysis for the UK government puts the potential system saving from LDES at £24–50bn between 2030 and 2050.

Great Britain still heavily depends on gas-fired generation to back up wind. About half of that gas comes from the North Sea today. As production declines, the UK could be importing up to 90% of its needs in peak winter periods. Gas plays a critical role in ensuring we have reliable power 24/7 to keep the lights on – so security over our future gas supply is essential for our energy and national security. With less than six days of national gas storage to fall back on, the country is vulnerable to import disruption and needs more gas storage. By comparison, big importers like the EU and China have storage capacity of around 80 days and 40 days respectively.

The cheapest electricity in Great Britain is the electricity we currently throw away. When the network cannot move wind power south to markets, turbines are paid to stop. That energy has no buyer, so its value to the system is effectively zero. MESH is designed to charge on exactly that power. Its grid connection point sits between the B6 and B7a boundaries, the two major constraints on the transmission system, and close to the large offshore wind farms of the East Irish Sea. It is in the right place to absorb surplus generation that would otherwise be curtailed.

EnergyPathways estimates suggest that MESH can deliver dispatchable electricity for as little as half the cost of gas-fired generation, with little or no additional subsidy cost.

How MESH works in practice

MESH is an integrated storage system built on three pillars: compressed air energy storage, strategic gas and hydrogen storage, and onshore hydrogen and graphite production. All of it rests on one geological asset. Beneath the East Irish Sea, around 18km off the Lancashire coast, lies a salt sequence 500–600m thick and made of virtually pure halite. That combination of purity, thickness and depth is ideal for building very large, gas-tight storage caverns.

Compressed air energy storage. The cycle has three stages:

• Charge. When wind output exceeds demand, surplus electricity arrives through import cables from the grid and nearby wind farms. It drives compression trains, which push air into four offshore salt caverns. Each cavern holds about 700,000m³, the volume of four St Paul’s Cathedrals.
• Store. The air is held under pressure in the salt for hours, days or weeks. Unlike a battery, the store does not degrade with use, and the asset is designed for a life of more than 30 years.
• Discharge. When renewables fall short, the air is withdrawn, heated and expanded through two generation trains, using a high-efficiency turbine designed for hydrogen fuel heating. Power returns to the grid through the export cable.

The result is around 300MW of output sustained for more than seven days: 55GWh in total. The plant can dispatch from a cold start within a couple of minutes.

Gas and hydrogen storage. A second set of caverns will hold natural gas, and in time hydrogen, as a strategic reserve. Gas is injected when supply is plentiful and withdrawn when the system is tight, at rates of up to 14mn m³/d. A full cycle takes about 90 days, which makes this a seasonal store. With 1.3bn m³ of working capacity, it could double the UK’s gas storage cover from six days to 12. The North Sea Transition Authority awarded MESH a gas storage licence in July 2026. Hydrogen will provide the pathway to decarbonise the store over time.

Hydrogen and graphite. Onshore at the Port of Barrow, a methane pyrolysis plant is planned to split gas into hydrogen and solid graphite without producing CO₂ from the process. Target output is 20,000t/y of hydrogen and 60,000t/y of graphite, a critical mineral for which the UK is wholly import dependent.

Together these pillars give the grid flexibility from seconds to seasons.

Set to be the UK’s largest LDES facility, a single MESH project would hold roughly 40% of the storage capacity of all 16 projects provisionally selected in Ofgem’s first cap-and-floor round (55GWh) and deliver it over a far longer duration (more than 100 hours, compared to 18 hours on average for the others).

Very large caverns drive a low unit cost: capital cost is estimated at £8,000–11,000/MWh of storage, with no loss of capacity over the life of the asset.

Ofgem’s cap-and-floor scheme is central to financing MESH. It guarantees a minimum revenue, which is what allows a long-life storage asset to raise project debt and equity at an efficient cost of capital. Ofgem and the Department for Energy Security and Net Zero (DESNZ) have invited MESH to participate in the second round, which government guidance suggests will launch towards the end of this year.  

First operations are targeted for the end of 2031, well inside the development timescales of pumped hydro or new nuclear. The first project needs four caverns. The licence area has potential for up to 60, which would take MESH to multi-TWh scale.

Part of the reason for the speed of development was the September 2025 designation of the project by the Secretary of State for Energy Security and Net Zero as a project of national significance under section 35 of the Planning Act 2008.This means that MESH can now follow the development consent order (DCO) route, a single streamlined process decided by the Secretary of State, which is expected to bring planning and licensing into an 18–24 month window. For an infrastructure project of this size, that certainty on timing is a significant step in reducing risk.

Innovation in the development approach

Compressing air generates a great deal of heat. In conventional compressed air plants much of this heat is lost, and when the time comes to use that potential energy it must be reheated by burning fuel before reaching the turbine. That is the main drag on efficiency.

In September 2026 EnergyPathways filed patent applications covering technology developed in-house to store that heat of compression in subsurface salt caverns and release it during the generation phase. The approach could lift round-trip efficiency to as much as 72%. It reduces fuel use and the associated emissions and cost, removes the need for expensive high-pressure thermal storage equipment at the surface, and keeps the plant footprint compact. The applications are subject to the normal examination and grant process.  

The project is now in a critical period, with engineering, regulatory and financing workstreams moving in parallel. As EnergyPathways progresses through front-end engineering and design (FEED) and the DCO process, its current schedule is to confirm the final investment decision on the compressed air project in 2028, with first operations in late 2031/early 2032.

Stopping the waste

Great Britain does not have a generation problem. It has a storage problem. We already produce more clean power than the system can use on windy days, and we will produce far more by 2030. The question is whether we keep paying to waste it or build the infrastructure to bank it.

Batteries alone cannot do that job in a wind-led system. They are not commercially viable. Storage will be needed that runs for days and at a scale that can reduce total system costs and lower energy bills. MESH provides that, with the geology, the partners, the government designation and a clear route to investment behind it. Storage of this kind is how we lower system costs, keep the lights on and strengthen the country’s energy security.

• Further reading: ‘How to build a bigger BESS’. Long-duration energy storage is increasingly seen as vital to a resilient power grid, and the UK should soon have a lot more of it.  

• ‘From reliance to resilience: how energy storage can unlock EU energy independence’. Long-duration energy storage capable of storing energy between eight and 24 hours is key to fulfilling Europe’s future flexibility needs. Therefore, European policy should support it, writes Oonagh O’Grady, Vice President International Origination at energy storage developer Hydrostor.