There are two main types of energy resources. These are renewable and non-renewable energy sources.

Renewable energy sources are those which will not run out and can be used over again. These include wind, tidal and solar energy.

Non-renewable energy sources can only be used once. They take millions of years to form e.g. oil, coal and natural gas.

Some resources are thought to be both renewable and non-renewable. These are:

• wood – when wood is used for fuel and replanted it is a form of renewable energy.
• biomass – changing farming wastes, grasses, trees, bark, sawdust, and other things into energy by burning it, changing it to a gas, or converting it to a liquid fuel.