Renewable energy sources are those obtained from inexhaustible natural resources on a human scale. This can be caused either because the sources are limitless (the Sun, wind, etc.) or because the natural resource has the capacity to regenerate itself naturally as it happens with the tides, waves, etc. The top 7 examples of renewable energy sources are shown in the following list:
Forest is one of the largest biomass energy source to date. Picture from Leo-setä (Flickr) (CC BY 2.0)
1. Solar Power
There are several ways to harness the solar radiation to converted into energy, among them, there are 3 very relevant which are; solar photovoltaics, solar thermal power and concentrated solar power (CSP) or thermoelectric solar power. Different applications can be used for each one of the solar energy sources, for instance, photovoltaics can be used to generate electricity while solar thermal power can be used to heat up water.
2. Wind Power
Wind power is a renewable energy source which uses wind mills or wind turbines to produce energy. This type of renewable energy is easily recognisable, normally installed in groups of windmills in the same location called a wind farm. There are wind mills with an output power raging from a few kW to a MW.
3. Hydropower
Hydropower uses the energy from the moving or running water to obtain electricity. This form of renewable energy source exists worldwide and it has been used since the 4th millennium BC. In the past, water wheels and watermills were built, nowadays, technological advances have moved to enclosed turbines which produce the electricity.
4. Marine Power
The exploitation, use or application of the energy carried by waters (oceans, marine currents, salinity, etc.) is called marine power. There are several types of renewable energy sources within the marines energies such as; wave power, osmotic power, marine current or OTEC (Ocean thermal Energy Conversion).
5. Tidal Power
Tidal power may be considered a marine energy as well, but due to their relevance, it is usually classified as a separate renewable energy source.
Tidal energy harness the movement produced in the water to generate electricity. It is a well know renewable energy source, especially in countries like France, UK or Canada where it is widely used. There are different methods to generate tidal power, such as tidal streams or currents, barrages, lagoons and Dynamic Tidal Power (DTP).
6. Geothermal Energy
Geothermal energy is one of the less known of the renewable energy sources. Its energy comes from the internal energy stored in the Earth. In 2010, 30% of the geothermal energy of the world was produced in United States, most of which production was located in a geothermal field in California.
7. Bioenergy
The energy made available from biological material is called bioenergy. Depending on its use or origin, the bioenergy has different names. If the energy is used as fuel, then it is called biofuel as well and if what is obtained from the biological material is gas, then it is called biogas. Other times it can be called biomass if it´s derived from living, or recently living organisms, normally wood, which remains the largest biomass energy source to date.