Tag: national grid

How to count carbon emissions

Iain Staffell, Imperial College London

31 August 2020

Opinion

Reduced demand, boosted renewables, and the near-total abandonment of coal pushed last quarter’s carbon emissions from electricity generation below 10 million tonnes.

Emissions are at their lowest in modern times, having fallen by three-quarters compared to the same period ten years ago.  The average carbon emissions fell to a new low of 153 grams per kWh of electricity consumed over the quarter.

The carbon intensity also plummeted to a new low of just 18 g/kWh in the middle of the Spring Bank Holiday.  Clear skies with a strong breeze meant wind and solar power dominated the generation mix.

Together, nuclear and renewables produced 90% of Britain’s electricity, leaving just 2.8 GW to come from fossil fuels.

The generation mix over the Spring Bank Holiday weekend, highlighting the mix on the Sunday afternoon with the lowest carbon intensity on record

National Grid and other grid-monitoring websites reported the carbon intensity as being 46 g/kWh at that time.  That was still a record low, but very different from the Electric Insights numbers.  So why the discrepancy?

These sites report the carbon intensity of electricity generation, as opposed to consumption.  Not all the electricity we consume is generated in Britain, and not all the electricity generated in Britain is consumed here.

Should the emissions from power stations in the Netherlands ‘count’ towards our carbon footprint, if they are generating power consumed in our homes?  Earth’s atmosphere would say yes, as unlike air pollutants which affect our cities, CO2 has the same effect on global warming regardless of where it is produced.

On that Bank Holiday afternoon, Britain was importing 2 GW of electricity from France and Belgium, which are mostly powered by low-carbon nuclear.  We were exporting three-quarters of this (1.5 GW) to the Netherlands and Ireland.  While they do have sizeable shares of renewables, they also rely on coal power.

Britain’s exports prevented more fossil fuels from being burnt, whereas the imports did not as they came predominantly from clean sources.  So, the average unit of electricity we were consuming at that point in time was cleaner than the proportion of it that was generated within our borders.  We estimate that 1190 tonnes of CO2 were produced here, 165 were emitted in producing our imports, and 730 avoided through our exports.

In the long-term it does not particularly matter which of these measures gets used, as the mix of imports and exports gets averaged out.  Over the whole quarter, carbon emissions would be 153g/kWh with our measure, or 151 g/kWh with production-based accounting.  But, it does matter on the hourly timescale, consumption based accounting swings more widely.

Imports and exports helped make the electricity we consume lower carbon on the 24th, but the very next day they increased our carbon intensity from 176 to 196 g/kWh.

When renewable output is high in Britain we typically export the excess to our neighbours as they are willing to pay more for it, and this helps to clean their power systems.  When renewables are low, Britain will import if power from Ireland and the continent is lower cost, but it may well be higher carbon.

Two measures for the carbon intensity of British electricity over the Bank Holiday weekend and surrounding days

This speaks to the wider question of decarbonising the whole economy.

Should we use production or consumption based accounting?  With production (by far the most common measure), the UK is doing very well, and overall emissions are down 32% so far this century.  With consumption-based accounting it’s a very different story, and they’re only down 13%*.

This is because we import more from abroad, everything from manufactured goods to food, to data when streaming music and films online.

Either option would allow us to claim we are zero carbon through accounting conventions.  On the one hand (production-based accounting), Britain could be producing 100% clean power, but relying on dirty imports to meet its entire demand – that should not be classed as zero carbon as it’s pushing the problem elsewhere.  On the other hand (consumption-based accounting), it would be possible to get to zero carbon emissions from electricity consumed even with unabated gas power stations running.  If we got to 96% low carbon (1300 MW of gas running), we would be down at 25 g/kWh.  Then if we imported fully from France and sent it to the Netherlands and Ireland, we’d get down to 0 g/kWh.

Regardless of how you measure carbon intensity, it is important to recognise that Britain’s electricity is cleaner than ever.

The hard task ahead is to make these times the norm rather than the exception, by continuing to expand renewable generation, preparing the grid for their integration, and introducing negative emissions technologies such as BECCS (bioenergy with carbon capture and storage).

Read full Report (PDF)   |  Read full Report   |   Read press release

Front cover of Drax Electric Insights Q2 2020 report

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

What are ancillary services?

21 August 2020

Power generation
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?

What causes power cuts?

16 January 2019

Power generation

On the night of 5 December 2015, 61,000 homes and properties across Lancaster were plunged into darkness. Storm Desmond had unleashed torrents of rain on Great Britain, causing rivers to swell and spill over. With waters rising to unprecedented levels, the River Lune began threatening to flood Lancaster’s main electricity substation, the facility where transformers ‘step down’ electricity’s voltage  from the transmission system so it can be distributed safely around the local area.

To prevent unrepairable damage, the decision was taken to switch the substation off, cutting all power across the region. Lights, phones, internet connections and ATMs all went dead across the city. It would take three days of intensive work before power was restored.

It was a bigger power outage than most, but it offers a unique glimpse into the mechanisms behind a blackout – not only how they’re dealt with, but how they’re caused.

What causes blackouts in Great Britain?  

When the lights go out, a common thought is that the country has ‘run out’ of electricity. However, a lack of electricity generation is almost never the cause of outages. Only during the miners’ strikes of 1972 were major power cuts the result of lack of electricity production.

Rather than meeting electricity demand, power cuts in Great Britain are more often the result of disruption to the transmission system, caused by unpredictable weather. If trees or piles of snow bring down one power line, the load of electric current shifts to other lines. If this sudden jump in load is too much for the other lines they automatically trip offline to prevent damage to the equipment. This in turn shifts the load on to other lines which also then trip, potentially causing cascading outages across the network.

Last March’s ‘Beast from the East’, which brought six days of near sub-zero temperatures, deep snow and high winds to Great Britain, is an example of extreme weather cutting electricity to as many as 18,000 people.

High-winds brought trees and branches down onto powerlines, while ice and snow impacted the millions of components that make up the electricity system. Engineering teams had to fight the elements and make the repairs needed to get electricity flowing again.

Lancaster was different, however. With the slow creep of rising rainwater approaching the substation, the threat of long lasting damage was plain to see in advance, and so rather than waiting for it to auto-trip, authorities chose to manually shut it down.

Getting reconnected

Electricity North West is Lancaster’s network operator and after shutting down the substation, it began the intensive job of trying to restore power. On Monday 7 December, two days after the storm hit, the first step of pumping the flooded substation empty of water had finally been completed and the task of reconnecting it began.

To begin restoring power to the region 75 large mobile generators were brought from as far away as the West Country and Northern Ireland and hooked up to the substation, allowing 22,000 customers to be reconnected.

Once partial power was restored, the next challenge lay in repairing and reconnecting the substation to the transmission network. While shutting the facility had prevented catastrophic damage, some of the crucial pieces had to be completely replaced or rebuilt. After three days of intensive engineering work the remaining 40,000 properties that had lost power were reconnected.

Preventing blackouts in a changing system

The cause and scale of Lancaster’s outage were unusual for Great Britain’s electricity system but it does highlight how quickly a power cut may arise. In a time of transition, when the grid is decarbonising and the network is facing more extreme weather conditions because of climate change, it could create even more, new challenges.

Coal is scheduled to be taken entirely off the system after 2025, making the country more reliant on weather-dependent sources, such as wind and solar – potentially increasing the volatility of the system.

On the other hand, growing decentralised electricity generation may reduce the number of individual buildings affected by outages in the future. Solar generation and storage systems present on domestic and commercial property may also reduce dependency on local transmission systems and the impact of disruptions to it.

The cables and poles that connect the transmission system will always be vulnerable to faults and disruptions. However, by preparing for the future grid Great Britain can reduce the impact of storms on the electricity system.

If you’re experiencing a power cut in your area, please call the toll-free number 105 (in England, Scotland and Wales) to reach your local network operator.