Renewable energy comes from natural resources that are constantly replenished. These resources include rivers, oceans, wind, sunlight, geothermal heat (heat from inside the Earth) and biomass (material from living things such as plants). Unlike fossil fuels—coal, oil and natural gas—renewable energy resources cannot be used up. They are always available. Renewable energies are used for generating electricity, heating buildings and water, cooking and powering vehicles.

Why use renewable energy?

Using fossil fuels in vehicles and power stations adds billions of tonnes of carbon dioxide to the atmosphere, contributing to global warming. To avoid catastrophic climate change, alternatives to fossil fuels need to be found—and fast. Burning fossil fuels also creates air pollution. Many people are also concerned by the radioactive waste created by nuclear power.

Reserves of fossil fuels are being used up and may soon run out. These fuels are also not spread evenly across the world. Those countries that lack them have to pay the high costs of importing them. Many renewable energy technologies, such as wind turbines or hydropower, can be used anywhere, including in developing countries.

Hydropower

Hydropower, which uses the energy of falling and running water, is used to generate electricity. In a hydro-electric power station, the water from a river is stored in a reservoir behind a dam. Some of the water from the reservoir is allowed to flow out through pipes into the turbines inside a power station. A turbine has blades that are spun by the force of the water. The turbine is connected to a generator, which produces an electric current.

Wave power

Wave power captures the energy of ocean waves and uses it to generate electricity. Some wave power devices float on the water's surface. The rise and fall of the waves drives pumps, which are linked to generators.

Solar power

Solar power converts sunlight into energy. Photovoltaic cells, also called solar cells, convert light into electric current. Photovoltaic cells are often installed on roofs.

Concentrated solar power is used in sunny regions to generate electricity in power plants. This method uses mirrors or lenses to focus sunlight into a small area, making it very hot. This heats water to drive a turbine, which is connected to an electrical generator.

Geothermal energy

Geothermal energy is heat generated and stored inside the Earth. It is commonly used in areas where hot rocks underground are close to the Earth’s surface. These are places where there is frequent volcanic activity, such as Iceland, New Zealand and the Philippines. Electricity is generated by using the geothermal heat to boil water, creating steam which turns turbines.

Biomass

There are five main types of biomass used for fuel: wood, crops grown especially for fuel, farming waste, food waste and industrial waste. Some biomass is turned into pellets or cubes for burning. Although biomass fuels are less polluting than fossil fuels, they do release some carbon dioxide when burnt.

Waste-to-energy

Burning is the commonest way of converting waste products into energy. After the materials have been collected, and recyclables and hazardous materials removed, the waste is burned in a waste-to-energy plant. This heats water to create steam, which powers turbines linked to electrical generators.