What are Alternative energy sources?

Before scientists discovered how to generate electricity, people had to use other sources of energy. For centuries, people burned wood or coal to heat their homes and cook their food. They built windmills and waterwheels that used the power of the wind and of water.
Today, many power stations burn fossil fuels, such as coal, oil,or natural gas to produce electricity. Other power stations turn nuclear energy into electricity.
But one day we might run out of these fossil fuels.
Or we might decide that they produce too much pollution.
We might also decide that we don't want nuclear power stations because of the dangerous materials they use and produce.
What will we do then?
We would have to look for alternative ways of producing the energy we need.

A solar panel is fitted on the roof of this house.
The panel collects energy from the sun and uses it to heat up water.
The hot water flows round the house and can be used for heating and washing.
Scientists have found ways to catch energy from the sun, and from the rocks below the ground. Energy from the sun is called solar energy. 
A solar panel can be fitted to the roof of your house to catch this energy.
Through the solar panel, the rays heat water that you can use for heating or for washing.
Energy trapped in the hot rocks below the earth's surface is called geothermal energy. 
In some countries, such as Iceland and New Zealand, geothermal energy is already being used. Hot rocks inside the earth heat water there. Pumps then bring this water to the surface, where it is piped to homes to heat them.
Scientists are now finding ways of trapping energy from the sun, the earth and the wind—energy that can, in certain cases, replace electricity as a power source.