Storing the future: LDES technologies

Introduction

As the UK accelerates towards Clean Power 2030, the role of long duration energy storage ("LDES") is rapidly becoming clearer. A generation mix increasingly dominated by intermittent renewable generation requires solutions that can store energy not just for hours, but for days or longer, ensuring that the UK has the necessary capacity to meet demand for – quite literally – a rainy day.

A case for BESS

The idea of storing energy alongside intermittent sources (e.g. solar, wind) in order to stabilise the grid is not new to the UK. The grid already relies on lithium-ion ("Li-ion") Battery Energy Storage Systems ("BESS") as an important component of the evolving energy market, and as an increasing number of renewable energy projects come online, so too has there been an increasing interest in co-location of BESS with intermittent generators. BESS is used to store surplus generated energy and can therefore balance the grid during peak demand and reduce energy costs by facilitating peak shaving and load shifting. So popular is the BESS market that applications for BESS projects were roughly 3 times oversubscribed in the recently concluded Gate 2 to Whole Queue ("G2TWQ") process. Battery operators have historically generated good revenues from several forms of market participation, including energy arbitrage, ancillary services and the Capacity Market ("CM"), but the past couple of years has seen an erosion of these revenue streams due to market cannibalisation. Tolling and floor agreements are consequently becoming increasingly common as a means to guarantee ROI for the long term.

However, the predominance of Li-ion BESS is not without its challenges. Thermal runaway remains an inherent safety risk, with several high profile battery fires worldwide reinforcing planning sensitivities at local level; the National Fire Chiefs Council (NFCC) has recently updated its guidance for managing the risks posed by BESS, with the guidance being far more extensive than its previous iteration. In addition, Li-ion batteries suffer from degradation over time, cannot be fully discharged without the battery being damaged, and have comparatively short lifecycles. End of life considerations are similarly problematic, with limited recyclability and reliance on materials whose extraction carries significant environmental costs (e.g. lithium, nickel and cobalt), including water depletion and contamination.

A case for LDES

Although BESS is supporting the UK to meet its clean power goals, it is estimated that the UK needs another 1.2GW of LDES in order to reach Clean Power 2030, and another 15GW by 2050. As we reported on here, it is consequently unsurprising to see the Government introduce a cap and floor scheme to support deployment of LDES ("C&F"). LDES encompasses a vast range of technologies, each with capacity to store energy for 8 consecutive hours or more without needing to be re-charged. These range from mature and well-established solutions (e.g. pumped storage hydro "PSH") to other emerging and more experimental methods (e.g. liquid air energy storage "LAES"). Many of them are more sustainable than current storage technologies, either because of the materials used or due to the longevity that they offer once installed.

We take a look below at some of the long duration technologies that have yet to establish a strong foothold in the UK and may stand to benefit from the C&F.

Pumped Hydro (PSH)

Water is pumped uphill and stored behind a dam. When energy is needed, the water is released and power is generated. It is a consistent, highly effective and particularly long-term storage solution as a PSH station can last for decades. That said, the CAPEX required is at the higher end of the energy storage scale, which is partly why no new fully operational PSH plants have been built in the UK for over 40 years. There are a number of proposed PSH sites in various stages of development across the country, with a combined potential storage capacity of around 10GWh, but they are far from completion with many in the pre-planning stage. Due to the geographical constraints of the technology, the majority of these are located in Scotland.

CAES (Compressed Air Energy Storage)

The concept of CAES has been around since the 1970s as a means of meeting peak demand whilst maintaining constant capacity in the nuclear power industry. When it comes to longevity, it offers one of the longest lifecycles - one facility in Germany has been in consistent operation since 1976. CAES systems store energy by compressing air and storing it underground or in purpose‑built vessels. When power is required, the compressed air is released and used to drive turbines. While technically proven in certain markets such as the US and boasting quicker development times and lower construction costs than many long duration technologies due to its ability to repurpose legacy industrial units and components, CAES is still developing in the UK and faces similar siting and infrastructure constraints to PSH.

LAES (Liquid Air Energy Storage)

Still a relatively novel technology, LAES involves a three-stage process in which air is compressed at high pressure and then cooled until it becomes a liquid. When energy is needed, the liquid is pumped out of storage and turns back into a gas, in doing so generating power. The concept has been around for some time and various testing sites exist around the world, but now the world's first full LAES plant is being built here in the UK near Carrington, Manchester. This venture is operated by Highview Power with backing and investment from the UK Government and the UK Infrastructure Bank and it will have a storage capacity of 300MWh – the equivalent of powering around half a million homes. It is due to start coming online in 2026, with full operation targeted for 2027. Highview Power also has two further LAES plants planned in Hunterston and Killingholme which have both passed the first stage of the C&F.

Vanadium Flow Batteries (VFBs)

VFBs store energy in liquid electrolytes rather than solid electrodes, enabling safer, non‑flammable long‑duration storage with no risk of thermal runaway. They are easily scalable by increasing electrolyte volume and tank size (which reduces cost per kilowatt hour), operate reliably across a wide range of temperatures, and use recyclable components—vanadium can be extracted for reuse as the electrolyte does not degrade, unlike Li‑ion. Although still uncommon in the UK storage market, China is reportedly testing the scalability of VFB projects, including a new VFB microgrid in Ningxia. Notably, VFBs accounted for 21 of the 77 successful projects to make it through the initial sift in the C&F. We are awaiting publication of the Initial Decision List of Projects at some point in the next couple of months (see here for the full timeline).

How we can help

At Foot Anstey, we regularly support clients with all stages of their renewable energy projects, including company structuring and financing, land acquisition, planning advice, applications for grants and subsidies, advice on grid connection, negotiation of land and supplier contracts, and dealing with disputes that may arise. If you would like to discuss new or existing developments, please do get in touch with us.

We also provide training on a range of topics, including those listed above, so please reach out if you are interested in arranging a session.