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Last Updated: Tuesday, 28 March 2006, 08:02 GMT 09:02 UK
In detail: Electricity calculator
For a more detailed explanation of how the electricity calculator was put together and how it works, click on the links below or scroll down the page.


The aim of the calculator is to give people the opportunity to explore what impacts different options for the UK's electricity supply in 2020 might have.


It focuses on three key outcomes: meeting demand, carbon emissions and cost.

The results generated by the calculator only reflect what could happen. The UK's electricity market is extremely complex and a number of assumptions and simplifications have had to be made in order to construct the calculator.

The following offers a more detailed explanation of how the calculator works.


Each of the generation sources has a slider that extends from 0kWh to 400 billion kWh. This represents 0-100% of projected UK electricity demand in 2020 based on provisional forecasts from the DTI's energy team.

The sliders have "current usage" markers that indicate how much each source contributes to today's electricity generation mix.

Fossil fuels
The fossil fuel slider refers to electricity generated by coal-fired and gas-fired power stations. Electricity generated from oil has not been included because it is projected to be less than 0.3% of total generation.

For each unit of electricity generated from fossil fuels, the calculator uses the ratio of 53% generated from gas-fired power stations and 47% from coal-fired plants. This figure is based on generation figures from the DTI's Digest of UK Energy Statistics (Dukes) 2005 edition.

Projections for 2020 suggest the fossil fuel ratio will be 78% generation from gas-fired power stations, and just 22% from coal-fired stations. However, the recent uncertainty over gas supplies to EU nations and the surge in gas prices raises questions about the accuracy of these projections. Accordingly, and based on the advice of analysts, we have used the current 53-47 mix in the calculator.

This option includes a range of sources from the renewable electricity portfolio: onshore and offshore wind, energy crops, tidal and wave, and solar photovoltaic.

The reason for having a mix of renewable energy sources is because it is unrealistic to have all electricity generation coming from one source, for example, onshore wind, given the irregular nature of the supply and the lack of viable options for storing electricity.

For cost, the calculator uses an escalating formula within the renewables slider. Initially it uses the price for onshore wind, the cheapest option. Selecting higher values on the slider means that additional, progressively more expensive options are brought in in the following order: offshore wind, energy crops, tidal/wave, photovoltaic. So as the slider is moved higher, the incremental cost increases, which is not the case for fossil fuels, nuclear or imports.

This slider refers to electricity generated in mainland Europe and transmitted to the UK by an "interconnector" - a high-capacity cable - under the English Channel.

The 2GW interconnector between France and the UK is usually used to import electricity when suppliers and generators need help to meet peak demands. It is also used to export electricity to the European electricity market when generators are producing more power than is needed by customers in the UK.

Because the calculator looks at how the UK can meet future demand for electricity, the interconnector in this context is only used for imports.

More interconnectors may be built in the future, and the calculator assumes no upper limit on overall capacity.


This slider allows the overall demand to be reduced by implementing a range of electricity saving measures. Some are based on changing consumers' behaviour (e.g. switching off TVs when not being used), while others involve improving the insulation of homes (e.g. loft insulation).

To reach the greatest level of demand reduction (80TWh), homes and businesses would have to reduce their electricity consumption by an average of about 20%.

For households' demand reduction, the following assumptions have been made:

  • There will be 28 million households in the UK in 2020
  • Electricity-only homes: five million
  • Domestic consumption: 29% of total demand for electricity

These assumptions, based on government figures, have been made in order to calculate what reductions can be made in terms of heating homes, which accounts for the majority of domestic energy needs.

The following factors have been used to calculate demand reduction:

  • New housing stock meeting latest building regulations
  • Heating homes to 21C (70F);
  • Energy efficient lighting
  • Draught-proofing
  • Loft insulation
  • Wall cavity insulation
  • Double glazing
  • Energy efficient (A+ rated) fridge freezers and washing machines
  • Switching off electrical goods when not being used
  • Washing clothes at 40C (104F)

A range of data sources have been used in the calculator's demand reduction formula, including:

  • DTI's 2005 Digest of UK Energy Statistics
  • DTI Energy Trends (December 2005)
  • House Condition Surveys for England, Wales, Scotland and Northern Ireland
  • Energy Saving Trust; Association for the Conservation of Energy (ACE)
  • Defra Climate Change Programme's Energy Efficiency Commitment (EEC)
  • Market Transformation Programme (MTP)

Some actions taken to reduce demand, such as switching off electronic equipment, will generate savings; but others, such as double-glazing, come at substantial costs.


CO2 emissions have been calculated using the following figures:

  • Coal - 910g/kWh
  • Gas - 360g/kWh
  • Nuclear - 5g/kWh
    (Source: Carbon Trust, DTI and BNFL)

The fossil fuel emissions have been weighted using the following ratio: gas 53%, coal 47% (for more details, see the "electricity generation options" explanation above).

We have made the assumption than none of the fossil-fuelled stations will use carbon capture and storage to reduce emissions. This assumption is based on the technology being currently unproven, and on the lack of financial drivers which would make its adoption economically attractive.

The target for reducing emissions from electricity generation by 2020 is based on the government's aspiration to cut carbon dioxide emissions by 60% from 1990 levels by 2050.

To derive the target used in the calculator, we make two assumptions.

First, we set the target for 2020 as a 30% reduction from 1990 levels. This is because 2020 is halfway from the base year, 1990, to 2050, and 30% is halfway to the 60% target.

Secondly, we assume that the electricity sector should not have to bear a disproportionate burden - ie, it should not be asked to make cuts in order to balance rising emissions in other sectors.

It is worth bearing in mind that while emissions from electricity generation sources may be displayed as being on target, any sizeable increase in emissions in other sectors, such as transport or aviation, is likely to result in the UK target as a whole being missed.

It is also worth bearing in mind that only emissions created in the UK count towards the nation's Kyoto Protocol target and the government's unilateral 60% CO2 figure.

Carbon emissions from nuclear power relate largely to ore refining and fuel processing, operations which are carried out overseas; so they are not included in the calculator.

Emissions from power stations in mainland Europe supplying UK demand are also not included.


Generation costs are based on figures from a report published by the Prime Minister's Strategy Unit (formerly known as the Performance and Innovation Unit) that was used in the formation of the Energy White Paper.

The average annual bill is calculated on the assumption that a household will use 3,946kWh of electricity and that generation costs will be 38% of an average bill.

The remaining 62% consists of transmission costs, assorted levies, and suppliers' markup.


New build figures take into account power stations and nuclear reactors that are set to be decommissioned or closed under the EU Large Combustion Plant Directive (LCPD).

All but three of Britain's nuclear stations will have closed by 2020.

So, based on figures from the government and the Association of Electricity Producers, will all of the large oil-fired plants and five or six coal-fired stations.

No gas stations are currently scheduled for closure.

All of these plans could change; fuel prices may fluctuate, new plant designs may come onto the market and the European Emissions Trading Scheme may produce substantial incentives to reduce greenhouse gas production.

The calculator counts "gross new build" rather than "net new build", within the caveats given above.

The average capacity of new power stations, wind turbines etc. used in the calculator are:

  • Coal - 1,800 MW
  • Gas - 700 MW
  • Nuclear - 1,200 MW
  • Onshore wind - 3 MW
  • Offshore wind - 5 MW

New build is only displayed if the generation figure exceeds the capacity of the remaining fleet in 2020.

Wind turbines
The number of new wind turbines does not exceed 9,255, even if 400bn kWh of electricity is selected on the renewable electricity slider. This is because the calculator is calibrated to switch to alternative renewable power sources once wind power reaches a certain level.

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