The Cruachan Expansion Project will be located in Scotland. (Credit: drax)
A view of the location of the project. (Credit: drax)
An infographic of how a pumped storage hydro project works. (Credit: drax)

The Cruachan Expansion Project (Cruachan 2) involves the construction of a 600MW underground pumped storage hydropower plant in Scotland, UK.

The expansion, set to be located to the east of the existing Cruachan power station, will increase the site’s total capacity to more than 1GW.

Renewable energy company Drax Group secured the development consent from the Scottish Government for the new plant in July 2023. The £500m project is part of Drax’s £7bn strategic investment plan in clean energy technologies between 2024 and 2030.

A comprehensive construction programme is slated to commence in 2025, and Cruachan 2 is expected to commence operations as soon as 2030.

During the construction phase, the project will create 1,000 jobs across the supply chain.

Once operational, the plant will strengthen energy security of the UK and support Scotland to achieve its net zero goal by 2045.

Cruachan Expansion Location and Site Details

The Cruachan 2 Plant will be located to the east of existing Cruachan facility inside Ben Cruachan, the highest mountain in Argyll, Scotland. The site is within the administrative boundary of Argyll and Bute Council (ABC).

It would be built within a new, hollowed-out cavern by excavating more than a million tonnes of rock. Like Cruachan 1, the expansion will also use Loch Awe as the lower reservoir and Cruachan Reservoir as the upper reservoir.

According to the Environmental Impact Assessment (EIA) Scoping Report for the Cruachan Expansion Project, the boundary for the project is approximately 419.82 hectares (ha) in size. However, this is likely to reduce as the design evolves.

Most of the site is accessible via A85 road.

Cruachan 2 Project Infrastructure

Key components of the Cruachan Expansion Project will include an additional intake structure,  an underground waterway system, a cavern powerhouse, an above-ground substation, and a ventilation shaft.

Other elements of the development will include building two screened inlet / outlet structures and stop logs, quayside, an administration building and access tunnels.

The intake structure, located within and adjacent to the Cruachan Reservoir, will transfer water into a new headrace tunnel and underground waterway system.

The underground waterway system will carry water from the upper to the lower reservoir via a series of underground shafts and tunnels.

Turbines and generators in the underground caverns will use the water to generate electricity.

The existing substation will be extended to establish a connection with the 275kV overhead circuits that connect to the Dalmally sub-station.

A quayside will be constructed on the shore of Loch Awe to transport heavy equipment via Loch and temporary storage of tunnel spoil before removal.

The above ground administration building will be located near the upper reservoir. The building will house workshops for daily operational and maintenance works.

To access the underground power plant, a 1,450m long main access tunnel would be constructed cross connecting the existing Cruachan 1 Power Station.

The existing service roads will be used and may be upgraded as required for the project.


Cruachan 2 will use reversible turbines to pump water from Loch Awe to the upper reservoir. This stored water will be used to generate renewable power created by the downflow.

This downflow is passed through the intake in the upper reservoir into the powerhouse cavern via underground tunnels. The water, travelling at a high velocity, drives turbines and generators to create electricity.

Eventually, the water falls into the lower reservoir via an outlet structure.

The 600MW cavern powerhouse will be composed of two 300MW generating units or three 200MW generating units or four 150MW units.

It will directly feed the renewable energy into the National Grid when the demand is higher. The reversible turbines can also operate in reverse to absorb excess renewable energy from the Grid.

The pumped storage hydropower plant will have a design life of 100 years.

Contractors Involved

Stantec UK prepared the Environmental Impact Assessment (EIA) Scoping Report for the Cruachan Expansion Project.

Studio Pietrangeli Consulting Engineers was selected in March 2023 by Drax as the Owner’s Engineer for the project.

In September 2023, Denmark-headquartered COWI won the contract to provide consultancy services before the renewable energy project advances to the Front-End Engineering and Design (FEED) phase. COWI will deliver the works in collaboration with Studio Pietrangeli.

Commissioned by Drax, KPMG prepared a report to identify different revenue stabilisation mechanisms to unlock private investment in storage technologies.