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Last Updated: Monday, 27 March 2006, 09:59 GMT 10:59 UK
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Q&A: Electricity calculator
To find out how to use the electricity calculator, how it was put together and the answers to other questions, use the links below or scroll down the page.

WHAT IS THE ELECTRICITY CALCULATOR?

The electricity calculator gives you the opportunity to choose how you would like the UK's electricity to be generated in 2020.

Once you have decided how the electricity should be generated, the calculator will work out the likely impact your choice will have in terms of carbon emissions, keeping the lights on and the cost to households.

The calculator is not absolutely accurate, because factors such as the future price of natural gas are inherently unpredictable. But we have tried to use the best figures available, and it gives an indication of the potential impact of your choices.

HOW SHOULD THE CALCULATOR BE USED?

The first screen of the calculator gives you a choice of four generation sources (fossil fuel, nuclear, renewables and imports) and demand reduction.

Each power source slider allows you to generate between 0kWh to 400bn kWh.

Markers show the level of "current usage". This indicates how much of today's electricity is generated from that particular source. For example, 80bn kWh is generated by nuclear power stations. The marker is there to help you decide whether you want to have more or less of that power source in your mix for 2020.

You can reduce demand by up to 80bn kWh (roughly 20% of expected demand in 2020), which means you will not have to generate so much electricity to meet the UK's overall demand. However, many of the measures used to reduce the amount of electricity used by households do cost money, and this will be reflected within the calculator in the final bill that people will have to pay.

Once you have decided on how you would like the UK's electricity generation mix to look, press the "calculate results" button.

The next screen shows the results of your selection. It will give an indication of the amount of carbon emissions, whether you have managed to keep the lights on, and how much the average household bill will change.

It will also show you how many (if any) power stations and wind turbines have to be built. It will also show what percentage of electricity is being imported from overseas and how many homes in the UK will have to be insulated to the highest possible standard.

It is important to remember that these figures are only an indication of what your selection could mean. They should not be viewed as what will happen. All the figures are based on projections, so could be subject to change e.g. rising gas prices, government intervention or technological advances.

WHERE HAVE THE FIGURES COME FROM?

The electricity calculator uses data based on a wide range of sources, including:

• Department of Trade and Industry (DTI)
• Downing Street's Performance and Innovation Unit (PIU)
• Department for Environment, Food and Rural Affairs (Defra)
• Office of the Deputy Prime Minister (ODPM)
• Ofgem
• Carbon Trust
• Energy Saving Trust
• Association for the Conservation of Energy (ACE)
• British Nuclear Fuels (BNFL)
• National Grid
• UK Sustainable Development Commission
• Nuclear Industry Association (NIA)
• British Wind Energy Association (BWEA)
• Association of Electricity Producers (AEP)

WHY HAS 2020 BEEN CHOSEN AS THE TARGET DATE?

It is a year that features prominently in a number of key reports that look at the future of the UK's energy supply.

It is also far enough in the future that options which take time, such as embarking on a programme of new nuclear build, could have reached fruition.

WHAT IS A KILOWATT HOUR (kWh)?

A kilowatt hour is the standard unit of electricity that is used to calculate your bill. The average home currently uses about 3,300 kWh of electricity a year.

IS THE CALCULATOR ACCURATE?

The calculator gives only an indication of what your selection could mean in 2020. Because the calculations are based on projections, the reality is that the figures will change between now and 2020.

The figures on the results pages broadly reflect what the situation will be in 2020 if the current projections remain unchanged.

However, the results do illustrate the general outcome of your selection, e.g. lower emissions but higher prices.

WHAT DOES "FOSSIL FUEL" MEAN IN THE ELECTRICITY GENERATION OPTIONS?

Fossil fuel refers to coal-fired and gas-fired power stations. We have made an assumption about what the mix between the two is likely to be based on government forecasts and analysts' advice.

WHAT DOES "RENEWABLES" MEAN IN THE ELECTRICITY GENERATION OPTIONS?

In the calculator, renewable refers to a portfolio of onshore and offshore wind farms, energy crops, wave and tidal power and photovoltaic panels (solar power).

WHAT DOES "IMPORTS" MEAN IN THE ELECTRICITY GENERATION OPTIONS?

Imports refer to electricity that is generated by power stations in mainland Europe, from which excess power is transmitted to the UK via an "interconnector" cable under the English Channel.

Because the electricity is generated in another country, the emissions are not included with UK targets as the emissions will be part of the orginating countries' emission quota.

WHY DOES THE DEMAND REDUCTION SLIDER ONLY ALLOW UP TO 80BN KWH?

This figure roughly equates to a 20% reduction of electricity demand in 2020.

A 20% reduction is technically feasible. A bigger reduction becomes more complex, involving a fundamental change to the way homes and offices are built.

The Energy Saving Trust is currently running a campaign calling on people to cut their domestic demand by 20%.

Some reports say it is technically possible to reduce demand by about 40%, but this includes micro-generation (the installation in homes of wind turbines, solar panels or mini-combined heating and power units).

This is actually another form of electricity generation so these "reductions" have been excluded from the calculator.

WHAT ARE THE "MORE INFO" TABS UNDER EACH OF THE SLIDERS ON THE FIRST SCREEN?

Clicking on the tabs reveals a brief explanation of the generation option or demand reduction. It provides information on what it means in terms of emissions, cost etc.

HOW IS THE NUMBER OF NEW POWER STATIONS CALCULATED?

The figure takes into account the number of power stations that are scheduled to be decommissioned or closed by 2020, and how many will have to be built if your selection exceeds the generating capacity of the remaining plants.

Most of the country's nuclear reactors and about a third of its coal-fired power stations are due to close by 2020.

WHY AM I GETTING A WARNING ON THE RESULTS PAGE, SAYING "ELECTRICITY GENERATED FAR EXCEEDS DEMAND"

It is probably because you have selected too much generation on your options. You should be aiming to generate between 360bn kWh and 400bn kWh of electricity, unless you have chosen to reduce demand.

If you decide to reduce demand, you do not have to generate so much electricity. For example, if you decide to reduce demand by 40bn kWh, you should aim to generate between 320-360bn kWh instead of 360-400bn kWh.

WHY DOES THE NUMBER OF WIND TURBINES NEVER EXCEED 9,255?

It is extremely unlikely that more than 50% of the UK's electricity will come from wind turbines. Generation is too sporadic to allow a greater dependence, and few options for storing electricity currently exist.

If you select more than 160bn kWh on the renewable slider then forms of renewable power other than wind are used. This choice is based on generation costs; in other words, the more renewable power you want, the more it will cost incrementally, with the cheapest options used first.

There are currently 1,446 wind turbines in the UK.

WHY IS MY SELECTION "AT THE MERCY OF INTERNATIONAL MARKETS"?

This appears if more than 30% of your electricity supply comes from imports. If demand for electricity increases in the countries we are importing from, then there is a risk that they will not be able to meet our demand, or would do so only at hugely inflated prices. This would increase the risk of power outages.

HOW ARE CARBON EMISSIONS CALCULATED?

They are calculated by adding together carbon emissions from the sliders at the points you have selected. In practice virtually all emissions come from your fossil fuel selection, with a much smaller amount from nuclear.

The target comes from the government's aim of cutting carbon emissions by 60% from 1990 levels by the year 2050.

WHY ARE THE EMISSIONS DISPLAYED AS MILLION TONNES OF CARBON, NOT CO2?

The government measures the UK's emissions in million tonnes of carbon (MtC). To convert your emissions figure into CO2, divide it by 12, then multiply it by 44.

WHY DO SOME SCENARIOS GENERATE COSTS THAT APPEAR LESS THAN TODAY'S BILLS?

The latest reliable data for electricity generation costs do not take into account the most recent surge in gas prices. The generation costs are based on long-term projections. The calculator has been adjusted to reflect the possible impact of high gas prices, but has not been weighted to reflect the short-term increases in fuel costs or concerns over the security of supplies.

You can find more information about the data sources and analyses used in compiling the electricity calculator here

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