Tag: Cruachan Power Station

Pumping power: pumped storage stations around the world

30 December 2020

Power generation
Loch Awe from Cruachan

Changing the world’s energy systems is a more complex task than just replacing coal power stations with wind farms. Moving to an energy system with more intermittent renewable sources like wind and solar will require greater levels of storage that can deliver electricity when it’s needed.

One of the long-established means of storing energy and using it to generate electricity when needed is through pumped hydropower storage. With upper and lower reservoirs of water, and turbines in between, these facilities act a bit like rechargeable batteries.

When there is excess electricity on the grid, the turbines are switched on to pump water from the lower to the higher reservoir (for example up a mountain or hill) where it’s stored. When electricity is needed, the water is released to flow from the higher reservoir toward the lower reservoir, passing through the turbines which generate electricity to send back to the grid.

Greater levels of intermittent renewables on energy systems around the world will make pumped storage all the more vital in helping to balance grids. Their mountainous locations also make pumped storage stations some of the most dramatic and interesting monuments in energy.

Here are some of the most interesting pumped hydro stations generating power and pumping water up mountains in the world:

1. The largest in the world (currently)

Bath County in Virginia, USA is dense with forests and mountain retreats, but below the scenery of the Allegheny Mountains lies the world’s biggest pumped hydro power station.

View of Appalachian mountains along Highway 220 in Warm Springs, Bath County, Virginia

The Bath County Pumped Storage Station has a maximum generation capacity of more than 3 gigawatts (GW) and total storage capacity of 24 gigawatt-hours (GWh), the equivalent to the total, yearly electricity use of about 6000 homes.

Construction began in March 1977 and upon completion in December 1985, the power station had a generating capacity of 2.1 GW. However, its six turbines were upgraded between 2004 and 2009 to over 500 MW per turbine. The power station’s upper reservoir can hold 14,000,000 cubic metres (m3) of water and its water level can drop by as much as 32 metres during operations.

While the amount of earth and rock moved during the construction of the dam and facilities would make a mountain more than 300 metres tall, the actual station occupies a relatively small amount of land to minimise its impact on the environment. The water from the upper reservoir has a use beyond power too – at times of drought it’s used to supplement river flow in the recreational area that surrounds the site.

2. The future largest in the world

Bath County will not be the world’s largest pumped hydro station for much longer. While China is already home to more of the top 10 largest pumped storage power stations than any other country, the Fengning Pumped Storage Power Plant in China’s Hebei Province will take the top position when completed in 2023, thanks to its 3.6 GW capacity.

Landscape of the Bashang grassland in Hebei, China

Construction first began on the monster project in June 2013 and is being developed in two 1.8 GW stages. The first stage is scheduled for completion in 2021, when six of the 12 planned 300 MW reversable pump turbine units roar into life.

The plant will serve Beijing-Tianjin-North Hebei electrical grid and highlights the rapid growth of renewables in the region. Fengning will act as a peaking plant to balance the expansive wind and solar parks in China’s northern Hebei and Inner Mongolia regions.

China has more installed pumped hydro storage capacity than any other country, thanks in large part to its extensive mountainous terrain (which can accommodate such facilities), as well as an increasing need to support growing intermittent renewable installations. The construction of Fengning, part of a pipeline of projects, will further the country’s capabilities, helping China reach as much as 40 GW of installed capacity in the coming years.

3. Most reversable turbines

Fengning will also take the record for the most individual turbine units in a pumped storage facility when it’s finished in 2023, a title that is currently jointly held by Huizhou Pumped Storage Power Station and Guangdong Pumped Storage Power Station. These two plants are the respective second and third largest pumped storage plants in the world today, each with eight reversable turbines.

Guangzhou City, Guangdong Province, China

While Guangdong Pumped Storage Power Station has a capacity of 2.4 GW, Huizhou has a slightly larger capacity of 2.448 GW. The increased number of turbines might mean more machinery to maintain and operate, but also offers the plants greater flexibility in how much electricity they absorb and generate.

4. Multiple dams and reservoirs

The Drakensberg Pumped Storage Scheme, located in the Drakensberg Mountains in the province of KwaZulu-Natal, South Africa, is a unique hydro facility thanks to its use of four dams. The Driekloof Dam, Sterkfontein Dam, Kilburn Dam and Woodstock Dam give the facility a generation capacity of 1 GW, and a total storage capacity of over 27 GWh. However, Drakensberg is not the largest facility in South Africa.

Drakensberg Mountains in South Africa

Drakensberg Mountains in South Africa

South Africa holds a total installed pumped storage capacity of nearly 3 GW from its four large facilities. The newest, and largest, is the Ingula Pumped Storage Scheme, which has a generation capacity of over 1.3 GW. Its name, ‘Ingula’, was inspired by the foamy river waters surrounding the facility and comes from the Zulu word for the creamy foam on the top of a milk vessel.

5. The oldest working pumped storage plant

Another country with the ideal terrain for pumped storage is Switzerland. The Alpine country’s landscape feeds water into Europe’s rivers such as the Rhine, making water a plentiful supply for the country’s energy. Hydropower as a whole accounts for around 57% of the country’s energy production and the country was one of the first to begin deploying pumped storage systems in the 1890s, although these were initially used for water management rather than supporting electricity generation.

Water dam and reservoir lake in Swiss Alps to produce hydropower

Switzerland is also home to the world’s oldest working pumped storage plant. The Engeweiher pumped storage facility was built in 1907 before reversable turbines were introduced in the 1930s. It was renewed in the early 1990s and is scheduled to continue operating until at least 2052.

6. The biggest in Europe

The Alps are also home to Europe’s biggest hydroelectric facility. In France, the Grand Maison hydroelectric power station operates in the Isère area of the Auvergne-Rhône-Alpes region, and has a capacity of 1.8 GW. During peak demand, it takes only three minutes for the station to supply its full 1.8 GW of power to the National Electricity Grid of France.

Grand Maison Hydroelectric Power Station

Sitting at an altitude of 1,698 metres the majority of the water that fills the upper reservoir, created by the Grand Maison Dam, comes from melted snow. This reservoir has a storage capacity of 140,000,000 m3 of water.

7. The biggest in the UK

Across the Channel, the UK also boasts impressive hydropower and pumped storage credentials, having used water for electricity generation since 1879. The UK has a total hydropower capacity of over 4.7 GW, including 2.8 GW of pumped storage, with the wet, mountainous landscapes of Scottish Highlands and Welsh countryside particularly well suited to hydropower facilities.

Dinorwig hydroelectric power station

The largest of these is the Dinorwig Hydro Power Station which sits at the edge of Snowdonia National Park in north west Wales, although it’s hard to spot as most of the machinery is found underground. With a total capacity of over 1.7 GW, this pumped storage plant can power 2.5 million homes and is known by locals as ‘Electric Mountain’.

8. The station lying between the lochs

Surrounded by Loch Etive and Loch Nant, and perched on the north side of Loch Awe, Drax’s Cruachan Power Station was built between 1959 and 1965, 1 km inside of a hollowed-out mountain in Argyll and Bute, Scotland. Upon completion, the power station, also known as the ‘Hollow Mountain’, was opened by Queen Elizabeth II and can currently generate 440 MW of hydroelectric power in 30 seconds, helping to maintain stability on the electricity grid.

Cruachan Dam in Argyll and Bute

A proposed sister station, Cruachan 2, which would stand adjacent to the existing facility, could enable Cruachan to produce up to twice as much power, increasing its support of renewables coming onto the grid.

9. The world’s smallest

The Goudemand apartment building in the city of Arras, France is home to an extremely small pumped storage hydroelectricity system, with no mountain in sight. The residential building was transformed in 2012 to become grid-independent through the installation of solar panels, wind turbines, batteries and a 200 square metre (m2) open air water tank sitting on its roof. This tank, 30 metres above the ground, acts as an upper reservoir and is connected to five 10 m2 plastic water tanks in the basement, the lower reservoir.

Arras, France

While the 3.5 KWh (kilowatt-hours) capacity of the building’s micro facility is small, it provides useful knowledge to researchers, opening up the possibility of small, modular pumped storage systems to be developed and deployed at scale in the future.

The myths, legends and reality of Cruachan Power Station’s mural

14 October 2020

Sustainable business

Down the kilometre-long tunnel that burrows into the dark rock of Ben Cruachan, above the giant rumbling turbines, sits something unusual for a power station: a work of art.

The wood and gold-leaf mural might seem at odds with the yellow metal turbines, granite cavern walls, and noise and heat around it, but it’s closely connected to the power station and its ties to the surrounding landscape.

The entrance tunnel might take engineers and machines to the heart of Ben Cruachan, but the mural transports viewers to the mountain’s mythical past. It tells the story of how this remarkable engineering achievement came to help power the country.

The narrative of the mural

Much like the machines and physical environment surrounding it, the Cruachan mural is big, measuring 14.6 metres long by 3.6 metres tall. Combining wood, plastic and gold leaf, the relief is interspersed with Celtic crosses, textures evocative of granite rock and gold orbs that resemble the urban lights Cruachan helps to power. Running from left to right, it tells a linear narrative that spans the history of the mountain.

An artist’s impression of the mural in the Visitor Centre at Cruachan

In the first of the mural’s three segments is a Scottish red deer, a native species that still thrives in Scotland today. Below it is the figure of the Cailleach Bheur, a legendary old woman or hag found across Gaelic mythology in Scotland, Ireland and on the Isle of Man. The Cailleach has a symbolic representation of a variety of roles in different folklores, but she commonly appears as a personification of winter, and with that, as a source of destruction.

In the context of Ben Cruachan, Cailleach Bheur is often taken to mean the ‘Old Hag of The Ridges,’ a figure who acts as the mythical guardian of a spring on the mountain’s peak. The mural tells her story, of how she was tasked to cover the well with a slab of stone at sundown and lift it away at sunrise. One evening, however, she fell asleep and failed to cover the well, allowing it to overflow and cause water to cascade down the mountain, flooding the valley below and drowning the people and their cattle.

The mural within the Turbine Hall at Cruachan Power Station undergoing maintenance  [November 2018]

This serves as the legendary origins of Loch Awe, from which Cruachan power station pumps water to the upper reservoir when there’s excess electricity on the grid.

The story claims the water washed a path through to the sea, creating the Pass of Brander. The site of a 1308 battle in the Scottish Wars of Independence, where Robert the Bruce defeated the English-aligned MacDougall and Macnaghten clans.

The mythical first section of the mural is separated by a Celtic-style cross from the modern second segment, which portrays the power station’s construction within Ben Cruachan. Here, four figures represent the four lead engineers of the project from the firms James Williamson & Partners, William Tawse Ltd, Edmund Nuttall Ltd and Merz & McLellan. They stand by the mountain, a roughly cut path running through its core.

At the base of the mural are the faces of 15 men lying on their sides. These are the  15 who were killed in  1962 when the ceiling of the turbine hall caved in during construction. Their uniform expressionless faces, however, turn them into symbols of the 30-plus workers who died while digging and blasting the power station’s tunnels and constructing the dam at the upper reservoir.

Next to this is a fairy tale portrayal of Queen Elizabeth II, who wears a gold grown and holds a sceptre from which electricity flows in a glowing lightning bolt through rock, commanding the power station into life.

The final third of the mural shows the whole power station system within the mountain. The upper reservoir sits nestled in the slopes of Ben Cruachan with water flowing down the mountain to the four turbines and Loch Awe below. Viewed as a whole, the mural takes the audience from mythology to the modern power station, which continues to play a vital role in the electricity system today.

Carving the Cruachan mural

The mural was created by artist Elizabeth Falconer, who was commissioned to create it to celebrate the power station’s opening by the Queen on 15 October 1965. At the time, only two of Cruachan’s four 100 megawatt (MW) reversible turbines were completed and operational, but it was still the first station of its kind to operate at such a scale. Two of the power station’s  turbines were modified with increased capacities meaning Cruachan can both use and generate up to 440 MW.

HRH Queen Elizabeth II opening Cruachan in 1965

HRH Queen Elizabeth II opening Cruachan on 15 October 1965

The project came to Falconer through her husband, a native of Aberdeen who worked as an architect partner to one of Cruachan’s engineering firms. The brief simply requested she create a piece to fill the empty space on the wall of the turbine hall. Deciding to dive into the history and mythology of the mountain, she initially carved the mural in London and only ventured into Hollow Mountain years after it was first put in place, to make renovations on the work.

Cruachan Power Station was a visionary idea and represented a considerable technical and engineering achievement when it opened. The designs and construction of the reversable turbines put this site at the cutting end of modern energy technology.

So, it’s fitting the mural appears distinctly modern in its design, yet tells a story that connects this modern power station to the ancient rock it lives within.

It’s Cruachan’s mural’s location inside the mountain that makes it so unique as a work of art. However, at a time when the electricity grid is changing to an increasingly renewable system, based more around weather and geography, the connections the mural makes between Scotland’s landscape and the modern power station, make it relevant beyond the turbine cavern.

Find out more about Cruachan Power Station

Capacity Market agreements for existing assets

9 March 2020

Investors
Engineer below Cruachan Power Station dam

RNS: 3530F
Drax Group plc
(“Drax” or the “Company”; Symbol:DRX)

Drax confirms that it has provisionally secured agreements to provide a total of 2,562MW of capacity (de-rated 2,333MW) from its existing gas, pumped storage and hydro assets(1). The agreements are for the delivery period October 2023 to September 2024, at a price of £15.97/kW(2) and are worth £37 million in that period. These are in addition to existing agreements which extend to September 2023.

Drax did not accept an agreement for the 60MW Combined Cycle Gas Turbine (CCGT) at Blackburn Mill.

A new-build CCGT at Damhead Creek and four new-build Open Cycle Gas Turbine projects participated in the auction but exited above the clearing price and did not accept agreements.

Enquiries:

Drax Investor Relations: Mark Strafford
+44 (0) 7730 763 949

Media:

Drax External Communications: Ali Lewis
+44 (0) 7712 670 888

Website: www.drax.com/uk

Notes:

  1. Existing assets – gas (Damhead Creek, Rye House, Shoreham and three existing small gas turbines at Drax Power Station), Cruachan Pumped Storage and the Galloway hydro scheme (Tongland, Kendoon and Glenlee).
  2. Capacity Market agreements stated in 2018/19 real-terms, with payments indexed to UK CPI.

END

Why spin a turbine without generating power?

12 February 2020

Power generation
Turbine at Cruachan Power Station

Massive spinning machinery is a big part of electricity generation whether it’s a wind turbine, hydro plant or biomass generator.

But big spinning turbines don’t just pump electricity out onto the grid. They also play a crucial role in keeping the electricity system stable, safe and efficient. This is because big, heavy spinning turbines add something else to the grid: inertia.

This is defined as an object’s resistance to change but in the context of electricity it helps the grid remain at the right frequency and voltage level. In short, they help the grid remain stable.

However, as electricity systems in Great Britain and other parts of the world move away from coal and gas to renewables, such as wind turbines, solar panels and interconnectors, the level of inertia on the system is falling.

“We need the inertia, we don’t need the megawatts,” explains Julian Leslie, Head of Networks at the National Grid Electricity System Operator (ESO). “But in today’s market we have to supply the megawatts and receive the inertia as a consequence.”

Turbine at Drax Power Station

Engineer inspecting turbine blades at Drax Power Station

The National Grid ESO is taking a new approach to this aspect of grid stability by using what are called synchronous condensers. These complicated-sounding pieces of machinery are actually quite straightforward in their concept: they provide inertia to the grid without generating unnecessary power.

These come in the form of:

  • Existing generators that remain connected to the grid but refrain from producing electricity.
  • Purpose built machines whose only function is to act as synchronous condensers, never generating real power. These may be fitted with flywheels to increase their mass and, in consequence, their inertia.

This means that spinning without generating is about to become a very important part of Great Britain’s electricity system.

Around and around

Electricity generators that spin at 3,000 rpm are described as synchronous generators because they are in sync with the grid’s frequency of 50Hz. These include coal, gas, hydro, biomass turbines and nuclear units. Most spin at 3000 rpm, some machines much less (e.g. 750 rpm). Thanks to the way they are designed, they are all synchronised together at the same, higher speed.

Then there are wind turbines where the generated power is not synchronised to the grid system. Termed asynchronous generators, these machines do not have readily accessible stored energy (inertia) and do not contribute to the stability of the system. Interconnectors and solar panels are also asynchronous.

It’s important that Great Britain’s whole grid is kept within 1% of the 50Hz frequency, otherwise the voltage of electricity starts to fluctuate, damaging equipment, becoming less efficient, even dangerous, or resulting in blackouts.

Say a power station or a wind farm were to drop offline, as occurred in August 2019, this would cause the amount of power on the grid to suddenly fall. But it is not just the power that changes – the frequency and voltage also fluctuate dramatically which can cause equipment damage and ultimately, towns, cities or widespread areas to lose power.

Running machines that have inertia act like the suspension on a car – they dampen those fluctuations, so they are not as drastic. The big spinning machines keep spinning, buying valuable milliseconds for the grid to react, often automatically, before the damage becomes widespread.

However, as a consequence of decarbonisation, more solar panels and wind turbines are now on the system and there are fewer spinning turbines, leading to lower levels of inertia on the grid.

“There are periods when renewable generation and flow from interconnectors are so great that it displaces all conventional, rotational power plants,” says Leslie. “Today, bringing more inertia onto the grid may mean switching off renewables or interconnectors, and then replacing them with rotating plants and the megawatts associated with that.”

Creating a market for inertia and synchronous condensers offers a new way forward – providing inertia without unneeded megawatts or emissions from fossil fuels.

A new spin on grid stability

At the start of 2020, The National Grid ESO began contracting parties, including Drax’s Cruachan pumped-hydro power station, to operate synchronous condensers and provide inertia to the grid when needed.

The plans mark a departure from the previous system where inertia and voltage control from electricity generators was taken for granted.

Cruachan Power Station is already capable of running its units in synchronous condenser mode (one of its units, opened up for maintenance, is pictured at the top of this article). This involves an alternator acting as a motor, offering inertia to the grid without generating unneeded electricity. Other service providers will repurpose existing turbines, construct new machines or develop new technologies that can electronically respond to the grid’s need for stability.

Synchronous condensers, or the idea of spinning a turbine freely without generating power, are not new concepts; power stations in the second half of the 20th century could shut down certain generating units but keep them spinning online for voltage control.

In the 1960s and 70s, some substations – where the voltage of electricity is stepped up and down from the transmission system – also deployed stand-alone synchronous condensers. These were also used to provided inertia as well as voltage control but are long since decommissioned.

Synchronous condenser installation at Templestowe substation, Melbourne Victoria, Australia. By Mriya via Wikimedia.

“Synchronous condensers are a proven technology that have been used in the past,” says Leslie. “And there are many new technologies we are now exploring that can deliver a similar service.”

Cheaper, cleaner, more stable

Commercial UK wind turbines

The National Grid ESO estimates the technology will save electricity consumers up to £128 million over the next six years. Savings, which come from negating the need for the grid to call upon fossil fuels for inertia as coal, oil and gas, become increasingly uneconomical across the globe as carbon taxes grow.

The fact that synchronous condensers do not produce electricity also saves money the grid may have had to pay out to renewable generators to stop them producing electricity or to storage systems to absorb excess power.

“It means the market can deliver the renewable flow without the grid having to pay to restrain it or to pay for gas to stabilise the system,” says Leslie. “Not only does this allow more renewable generation, but it also reduces the cost to the consumer.”

In a future energy system, where there is an abundance of renewable electricity generations, synchronous condensers will be crucial in keeping the grid stable. The National Grid ESO’s investment in the technology further highlights the importance of new ideas and innovation to balance the grid through this energy transition.

Synchronous generation provides benefits to system stability beyond the provision of inertia. In a subsequent article we’ll also explore how synchronous condensers can assist with voltage stability and help regional electricity networks and customers to remain connected to the national system during and after faults.

Read about the past, present and future of the country’s electricity system in Could Great Britain go off grid? 

Capacity Market agreements for existing assets and review of coal generation

31 January 2020

Investors
Drax's Kendoon Power Station, Galloway Hydro Scheme, Scotland

RNS Number : 6536B

T-3 Auction Provisional Results

Drax confirms that it has provisionally secured agreements to provide a total of 2,562MW of capacity (de-rated 2,333MW) from its existing gas, pumped storage and hydro assets(1). The agreements are for the delivery period October 2022 to September 2023, at a price of £6.44/kW(2) and are worth £15 million in that period. These are in addition to existing agreements which extend to September 2022.

Drax did not accept agreements for its two coal units(3) at Drax Power Station or the small Combined Cycle Gas Turbine (CCGT) at Blackburn Mill(4) and will now assess options for these assets, alongside discussions with National Grid, Ofgem and the UK Government.

A new-build CCGT at Damhead Creek and four new-build Open Cycle Gas Turbine projects participated in the auction but exited above the clearing price and did not accept agreements.

T-4 Auction

Drax has prequalified its existing assets(5) and options for the development of new gas generation to participate in the T-4 auction, which takes place in March 2020. The auction covers the delivery period from October 2023.

CCGTs at Drax Power Station

Following confirmation that a Judicial Review will now proceed against the Government, regarding the decision to grant planning approval for new CCGTs at Drax Power Station, Drax does not intend to take a Capacity Market agreement in the forthcoming T-4 auction. This project will not participate in future Capacity Market auctions until the outcome of the Judicial Review is known.

Enquiries:

Drax Investor Relations
Mark Strafford
+44 (0) 7730 763 949

Media:

Drax External Communications
Matt Willey
+44 (0) 0771 137 6087

Photo caption: Drax’s Kendoon Power Station, Galloway Hydro Scheme, Scotland

Website: www.drax.com/uk

Winter on the Hollow Mountain

15 January 2020

Power generation
Winter snow scene around the Hydro electric Dam on Ben Cruachan,above Loch Awe, Argyll, Scotland

Scotland’s landscape is defined by its weather. The millennia of wind, rain and snow has battered the country, ebbing away at its rivers, mountains, valleys and deep lochs forged by ice ages and volcanos. Weather also plays an important role in the country’s power generation. The country has more than 9 gigawatts (GW) of installed wind power – enough to sometimes meet double Scotland’s electricity demand – as well as having a long history of hydropower.

But while it is an intrinsic part of the country, Scotland’s weather can be anything but pleasant. Rain can be persistent and when the temperature drops in winter, it turns to snow – a lot of it. Scotland gets more snow than any other part of the UK.

Scottish poet Robert Burns described the harshness of the winter months in his 1781 poem Winter A Dirge:

“The wintry west extends his blast,

And hail and rain does blaw;

Or the stormy north sends driving forth

The blinding sleet and snaw:”

Sleet and ‘snaw’ (snow) fall occurs on average for 38 days a year in Scotland, compared to an average of 23 days across the rest of the United Kingdom, and can remain covering mountaintops long into spring.

Ben Cruachan Mountain

Ben Cruachan

The peak of Ben Cruachan in the Western Highlands is no exception. Cruachan Power Station, on the slopes of the mountain, however, must be ready to either generate or absorb electricity through all forms of weather – even the most severe.

“On a few occasions the snowfall has been so extreme that we’ve been unable to access the dam for a few weeks at a time,” says Gordon Pirie, a Civil Engineer at Cruachan. “Thankfully, we have enough controls in place where we are still able to monitor and operate things remotely.”

Mountain road from Cruachan Power Station to its dam blocked due to snow

Mountain road from Cruachan Power Station to its dam blocked due to snow

This mountainside location and winter weather can make for tough working conditions, but Cruachan is designed to handle it. In fact, in some cases it benefits from it.

Taking advantage of wet weather

Cruachan is built around the geography and climate of the Highlands. It stores water in an upper reservoir 400 meters (1,312 feet) up Ben Cruachan and uses its elevation to run it down the mountain, spin a turbine and generate power.

And when there is excess electricity being generated nationally, the same turbines reverse and use the excess electricity to pump water from Loch Awe up to the reservoir, helping to balance the grid. This acts as a form of energy storage by essentially stockpiling the excess electricity in the form of water held in the top reservoir.

For the most part the water used to generate electricity comes exclusively from Loch Awe and is passed up and down the mountain. However, 10% of it comes for ‘free’, as it’s collected from natural rainfall and surface water that makes its way to the upper reservoir through Cruachan’s aqueducts. This system of 14 kilometres of interconnected concrete pipes covers a 23 square kilometre radius around the reservoir and is designed to bring in water from 75 intakes dotted around the top of the mountain.

A North of Scotland Hydro-Electric Board diagram from c.1960s showing the aqueducts feeding Cruachan’s dam; click to view/download.

A North of Scotland Hydro-Electric Board diagram from c.1960s showing the aqueducts feeding Cruachan’s dam; click to view/download.

Some of these intakes are as small as street drains, while others are large enough to drive a Land Rover into. It’s part of Pirie’s job to keep them in good working order so they continue to deliver water to the reservoir. As the intakes are scattered around the mountaintop, they must be able to deal with whatever the Scottish winter throws at them.

Gordon Pirie, Civil Engineer and Cruachan Power Station dam

Gordon Pirie, Civil Engineer and Cruachan Power Station dam

“Even in freezing conditions the water will still flow through the aqueduct system, the intakes have a built-in feature which allows the water to flow into them even if the surface is frozen solid,” explains Pirie. “Any snow or frost on the ground eventually thaws and makes its way to the reservoir.”

As spring arrives and snow begins to thaw across the Highlands, greater volumes of water will run off into the reservoir and the power station’s engineers work to manage the water level.

Keeping water pressure under control

Cruachan Dam

Thawing snow can bring greater volumes of water into the reservoir.

The power station must be able to pump water and absorb excess electricity from the grid at a moment’s notice. This ability to turn excess electricity into stored energy makes Cruachan hugely useful in controlling the grid’s voltage, frequency and in keeping it stable. However, there must be enough space available in the reservoir for the water being pumped up the mountainside to enter – even when excessive rainfall or melting snow begins to naturally fill it up.

The power station can control the reservoir levels through a number of means. This includes the ability to close off an aqueduct, or to run the turbines without generating electricity so the team can move water from the reservoir into Loch Awe below.

If the water level and pressure on the dam reaches dangerous levels a ‘dispenser valve’ can be opened in an emergency, sending a jet of water flying out the dam to cascade safely down the mountainside. However, outside of testing, this has never been necessary to do. 

And while the weather might be the most persistent natural force the power station must deal with, it’s not the only one. “Recently we had an issue with a bat roosting within one of the tunnels in which we were carrying out stabilisation works,” recalls Pirie. “It was looking for a suitable location to hibernate for the winter and the tunnel provided the ideal environment. We had to stop works to have a bat survey undertaken and apply for a bat license.”

Cruachan’s location makes for stunning views of the Highlands, but occasionally brutally cold and perilously wet conditions come with the territory. For the power station team, working with the sometimes-despairing weather is all part of what allows the Hollow Mountain to operate as it has done for more than half a century.

The Highlands around Ben Cruachan are rich with wildlife. Educational information on area’s flora and fauna can be explored at the Cruachan Power Station visitor centre.

The Highlands around Ben Cruachan are rich with wildlife. Educational information on area’s flora and fauna can be explored at the Cruachan Power Station visitor centre.

Visit Cruachan — The Hollow Mountain to take the power station tour.

The men who built a power station inside a mountain

12 November 2019

Power generation
Cruachan tunnel tigers

Travelling through the Highlands towards the West Coast of Scotland, you pass the mighty Ben Cruachan – its 1,126 metre peak towers over the winding Loch Awe beneath. It is the natural world on a huge scale, but within its granite core sits a manmade engineering wonder: Cruachan Power Station.

Opened by The Queen in 1965, it is one of only four pumped-hydro stations in the UK and today remains just as impressive an engineering feat as when it was first opened.

Cruachan is operated safely and hasn’t had a lost time injury in 15 years. The robust health and safety policies and practices employed at the power station were not in place all those decades ago.

It took six years to construct, enlisting a 4,000-strong workforce who drilled, blasted and cleared the rocks from the inside of the mountain, eventually removing some 220,000 cubic metres of rubble. The work was physically exhausting – the environment dark and dangerous.

Nicknamed the ‘Tunnel Tigers’, the men that carried the work out came from far and wide, attracted to its ambition as well as a generous pay packet reflective of the danger and difficulty of the work. But few of them were fully prepared for the extent of the challenge.

One labourer, who started at Cruachan just after his 18th birthday, recalls: “I was in for a shock when I went down there. The heat, the smoke – you couldn’t see your hands in front of you.”

Inside the mountain

The work of hollowing out Ben Cruachan was realised by hand-drilling two-to-three metre deep holes into the granite rockface. An explosive known as gelignite, which can be moulded by hand, was packed into the drilled holes and detonated. The blasted rocks were removed by bulldozers, trucks and shovels, before drilling began on the fresh section of exposed granite. In total, 20km of tunnels and chambers were excavated this way, including the kilometre-long entrance tunnel and the 91-metre-long, 36-metre-high machine hall.

Wilson Scott was just 18 when he got a job working as a labourer at Cruachan while the machine hall was being cleared out.

“The gelignite, it had a smell. Right away I was told not to put it near your face,” he says, “It’ll give you a splitting headache and your eyes will close with the fumes that come off it. It was scary stuff.”

This process allowed for rapid expansion through the mountain. With three or four blasts each 12-hour shift, some 20 metres of rock could be cleared in the course of a day. Activity was constant, and to save the men having to make the journey back up to the surface, refreshments came to them.

“There was a bus that went down the tunnel at 11 o’clock with a huge urn of terrible tea,” says Scott. “Most of the windows were out of the bus because the pressure of the blasting had blown them in.”

The tea did little to make the environment hospitable, however. From the water dripping through the porous rocks making floors slippery and exposed electrics vulnerable, to the massive machinery rushing through the dense dust and smoke, danger was ever-present. Loose rocks as large as cars would often fall from exposed walls and ceilings while the regular blasting gave the impression the entire mountain was shaking.

“I’ll tell you something: going into that tunnel the first time,” Scott says. “It was a fascinating place, but quite a scary place too.

Above them, on top of the mountain, a similarly intrepid team tackled a different challenge: building the 316-metre-long dam. They may have escaped the hot and humid conditions at the centre of Cruachan, but their task was no less daunting.

Cruachan dam construction, early 1960s

Cruachan dam construction, early 1960s

On top of the dam

Out in the open, 400 metres above Loch Awe, the team were exposed to the harsh Scottish elements. John William Ross came to Cruachan at the age of 35 to work as a driver and spent time working in the open air of the dam. “You’d get oil skins and welly boots, and that was it. We didn’t have gloves, if your hands froze – well that’s tough luck isn’t it.” Mr Ross sadly passed away recently.

Charlie Campbell, a 19-year-old shutter joiner who worked on the dam found an innovative way around the cold. “You’d put on your socks, and then you’d get women’s tights and you’d put them over the top of the socks, and then you’d put your wellies on and that’d keep your feet a wee bit warmer. We thought it did anyway. Maybe it was just the thought of the women’s stockings.”

Pouring the concrete of the dam – almost 50 metres high at its tallest point – was precarious work, especially given the challenges of working with materials like concrete and bentonite (a slurry-like liquid used in construction).

“It was horrible stuff. It was like diarrhoea, that’s the only way of explaining it,” says Campbell. “There was a boy – Toastie – I can’t remember his real name. He fell into it. They had quite a job getting him out, they thought he was drowned, but he was alright.”

Many others were not alright. The danger of the work and conditions both inside and on top of the mountain meant there was a significant human cost for the project. During construction, 15 people tragically lost their lives.

Today a carved wooden mural hangs on the wall of the machine hall to capture and commemorate the myth of the mountain and the men who sadly died – a constant reminder of the bravery and sacrifice they made.

The men that made the mountain

The Cruachan ‘Tunnel Tigers’

The Tunnel Tigers were united in their efforts, but came from a range of backgrounds and cultures. Polish and Irish labourers worked alongside Scots, as well as displaced Europeans, prisoners of the second world war and even workers from as far as Asia. The men would work 12, sometimes 18-hour shifts, seven days a week. Campbell adds that some men opted to continue earning rather than rest by doing a ‘ghoster’, which saw them working a solid 36 hours.

Many men would make treble the salary of their previous jobs, with some receiving as much as £100 a week, at a time when the average pay in Scotland was £12. Some teams’ payslips were stamped with the words ‘danger money’ – illustrative of the men’s motivation to endure such life-threatening work.

While it was a dangerous and demanding job, many of the Tigers look back with fond memories of their time on the site and many stayed in the area for years after. “It was an experience I’m glad I had,” says Scott. “It puts you in good stead for the rest of your days.”

As for Cruachan Power Station, its four turbines are still relied on today by Great Britain to balance everyday energy supply. As the electricity system continues to change, the pumped hydro station’s dual ability to deliver 440 megawatts (MW) of electricity in just 30 seconds, or absorb excess power from the grid by pumping water from Loch Awe to its upper reservoir, is even more important than when it opened.

Standing at the foot of a mountain more than 50 years ago, the men about to build a power station inside a lump of granite may have found it unlikely their work would endure into the next millennium. They may have found it unlikely it was possible to build it at all. But they did and today it remains an engineering marvel, a testament to the effort and expertise of all those who made it.

Visit Cruachan – The Hollow Mountain

From coal to pumped hydro storage in 83 mountainous miles

7 October 2019

Power generation
Moving of transformers from Longanett to Cruachan

Nestled in in the Western Highlands in Scotland, Cruachan Power Station is surrounded by a breathtaking landscape of plunging mountainsides and curving lochs, between which weave narrow roads.

It makes for scenic driving. What might be trickier, however, is transporting 230 tonnes of electrical equipment up and down said mountains, navigating narrow bends.

But that’s exactly what a team from Drax was tasked with when it came to moving two 115 tonne transformers, the equipment used to boost electricity’s voltage. They were in storage 83 miles away at Longannet, currently being demolished, near Fife.

“You’re moving a piece of equipment that is designed to stay in one place. It’s not designed to go on the roads,” explains Jamie Beardsall, an Electrical Engineer from the EC&I Engineering team who worked on the project. “You’re very aware of your environment and the risks. Everything is checked and doubled checked.”

Transformers being driven to Drax’s Cruachan pumped storage hydro power station

The complicated task required colleagues from both Cruachan and Drax power stations to collaborate from the very beginning. Gary Brown, Mark Rowbottom and Jamie from the EC&I Engineering team based in Yorkshire teamed up with Gordon Pirie and Roddy Davies from Scotland who met frequently and planned the project alongside specialist transport contractor, ALE, which advised on heavy lifting and movement.

Planning and execution of the works also required constant liaison and coordination with the police and highway authorities in both Scotland and England. But more than that, the transformers’ one-by-one journey from the demolition site of what was once Europe’s biggest coal-fired power station, to a hydro-powered energy storage site on the other side of Scotland, represents the continual shift of Great Britain’s electricity away from fossil fuels.

Stepping up voltage

Transformers are an essential part of the electricity system. By increasing or decreasing the voltage of an electrical current they can enable it to traverse the national grid or make electricity safe to enter our homes.

“When we generate electricity, it is at a lower voltage than we need to send it out to the national grid,” says Beardsall. “We use transformers to increase the voltage so it can go out to the national grid and be transmitted over long distances more efficiently. We then reduce the voltage again so it can be brought safely into our homes.”

While all transformers apply the same principles for stepping voltage up and down, the two transformers that were transported through the Highlands to Cruachan were designed specifically for the pumped storage hydro power station, but stored at Longannet where there was more space. At the time, both stations where owned by Scottish Power. Cruachan was purchased by Drax on the last day of 2018.

Engineers at Cruachan Power Station in front of one of the original transformers

When transported, each transformer weighs 115 tonnes and is almost four metres high. Transporting them isn’t as simple as loading them into the back of a van.

“You can’t transport them in a fully built state, they would be too heavy and wouldn’t go under bridges,” says Beardsall. “We had to strip them back to the core and now we’re working to reassemble them on site.”

Cutting down to the core

Each transformer consists of two main components; a core made of iron, and two windings made of copper. The transformer itself has no moving parts. When a voltage is applied to one of the transformer windings (the primary winding), a magnetic field is created in the iron core. This field then induces a voltage into the other winding (the secondary winding). Depending on the number of coils on each set of windings, the output voltage will increase or decrease. More coils on the secondary winding steps the voltage up, fewer coils on the secondary steps the voltage down.

This entire apparatus is submerged in an oil to provide insulation and keep the transformer cool, meaning the first step was to drain 50,000 litres of oil from each transformer. This was then sent to a refinery to be processed, cleaned and stored until the transformers are reassembled at Cruachan.

Oil removed, the Drax engineers oversaw and managed the dismantling of the transformers at Longannet. Once the transformers were stripped down to a state suitable for movement, they were loaded up one-by-one for transportation.

Meanwhile, at Cruachan, engineers worked on construction of a purpose built bunded area for storage of the transformers. The transformers were destined to be stored on land outside the main admin buildings, adjacent to Loch Awe.

Loch Awe at Cruachan Power Station

The Loch itself is a beautiful place with abundant animal and birdlife – and a fish farm is located almost directly opposite the power station. In the event of a transformer leaking, the natural environment must be protected. An oil-tight storage area was therefore built, to ensure that no oil would end up in the Loch.

The road to Cruachan

Rather than heaving each of the transformers onto a trailer, each one was raised using hydraulic jacking equipment. A trailer was then driven underneath, and the transformer lowered onto it.

“The trailer is specifically designed to take the transformers and fit certain dimensions,” explains Beardsall. “It has 96 wheels over 12 sets of axles, each of which can be turned individually to assist in navigating around tight spots.”

The trailers are towed by large tractor units, each weighing over 40 tonnes. These provided the motive power to move the transformers. Each was moved in two stages over the space of two weeks. The first transformer over the course of a weekend, the second in the middle of the night some 10 days later.

“When we could go was governed by the police and highways agencies as they need to close the roads,” says Beardsall. “We set off from Longannet at 7pm on the Friday evening and moved them 60 miles along the route to a layby where we stored them. That leg took approximately five hours. Then the second leg was the last 25 miles to Cruachan, carried out on the Sunday morning of the same weekend.”

Navigating the Highlands with 115 tonnes of hugely valuable equipment is where the real challenge came in. Hills, dips and tight turns made for slow progress.

Generator transformer at Cruachan Power Station

The original generator transformer at Cruachan Power Station

“The average speed was about 10mph, but we’re going through the Highlands so it was quite a bit slower than that in some places. We occasionally hit 20+ mph at points, but that was definitely for the minority of the time!” says Beardsall. “Some of the roads were so narrow it was difficult to get two cars past each other. The contractors also had to put metal plating over bridges because they weren’t strong enough to take the load.”

Having safely arrived at Cruachan, the transformers are being stored at surface level until they are needed, at which time they will be taken down the half-a-mile-long tunnel into the energy storage station.

“Typically a transformer has a design life of 25 years, although they can last longer” explains Beardsall. “There are four units at Cruachan and the transformers for two of these units have already been replaced, so these transformers would be used to replace the existing transformer for the two remaining units should it ever be needed. The existing transformer having been in operation since 1965.”

Moving heavy objects is part and parcel of running Drax’s multiple power stations around the country. However, navigating the Highlands, the very terrain which makes Cruachan possible, added a unique challenge for Drax’s engineers.

Visit Cruachan Power Station – The Hollow Mountain

Read the press release

In energy storage timing is everything

21 August 2019

Power generation
Cruachan Power Station

Electricity is unlike any other resource. The amount being generated must exactly match demand for it, around the clock.

Managing this delicate balancing act is the job of the National Grid Electricity System Operator (ESO), which works constantly to ensure supply meets demand and the grid remains balanced. One of the ways it does this is by storing energy when there is too much and deploying it when there is too little.

Although there are many different ways of storing energy at a small scale, at grid level it becomes more difficult. One of the few ways it is currently possible is through pumped hydro storage. Cruachan Power Station in the Highlands of Scotland is one of four pumped storage facilities in Great Britain. It uses electrically-driven turbines to pump water up a mountain into a reservoir when there is excess electricity on the grid, and then releases the water stored in the reservoir back down, to spin the same turbines to generate power when it’s needed quickly.

The dual capabilities of these turbines are unique to pumped hydro storage and contribute to the overall grid’s stability. However, what dictates when Cruachan’s turbines switch from pump to generate and vice versa is all a matter of what the grid needs – and when.

The switch from pump to generate

While the machine hall of Cruachan Power Station is an awe-inspiring place for its size and location 396 metres beneath Ben Cruachan, it generates electricity much like any other hydropower station: harnessing the flow of water to rotate any number of its four 100+ megawatt (MW) turbines.

This mode – simply called ‘generate mode’ – is usually employed during periods of peak power demand such as mornings and evenings, during a major national televised event, or when wind and solar energy output drops below forecast. As a result, starting up and generating millions of watts of electricity has to be fast.

“It takes just two minutes for a turbine to run up from rest to generate mode,” says Martin McGhie, Operations and Maintenance Manager at the power station. “It takes slightly longer for the turbines to run down from generate to rest, but whatever function the turbines are performing, they can reach it within a matter of minutes.”

The reverse of generate mode is pump mode, which changes the direction of travel for the water, this time using electricity from the grid to pump water from the vast Loch Awe at the foot of Ben Cruachan to the upper reservoir, where it waits ready to be released.

In contrast to generate mode, pump mode typically comes into play at times when demand is low and there is too much power on the system, such as during nights or at weekends, when there is excessive wind generation. However, the grid has evolved since Cruachan first began generating in 1965 and this has changed when it and how it operates.

“In the early days, Cruachan was used in a rather predictable way: pumping overnight to absorb excess generation from coal and nuclear plants and generating during daytime peak periods,” says Martin. “The move to more renewable energy sources, like wind, mean overall power generation is more unpredictable.”

He continues: “There has also been a move from Cruachan being primarily an energy storage plant to one which can also offer a range of ancillary services to the grid system operator.”

The benefits of Spin mode

In between pumping water and generating power, Cruachan’s turbines can also spin in air while connected to the grid, neither pumping not generating. This is essentially a ‘standby mode’ where the turbines are ready to either quickly switch into generation or pumping at a moment’s notice (they spin one way for ‘spin pump’; the other for ‘spin generate’). These spin modes are requested by the ESO to ensure reserve energy is available to respond rapidly to changes on the grid system.

In spin generate mode, the generator is connected up to the grid but the water is ejected from the space around the turbine by injecting compressed air. The turbine does not generate power but is kept spinning, allowing it to quickly start up again. As soon as the grid has an urgent need for power, the air is released and the water from the upper reservoir flows into the turbine to begin generation in under 30 seconds.

Spin pump works on the same basis as spin generate, but with the turbine rotating in the opposite direction, ready to pump at short notice. This allows Cruachan to absorb excess generation and balance the system as soon as the ESO needs it.

“The use of spin mode by the ESO is highly variable and dependant on a number of factors e.g. weather conditions or the state of the grid system at the time” says Martin. This unpredictability of the increasingly intermittent electricity system makes the flexibility of Cruachan’s multiple turbines all the more important.

Ready for the future grid

It’s not only the types of electricity generation around the system that are changing how Cruachan operates. Martin suggests that the way energy traders and the ESO use Cruachan will continue to evolve as the market requirements and opportunities change.

Technology is also changing the market and Martin predicts this could affect what Cruachan does. “In the future we will face competition from alternative storage technologies, such as batteries, electric vehicles, as well as competition for the other ancillary services we offer.”

However, Cruachan’s flexibility to generate, absorb or spin in readiness means it is prepared to adjust to any future changes.

“Cruachan is always ready to modify or upgrade to meet requirements, as we have done in the past,” says Martin. “The priority is always to be able to deliver the services required by the grid system operator – in characteristic quick time.”

Visit Cruachan — The Hollow Mountain to take the power station tour.

Read our series on the lesser-known electricity markets within the areas of balancing services, system support services and ancillary services. Read more about black start, system inertia, frequency response, reactive power and reserve power. View a summary at The great balancing act: what it takes to keep the power grid stable and find out what lies ahead by reading Balancing for the renewable future.