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Renewable Energy Definitions

General Definition

Renewable energy is generally defined as energy that comes from resources which are naturally replenished on a human timescale such as sunlightwindraintideswaves and geothermal heat. Renewable energy replaces conventional fuels in four distinct areas: electricity generationhot water/space heatingmotor fuels, and rural (off-grid) energy services.

Based on REN21‘s 2014 report, renewables contributed 19 percent to our energy consumption and 22 percent to our electricity generation in 2012 and 2013, respectively. Both, modern renewables, such as hydro, wind, solar and biofuels, as well as traditional biomass, contributed in about equal parts to the global energy supply. Worldwide investments in renewable technologies amounted to more than US$ 214 billion in 2013, with countries like China and the United States heavily investing in wind, hydro, solar and biofuels.

Renewable energy resources exist over wide geographical areas, in contrast to other energy sources, which are concentrated in a limited number of countries. Rapid deployment of renewable energy and energy efficiency is resulting in significant energy securityclimate change mitigation, and economic benefits. In international public opinion surveys there is strong support for promoting renewable sources such as solar power and wind power. At the national level, at least 30 nations around the world already have renewable energy contributing more than 20 percent of energy supply. National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond.

While many renewable energy projects are large-scale, renewable technologies are also suited to rural and remote areas and developing countries, where energy is often crucial in human developmentUnited Nations‘ Secretary-General Ban Ki-moon has said that renewable energy has the ability to lift the poorest nations to new levels of prosperity.



Windenergy or Windpower is a source of renewable energy. With this type of energy, the kinetic energy of the wind, which is created by moving air masses in the atmosphere, is technically used to generate electrical energy. Energy from wind has been used for ages to make energy from the environment available for technical processes. In the past this was mainly done via windmills or sailboats, while today the generation of electrical energy using wind turbines is the by far most important application of the technology. At optimal locations this technology can economically cope with conventional power plants. End of 2012 more than 100 countries had more than 200.000 wind turbines running, with a total of 282 Gigawatt of net power installed which harvested a yearly production of app. 580 TWh of of wind energy. With that amount of energy all of Germany’s energy needs of app. 594,5 TWh, or more than 3 % of the worldwide yearly consumption could be supplied. Other modern usages of windenergy  are being found in mostly non-commercial sailboats.

Wind power is very consistent from year to year but has significant variation over shorter time scales. It is therefore used in conjunction with other sources to give a reliable supply. As the proportion of windpower in a region increases, a need to upgrade the grid, and a lowered ability to supplant conventional production can occur. Power management techniques such as having excess capacity, geographically distributed turbines, dispatchable backing sources, sufficient hydroelectric power, exporting and importing power to neighboring areas, or reducing demand when wind production is low, can in many cases overcome these problems. In addition, weather forecasting permits the electricity network to be readied for the predictable variations in production that occur.



Solarenergy or the Energy from the Sun is the radiation of the sun, which can be transformed into electrical current, heat, or chemical energy. This energy can be used for technical processes (e.g. heating water, driving electrical motors, etc.). The sun’s radiation is an electromagnetic radiation source, created on the surface of the sun at a temperature of app. 5500 °C called black body radiation, being created through fusion processes in the core of the sun. Solar energy can be used directly as in photovoltaic or sun collectors, or indirectly (with the help of hydropower plants, wind turbines or biomass. 

Today Solar PV is the third most important renewable energy source in terms of globally installed capacity after hydro and wind power. More than 100 countries use solar PV. Installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building. In 2013, the fast-growing capacity of worldwide installed solar PV increased by 38 percent to 139 gigawatts (GW). This is sufficient to generate at least 160 terawatt hours (TWh) or about 0.85 percent of the electricity demand on the planet. China, followed by Japan and the United States, is now the fastest growing market, while Germany remains the world’s largest producer, contributing almost 6 percent to its national electricity demands.



Hydroelectric power plants generate electrical or mechanical power from the kinetic energy of flowing water. By this we make technical use of the energy of flowing water for the good of mankind. This can be achieved through turbines in flowing bodies of water (rivers) or with the means of tidal power plants on the open sea. All hydroelectric power plants hold back water at higher elevation through dams. The kinetic energy of the flowing water is directed through a turbine or over a water wheel, which drives an electric generator, which transforms the mechanical energy in electrical energy.

Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing around 17 percent of domestic electricity use. There are now four hydroelectricity stations larger than 10 GW: the Three Gorges Dam and Xiluodu Dam in China, Itaipu Dam across the Brazil/Paraguay border, and Guri Dam in Venezuela.



Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The geothermal energy of the Earth’s crust originates from the original formation of the planet (20%) and from radioactive decay of materials (80%). The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots γη (ge), meaning earth, and θερμος (thermos), meaning hot.

Earth’s internal heat is thermal energy generated from radioactive decay and continual heat loss from Earth’s formation. Temperatures at the core–mantle boundary may reach over 4000 °C (7,200 °F). The high temperature and pressure in Earth’s interior cause some rock to melt and solid mantle to behave plastically, resulting in portions of mantle convecting upward since it is lighter than the surrounding rock. Rock and water is heated in the crust, sometimes up to 370 °C (700 °F).

From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation. Worldwide, 11,700 megawatts (MW) of geothermal power is online in 2013. An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications in 2010.

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed in place of fossil fuels.