Renewable energies include all energy sources that do not come from finite resources. They include wind energy, hydropower, solar energy (solar thermal, photovoltaics), bioenergy (biomass and biogas) and geothermal energy.
All renewable energies are based on three sources: The nuclear fusion of the sun, tidal power due to planetary motion, and the geothermal energy of the Earth's core – whereby solar energy is by far the most abundant form. Each year it supplies energy roughly equivalent to 10,000 times the current global energy demand to the Earth's surface.
Their limitlessness or renewability sets renewable energies apart from fossil fuels, which have formed over millions of years and therefore cannot be regenerated in the short term.
Secondary forms of energy that are derived from renewable resources, such as electricity, heat or biogas, are also often imprecisely referred to as renewable energies in common parlance. In addition to an increasingly efficient use of energy, including building modernization and the use of energy-saving technologies, the use of renewable energy is considered the most important component of a sustainable energy supply. The use of solar, wind, hydro, bioenergy and geothermal energy not only reduces CO2 emissions, but also our dependence on fossil fuels.
Renewable energy sources are becoming increasingly important. The International Energy Agency (IEA) forecasts that by 2030 more than a quarter of all energy consumption worldwide can be covered by renewable energies. Studies by institutions such as the German federal government’s Scientific Advisory Council on Global Change (WBGU) forecast that renewable energy will ensure half of the global energy supply by 2050.