Tag: electricity system balancing and ancillary services

The cost of staying in control

What: Industrial landscape with cables, pylons and train at sunset Where: Somerset, UK When: January 2016

The cost of keeping Britain’s power system stable has soared, and now adds 20% onto the cost of generating electricity.

The actions that National Grid takes to manage the power system have typically amounted to 5% of generation costs over the last decade, but this share has quadrupled over the last two years.  In the first half of 2020, the cost of these actions averaged £100 million per month.

Supplying electricity to our homes and workplaces needs more than just power stations generating electricity.

Supply and demand must be kept perfectly in balance, and flows of electricity around the country must be actively managed to keep all the interconnected components stable and prevent blackouts.  National Grid’s costs for taking these actions have been on the rise, as we reported over the previous two summers; but recently they have skyrocketed.

At the start of the decade, balancing added about £1/MWh to the cost of electricity, but last quarter it surpassed £5/MWh for the first time (see below).

Balancing prices have risen in step with the share of variable renewables.  The dashed line below shows that for every extra percent of electricity supplied by wind and solar adds 10 pence per MWh to the balancing price.  Last quarter really bucks this trend though, and balancing prices have risen 35% above the level expected from this trend.  The UK Energy Research Centre predicted that wind and solar would add up to £5/MWh to the cost of electricity due to their intermittency, and Britain has now reached this point, albeit a few years earlier than expected.

This is partly because keeping the power system stable is requiring more interventions than ever before.  With low demand and high renewable generation, National Grid is having to order more wind farms to reduce their output, at a cost of around £20 million per month.  They even had to take out a £50+ million contract to reduce the output from the Sizewell B nuclear reactor at times of system stress.

Two charts illustrating the costs of balancing Great Britain's power system

[Left] The quarterly-average cost of balancing the power system, expressed as a percentage of the cost of generation. [Right] Balancing price shown against share of variable renewables, with dots showing the average over each quarter

A second reason for the price rise is that National Grid’s costs of balancing are passed on to generators and consumers, who pay per MWh.  As demand has fallen by a sixth since the beginning of the coronavirus pandemic, the increased costs are being shared out among a smaller baseOfgem has stepped in to cap the balancing service charges at a maximum of £10/MWh until late October.  Their COVID support scheme will defer up to £100 million of charges until the following year.

For a quarter of a century, the electricity demand in GB ranged from 19 to 58 GW*.  Historically, demand minus the intermittent output of wind and solar farms never fell below 14 GW.  However, in each month from April to June this year, this ‘net demand’ fell below 7 GW.

Just as a McLaren sports car is happier going at 70 than 20 mph, the national grid is now being forced to operate well outside its comfort zone.

This highlights the importance of the work that National Grid must do towards their ambition to be ready for a zero-carbon system by 2025.  The fact we are hitting these limits now, rather than in a few years’ time is a direct result of COVID.  Running the system right at its limits is having a short-term financial impact, and is teaching us lessons for the long-term about how to run a leaner and highly-renewable power system.

Chart: Minimum net demand (demand minus wind and solar output) in each quarter since 1990

Minimum net demand (demand minus wind and solar output) in each quarter since 1990

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Front cover of Drax Electric Insights Q2 2020 report

Electric Insights Q2 2020 report [click to view/download]

What are ancillary services?

Ancillary services

What are ancillary services?

Ancillary services are a set of processes that enable the transportation of electricity around the grid while keeping the power system operating in a stable, efficient and safe way.

Why do we need ancillary services? 

When electricity makes its way through the country, it needs to be managed so that the power generation and electricity useage levels are equal.

The regulating of elements such as frequency and voltage has to be carefully managed, so that the massive amounts of electricity moving – or transmitted – are able to be used safely in homes,  businesses, schools and hospitals around the country.

Ancillary services enable the power system to operate in a stable, efficient and safe way.

 What do ancillary services offer?

Ancillary services include a wide variety of electrical efficiency and safety nets, all focussed on ensuring the power system delivers enough output to meet demand yet remains stable:

Frequency: The UK’s power system runs at a frequency of 50 hertz – to stay balanced, it has to remain at that frequency. Turbines and generators adjust the speed at which they spin automatically to increase or decrease power in line with demand and ensure that the system is kept stable.

Voltage: Different parts of the UK’s transmission system use voltages of either 400, 275 or 132 kilovolts. To ensure that voltage remains within 5% of those figures at all times, to be safe for domestic electricity use, power stations can produce or re-absorb excess energy as reactive power, keeping the overall system reliable.

Inertia: Turbine use is important in keeping the system operating in its current state, even with disruptions and sudden changes. The electricity system uses the weight of heavy spinning turbines to create stability, acting as dampeners and smoothing out unexpected changes in frequency across the network.

Reserve: An important part of ancillary servicing is making sure that there are no surprises – so holding back powerto release if something unexpected happens means that the network can function confidently, knowing that there are generators and other power providers such as pumped hydro storage waiting ready to back it up.

Key facts about ancillary services

Who manages ancillary services?

In the UK the grid’s stability is managed by National Grid Electricity System Operator (ESO) – a  separate company of National Grid Electricity Transmission (ET). The ESO works with ancillary service providers to either sign long-term contracts or make short term requests for a service.

These partners are often power stations, such as Drax Power Station, which have large spinning turbines capable of controlling voltage, frequency, providing inertia and serving as a source of reserve power. 

What is the future of ancillary services, as we move to a more renewable system?

As the UK’s electricity system continues to change, so to do its requirements for different ancillary services. The switch from a few very large power stations to a greater variety of different electricity sources, some of which may be dependent on the weather, as well as changes in how the country uses electricity, means there is a greater need for ancillary services to keep the grid stable.

These services have historically been delivered by thermal power stations, but new innovations are enabling wind turbines to provide inertial response and overcome changes in frequency, and batteries to store reserve power that can then be supplied to the power system to ensure balance.

Ancillary Services

Ancillary services fast facts  

  • Batteries can in some cases be cheaper ancillary alternatives to conventional sources of energy. The Hornsdale Power Reserve, which runs on a Tesla battery in South Australia, lowered the price of frequency ancillary services by 90% after just four months of use.
  • Ancillary services usually work from habit; knowing when to slow electricity production, or increase supply based around the general public’s standard working hours, dinner time and the early morning rush.
  • But during the COVID-19 lockdown, electricity consumption on weekdays fell by 13% and so National Grid ESO had to intervene with ancillary services to keep the lights on.
  • Every year, the ESO’s ancillary services move 300 terawatt hours (TWh) of electricity, which is equal to 4 trillion kettles boiling at once.

With recent innovations around renewable energies, there are a wider variety of ways for ancillary services to generate power.

Go deeper

Button: What is decarbonisation?

How electrical transformers work

Getting electricity safely and efficiently from generators, through power lines and across the country into our devices is a careful balancing act. One of the vital aspects of this is the voltage.

An electrical substation with transformers.

The National Grid’s transmission lines work at a voltage of 400,000 volts (v) and 275,000v, but if electricity were to enter homes at this voltage it would quickly damage anything it powered. Instead, regional distributors deliver electricity into homes at a much lower level of 230v.

Achieving a voltage level that’s safe to use requires stepping it up or down through transformers – huge pieces of electrical grid equipment that use a simple idea to have a big impact.

Why we need transformers

Voltage is like water pressure. Having high voltage transmission lines means the charged electrons that make up electricity are moving very efficiently through the system, with less energy being lost as heat along the way. However, that same ‘pressure’ is too much for just charging a phone. It would likely overload the device’s circuits and leave the user with a smouldering mess.

That’s where transformers step in. Electricity is produced at a variety of voltages around Great Britain, depending on different types of generation. In order to send it to where the demand is without losing too much energy as heat along the journey, a transformer attached to large power generators such as Drax’s biomass power plant or Beatrice offshore wind farm increases the voltage to 400,000v or 275,000v. The voltage depends on what part of the national transmission system the power station is connected to.

When the electricity arrives via pylons at a particular region of Great Britain, another transformer brings the voltage down to 132,000v for the regional distribution system. Subsequently, another reduces it to 11,000v in towns and villages, before a final transformer reduces the voltage to a safe 230v for use in homes and businesses.

Keeping the voltage high is useful in preventing energy loss to heat, but it also does something else important to the electricity shooting around the country.

Keeping voltage high to cut down current

If voltage is the water pressure, then current is the actual water particles moving through the pipes. In electrical terms the current is the charged electrons that actually power our lights and devices.

When these electrons travel along the electricity grid’s cables, they face resistance (imagine a partial blockage in a water pipe) this causes some electrical energy to be lost to heat. Getting the right amount of electricity needed around the country means keeping energy loss as low as possible. If the current is lower, fewer charged electrons are bumping into resistance at any one point in the system and less electrical energy is being lost.

Conveniently for the grid, raising the voltage of electricity causes the current to decrease and vice versa. How transformers actually do this is all a matter of coils. 

Super transformer at Cruachan Power Station

Transformer at Cruachan Power Station

Winding voltage up and down

Transformers work using the principal of electromagnetic induction, something the British scientist Michael Faraday first realised in 1831. He noticed that when a magnet moved through a coil of copper wires, a current flowed through those wires. It’s this same principal that enables spinning turbines to generate electricity today.

Michael Faraday

Michael Faraday

Similarly, when a current flows through a copper coil wrapped around an iron core, the core becomes magnetic.

Faraday did experiment with running currents through multiple copper coils, but it was scientist and Irish priest Father Nicholas Callan who in 1836 discovered the underlying principal of many of the world’s transformers today. He found if two separate sets of copper wires were wound around each end of an iron core and an electrical current was passed through one of them (the primary winding) then a magnetic field is created that causes an electric current to flow in the secondary winding.

However, things change depending on how many times each wire is wound around the core. If there are more turns in the secondary winding than the primary one, then when a current is induced the voltage increases. When there are fewer turns in the secondary winding than the primary, the voltage decreases.

Callan's Induction Coil

Callan’s Induction Coil (1845)

Moreover, Father Callan discovered that the increase or decrease in voltage is directly proportional to the number of turns in the windings. So, theoretically, if an electrical current with a voltage of 5v is passed through a primary winding with 10 turns and creates a current in a secondary winding with 20 turns, the voltage will also double, in this case to 10v.

Father Callan’s invention is known as an induction coil, where the two sets of windings share a long, thick iron rod. Since then the transformer has undergone continual revision, optimisation and specialisation for different use cases. However, the underlying principal of using electromagnetic induction to increase and decrease voltage remains the same.

From homes to power stations

One of the most common types of transformers are distribution transformers – the kind often found on utility poles near homes. These transformers perform the final step down from local distribution systems to 230v as the electricity enters homes and businesses.

These often use an iron core that takes the form of a hollow square with windings wrapped around both ends. When a current passes through and magnetises the core it causes it to expand and contract in a process known as magnetostriction, which sometimes causes enough vibration to produce an audible hum.

A transformer being moved from Longannet to Cruachan Power Station in 2019.

A transformer being moved from Longannet to Cruachan Power Station in 2019.

In these type of transformers it’s safe for the current to be transferred through the air between the two windings, but when higher voltages are being used, such as at Cruachan Power Station – the biggest pumped storage facility in Scotland – different approaches are needed. Large power station-scale transformers are submerged in a special insulating oil inside a metal container. The oil provides electrical insulation to prevent short circuits while also cooling the core and windings, preventing damage and failure.

Even as the main sources of Great Britain’s electricity change from coal and nuclear power stations to wind farms and solar panels, transformers will remain an essential part of the grid, in getting the right amount of power to where we need it – fast.

Under lockdown, every day is a Sunday

empty UK motorway in England at sunset with no traffic

On March 23rd the UK took an unprecedented move to tackle the coronavirus. Most business that had not already closed moved online, with millions of people now working from home. This had a huge impact on electricity demand: consumption on weekdays fell by 13% to its lowest levels since 1982 – a time when there were 10 million fewer people in the country, and GDP was a third lower than today.

Other regions have seen a similar collapse in electricity demand. Spain, Italy and France have all seen electricity demand fall by 10-15% according to analysis by Ember. Across the Atlantic, New York City has seen similar reductions.

Demand has fallen for a simple reason: with schools and workplaces now closed or running with a greatly reduced staff – machinery, computers, lights and heaters are not drawing power. Electric rail, tram and tube systems are also running a reduced service. On the contrary, with more people at home, household electricity consumption has increased. Octopus Energy estimate that during social distancing (before the stricter lockdown came into effect) homes were consuming up to a third more electricity, adding £20 per month to the typical bill.

The impact of lockdown on Britain’s electricity demand is much like living through a month of Sundays. The average profile for a March weekend day in previous years looks very similar to the daily profile for weekdays since lockdown begun – both in the amount of electricity consumed and the structure. Post-lockdown weekends have even lower demand, tracking 11% below weekday demand.

People no longer have to get up at the crack of dawn for work. On a typical weekday morning, demand would rise by 10 GW over two hours from 5:30 to 7:30 AM. Now it takes more than twice as long – until midday – for this rise to occur. At the other end of the day, there would normally be a small peak in demand around 8 PM from people gathering in pubs and restaurants up and down the country. Both on weekdays and weekends, demand begins falling earlier in the evening as the sofa has become the only available social venue.

urban street cafe empty without visitors

With lower demand comes lower power prices. Wholesale electricity prices are typically 7% lower on Sundays than on weekdays for this reason. March saw the lowest monthly-average power price in 12 years, down one-third on this month last year. Prices were already heading downwards because of the falling price of gas, but the lockdown has amplified this, and negative prices have become commonplace during the middle of the day. There was not a visible impact on carbon emissions during the first quarter of the year, as only the last week of March was affected. However, as lockdown continued into April and May, emissions from power production in Britain have fallen by 35% on the same period last year. The effect is slightly stronger across Europe, with carbon emissions falling almost 40% as dirtier coal and lignite power stations are being turned down.

Will some of these effects persist after lockdown restrictions are eased? It is too early to tell, as it depends on what long-lasting economic and behavioural changes occur. Electricity demand is linked with the country’s GDP, which is set to face the largest downturn in three centuries. Whether the economy bounces back, or is afflicted with a lasting depression will be key to future electricity demand. It will also depend on behavioural shifts. People are of course craving their lost freedoms, many may appreciate not going back to a lengthy daily commute – and the rise of video conferencing and collaboration apps has shown that remote working may finally have come of age. With even a small share of the population continuing to work from home on some days, there could be a lasting impact on electricity demand for years to come.

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How electricity is made

Every morning we take electricity as a given. We switch on lights, charge phones and boil kettles without thinking about where this power comes from.

The electronic devices and appliances that make up our daily routines are not particularly energy intensive. Boiling a kettle only uses 93 watts, toasting for three minutes only requires 60 watts, while cooking in a microwave for five minutes takes 100 watts.

However, when people are waking up and making breakfast in almost 30 million households around the UK, those small amounts soon create a significant demand for electricity. On a typical winter’s morning, this combined demand spikes to more than 45 gigawatts (GW).

So this is what it takes to power your breakfast – from the everyday toaster in your kitchen backwards through thousands of miles of cables to the hundreds of thousands of tonnes of machinery in wind farms, hydro-electric dams and at power stations such as Drax where electricity generation begins.

The grid 

The journey starts in the home where all our electricity usage is tracked by meters. These are becoming increasingly ‘smart’, displaying near real-time information on energy consumption in financial terms and allowing more accurate billing. There are already 7.7 million smart meters installed around the UK, but that number is set to triple this year, paving the way for a smarter grid overall.

What brings electricity into homes is perhaps the most visible part of the energy system on the UK’s landscape. The transmission system is made up of almost 4,500 miles of overhead electricity lines, nearly 90,000 pylons and 342 substations, all bringing electricity from power stations into our homes.

Making sure all this happens safely and as efficiently as possible falls to the UK’s nine regional electricity networks and National Grid. Regional networks ensure all the equipment is in place and properly maintained to bring electricity safely across the country, while National Grid is tasked with making sure demand for electricity is met and that the entire grid remains balanced.

The station cools down

One of the most distinctive symbols of power generation, cooling towers carry out an important task on a massive scale.

Water plays a crucial role in electricity generation, but before it can be safely returned to the environment it must be cooled. Water enters cooling towers at around 40 degrees Celsius, and is cooled by air naturally pulled into the structure by its unique shape.

This means those plumes exiting from the top of the towers are, rather than any form of pollution, only water vapour. And this accounts for just 2% of the water pumped into the towers.

Drax counts 12 cooling towers, each 114 metres tall – enough to hold the Statue of Liberty with room to spare. Once the water is cooled it is safe to re-enter the nearby River Ouse.

The station’s bird’s-eye view

The control room is the nerve centre of Drax Power Station. From here technicians have a view into every stage of the power generation process.  The entire system controls roughly 100,000 signals from across the power station’s six generating units, water cooling, air compressors and more.

While once this area was made up of analogue dials and controls, it has recently been updated and modernised to include digital interfaces, display screens and workstations specially designed by Drax to enable operators to monitor and adjust activity around the plant.

The heart of power generation 

At the epicentre of electricity generation is Drax’s six turbines. These heavy-duty pieces of equipment do the major work involved in generating electricity.

High-pressure steam drive the blades which rotates the turbine at 3,000 revolutions per minute (rpm). This in turn spins the generator where energy is converted into the electricity that will eventually make it into our homes.

These are rugged pieces of kit operating in extreme conditions of 165 bar of pressure and temperatures of 565 degrees Celsius. Each of the six turbine shaft lines weighs 300 tonnes and is capable of exporting over 600 megawatts (MW) into the grid.

One of the most important parts of the entire process, turbines are carefully maintained to ensure maximum efficiency. Even a slight percentage increase in performance can translate into millions of pounds in savings.

Turning fuel to fire

To create the steam needed to spin turbines at 3,000 rpm, Drax needs to heat up vast amounts of water quickly and this takes a lot of heat.

The power station’s furnaces swirl with clouds of the burning fuel to heat the boiler. Biomass is injected into the furnace in the form of a finely ground powder. This gives the solid fuel the properties of a gas, enabling it to ignite quickly. Additional air is pumped into the boiler to drive further combustion and optimise the fuel’s performance.


How do you turn hundreds of tonnes of biomass pellets into a powder every day? That’s the task the pulveriser take on. In each of the power plant’s 60 mills, 10 steel and nickel balls, each weighing 1.2 tonnes, operate in extreme conditions to crush, crunch and pulverise fuel.

These metal balls rotate 37 times a minute at roughly 3 mph, exerting 80 tonnes of pressure, crushing all fuel in their path. Air is then blasted in at 190 degrees Celsius to dry the crushed fuel and blow it into the boiler at a rate of 40 tonnes per hour.

The journey begins: biomass arrives

Biomass arrives at Drax by the train-load. Roughly 14 arrive every day at the power station, delivering up to 20,000 tonnes ready to be used as fuel.

These trains arrive from ports in Liverpool, Tyne, Immingham and Hull and are specially designed to maximise the efficiency of the entire delivery process, allowing a full train to unload in 40 minutes without stopping.

The biomass is then taken to be stored inside Drax’s four huge storage domes. Each capable of fitting the Albert Hall inside, the domes can hold 300,000 tonnes of compressed wood pellets between them.

Here the biomass waits until it’s needed, at which point it makes its way along a conveyor belt to the pulveriser and the process of generating the electricity that powers your breakfast begins.