Hunterston, North Ayrshire - Millennium Series

Executive Overview

The Hunterston Millennium Series is a 300 MW / 3,200 MWh hybrid liquid air and battery energy storage facility under development by Highview Power at the former Hunterston Coal Terminal (now Hunterston PARC) in North Ayrshire, Scotland. It is part of Highview's second phase LDES programme, targeting 4 GWh of storage across four projects in Scotland and northern England. The project has secured £130 million in financing from investors including Mosaic Capital, Scottish National Investment Bank, Centrica, Goldman Sachs, KIRKBI, Sumitomo, and Rio Tinto, and has been welcomed by the Scottish First Minister. Planning permission has been secured for grid connection and infrastructure; full LAES system build-out planning permission is still required. The Ofgem cap-and-floor scheme for long-duration storage (launched April 2025, final awards expected summer 2026) has Hunterston among Highview's two advanced projects. At 3,200 MWh / 300 MW, Hunterston would be the world's largest LAES facility on completion — eight times larger than Highview's Carrington (Manchester) 300 MWh project.

How It Works & Differentiation

Liquid air energy storage charges by cooling ambient air to –196°C until it liquefies (700 litres of air condenses into 1 litre of liquid), storing it in insulated low-pressure tanks. During discharge, liquid air is vaporised and expanded through turbines to generate electricity; residual cold from the process is recovered to improve the next charging cycle. The Hunterston configuration is a hybrid system combining LAES with lithium-ion batteries, optimising for both frequency response (batteries) and energy arbitrage (LAES). The first build phase provides grid connection and stability services; the full LAES build-out follows. Highview's multi-week energy retention capability differentiates the technology from batteries for seasonal and multi-day storage applications.

Commercialization & Traction

Highview Power's total investment portfolio now exceeds £500 million, underpinning a broader £2 billion deployment plan to deploy 6.4 GWh of LAES by 2030. The UK's NESO has identified an 81 GWh LDES requirement by 2030 as part of the Clean Power 2030 mandate, including 58 GWh of non-battery storage requiring approximately £20 billion of investment. Highview's second phase programme — Hunterston plus three further sites — targets 6.4 GWh of LAES capacity as part of that buildout. The Hunterston site at Peel Ports provides direct marine access and proximity to Scotland's high-wind offshore capacity, creating structural over-generation requiring long-duration storage. Over 1,000 jobs are expected onsite during construction, with 650 further supply chain jobs.

Scalability & Strategic Context

The UK has built no new long-duration storage in 40 years. The 2.8 GW of existing LDES across four pumped storage hydro facilities in Scotland and Wales represents the entire current national LDES stock. Highview's deployment at brownfield industrial sites — former coal terminals, industrial ports — circumvents the main barrier to new pumped storage (terrain and water availability) and offers a replicable site type available across the UK and globally. The Hunterston project's completion would validate LAES at commercial scale for the first time, enabling a wider pipeline that Highview estimates at more than 10 GWh across the UK alone and with additional projects in Australia and Japan.