ROMSO Cyprus Knowledge Base

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Renewable energies (sometimes abbreviated EnR) come from energy sources whose natural renewal is fast enough to be considered inexhaustible in human time. They come from natural cyclic or constant phenomena induced by stars: the Sun mainly for the heat and light it produces, but also the attraction of the Moon (mares) and the heat generated by the Earth (geothermal). Their renewable nature depends on the speed at which the source is consumed and the speed at which it is renewed.

The share of renewable energy in the global final energy consumption was estimated at 17.9% in 2018, including 6.9% of traditional biomass (wood, agricultural waste) and 11.0% of "modern" renewable energy: 4.3% of heat generated by renewable thermal energy (biomass, geothermal, thermal solar), 3.6% of hydropower, 2.1% for other electric renewables (wind, solar photovoltaic, geothermal, biomass, biogas) and 1% for biofuels; their share in electricity generation was estimated in 2018 at 26.4%.

Intermittent renewables cannot modulate their production according to electricity demand. In the absence of large-scale energy storage, they must therefore be coupled with flexible sources of electricity such as fossil fuel (coal or gas-fired), hydropower or nuclear power.

Elements of definitions
The Sun is the main source of energy for the various forms of renewable energy: solar radiation is the energy carrier for the transport of energy that can be used (directly or indirectly) during photosynthesis, or in the cycle of water (which allows hydropower) and wave energy, the difference in temperature between the surface waters and the deep waters of the oceans (thermal energy of the seas), or the ionic diffusion caused by the arrival of fresh water in sea water (osmotic energy). This solar energy, combined with the rotation of the Earth, is the source of winds (wind energy) and sea currents (hydrolian).

The internal heat of the Earth (geothermal) is assimilated to a form of renewable energy, and the Terre-Lune system generates the tides of the oceans and seas allowing the development of tidal energy.

Both solar energy and the Earth's internal heat come from nuclear reactions (nuclear fusion in the case of the Sun, nuclear fission in the internal heat of the Earth).

Fossil fuels and minerals (fissile isotopes) are not renewable sources of energy, as resources are consumed at a rate much higher than the rate at which they are naturally created or available