Methodology and sources
The British electricity system is undergoing huge changes. It is under pressure to decarbonise, to replace old technologies with new, lower carbon ones and to keep costs as low as possible. Understanding these changes requires a better understanding of the electricity system itself: there are many sources of information on generation and demand in Britain but these are often difficult to interpret and understand.
Electric Insights was established by Drax Group to help inform and enlighten the debate on Britain’s electricity. It is an independent and transparent analysis of supply, demand, price and environmental impacts, made entirely using publicly available data.
Drax Group owns and operates the UK’s largest power station, supplying 6% of the country’s electricity needs, including 15% of its renewable power, and a host of system support services. Three of its six 645 megawatt (MW) power generation units have been upgraded from burning coal to use compressed wood pellets, a form of biomass sourced from responsibly managed working forests. A fourth coal unit is being converted to use the low carbon fuel in 2018. Dr Iain Staffell is a Lecturer in Sustainable Energy at Imperial College London, and was commissioned to design the methodology for processing and presenting the data, and for writing the reports. Signal:Noise is a data design agency helping to make sense of the complex world, and was commissioned to build the Electric Insights website.
The Electric Insights website and quarterly reports use free and public data that is sourced from National Grid (Britain’s system operator), Elexon (who run the wholesale electricity market) and Sheffield Solar (who estimate the power output from the country’s 1 million solar panels). The methodology for acquiring, processing and presenting data has been written up as an academic paper. It is published in the journal Energy Policy and is available to read for free here.
A leading UK academic (Dr Grant Wilson) was also commissioned to perform an independent quality assurance of the mathematics and code used to produce these reports and website.
This website relies on data drawn in from external sources. Sometimes parts of the received data are missing, for example the output from nuclear power or interconnectors has not been reported. No attempt is made to correct for missing data, as this would involve making judgements and estimates. Instead, the unaltered data are presented, so there may be times where it looks like most of Britain’s power stations have gone offline for an hour or two, but that is not the case.
Electricity prices are always delayed half an hour behind the other data, as displaying current prices would interfere with the fair operations of the electricity market.
Units and Conventions
The electricity sector has many accounting conventions to be aware of. Power flow is measured in gigawatts (GW), volumes of energy are measured in gigawatt-hours (GWh) or terrawatt-hours (TWh). Producing 1 GW constantly for an hour would give 1 GWh = 0.001 TWh. Producing 1 GW constantly for a year would give 8760 GWh = 8.76 TWh, which is enough to power 2.65 million homes. The UK as a whole uses around 300 TWh of electricity a year.
Supply and demand are measured in real time by flows into and out of the transmission network. The major power stations that connect into this network are metered, but an increasing amount of generators are now integrated with consumers, making them invisible to National Grid, the UK’s system operator. The exclusion of embedded generation from many data sources is an increasing problem, as this discounts much of Britain’s wind capacity and all of its solar capacity, both of which have grown significantly.
National Grid’s measure of ‘Total System Demand’ is used, which includes hydro storage pumping, exports and losses. Demand that is met by ‘embedded’ generation from small wind and solar plants is added back on, to give the gross demand from all consumers. Occasional gaps in the data are filled by taking the average of neighbouring half-hour periods, or using other data provided by National Grid.
Britain spends around £25–30 billion a year on electricity generation, and a further £1 billion on balancing the system. These balancing costs are likely to increase significantly as flexible fossil fuel plants close and the UK becomes more dependent on weather dependent and more distant sources of power. Over 90% of electricity is bought on long-term contracts between generators and retailers to give them stability and security. About 5% is traded on the day-ahead power exchange, for which prices are publicly available.
The data shows prices on the wholesale spot market, for power bought at the time of delivery. Electricity prices are given in pounds per MWh, as given by Elexon. Note that £10/MWh = 1 pence/kWh. These are the raw prices for electricity generation, and do not include fees for transmission, balancing and distribution, taxes and green levies.
This shows the temperature at noon averaged over the whole country, as given by Elexon. Temperature has an important influence on electricity demand during winter because of the 2.5 million homes with electric heating.
The contribution of each technology to supply is taken from both Elexon and National Grid data where necessary.
- Nuclear is as given by Elexon
- Biomass is taken to be ‘biomass’ and ‘other’ generation listed by Elexon, as this category consists entirely of coal-to-biomass conversions and biomass combined heat and power (CHP) plants.
- Imports and Storage are grouped together as each is relatively small by itself. Imports consists of links to Ireland, France and the Netherlands, and storage mostly consists of pumped-hydro. We present the net contribution to meeting demand, which is imports + discharge from storage – exports – recharging storage. Import and discharge data comes from Elexon, export and recharging data from National Grid.
- Hydro is as given by Elexon, and consists of only the ‘renewable’ plants powered by water (run-of-river), and does not include pumped storage.
- Wind is the sum of Elexon’s data for the largest wind farms in Scotland and offshore, and National Grid’s data on smaller ‘embedded’ wind farms.
- Solar is as given by Sheffield Solar.
- Gas consists of combined cycle gas turbines (CCGTs) as given by Elexon.
- Coal is as given by Elexon.
Note that open cycle gas turbines (OCGTs) and oil are ignored, as each contributes less than 0.1% of total generation.
For wind farms we show the amount of electricity that was generated and delivered to the grid. Sometimes wind farms are capable of generating, but cannot deliver their power because there is not enough transmission capacity to get the electricity to consumers. This excess power must be ‘constrained’ (i.e. wasted), and is not shown in our data. The amount and cost of constraining wind farms was calculated separately using Elexon’s Derived BM Unit Data.
We show the total emissions from British electricity consumption in tonnes per hour (including emissions from imported power), and the ‘carbon intensity’ of electricity – total emissions divided by total demand in grams per kilowatt hour (g/kWh).
Emissions come from burning fossil fuels in British power stations, and include emissions released abroad for electricity that Britain imports, and emissions from producing and transporting biomass from abroad which Britain imports. This is known as consumption-based (as opposed to production-based) accounting, and yields higher estimates than given by the UK government because of imports and transportation.
Emissions are estimated from the carbon intensity of each generating technology, multiplied by their power output in each half hour. The carbon intensities for fossil-fuel plants were estimated using data on the historic electricity output and fuel consumption for the period 1996 to 2015. The carbon intensity of nuclear and renewables are taken to be zero, as the life-cycle emissions from constructing power stations are not included for any technology. The average carbon intensity of imported electricity was calculated using monthly generation mix data, and the estimated carbon intensities of fossil plants.
The carbon intensity of biomass is based on processing and transportation, based on independently assured data published by Ofgem, and reports by the UK government and European Commission. In line with Government practice, emissions from combustion of biomass are not reported here as they are part of a cycle of emission and reabsorption by the next generation of feedstock. Legislative requirements for sustainable forest management ensure that this cycle is maintained in order to receive subsidies (such as the UK Renewables Obligation), which requires all biomass harvesting to maintain the productivity of the area and to ensure that wood is extracted from the area at a rate which does not exceed its long term capacity to produce wood.
A summary of the power station generating efficiencies, and the carbon emissions from their electricity production is given below. These figures are used in the Electric Insights to estimate carbon emissions from the British electricity system.
Average Power Station Efficiency Average Carbon Intensity (g / kWh) Coal 34.3% 937 Oil 27.1%985 Gas OCGT 28.3% 651 Gas CCGT 46.7% 394 Nuclear 34.6% 0 Biomass 29.0% 121 French Imports 53 Dutch Imports 474 Irish Imports 458