Tag: Cruachan

Harnessing Scotland’s landscape to power a renewable future

Key takeaways:

  • Scotland’s ambitious plan to expand its wind capacity­ and reach net zero by 2045 will require greater levels of energy storage
  • Plans to expand the storage and generation capacity of Cruachan pumped storage hydro station from 440 MW to over 1 GW can help support a re­­newable future
  • Greater levels of energy storage can also reduce the costs of operating the grid and enable the greater utilisation of renewable electricity sources such as wind.
  • Expansion plans for Cruachan would bring as many as 900 jobs during the construction phase across the supply chain and continue Drax’s commitment to local communities and environments
  • The project is a large-scale and long-term infrastructure solution to some of the critical issues faced by Scotland’s electricity network.

The hit Star Wars TV series Andor might be set a long time ago in a galaxy far, far away, but audiences in Argyll and Brute may recognise a local landmark on the titular distant planet.

Cruachan Power Station’s 316-metre-long buttress-style dam served as a setting for the space thriller. However, here on planet Earth, it has another big role to play in supporting Scotland and the UK’s efforts to reach net zero emissions.

The pumped storage hydro station, known as the ‘Hollow Mountain’, complements Scotland’s wider strategy to expand its onshore wind capacity to 20 gigawatts (GW) by 2030. The plant’s ability to absorb excess electricity at times of low demand, and discharge it again when needed, allows it to play a key role in balancing and supporting the national transmission system.

As Scotland and the rest of the UK move to a future increasingly powered by intermittent renewables, ambitious plans to increase Cruachan’s capacity to more than 1GW, will also help create jobs in Argyll and Bute and support communities through the net zero transition.

Scotland’s wind power potential

Scotland’s famously blustery, wet weather and dramatic landscapes of mountains and lochs has long enabled it to pioneer hydro schemes along its rivers, pumped storage hydro on its mountainsides, and wind turbines on and offshore.

Wind power contributed heavily to Scotland achieving 97% renewable electricity generation in 2020. And with more than 17 GW of additional capacity in the pipeline, Scotland has the potential to be the wind powerhouse of the UK – in 2021, Scotland exported 33% of its generation in net transfers to England and Northern Ireland, having previously set a record 37.3% in 2020.

However, simply generating a lot of power isn’t the whole story. Generating too much power can even be a problem for grids if there is nowhere for that power to go. Currently, constraints in the transmission system limit how much power can be exported from Scotland to meet demand in other parts of the UK.

When generators start producing these surpluses, the grid operator has to pay wind farms to turn them off. It’s estimated that wind curtailment costs added £806m to energy bills in Britain in 2020 and 2021. This is where energy storage comes in, offering somewhere for power to be redirected and reducing curtailment costs.

Enter Cruachan. At maximum load Cruachan Power Station can generate 440 MW, enough to power 1 million homes, when water from the upper reservoir is released, flowing through the plant’s four turbines, and entering Loch Awe below. But when there is more electricity on the system than demand, excess electricity can be used to power turbines that pump water up from Loch Awe to the upper reservoir where it’s stored until needed.

Pumped storage hydro, as this system is called, offers long-term, large-scale energy storage to the UK’s electricity system, helping to reduce costs and prepare for a renewable-led future.

The large-scale, long-term storage solution

Since opening in the 1960s Cruachan has only become more important in helping to stabilise an increasingly renewable UK, while supplying ancillary services like inertia to the grid. The Cruachan expansion plan to expand the facility and bring its ability to absorb and discharge electricity to more than 1 GW can offer a host of benefits to the grid and power to consumers across the country.

Cruachan’s ability to reach full generating capacity in less than 30 seconds means that it can respond quickly to fluctuations in supply and demand. When Cruachan provides power back to the system in times of high demand, it can in turn lead to lower peak power prices. This becomes even more important at a time of high gas prices, when ordinary consumers are feeling the impact of rising energy costs more than ever.

Increasing Cruachan’s capacity to generate and absorb power can help reduce transmission system costs and wind curtailment. It also offers a zero-carbon source of stabilising ancillary services to the grid, which have historically been provided by gas generators. As the proportion of gas generation decreases and the proportion of intermittent renewables generation increases, low-carbon generators that are able to provide these services will become increasingly more important.

Importantly, the Cruachan expansion is a long-term solution. The expanded facility would have an operational life span of more than half a century, significantly longer than the 10-15 years offered by lithium-ion battery storage solutions.

However, there is a need for a financial mechanism to de-risk the project for investors and offer value for money for consumers. The cap and floor mechanism, which ensures generating revenues remain within a specific range, is currently used for interconnectors to stabilise revenues by offering sufficient certainty to investors that income will cover the cost of debt, which unlocks finance for new projects. A similar mechanism could be introduced to support energy storage technologies that will be needed to support a renewable future, such as the Cruachan expansion. The UK government must act quickly to implement the mechanism and realise the opportunity that storage can provide to the UK and Scotland.

Making the Cruachan expansion a reality  

Expanding Cruachan is a long-term, large-scale project that will create a range of jobs and economic benefits and help support the local economy through the transition to net zero.

“I am absolutely delighted that Drax is progressing plans to expand the Ben Cruachan site,” says Jenni Minto, Member of Scottish Parliament. “This will not only support 900 jobs and create a pumped storage facility that will be able to provide enough renewable energy to power a million homes, it will provide £165 million benefit to the local economy during construction.”

In addition to 150 on-site local construction jobs, the project’s supply chain will create opportunities across a range of industries, from quarrying and engineering, to transport and hospitality.

 “The Cruachan extension is a really exciting project and one that’s really important for Scotland.” says Claire Mack, CEO Scottish Renewables. “It brings together a number of our really important skills, including civil engineering and electrical engineering. What we really want to see is a renewables industry that’s thriving but also driving economic gain in Scotland.”

Cruachan has operated in the region for more than half a century and has supported local communities through more than just job creation. This includes a donation to The Rockfield Centre in Oban to help fund a new community hub, offering education as well as a social space. Following Cruachan’s appearance in Andor, Drax also made a five-figure donation to several charities and good causes across Argyll, including Oban Mountain Rescue’s efforts to create a rural defibrillator network.

As well as lending a helping hand to local communities, Cruachan’s teams have always taken precautions to minimise any impact on the natural environment and preserve the area’s biodiversity and natural beauty.

The Cruachan expansion is an engineering project on an epic scale. It will involve carving huge new underground caverns, tunnels, and waterways out of the rock below Ben Cruachan. But in doing so it will create long-term opportunities for the local community and a key piece of infrastructure to take Scotland into a net zero future.

The next PM must move fast to unlock investment in long duration energy storage

For many years energy security was an issue resolved by complex, continent-wide gas pipelines which stretched from Russia into the heart of Europe.

We now know this reliance on Russian gas didn’t strengthen Europe’s energy security – in fact it weakened it.

The UK is less reliant on foreign gas than many countries in Europe in part due to the renewables revolution which has transformed our energy system over the last decade.

The rollout of biomass, wind and solar power has enabled the UK to decarbonise its power grid at a faster rate than any other major economy. And in order to reduce energy bills in the years ahead we need to have more clean, green, renewable power, which is generated in the UK for the UK.

Getting more green energy onto the grid can only be achieved through partnerships between government and private companies. For businesses like Drax, that means having the right policies now, to make large-scale investment decisions for the future, in vital green energy technologies like pumped storage hydro and bioenergy with carbon capture and storage (BECCS).

Drax has submitted planning applications for two major infrastructure projects designed to deliver both of these vital technologies in the 2020s. They form part of a £3bn investment strategy which Drax stands ready to implement this decade, underlining the company’s significant role as a growing, global business at the heart of the green energy transition.

Alongside strengthening the UK’s long-term energy security, these projects will support thousands of jobs and provide a real opportunity for economic growth.

Engineers at Cruachan Power Station

We aim to double the capacity of our Cruachan pumped hydro storage facility in Scotland, supporting energy security and further decarbonisation of the grid, at lower costs.

Over the last two years, due to bottlenecks on the transmission system and a lack of energy storage capacity, enough wind power to supply 800,000 homes each year with renewable electricity, went to waste.

As household bills and global temperatures continue to rise, we can’t afford to let renewable power go to waste like this. We need more storage to harness the wind power available now, as well as the increased capacity being developed the coming years.

The only proven grid scale technology that can store vast quantities of energy for long durations is pumped storage hydro. Sites like Cruachan act like giant water batteries, using excess power from the grid to pump water to an upper reservoir where it is stored, before re-releasing it to generate electricity.

While the UK’s policy and market support mechanisms have evolved to support new build renewables, the current framework isn’t suitable for pumped storage projects that can have a lifespan of many decades.

Drax’s plans would enable more homegrown renewable power to come online to strengthen the UK’s energy security and lower carbon emissions. This additional capacity could be available within eight years.

To secure private investment in these projects, get shovels in the ground and work underway, developers need to know the policy environment they will be operating in.

Abandoning or delaying net zero will not save the country money, it will increase our reliance on foreign gas, leaving households at the mercy of international markets which no UK government can control.

Find out more about Cruachan 2 here.

In Scotland alone there is more than 4.3 GW of storage projects in planning or awaiting construction – this is enough capacity to power around three million homes.

Drax, alongside the developers of some of these other projects, has put forward plans for policies which would create the certainty needed to incentivise investment and kick start work to build the storage capacity this country needs for energy security.

These include introducing a cap and floor regime – the same support mechanism which was instrumental in the successful roll-out of interconnectors in Britain.

I urge the new Conservative Party leader to make the government’s response to these proposals a priority, as part of the package of measures needed to bolster the UK’s long term energy security and to bring the longer-term cost of energy down.

With the right policies to unlock investment, the UK can lead the world in energy storage technologies which are urgently needed to keep the lights on, cut carbon emissions and keep us on track to reach net zero.

This article was first published by Business Green

Getting Britain ready for the next generation of energy projects

Key takeaways:

  • As the UK continues to expand its renewable capacity the cost of curtailing wind generation at times of low demand is increasing, adding £806 million to bills over the last two years.
  • Curtailment costs arise from the grid paying to turn down generation due to energy balancing or system balancing issues.
  • Long-duration storage, such as pumped storage hydro, offers a way to absorb excess wind power, reducing the cost of keeping the system balanced.
  • Drax’s plans to expand Cruachan Power Station would increase the amount of excess power it can absorb from 400 MW to over one gigawatt, and rapidly deliver the same amount back to the grid when needed.
  • New financial mechanisms, such as a cap and floor regime, are needed to enable investors to back capital-intensive, long-term projects that will save consumers and the grid millions.

Meeting big ambitions takes big actions. And there’re few ambitions as big, or as urgent, as achieving a net zero power sector by 2035.

This energy transition must mean more low carbon power sources and fewer fossil fuels. But delivering that future requires new ways of managing power, balancing the grid and a new generation of technologies, innovation, and thinking to make big projects a reality.

As the system evolves and more renewables, particularly wind, come online, the UK is forecast to need 10 times more energy storage to deliver power when wind-levels drop, as well as absorb excess electricity when supply outstrips demand, and to maintain grid stability. Pumped hydro storage offers a tried and tested solution, but with no new long-duration storage projects built for almost 40 years in the UK, the challenges of bringing long-term projects to fruition are less engineering than they are financial.

Drax’s plan to expand Cruachan Power Station to add as much as 600 megawatts (MW) of additional capacity will help support a renewable, more affordable, net zero electricity system. But government action is needed to unlock a new generation of projects that deliver electricity storage at scale.

Reigning in excess wind power

Wind is the keystone power source in the UK’s renewable ambitions. Wind capacity increased from 5.4 GW in 2010 to 25.7 GW in 2021 – enough to provide renewable power for almost 20 million homes – and the government aims to increase this to 50 GW by 2030.

However, wind comes with challenges: the volume of electricity being generated must always match the level of demand. If there is a spike in electricity demand when there are low wind-levels, other technologies, such as electricity storage or carbon-emitting gas power, are required to make up the shortfall.

Conversely, if there is too much wind power being generated and not enough demand for electricity the grid often has to pay windfarms to stop generating. This is known as wind curtailment and it’s becoming more expensive, growing from £300 million during 2020 to more than £500 million in 2021.

An independent report by Lane Clark & Peacock (LCP), by Drax, found that over the last two years curtailing wind power added £806 million to energy bills in Britain.

There can also be a carbon cost to curtailing wind power. As more intermittent renewables come onto the system the grid can become more unstable and difficult to balance. In such an event the National Grid is required to turn to fossil fuel plants, like gas generation, that can deliver balancing and ancillary services like inertia, voltage control and reserve power that wind and solar can’t provide.

“It’s lose-lose for everyone,” says Richard Gow, Senior Government Policy Manager at Drax. “Consumers are paying money to turn off wind and to turn up gas generation because there’re not enough sources of ancillary services on the system or renewable power can’t be delivered to where it’s needed.”

“Curtailment costs have spiked this year because of gas prices, and while they might dip in the next two or three years, curtailment costs are only ever going to increase. If there’s wind power on the system without an increase in storage, the cost of managing the system is only going to go up and up.”

Source: the LCP’s ‘Renewable curtailment and the role of long duration storage’ report, click to view/download here.

The proposed Cruachan 2 expansion would help the grid avoid paying to turn off wind farms by increasing the amount it would be able to absorb from 400 MW to over 1,000 MW, and rapidly deliver the same amount of zero carbon power back to the grid should wind levels suddenly drop or the grid need urgent balancing.

Adding this kind of capability is a huge engineering project, involving huge new underground caverns, tunnels and waterways carved out of the rock below Ben Cruachan. However, the challenge in such a project lies less with the scale of the engineering than with its financeability.

From blueprints to real change

The original Cruachan Power Station’s six-year construction period began in 1959. The work of digging into the mountainside was carried out by a team of 1,300 men, known affectionately as the Tunnel Tigers, armed with hand drills and gelignite explosives in an era before modern health and safety practices.

Engineer working at Cruachan Power Station

Expanding Cruachan in the 21st century will be quite a different, and safer process, and one that’s practically, straightforward.

“There is no reason why we physically couldn’t build Cruachan 2,” says Gow. “Detailed engineering work has indicated that this is a very feasible project. There’s no technological reason or physical constraint that would prevent us. It has a large upfront cost, and requires drilling into a mountain, but the challenge is much more on the financial, particularly securing the investment, side of the project.”

Pumped storage hydro facilities today generate their revenues from three different markets: the capacity market, where they receive a flat rate per kilowatt they deliver to the grid; the wholesale and balancing market, where they buy power to store when it’s abundant and cheap and sell it back to the grid when it’s needed, more valuable and used to support the Electricity System Operator in matching supply and demand on a second-by-second basis; and through ancillary services contracts, dedicated to specific stability services.

These available markets present challenges for ambitious, capital-intensive projects designed to operate at scale. With the exception of the capacity market, revenues from these markets are often volatile and difficult to forecast, with no long-term contracts available.

Sourcing the investment needed to build projects on the scale of Cruachan 2 requires mechanisms to attract investors comfortable with long project development lead times that offer stable, low risk, rates of return in the long-term.

Cap and floor

An approach that can provide sufficient certainty to investors that income will cover the cost of debt and unlock finance for new projects is known as a ‘cap and floor’ regime.

With cap and floor, a facility’s revenues are subject to minimum and maximum levels. If revenues are below the ‘floor’ consumers would top-up revenues, while earnings above the ‘cap’ would be returned to consumers. This means investors can secure upfront funding safe in the knowledge of revenue certainty in the long term, whilst also offering protection to consumers.

Such an approach won’t attract investors looking to make a fast buck, but the vital role that it could play in the ongoing future of the UK energy system offers a long-term, stable return. At the same time, the system would save both the grid and energy consumers hundreds of millions of pounds.

The cap and floor system is also not unique, with a similar approach currently used for interconnectors, the sub-marine cables that physically connect the UK’s energy system to nearby countries allowing the UK to trade electricity with them. This means investors are already familiar with cap and floor structures, how they operate and what kind of returns they can expect.

“It’s not just pumped storage hydro that this could apply to,” explains Gow. “There are other, different large-scale, long-duration storage technologies that this could also apply to.”

“It would give us revenue certainty so that we can invest to support the system and reduce the cost of curtailment while ensuring consumers get value for their money.”

The Turbine Hall inside Cruachan Power Station

Cruachan was originally only made possible through the advocacy and actions of MP and wartime Secretary of State for Scotland Tom Johnston. Then it was needed to help absorb excess generation from the country’s new fleet of nuclear power stations and release this to meet short term spikes in demand. Today it’s renewable wind the system must adapt to.

For the UK to continue to meet an ever-changing energy system the government must be prepared to act and enable projects at scale, that bring long-term transformation for a net zero future.

Cruachan Power Station: Protecting biodiversity while generating power

Key points:

  • The Scottish Highlands are home to a wide variety of landscapes, with a wealth of biodiversity that must be preserved.
  • Cruachan pumped storage hydro station sits within Ben Cruachan and has operated for nearly 60-years without damaging wildlife.
  • Regular surveys and reporting allow Drax to understand the health of different fauna and species over time.
  • It’s promising that even species of bird and insects that are declining in other parts of the UK are regularly spotted around Cruachan.
  • The expansion of the power station has required and will continue to need careful assessment of the area’s biodiversity to minimise any impact the project could cause.

The Scottish Highlands are home to some of the UK’s most stunning natural wonders. From dramatic plunging lochs to the craggy, ice capped Munros, the varied landscape holds some of the most biodiverse areas in the UK. The region’s fauna ranges from red deer to golden eagles, while its flora includes the ancient oak and moss-covered forests that make up the ‘temperate rainforest’ of the Atlantic coast.

Preserving these landscapes and the life that thrives in them is crucial to both the environment and economy of the region. It’s the job of Roddy Davies, Health, Safety, and Environmental Advisor at Drax’s Cruachan Power Station to ensure operations at the site do not damage the natural environment.

“This is a very biodiverse, rich environment. There are a lot of different species, a large variety of natural habitats and plant life,” says Davies. “It’s good that we can say we’ve operated here for nearly 60 years, and all of that is still there. It’s testament that we don’t have a demonstrable negative effect on the wildlife that lives around us.”

Source: Blue Leaf Nature

Energy storage inside a mountain

The pumped storage hydro station sits a kilometre inside Ben Cruachan, a Munro peak in the Western Highland region of Argyll and Bute. It’s not an area you would normally associate with power generation, but it’s perfect for pumped storage hydro. The site has two bodies of water at differing elevations, Loch Awe at the bottom and a reservoir at the top allowing Cruachan to generate power when it’s needed, as well as absorb electricity when there is an excess on the grid by pumping water back up the mountain. Storing it until power is needed and helping to keep the grid balanced.

The subterranean nature of the power station means the massive machinery, including the four reversible turbines, and the heat and noise they generate, is hidden underground.

Features on the surface are limited to a few buildings by the entrance tunnel at the banks of Loch Awe, and the dam which contains the upper reservoir on the slopes of Ben Cruachan, as well as several pylons and cables transporting electricity. Even the 316-metre buttress dam takes the landscape into account.

“When Cruachan was built in the ’50s and ’60s, the visual impact of it was very much in the minds of the people who built it and the authorities who approved it. The dam is almost impossible to see from a public place,” explains Davies. “Our presence on the surface is very limited. All the busy goings-on are underground. There’s lots of noise underground, but it doesn’t travel outside.”

Ensuring that the area surrounding Drax’s operation continues to function without damaging the surrounding environment is an ongoing process. Davies deploys annual biodiversity surveys and reporting that gives Drax over a decade of information and analysis to help identify trends.

The wildlife of Ben Cruachan

The Cruachan Power Station Biodiversity Survey for 2021 is the 11th completed by Blue Leaf Nature, a biodiversity service provider. The comprehensive report highlights the incredible diversity of fauna surrounding Cruachan, some of which are declining in other parts of the country.

While the majestic red stags found in other parts of the Highlands are extremely uncommon around Cruachan, 2021 was a particularly exciting year for other types of large mammals. Pine martens – a cat-sized relative of the weasel – are relatively common, appearing alongside red squirrels, red foxes, and otters. Badgers were also added to the site’s list of species for the first time.

Source: Blue Leaf Nature

Mammals, however, are exceeded by the range of birds found around Cruachan, with 53 different species spotted in 2021. Of these, 17 species appear on the Birds of Conservation Concern Five’s red list, the highest threat status to the UK’s bird population, including the Ring Ouzel, Yellowhammer and Tree Pipet. A further 27 appear on the Regional International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. Additionally, six of the spotted species are considered endangered (including Herring Gull and Northern Wheatear) and 11 vulnerable by the IUCN.

Sightings of these threatened species around Cruachan come despite particularly unfavourable weather in 2021. One of the driest Aprils on record followed by an exceptionally wet May disrupted the bird breeding season. This in turn resulted in a difficult nesting season, exacerbated by food shortages due to the weather’s effect on insect life.

In the report’s survey of invertebrates, 150 different species were recorded in 2021, down from 170 in 2018. However, it’s promising that among Cruachan’s creepy-crawlies are many that are in decline elsewhere in the UK, with the numbers of some important insect types are increasing. Dragonfly and damselfly species, for example, increased from five in the previous survey to nine in 2021.

Moths and butterflies are particularly important to monitor, as Davies explains: “they’re a very strong indicator species for the health and quality of an ecosystem. They’re also very sensitive to climatic changes and  react quickly to temperature change.”

Source: Blue Leaf Nature

In 2021, 78 moth species were recorded around Cruachan, including one of Butterfly Conservation’s noted priority species (Yellow-ringed carpet), as well as six species that feature on IUCN’s red or amber lists. There were 11 butterfly species recorded in 2021, including four priority species, as well as two newly spotted species: the Small Copper and the Chequered Skipper.

That species in decline around the country are increasingly thriving at Cruachan is further testament to the power station’s lack of disruption to the environment. And as the UK’s electricity system continues to evolve, and Cruachan power station with it, closely observing the surrounding environment and its inhabitants will become even more important.

Expanding Cruachan while preserving nature

While Cruachan first started generating and storing power in the 1960s, its capabilities are becoming ever more critical as the national grid decarbonises and power generation becomes increasingly decentralised. This is why Drax is undertaking an ambitious project to expand Cruachan.

Cruachan 2 would add a further 600 MW of generation capacity to the plant for a total of 1.04 GW of power. By providing stability services to the grid, the expansion could enable an additional 300-gigawatt hours of renewable power to come online.

Source: Blue Leaf Nature

The project is epic in scale. New underground tunnels and subterranean caverns will house the reversible pump-turbines and will be carved out of the mountain, vastly increasing the size of the power station. But as with any activity in such a landscape, careful planning is essential. Detailed surveys and assessments of the area are a key requirement for planning approval.

“We need to acknowledge what’s here and show that we understand what surveys have found,” says Davies. “Then we have to present our proposals for how we will protect them and mitigate any potential disturbance.”

An advantage of pumped storage hydro is that much of the intensive excavating and construction work will take place underground, with little disturbance on the surface. Cruachan 2 has the added benefit of utilising Cruachan’s existing infrastructure. For example, it would not require flooding a valley to create a new upper reservoir.

Ultimately, Cruachan’s half century-plus of operation has not damaged or degraded the biodiversity of the Western Highlands landscape. And Davies is keen to ensure that legacy is preserved: “As a company, it’s not just something we have to do; we have a moral responsibility to be a responsible operator and look after what’s around us.”

View the Cruachan Power Station Biodiversity Survey 2021 here and find out more about Green Tourism at Cruachan here

Storage solutions: 3 ways energy storage can get the grid to net zero

Key points:

  • Energy storage plays a crucial role in the UK electricity system by not only providing reserve power for when demand is high but also absorbing excess power when demand is low.
  • The UK’s electricity system’s growing dependency on intermittent renewables means the amount of energy storage needed will increase to as much as 30 GW by 2050.
  • There are three different durations of energy storage needed to help balance the grid: short-term, day-to-day and long term.
  • It will take a range of technologies including batteries, pumped storage hydro and new approaches to meet the storage demands of a net zero grid.

When you turn on a lightbulb – in 10, 20, or 30 years – the same thing will happen. Electricity will light up the room. But where that electricity comes from will be different. As the country moves toward net zero emissions, low carbon and renewable power sources will become the norm. However, it’s not as simple as swapping in renewables for the fossil fuels the grid was built around.

Weather dependant sources, like wind and solar, are intermittent – meaning other sources are needed at times when there’s little wind or no sunshine to meet the country’s electricity demand. Equally as challenging to manage, however, is what to do when there’s an excess of power being generated at times of low demand.

Energy storage offers a low carbon means of delivering power at times of low supply, as well as absorbing any excess of generated power when demand is low, helping to balance and stabilise the grid. As the electricity system transforms through a range of low-carbon and renewable technologies, the amount of energy storage on the UK grid will need to expand from 3 GW of today to over 30 GW in the coming decades.

The storage solution

Even as the UK’s electricity system transforms, from fossil fuels to renewables, the way the grid operates remains primarily the same. Central to that is the principle that the supply of electricity being generated must always match the demand on a second-by-second basis.

Too little or too much power on the system can cause power outages and damage equipment. National Grid needs to be able to call on reserve power sources to meet demand when supply is low or pay to curtail renewable sources’ output when demand drops. During the summer of 2020, for example, lower demand due to Covid-19 coupled with high renewable output resulted in balancing costs 40% above expectations.

“There is a lot of offshore wind coming online in Scotland, as much as 11 GW by 2030 and a further 25 GW planned,” explains Steve Marshall, a Development Manager at Drax.

Offshore wind farm along the coast of Scotland

“It’s great because it increases the amount of renewable power on the system, but the transmission lines between Scotland and England can become saturated as much as 30-40% of the time because there is too much power.”

Electricity storage can provide a source of reserve power, as well as absorb excess electricity. These capabilities are crucial for balancing the grid and ensuring that frequency remains within a stable operating range of 50 Hertz, as well as providing other ancillary services.

Whether it’s absorbing power or delivering electricity needed to keep the grid stable, in energy storage, timing is everything.

There are three main time periods electricity storage needs to operate over:

  1. Fast-acting, short term electricity

Because electricity supply must always match demand, sudden changes mean the grid needs to respond immediately to ensure frequency and voltage remain stable, and electricity safe to use.

Batteries are considered the fastest technology for responding to a sudden spike in demand or an abrupt loss of supply.

Battery technology has evolved rapidly in recent decades as innovations like lithium-ion batteries, such as those used in electric cars, and emerging solid-state batteries become more affordable and more commonplace. This makes it more feasible to deploy large-scale installations that can absorb and store excess power from the grid.

“Batteries are good for near-instantaneous responses. It can be a matter of milliseconds for a battery to deploy power,” says Marshall. “If there’s a sudden problem with frequency or voltage, batteries can respond – it’s something that’s quite unique to them.”

The speed at which batteries can deploy and absorb electricity makes them useful grid assets. However, even very large battery setups can only discharge power for around two hours. If, for example, the wind dropped off for a long period the grid needs a longer-duration supply of stored power.

  1. Powering day-to-day changes in supply, demand, and the grid

When it comes to managing the daily variations of supply and demand the grid needs to be able to call on reserves of power for when there are unexpected changes in the weather or electricity demand from users. Pumped storage hydro power offers a low carbon way to provide huge amounts of electricity, quickly and for periods that can last as long as eight or even 24 hours.

The technology works by moving water between two reservoirs of water at different elevations. When there is demand for electricity water is released from the upper reservoir, which rushes down a series of pipes, spinning water turbines, generating electricity. However, when there is an excess of power on the electricity system the same turbines can reverse and absorb electricity to pump water from the lower to the upper reservoir, storing it there as a massive ‘water battery’.

Pumped storage hydro is a long-established technology, having been developed since the 1890s in Italy and Switzerland. In the UK today there are four pumped storage hydro power stations in Scotland and Wales, with a total capacity of 2.8 GW.

Among those is the Drax-owned Cruachan Power Station in the Scottish Highlands. The plant is made up of four generating/pumping turbines located inside Ben Cruachan between Loch Awe and an upper reservoir holding 10 million cubic metres of water.

Turbine Hall at Cruachan Power Station

Pumped hydro storage facilities can rapidly begin generating large volumes of power in as little as 30 seconds or less. The ability to switch their turbines between different modes – pump, generate, and spin mode to provide inertia to the gird without producing power – make pumped storage hydro plants versatile assets for the gird.

“How Cruachan operates depends on weather,” says Marshall. “We make as many 1000 mode changes a month, that’s how frequently Cruachan is called on by National Grid.”

As the electricity system transforms there will be a greater need for flexible energy storage like pumped storage hydro, this is why Drax is kickstarting plans to expand Cruachan Power Station, however, the specific conditions needed for such facilities can make new projects difficult and expensive.

Cruachan 2, to the east of the original power station, will add up to 600 MW in generating capacity, more than doubling the site’s total capacity to more than 1GW. By increasing the number of turbines operating at the facility it increases the range of services that the grid can call upon from the site.

  1. Long-term electricity solutions

However, storage technologies as they exist today cannot alone offer all the solutions the UK will need to achieve its net zero targets. While technologies like pumped storage can generate for the better part of a day, longer periods of unfavourable conditions for renewables will need new approaches.

In March 2021, for example, the UK experienced its longest cold and calm spell in more than a decade, with wind farms operating at just 11% of their capacity for 11 days straight, according to Electric Insights.

The shortfall in the country’s primary source of renewable power was made up for by gas power stations. But in a net zero future, such responses will only be feasible if they’re part of carbon capture and storage systems or replaced by other carbon neutral or energy storage solutions.

Generating enough power to supply an electrified future, as well as being able to take pressure off the grid and provide balancing services will require a range of technologies working in tandem over extended periods.

Interconnectors with neighbouring countries, for example, can work alongside storage solutions to shed excess power to where there is greater demand. Similarly, rather than curtailing wind or solar power, extra electricity could be used for electrolysis to produce hydrogen. Other functions may include demand side response where heavy power users are incentivised to reduce their electricity usage during peak periods helping to reduce demand.

To achieve stable, reliable, net zero electricity systems the UK needs to act now to not only replace fossil fuels with renewables but put the essential energy storage and balancing solutions in place, that means electricity is there when you turn on a lightbulb.

Expanding Cruachan: An epic energy storage project to help unlock a renewable future

Loch Awe from Cruachan

At the beginning of March 2021, Britain experienced its longest ‘wind drought’ in a decade. For eleven days, wind output averaged just 11% of the UK electricity mix – less than a quarter of the average output in the month before and the month after. The power system was able to cope as gas power stations made up most of the shortfall.

But keeping the lights on will become increasingly challenging as electricity generation shifts from carbon-intensive coal and gas towards weather-dependent wind and solar technologies, where supply is variable and intermittent. One solution to maintain a stable, resilient power supply as the electricity system decarbonises is increasing the amount of long-duration energy storage that can plug gaps and balance the gird.

Pumped hydro storage – a tried and tested solution

The largest-capacity form of electricity storage by far, pumped storage hydro plays a key role in the energy mix and stabilising the grid. Which is why, following a feasibility study, Drax has kickstarted plans to extend our pumped hydro storage power station at Cruachan in the Scottish Highlands.

By drilling a second cavern inside Ben Cruachan, Cruachan 2, to the east of the original power station, will add up to 600 MW in generating capacity, more than doubling the site’s total capacity to more than 1GW. It’s an epic project and one that could provide power for around a million homes.

The original Cruachan facility has been supplying and absorbing excess power to the grid since 1965. Acting as a ‘green battery’, it stores low-carbon energy when there is over supply and releases it when demand is high.

Designed at a time when the grid was powered by nuclear or coal-fired plants that could only adjust output slowly, Cruachan’s technology is still cutting edge and has proved equally successful at balancing more volatile supply and demand as power generation has shifted towards renewables and low-carbon sources.

“Cruachan plays a critical role in the UK energy system today because it provides a unique range of services for a single asset – it can both generate electricity at 440 MW but it can also pump which means it takes that power off the system so in effect you can deploy greater renewable resources. And if there’s too much wind in the system, rather than curtail wind farms you can pump to take 482 MW off the system,” says Steve Marshall, Development Manager at Cruachan 2.

Cruachan Power Station

Pumped Storage Hydro (PSH) at Cruachan Power Station [click to view/download]

Enabling more renewables on the system

As Marshall points out, too much wind can be as problematic as too little. With the government’s ambition to quadruple offshore wind capacity by 2030 to 40 gigawatts (GW), the grid will have to manage significantly more wind-generated power, and consequently much greater fluctuations in supply.

Currently, the demand left to be met by renewable generation ranges from 10 GW to 30 GW throughout the year. But modelling by Imperial College London suggests that with 40 GW of offshore wind this range could expand, from 30 GW right down to minus 30 GW, in other words, renewables would produce significantly more than national demand. Without long-term storage capacity, this energy will be wasted, forcing the grid to pay wind farms to stop generating.

“There’s a lot of offshore wind coming online in Scotland that has to be transported through the transmission system to England where the demand is,” says Marshall. “The transmission system in 2030 could become saturated more than 20-30% of the time because there’s too much renewable power. You have a choice: either build more transmission lines or more energy storage that can take that power off the system.”

Turbine Hall at Cruachan Power Station

Plugging the inertia gap

As well integrating more renewables into the electricity mix, the Cruachan expansion may also help meet the inertia shortfall. Inertia – stored kinetic energy – acts as a ‘shock absorber’ in the system, smoothing out sudden changes in power supply and demand and ensuring that frequency remains stable at 50 Hz. This is a critical, as just 1% variation above or below this standard can damage equipment and infrastructure.

Many renewable technologies, such as wind turbines and solar PV panels, aren’t built around spinning turbines that synchronise with the grid and so lack inherent inertia. Cruachan’s turbines, on the other hand, spin at 500/600rpm and produce electricity at the grid frequency of 50 Hz providing inertia that helps the grid remain stable. Indeed in 2020, National Grid ESO contracted a unit at Cruachan to provide inertia 24/7 as part of a 6 year contract

“The grid calls on Cruachan three to four hundred times a month, with generation mode changes ranging from hours to very short bursts,” explains Marshall. Increasing the number of turbines would allow Cruachan to respond to a greater range of the grid’s needs.

With more units you have more flexibility,” says Marshall. “If you start to change the generating unit sizes to 150 MW or 200MW machines you get different levels of inertia that offers more options to the grid.”

Building on Cruachan’s legacy

While automated drilling processes mean that the rock will no longer need to be excavated by ‘Tunnel Tigers’, the crews that hand-drilled, blasted, and excavated granite from the mountainside, Cruachan 2 will still create an estimated 300 jobs during peak construction and support around 900 jobs across the country. And by bringing around 300 GW a year of renewable energy to the grid, and reducing requirement for further transmission lines the expansion has the potential to save consumers more than £350 million in energy costs by 2050.

“With the increased deployment of renewables there is a need for more assets like Cruachan,” says Marshall. The ambition is to have Cruachan 2 operational by 2030 and work could start as early as 2024.

But progress is dependent on the government providing support through a revenue stabilisation mechanism for such a long-term, large-scale energy storage project. A study by KPMG found that a Cap and Floor regime, similar to what has unlocked a wave of investment in cross-border inter-connectors, could be the best mechanism for long-duration storage. If this is forthcoming, the expansion could play a vital role in stabilising the grid and smoothing the UK’s transition to a net zero power system.