Author: Alice Roberts

What is a fuel cell and how will they help power the future?

A model fuel cell car

NASA Museum, Houston, Texas

How do you get a drink in space? That was one of the challenges for NASA in the 1960s and 70s when its Gemini and Apollo programmes were first preparing to take humans into space.

The answer, it turned out, surprisingly lay in the electricity source of the capsules’ control modules. Primitive by today’s standard, these panels were powered by what are known as fuel cells, which combined hydrogen and oxygen to generate electricity. The by-product of this reaction is heat but also water – pure enough for astronauts to drink.

Fuel cells offered NASA a much better option than the clunky batteries and inefficient solar arrays of the 1960s, and today they still remain on the forefront of energy technology, presenting the opportunity to clean up roads, power buildings and even help to reduce and carbon dioxide (CO2) emissions from power stations.

Power through reaction

At its most basic, a fuel cell is a device that uses a fuel source to generate electricity through a series of chemical reactions.

All fuel cells consist of three segments, two catalytic electrodes – a negatively charged anode on one side and a positively charged cathode on the other, and an electrolyte separating them. In a simple fuel cell, hydrogen, the most abundant element in the universe, is pumped to one electrode and oxygen to the other. Two different reactions then occur at the interfaces between the segments which generates electricity and water.

What allows this reaction to generate electricity is the electrolyte, which selectively transports charged particles from one electrode to the other. These charged molecules link the two reactions at the cathode and anode together and allow the overall reaction to occur. When the chemicals fed into the cell react at the electrodes, it creates an electrical current that can be harnessed as a power source.

Many different kinds of chemicals can be used in a fuel cell, such as natural gas or propane instead of hydrogen. A fuel cell is usually named based on the electrolyte used. Different electrolytes selectively transport different molecules across. The catalysts at either side are specialised to ensure that the correct reactions can occur at a fast enough rate.

For the Apollo missions, for example, NASA used alkaline fuel cells with potassium hydroxide electrolytes, but other types such as phosphoric acids, molten carbonates, or even solid ceramic electrolytes also exist.

The by-products to come out of a fuel cell all depend on what goes into it, however, their ability to generate electricity while creating few emissions, means they could have a key role to play in decarbonisation.

Fuel cells as a battery alternative

Fuel cells, like batteries, can store potential energy (in the form of chemicals), and then quickly produce an electrical current when needed. Their key difference, however, is that while batteries will eventually run out of power and need to be recharged, fuel cells will continue to function and produce electricity so long as there is fuel being fed in.

One of the most promising uses for fuel cells as an alternative to batteries is in electric vehicles.

Rachel Grima, a Research and Innovation Engineer at Drax, explains:

“Because it’s so light, hydrogen has a lot of potential when it comes to larger vehicles, like trucks and boats. Whereas battery-powered trucks are more difficult to design because they’re so heavy.”

These vehicles can pull in oxygen from the surrounding air to react with the stored hydrogen, producing only heat and water vapour as waste products. Which – coupled with an expanding network of hydrogen fuelling stations around the UK, Europe and US – makes them a transport fuel with a potentially big future.

Fuel cells, in conjunction with electrolysers, can also operate as large-scale storage option. Electrolysers operate in reverse to fuel cells, using excess electricity from the grid to produce hydrogen from water and storing it until it’s needed. When there is demand for electricity, the hydrogen is released and electricity generation begins in the fuel cell.

A project on the islands of Orkney is using the excess electricity generated by local, community-owned wind turbines to power a electrolyser and store hydrogen, that can be transported to fuel cells around the archipelago.

Fuel cells’ ability to take chemicals and generate electricity is also leading to experiments at Drax for one of the most important areas in energy today: carbon capture.

Turning COto power

Drax is already piloting bioenergy carbon capture and storage technologies, but fuel cells offer the unique ability to capture and use carbon while also adding another form of electricity generation to Drax Power Station.

“We’re looking at using a molten carbonate fuel cell that operates on natural gas, oxygen and CO2,” says Grima. “It’s basic chemistry that we can exploit to do carbon capture.”

The molten carbonate, a 600 degrees Celsius liquid made up of either lithium potassium or lithiumsodium carbonate sits in a ceramic matrix and functions as the electrolyte in the fuel cell. Natural gas and steam enter on one side and pass through a reformer that converts them into hydrogen and CO2.

On the other side, flue gas – the emissions (including biogenic CO2) which normally enter the atmosphere from Drax’s biomass units – is captured and fed into the cell alongside air from the atmosphere. The CO2and oxygen (O2) pass over the electrode where they form carbonate (CO32-) which is transported across the electrolyte to then react with the hydrogen (H2), creating an electrical charge.

“It’s like combining an open cycle gas turbine (OCGT) with carbon capture,” says Grima. “It has the electrical efficiency of an OCGT. But the difference is it captures COfrom our biomass units as well as its own CO2.”

Along with capturing and using CO2, the fuel cell also reduces nitrogen oxides (NOx) emissions from the flue gas, some of which are destroyed when the O2and CO2 react at the electrode.

From the side of the cell where flue gas enters a CO2-depleted gas is released. On the other side of the cell the by-products are water and CO2.

During a government-supported front end engineering and design (FEED) study starting this spring, this COwill also be captured, then fed through a pipeline running from Drax Power Station into the greenhouse of a nearby salad grower. Here it will act to accelerate the growth of tomatoes.

The partnership between Drax, FuelCell Energy, P3P Partners and the Department of Business, Energy and Industrial Strategy could provide an additional opportunity for the UK’s biggest renewable power generator to deploy bioenergy carbon capture usage and storage (BECCUS) at scale in the mid 2020s.

From powering space ships in the 70s to offering greenhouse-gas free transport, fuel cells continue to advance. As low-carbon electricity sources become more important they’re set to play a bigger role yet.

Learn more about carbon capture, usage and storage in our series:

What makes a mountain right for energy storage

Cruachan pylons

Electricity generation is often tied to a country’s geography, climate and geology. As an island Great Britain’s long coastline makes off-shore wind a key part of its renewable electricity, while Iceland can rely on its geothermal activity as a source of power and heat.

One of the most geographically-influenced sources of electricity is hydropower. A site needs a great enough volume of water flowing through it and the right kind of terrain to construct a dam to harness it. Even more dependent on the landscape is pumped hydro storage.

Pumped storage works by pumping water from one source up a mountain to a higher reservoir and storing it. When the water is released it rushes down the same shafts it was pumped up, spinning a turbine to generate electricity. The advantage of this is being able to store the potential energy of the water and rapidly deliver electricity to plug any gaps in generation, for example when the wind suddenly dropsor when Great Britain instantly requires a lot more power.

This specific type of electricity generation can only function in a specific type of landscape and the Scottish Highlands offers a location that ticks all the boxes.

The perfect spot for pumped storage

Cruachan Power Station, a pumped hydro facility capable of providing 440 megawatts (MW) of electricity, sits on the banks of Loch Awe in the Highlands, ready to deliver power in just 30 seconds.

“Here there is a minimum distance between the two water sources with a maximum drop,” says Gordon Pirie, Civil Engineer at Cruachan Power Station, “It is an ideal site for pumped storage.”

The challenge in constructing pumped storage is finding a location where two bodies of water are in close proximity but at severely different altitudes.

From the Lochside, the landscape rises at a dramatic angle, to reach 1,126 metres (3,694 feet) above sea level at the summit of Ben Cruachan, the highest peak in the Argyll. The crest of Cruachan Dam sits 400.8 metres (1,315 feet) up the slopes, creating a reservoir in a rocky corrie between ridges. The four  100+ MW turbines, which also act as pumps, lie a kilometre inside the mountain’s rock.

“The horizontal distance and the vertical distance between water sources is what’s called the pipe-to-length ratio,” explains Pirie. “It’s what determines whether or not the site is economically viable for pumped storage.”

The higher water is stored, the more potential energy it holds that can be converted into electricity. However, if the distance between the water sources is too great the amount of electricity consumed pumping water up the mountain becomes too great and too expensive.

The distance between the reservoir and the turbines is also reduced by Cruachan Power Station’s defining feature: the turbine hall cavern one kilometre inside the mountain…

Carving a power station out of rock

The access tunnel, cavern and the networks of passageways and chambers that make up the power station were all blasted and drilled by a workforce of 1,300 men in the late 1950s to early 1960s, affectionately known as the Tunnel Tigers.

This was dangerous work, however the rock type of the mountainside was another geographic advantage of the region. “It’s the diorite and phyllite rock, essentially granite, so it’s a hard rock, but it’s actually a softer type of granite, and that’s also why Cruachan was chosen as the location,” says Pirie.

The right landscape and geology was essential for establishing a pumped storage station at Cruachan, however, the West Highlands also offer another essential factor for hydropower: an abundance of water.

Turning water to power

The West Highlands are one of the wettest parts of Europe, with some areas seeing average annual rain fall of 3,500 millimetres (compared to 500 millimetres in some of the driest parts of the UK). This abundance of water from rainfall, as well as lochs and rivers also contributes to making Cruachan so well-suited to pumped storage.

The Cruachan reservoir can contain more than 10 million cubic metres of water. Most of this is pumped up from Loch Awe, which at 38.5 square kilometres is the third largest fresh-water loch in Scotland. Loch Awe is so big that if Cruachan reservoir was fully released into the loch it would only increase the water level by 20 centimetres.

However, the reservoir also makes use of the aqueduct system made up of 19 kilometres of tunnels and pipes that covers 23 square kilometres of the surrounding landscape, diverting rainwater and streams into the reservoir. Calculating quite how much of the reservoir’s water comes from the surrounding area is difficult but estimates put it at around a quarter.

“There are 75 concrete intakes dotted around the hills to gather water and carry it through the aqueducts to the reservoir,” says Pirie. “The smallest intake is about the size of a street drain in the corner of a field and the largest one is about the size of a three-bedroom house.”

Pumped storage stations offer the electricity system a source of extra power quickly but it takes the right combination of geographical features to make it work. Ben Cruachan just so happens to be one of the spots where the landscape makes it possible.

Is there such a thing as energy ‘terroir’?

‘Terroir’ comes from the French word ‘terre’, meaning land, earth or soil. In the French wine industry, it refers to the land from which grapes are grown. It is believed the terroir gives the grapes a unique quality specific to that particular growing site.

Terroir dictates the type of wine that comes from a region – it’s the reason we call one bottle a Bordeaux, and another a Côtes Du Rhone.

But could the idea of terroir hold relevance beyond just wine? What if we looked at electricity in the same way?

Certain environments are better placed to produce certain types of electricity.

These are some of the regions making the most of their unique location and landscape to produce electricity that makes sense for them.

La Rance tidal barrage

Brittany, France

Brittany boasts one third of mainland France’s coasts, and has long been a top destination for surfers, with waves as high as 7.6 metres in some places. With such tempestuous waters, it’s the perfect location for La Rance Tidal Power Station –the world’s first station of its kind. Opened in 1966, the site was chosen because it has the highest tidal range in France.

Tidal barrages like La Rance harness the potential energy in the difference in height between low and high tides.

The barrage creates an artificial reservoir to enable different water levels, which then drives turbines and generators to produce electricity.

While the station has been operating for close to 50 years, old tidal mills are still dotted around the Rance river, some dating back to the 15th century – proof that tidal power has deep roots in this region.

Xinjiang, China  

Whilst China may have some of the world’s most polluted cities, it is also the world’s biggest producer of renewable energy – including wind power. With one of the largest land masses on the planet, one in every three of the world’s wind turbines is in China, with the government installing one per hour in 2016.

In places like Xinjiang, China’s most westerly province, the windy weather used to be a nuisance, with overturned lorries and de-railed trains being a regular sight. This is caused by mountain ranges between Dabancheng and Ürümqi which form a natural wind tunnel, increasing the wind speed as air passes through. These days the region is harnessing this same wind to produce incredible amounts of electricity – with 27.8 terwatt hours (TWh) of electricity coming from the region in the first nine months of 2018.

Onshore wind farm in Xinjiang

Xinjiang local Wu Gang founded Goldwind to build China’s first windfarm here in the 1980s. Today it’s the world’s second largest turbine maker. The turbines work on a simple premise: wind turns the turbine blades which are connected to a rotor, causing it to spin. This in turn is connected to a generator, which takes the wind’s kinetic energy to produce electricity.

Hengill, Iceland

Iceland sits where the North American and Eurasian tectonic plates meet, meaning that magma rises close to the surface, bringing with it a lot of energy potential. One example of how the Icelandic people are harnessing this power is The Hellisheiði, the second largest geothermal power station in the world.

Here, high-pressure geothermal steam is extracted from 30 wells, ranging from 2,000 to 3,000 metres deep, and is used to turn turbines and generate electricity. This renewable plant has a capacity of 303 megawatts (MW) of electricity, which is used to power the capital city of Reykjavik.

The site was chosen due to its location in the Hengill volcanic area in the south of Iceland, one of the most active geothermal areas on the planet. Here, a giant magma chamber sits underground, with thousands of hot springs above. According to Iceland’s National Energy Authority, geothermal power from sites like this accounts for 25% of the country’s electricity production and 66% of primary energy usage.

But Icelanders aren’t only using the geothermal landscape for energy production – chefs here can cook food simply by burying it in the ground, producing delicacies like rúgbrauð, which translates as ‘hot spring bread’.

Ouarzazate, Morocco

From Iceland’s below-zero temperatures to Morocco, a popular holiday destination for sun-seekers, with 330 days of sunshine a year. Morocco lays claim to a chunk of the Sahara Desert, famously known as one of the hottest climates in the world. Where better, then, to situate the world’s largest solar thermal power plant?

Noor solar thermal plant

The Moroccan city of Ouarzazate, nicknamed the ‘door of the desert’ plays host to the huge Noor Complex, which is still under construction and is being implemented in four parts. The latest piece of the puzzle is Noor III, which was hooked up to Morocco’s electricity grid last year. Here, 7,400 mirrors reflect sun rays onto Noor III’s tower, the highest solar-thermal tower in the world, concentrating at the top of the building to create around 500ºC of heat. This heats up the molten salts inside the tower, which travel through a series of pipes, creating high pressure steam. This steam then moves a turbine to generate electricity.

Molten salts are used at Noor III because they can operate at high temperatures and store heat effectively, so that the site can continue to produce energy for up to 7.5 hours when there’s no sun. Once up and running, the plant will generate enough energy to power 120,000 homes with no atmospheric emissions of carbon dioxide (CO2). Along with the other projects at the Noor Complex, Noor III is helping Morocco to achieve its goal of obtaining 42% of its power from renewable sources by 2020.

Ben Cruachan, Scotland

The sun rays that shine on the Noor Complex are few and far between in the Highlands, but there are mountains a-plenty – Ben Cruachan being one of them. Ben Cruachan is the highest point in the Argyll and Bute area of Scotland and is right next to the picturesque Loch Awe. This provides the backdrop for the world’s first high head reversible pumped-storage hydro scheme, built by British engineer Edward McColl over 50 years ago.

Cruachan Power Station’s reservoir and Loch Awe, viewed from the top of Ben Cruachan

With the help of a 4,000-strong army of workers nicknamed the Tunnel Tigers, McColl turned the slopes of Ben Cruachan into a geological battery which Great Britain still relies on today.

It works by using excess electricity on the national grid to pump water from Loch Awe at the foot of the mountain up to the Cruachan Reservoir 300 metres above. During times of heightened demand – like when everyone puts the kettle on during a Coronation Street ad break or when the wind speed suddenly drops around breakfast time – this water is released back down the mountain to turn the turbines that live inside the hollowed mountain.

In this way, Cruachan Power Station can meet the nation’s energy needs within seconds, whereas gas or nuclear stations would take many tens of minutes or hours to reach such capacity.

While Ben Cruachan lends itself perfectly to this pumped-storage hydro facility, it is only one of four such sites in the UK. The challenge in installing more is that there are only a few sites which are mountainous with suitably large bodies of water nearby – things that are inherently necessary for pumped-storage hydroelectricity.

The growing importance of ‘terroir’

All of these places embrace the land around them to produce energy in inventive ways, and as levels of decarbonisation grow around the world, there are an increasing number of places using what’s available close to home for energy solutions.

Take Barbados, a country that has traditionally relied on imported fossil fuels for 96% of its electricity. But with short driving distances and 220 days of pure sunlight every year, the government has seen the potential for electric vehicles run by solar power. With modular solar carports now a regular sight in Barbados, the island has become one of the world’s top users of EVs – preserving the picturesque landscape and reducing its dependence on imported petrol.

Solar panels above an office car park in Barbados

Meanwhile Palau, a small Pacific island nation, is building the world’s largest microgrid, consisting of 35 MW of solar panels and 45 MWh of energy storage. For a nation threatened by rising sea levels, making use of its geographic features allows it to work towards its 70% renewable energy target by 2050 and reduce its reliance on imports.

As more countries continue to move away from fossil fuels, taking advantage of their unique ‘terroir’ will increasingly enable them to produce electricity that works with their landscape.

The different ways water powers the world

If the spectacular Roman aqueducts that still dot the landscape of Europe tell us anything, it’s that hydraulic engineering is nothing new. For thousands of years water power has been used to grind wheat, saw wood, and even tell the time.

Craigside in Northumberland

By the 19th century, water was able to go beyond performing rudimentary mechanical tasks and generate electricity directly. Cragside in Northumberland, England  became the first house powered entirely by hydroelectricity in 1878. By 1881, the whole town of Niagara Falls on the US-Canada border was being powered by the force of its eponymous river and waterfall.

Hydropower has many advantages: it’s predictable, consistent, often zero or low carbon and it can provide a range of ancillary services to power transmission systems. In Great Britain, there is 1.7 gigawatts (GW) of installed hydropower and another 2.8 GW of pumped hydro storage capacity, but it remains a small part of the overall electricity mix. In the fourth quarter of 2018, the 65% of British hydropower that is connected to the national grid accounted for less than one per cent electricity generation or 545,600 megawatt hours (MWh). By contrast, wind accounted for 14% of total generation that quarter (almost 9.5 million MWh).

While hydropower projects can be expensive to construct, operational and maintenance costs are relatively low and they can run for an extremely long time – the Lanark Hydro Electric Scheme in Scotland, which Drax recently acquired, has been producing power since 1927.

Today, hydropower installations are found at all scales, all around the world. But the term hydropower covers many different types of facility. These are some of the ways water is used to generate electricity.

Impoundment power plants

The simplest and most recognisable form of hydropower, impoundment facilities, work by creating a reservoir of trapped water behind a dam that is then selectively released, the water flows through a turbine, spinning it, which in turn activates a generator to produce electricity.

From the Hoover Dam on the Nevada-Arizona border, to the Three Gorges Dam in China – the world’s largest power station of any type, with a generating capacity of 22.5 GW – impoundment dams are some of the most iconic structures in modern engineering.

Three Gorges Dam, China

As well as having the potential to provide large quantities of baseload power, they can react extremely quickly to grid demands – just by opening or closing their floodgates as the power system operator requires.

Run-of-river generation

Rather than storing and releasing power from behind a dam, run-of-the-river generators channel off part of a river and use its natural flow to generate power.

Tongland Power Station, Galloway Hydro Scheme

Because it doesn’t require large dams or reservoirs, run-of-river can be less environmentally disruptive, as there is not always a need for large scale construction and flooding is less common.

Stonebyres Power Station, Lanark Hydro Scheme

While run-of-river facilities tend to be smaller and less flexible than impoundment, they still have significant generating potential – the Jirau hydro-electric power plant on the Madeira river in Brazil has a generating capacity of 3.7 GW.

Pumped storage 

Water can also be good for storing energy that can then be converted to electricity. Pumped hydro storage facilities operate by pumping water uphill to a reservoir when electricity is cheap or plentiful, then letting it flow back downhill through tunnels to a series of turbines that activate generators to generate electricity (in the same way as an impoundment dam) when electricity is in high demand.

Dam and reservoir, Cruachan Power Station

Their ability to both produce and absorb electricity makes them a vital part of electricity networks, playing the role of energy storage systems. In fact, a massive 97% of all global grid storage capacity is in the form of pumped hydro. Their function as giant batteries will only become more important as intermittent renewable sources like wind and solar become more prevalent in the energy mix.

Outlet and loch, Cruachan Power Station.

So too will their ability to ramp up generation very quickly. Drax’s recently acquired Cruachan Power Station in Scotland can go from zero to 100 MW or more in less than 30 seconds when generation is called upon – for example, when there is a sudden spike in demand.   

Tidal range generation

Swansea Bay

The sea is also an enormous source of potential hydropower. Tidal range generation facilities exploit the movement of water levels between and high and low tide to generate electricity. Tidal dams trap water in bays or estuaries at high tide, creating lagoons. The dam then releases the water as the rest of the tide lowers, allowing it to pass through turbines, generating power.

There are limitations – like wind and solar’s dependence on the wind blowing and the level of sunlight, operators can’t control when tides go in or out. But its vast generating potential means that it could be a valuable source of baseload power if it were to be deployed more widely.

Great Britain in particular has major opportunities for tidal generation. The Severn Estuary between England and Wales has the second highest tidal range in the world (15 metres), and a barrage built across the estuary could have a generating capacity of up to 8.6 GW – enough to meet 6% of the Britain’s total electricity demands. Some environmental groups worry about the impact such projects could have on wildlife.

Due to the level of public funding required, the government rejected that plan in 2010, in favour of pursuing its nuclear policy. A second attempt at securing a government-backed investment contract, known as a CfD, for a smaller 320 MW ‘pathfinder’ project in Swansea Bay was also rejected, in 2018. The Welsh government is however supportive of the project, which already has planning permission.

Tidal stream generation

Rather than building a dam, tidal stream generators work like underwater wind turbines. Sturdy propellers or hydrofoils (wing-like blades which oscillate up and down rather than spinning around) are positioned underwater to transform the energy of tidal streams into electricity.

While tidal streams move far slower than wind, the high density of water compared to air means that more power is generated, even at much lower velocities.

Not reliant on large physical structures, tidal stream generators are a relatively cheap form of hydropower to deploy, and make a much smaller impact on their environment than tidal barrages.

Wave generation

Unlike tidal power, which is generated by the gravitational effects of the sun and moon on the Earth’s oceans, wave power ultimately comes from the winds that whip up the ocean’s surface.

There are a number of different methods that turn waves into generation, including funnelling waves into a tube floating on the surface of the water that contains electricity-generating turbines, or by using the vertical bobbing movement of a tethered buoy to pull and spin a fixed generator.

An electricity-generating buoy awaiting installation in Spain

Wave power has yet to be widely implemented, but it has significant potential. It’s estimated that the waves off the coasts of the USA could have provided 66% of the country’s electricity generation needs in 2017 alone. Effectively commercialising wave power could provide another vital tool in developing a sustainable energy landscape for the coming future.

Tidal and wave power generation are less established generation technologies than their land-based cousins but they hold huge potential in delivering more sources of reliable, zero emissions electricity for energy systems in coastal locations around the world.

Supporting our employees’ mental health

It’s a free and confidential 24-hour service which offers support on anything from financial stress and family and relationship issues to addiction, housing concerns or legal information. There is a phoneline and an app and users can be referred for six sessions of counselling per issue, per year.

Opus Energy ran 15 voluntary workshops to help our leaders understand the benefits of this service and they were attended by 113 managers.

As a result of Opus Energy’s initiative first launched in 2017 to train Mental Health First Aiders, we now have 20 employees qualified to offer a first line of response across the business. They are available to all employees should they would want to speak with a peer about any mental health issues.

A further 16 employees will train as Mental Health First Aiders in 2019.

When would you need a battery the size of a mountain?

Turbine hall, Cruachan Power Station

What’s the biggest battery you can think of? A car battery? A grid-scale lithium-ion array? What about a battery the size of a mountain?

That’s what you’ll find on the banks of Loch Awe in Argyll, Scotland. Cruachan Power Station is a pumped hydro storage facility comprised of nearly 20 km of tunnels and chambers cutting through the mountain of Ben Cruachan.

Built in the 1960s, the site, known as ‘The Hollow Mountain’ entails a subterranean power station, a reservoir, a dam, and the loch itself. These components all work together to store a huge amount of energy, or enough to power more than 880,000 homes, at a moment’s notice.

This probably doesn’t fit your image of what a battery looks like. But the principle is the same. The purpose of any battery, from the AAs in your remote control to the one in your phone that you charge every night, is to store power for future use.

In an AA battery, that storage takes the form of chemicals within the battery which release electricity under the right conditions. In pumped hydro, the purpose is the same, but instead of being stored in chemicals, that energy is stored in the gravitational potential energy of 10 million cubic meters of water, sitting poised to spin Cruachan’s turbines and generate 440 megawatts (MW) of electricity.

Such a huge amount of water is the equivalent of around seven gigawatt-hours (GWh) of energy. If the reservoir is full, the Hollow Mountain can power a city for more than 15 hours.

How pumped hydro works

Cruachan Power Station is one of only four such storage facilities in the UK. Inside the mountain, 396 metres beneath the surface, is a chamber about the size of a football pitch, and the height of a seven-storey building. Here sit four electricity-generating turbines, each weighing around 650 tonnes.

A series of tunnels and channels connect these turbines to two enormous bodies of a water: Loch Awe at the base and the Ben Cruachan reservoir further up the mountain.

The turbines can function both as pumps and as generators. When there is an excess of power on the grid, and electricity is cheap, the turbines consume electricity and work to pump water up from the loch below to the reservoir 300 metres above.

Then, when electricity demand rises, the turbines reverse direction. Now the water flows down from the reservoir and through the turbines, which switch to generating electricity and supply it to the grid.

This is an extremely quick process. Unlike coal or nuclear stations, which can take hours to get up to full capacity, Cruachan can go from standstill to generating within two minutes – perfect for reacting to variance in grid demand at short notice.

Often National Grid ESO (electricity system operator) keeps one or more of Cruachan’s four units spinning in air. Compressed air is used to evacuate water from around a turbine to allow it to spin. When necessary, it can go from zero megawatts to 100 MW or more in less than 30 seconds.

In any given day, the system operator may call on Cruachan Power Station multiple times as the requirements to manage the grid constantly change.

Cruachan is a net generator of power across the year thanks to the large amount of water flowing into its reservoir from a system of aqueducts. However, pumped hydro is primarily about storing energy – not actively producing it in the way wind, solar, gas, biomass or conventional hydropower facilities might.

In fact, the UK’s four pumped hydro power stations are a combined net consumer of electricity. But this is the case with regular batteries as well, when construction is factored in.

Nevertheless, pumped hydro storage is still efficient – around 70% to 80% of the electricity used in pumping is recovered in generation. Sometimes, the convenience of getting access to power when it’s needed is more valuable than how much power is conserved.

The need for storage

But why store so much energy in such an improbable location to begin with?

There are two key reasons: The first is that the grid doesn’t operate under the same conditions all the time. Great Britain will use more or less electricity owing to its needs. For example, overnight there is a lower demand than at 5pm on a weekday evening. This means sometimes the grid is demanding more electricity than is being supplied, and sometimes vice versa.

Secondly, there’s the increasing level of intermittent energy sources, like wind and solar, supplying low carbon electricity. These sources are highly dependent on the weather and can’t be easily turned up or down in response to grid conditions.

Batteries can address these two issues. In times of higher electricity supply than demand, storage systems can absorb and store electricity from the grid, which helps balance frequency and prevent surges; and in times of high demand, then can quickly deliver electricity where it’s needed.

Pumped hydro is an important part of this equation – in fact, while other types of grid-scale batteries are receiving significant investment, they are still in their infancy. Pumped storage, by contrast, already accounts for 95% of all installed storage capacity in the world, around 130 GW.

What does the future hold for pumped hydro?

One of the challenges in installing more pumped hydro storage is finding suitable geography – places which are both mountainous, with nearby suitably large bodies of water.

However, there have been experiments into river and tidal-based pumped hydro storage projects. Senator Wash Dam on the Colorado River uses pumping to store water upstream from the Imperial Hydropower Dam so it can be released when needed, while the Rance Tidal Power Station in France pumps sea water behind the barrage to allow it to start up faster.

Storage solutions will become more important as electricity systems increasingly move towards renewable and low carbon sources. Pumped storage helps to meet peak-time demand and provide grid stability by making use of the landscape and gravity to deliver electricity when it’s needed.

Guided tours of Cruachan: The Hollow Mountain are available via

Meet the apprentices powering our future

“Different people do things different ways,” says Sam Stocks, an apprentice engineer at Drax Power Station. It’s a sentiment echoed by corporate administration apprentice Chloe Carpenter at Opus Energy. Asked to describe her role, she says, “[It’s] a very different kind of job.”

Chloe and Sam are just two of a number of apprentices at Drax Group who are working across the UK. And while they’re proud to do things differently, they do have something in common – they’re all hands-on, practical people who would rather get stuck in on a project than sit still and hear about it in the classroom.

“I chose an apprenticeship over higher education because I’m more of a doing person,” says Molly Fensome, a corporate administration apprentice. Sam agrees. “I like to be hands-on,” he says. “I don’t like being sat in a classroom.”

They are doing things their way – engineering their own futures while growing personally and professionally. And ensuring the future of our energy supply in the process.

Finding a strong sense of identity

For Sam, working at Drax wasn’t just a sensible career move, it was also following in his family’s footsteps. “My grandad worked in the power station industry all his life. [My family] know exactly what I’m like and they knew what type of place this was to work.”

Drax’s transformation from a coal-powered plant to a modern, sustainable electricity company means Sam’s work is building a power framework for future generations, while also paying homage to his grandad’s career.

Jake Dawson, an electrical engineer apprentice, followed a similar path into the power industry. Being born and bred in the area, Drax Power Station has always been a part of his geography. “Because I’m such a local lad it was perfect for me,” he says.

In his role, Jake can play a key part in the region where he grew up. A recent Oxford Economics report shows that Drax contributes £431 million to Yorkshire and the Humber economy and supports over 3,200 jobs.

A role in a team

Drax is a large organisation, but for Chloe finding role models within her team she can look up to and take guidance from has been easy. “Mentoring sessions are relaxed and you build a special bond with that person,” she says. “You can talk to them about work, outside of work – anything. They’ll always be there for you.”

Corporate administration apprentice Matt Donnelly has had a similar experience, adding that he’s seen his confidence grow, and feels he has made lifelong friends in his role.

Ultimately, it’s not just that they are given the right support, but that apprentices are integrated as a part of the company from day one. “My favourite part of my apprenticeship so far is being part of the team,” says Chloe. “Because you feel like you’re not just an apprentice, but you’re also one of them.”

Being part of something bigger

Sam remembers his first day at Drax Power Station: “It was overwhelming, you don’t actually realise how big it is and realise how many people work here. It’s just normal now, if I go anywhere else, I’m thinking, ‘That’s not as big as at work.’”

It’s not just its size that makes the UK’s biggest single site renewable power station stand out, but the potential for career development there. It’s this that Jake had on his mind when he first made the decision to become an apprentice. He was working in an unskilled job with little opportunity, but he knew he had it in him to find something bigger.

His outlook today as a Drax apprentice is very different. “My aim after the four years is to carry on growing as a person, increasing all my skills that I have, and maybe eventually becoming a supervisor or an engineer, who knows?”

This mindset of striving for better is evident across apprentices. It’s what drove them to join the programme in the first place. “Instead of going somewhere like uni and then possibly coming out without a job, you’ve got a job, and you’re actually learning as you’re doing it,” says Sam. “The skill set that I’ve learnt now – I’ll probably go anywhere in the world with it.”

Find out more about apprenticeships at Drax

Can Great Britain keep breaking renewable records?

How low carbon can Britain’s electricity go? As low as zero carbon still seems a long way off but  every year records continue to be broken for all types of renewable electricity. 2018 was no different.

Over the full 12-month period, 53% of all Britain’s electricity was produced from low carbon sources, which includes both renewable and nuclear generation, up from 50% in 2017.  The increase in low carbon shoved fossil fuel generation down to just 47% of the country’s overall mix.

The findings come from Electric Insights, a quarterly report commissioned by Drax and written by researchers from Imperial College London.

The report found electricity’s average carbon intensity fell 8% to 217 grams of carbon dioxide per kilowatt-hour of electricity generated (g/kWh), and while this continues an ongoing decline that keeps the country on track to meet the Committee on Climate Change’s target of 100 g/kWh by 2030, it was, however, the slowest rate of decline since 2013.

It also highlights that while Britain can continue to decarbonise in 2019, the challenges of the years ahead will make it tougher to continue to break the records it has over the past few years.

The highs and lows of 2018

Last year, every type of renewable record that could be broken, was broken. Wind, solar and biomass all set new 10-year highs for respective annual, monthly and daily generation, as well as records for instantaneous output (generation over a half-hour period) and share of the electricity mix. The result was a new instantaneous generation high of 21 gigawatts (GW) for renewables, 58% of total output.

Wind had a particularly good year of renewable record-setting. It broke the 15 GW barrier for instantaneous output for the first time and accounted for 48% of total generation during a half hour period at 5am on 18 December.

Overall low carbon generation, which takes into account renewables and nuclear (both that generated in Britain and imported from French reactors), had an equally record-breaking year with an average of almost 18 GW across the full year and a new record for instantaneous output of 30 GW at 1pm on 14 June – nearly 90% of total generation over the half hour period.

While low carbon and individual renewable electricity sources hit record highs, there were also some milestone lows. Coal accounted for an average of just 5% of electricity output over the year, hitting a record low in June, when it made up just 1% of that month’s total generation. Fossil fuel output overall had a similarly significant decline, hitting a decade-low of 15 GW on average for 2018 – 44% of total generation over the year.

One fossil fuel that bucked the trend, however, was gas, which hit an all-time output of 27 GW for instantaneous generation on the night of 26 January. There was low wind on that day last year, plus much of the nuclear fleet was out of action for reactor maintenance. In one case, with seaweed clogging a cooling system.

This was all aided by an ongoing decline in overall demand as ever smarter and more efficient devices helped the country reach the decade’s lowest annual average demand of 33.5 GW. More impressive when considering how much the country’s electricity system has changed over the last decade, however, is the record low demand net of wind and solar. Only 9.9 GW was needed from other energy technologies at 4am on 14 June.

How the generation mix has changed

The most remarkable change in Britain’s electricity mix has been how far out of favour coal has fallen. From its position as the primary source from 2012 to 2014, in the space of four years it has crashed down to sixth in the mix with nuclear, wind, imports, biomass and gas all playing bigger roles in the system.


This sudden decline in 2015 was the result of the carbon price nearly doubling from £9.54 to £18.08 per tonne of carbon dioxide (CO2) in April, making profitable coal power stations loss-making overnight. With coal continuing to crash out of the mix, biomass has become the most-used solid fuel in Britain’s electricity system.

Interconnectors are also playing a more significant part in Britain’s electricity mix since their introduction to the capacity market in 2015. Thanks to increased interconnection to Europe, Britain is now a net importer of electricity, with 22 TWh brought in from Europe in 2018 – nine times more than it exported.

While more of Britain’s electricity comes from underwater power lines, less of it is being generated by water itself. Hydro’s decline from the fifth largest source of electricity to the eighth is the most noticeable shift outside coal’s slide. New large-scale hydro installations are expensive and a secondary focus for the government compared with cheaper renewables.

Hydro’s role in the electricity mix is also affected by drier, hotter summers, which means lower water levels. For solar, by contrast, the warmer weather will see it play a bigger role and it’s expected to overtake coal in either 2019 or 2020.

What is unlikely to change in the near-future, however, is the position at the top. In 2018 gas generated 115 TWh – more than nuclear and wind combined. But this is just one constant in a future of multiple moving and uncertain parts.

2019: a year of unpredictability

Britain is on course to leave the EU on 29 March. The effects this will have on the electricity system are still unknown, but one influential factor could be Britain’s exit from the Emissions Trading Scheme (ETS), the EU-wide market which sets prices of carbon emitted by generators. This may mean that rather than paying a carbon price on top of the ETS, as is currently the case, Britain’s generators will only have to pay the new, fixed carbon tax of £16 per tonne the UK government says will come into play in April, topped up by the carbon price support (CPS) of £18/tonne.

Lower prices for carbon relative to the fluctuating ETS + CPS, could make coal suddenly economically viable again. The black stuff could potentially become cheaper than other power sources. This about-turn could cause the carbon intensity of electricity generation to bounce up again in one or more years between 2019 and 2025, the date all coal power units will have been decommissioned.

The knock-on effect of lower carbon prices, combined with fluctuations in the Pound against the Euro, could see a reverse from imports to exports as Britain pumps its cheap, potentially coal-generated, electricity over to its European neighbours. That’s if the interconnectors can continue to function as efficiently as they do at present, which some parties believe won’t be the case if human traders have to replace the automatic trading systems currently in place.

Sizewell B Nuclear Power Station

A reversal of importing to exporting could also reduce the amount of nuclear electricity coming into the country from France. Future nuclear generation in Britain also looks in doubt with Toshiba and Hitachi’s decisions to shelve their respective plans for new nuclear reactors, which could leave a 9 GW hole in the low-carbon base capacity that nuclear normally provides.

Renewables have the potential to fill the gap and become an even bigger part of the electricity system, but this will require a push for new installations. 2018 saw a 60% drop in new wind and solar installations and less than 2 GW of new renewable capacity came onto the system, making it the slowest year for renewable growth since 2010.

Britain’s electricity has seen significant change over the last decade and 2018 once again saw the country take significant strides towards a low carbon future, but challenges lie ahead. Records might be harder to break, but it is important the momentum continues to move towards renewable, sustainable electricity.

Explore the quarter’s data in detail by visiting the full report.

Commissioned by Drax, Electric Insights is produced, independently, by a team of academics from Imperial College London, led by Dr Iain Staffell and facilitated by the College’s consultancy company – Imperial Consultants.