The Scottish government has given the go-ahead for a 600MW 'hollow mountain' pumped hydro plant to store energy from renewable sources when supply outstrips demand – but its developer said UK-level changes are needed to bring projects such as the so-called 'water battery' forward.

The UK’s Drax Group announced that it had been given the green light for a new £500m ($645m) underground pumped storage hydropower facility at its existing Cruachan Power Station, which will be constructed in the side of a mountain.

The new facility will more than double the current 440MW capacity of the plant, which is built into the side of Ben Cruachan mountain in Argyl. Drax says that, “with the right support from the UK government”, it could come online as soon as 2030.

Pumped storage plants act like giant water batteries by using reversible turbines to pump water from a lower reservoir to an upper reservoir which stores excess power from sources such as wind farms when supply outstrips demand. The turbines are then reversed to bring the stored water back through the plant to generate power when it is needed.

Will Gardiner, Drax Group CEO, said: “This is a major milestone in Drax’s plans to build Britain’s first new pumped-storage hydro plant in a generation.

“These plants play a critical role in stabilising the electricity system, helping to balance supply and demand through storing excess power from the national grid. When Scotland’s wind turbines are generating more power than we need, Cruachan steps in to store the renewable electricity so it doesn’t go to waste.”

Drax says the expansion does however require an “updated financial stabilisation mechanism” from the UK government.

“The current absence of a framework for large-scale, long-duration storage technologies has resulted in no new plants being constructed in the UK since 1984, despite their critical role in the decarbonisation process.”

Visiting the plant, Scotland’s first minister Humza Yousaf said that hydro power has “real potential to play a greater role in our transition to net zero” and to help ensure a “resilient and secure electricity supply across the UK.”

Yousaf said the expansion would “strengthen our energy security by providing much needed resilience in the system”.

He added that the Scottish government will continue to urge its UK counterpart to provide an “appropriate market mechanism for hydro power and other long duration energy storage technologies, to ensure that the potential for hydro power is fully realised”.