Solar power - energy from the Sun

We've used the Sun for drying clothes and food for thousands of years, but only recently have we been able to use it for generating power.

The Sun is 150 million kilometres away, and amazingly powerful.

Just the tiny fraction of the Sun's energy that hits the Earth (around a hundredth of a millionth of a percent) is enough to meet all our power needs many times over.

In fact, every minute, enough energy arrives at the Earth to meet our demands for a whole year - if only we could harness it properly.Nuclear Power -

energy from splitting Uranium atomsNuclear power is generated using Uranium, which is a metal mined in various parts of the world.

The first large-scale nuclear power station opened at Calder Hall in Cumbria, England, in 1956.

Some military ships and submarines have nuclear power plants for engines.

Nuclear power produces around 11% of the world's energy needs, and produces huge amounts of energy from small amounts of fuel, without the pollution that you'd get from burning fossil fuels.

Wind

We've used the wind as an energy source for a long time.

The Babylonians and Chinese were using wind power to pump water for irrigating crops 4,000 years ago, and sailing boats were around long before that.

Wind power was used in the Middle Ages, in Europe, to grind corn, which is where the term "windmill" comes from.

Tidal power -

energy from the sea

The tide moves a huge amount of water twice each day, and harnessing it could provide a great deal of energy - around 20% of Britain's needs.

Although the energy supply is reliable and plentiful, converting it into useful electrical power is not easy.

There are eight main sites around Britain where tidal power stations could usefully be built, including the Severn, Dee, Solway and Humber estuaries. Only around 20 sites in the world have been identified as possible tidal power stations.Hydroelectric power - energy from falling waterWe have used running water as an energy source for thousands of years, mainly to grind corn.

The first house in the world to be lit by hydroelectricity was Cragside House, in Northumberland, England, in 1878.

In 1882 on the Fox river, in the USA, hydroelectricity produced enough power to light two paper mills and a house.

Nowadays there are many hydro-electric power stations, providing around 20% of the world's electricity. The name comes from "hydro", the Greek word for water.

Fossil Fuels

Coal is crushed to a fine dust and burnt. Oil and gas can be burnt directly.Pumped Storage Reservoirs -

storing energy to cope with big demandsPumped storage reservoirs aren't really a means of generating electrical power. They're a way of storing energy so that we can release it quickly when we need it.

Demand for electrical power changes throughout the day. For example, when a popular TV programme finishes, a huge number of people go out to the kitchen to put the kettle on, causing a sudden peak in demand. This is called a "TV pickup".

If power stations don't generate more power immediately, there'll be power cuts around the country - traffic lights will go out, causing accidents, and all sorts of other trouble will occur.

The problem is that most of our power is generated by fossil fuel power stations, which take half an hour or so to crank themselves up to full power. Nuclear power stations take much longer.

Wave power

Ocean waves are caused by the wind as it blows across the sea. Waves are a powerful source of energy.

The problem is that it's not easy to harness this energy and convert it into electricity in large amounts. Thus, wave power stations are rare.

Geothermal - heat from underground

The centre of the Earth is around 6000 degrees Celsius - easily hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius.

In general, the temperature rises one degree Celsius for every 36 metres you go down.

In volcanic areas, molten rock can be very close to the surface. Sometimes we can use that heat.

Geothermal energy has been used for thousands of years in some countries for cooking and heating.

The name "geothermal" comes from two Greek words: "geo" means "Earth" and "thermal" means "heat".

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