What is clean energy?

If we are rigorous, clean or green energies do not exist, as they are those that do not emit any type of pollutant or harm the environment during their production or consumption. For this reason, in general, the definition is broadened and, as explained by the United States Department of Energy (DOE), the term ‘clean’ includes all energy sources that pollute little and, above all, emit few greenhouse gases (GHG) compared to fossil fuels.

The most common types of clean energy

As shown in the graph, nuclear energy is the cleanest form of energy in terms of carbon dioxide emissions over its entire life cycle.

Nuclear energy is clean throughout its generation, as it is considered almost inexhaustible thanks to the current known reserves of uranium, those yet to be released, the existence of other fuels that can be used in nuclear reactors, such as thorium, or processes such as reprocessing that allow greater use to be made of the fuel.

The reaction in the reactor is fission or fusion and not combustion, so no greenhouse gases are emitted in the production of electricity. What you see in the cooling towers that some nuclear power plants have is water vapor that is emitted into the atmosphere.

In addition, a large amount of energy can be generated with very little fuel thanks to a uranium pellet.

Energy is obtained in two ways: nuclear fusion and nuclear fission. In fusion, energy is released when the nuclei of atoms combine or fuse to create a larger nucleus, and in fission, the nuclei split into smaller ones, in turn releasing energy.

So when is carbon dioxide emitted in nuclear power? In the construction of the nuclear power plant, when the uranium is mined, in the means of transport when it is taken to the mills to be converted into nuclear fuel, and when the fuel is removed after it leaves the reactor to be taken back to the facility for waste management or reprocessing. The more sustainable these steps are, the more nuclear-related emissions will be reduced.

They are also considered clean energy:

• Wind. It is obtained by transforming the kinetic energy of the wind into electricity and can be of two types depending on where the wind turbines are located: onshore or offshore.
• Photovoltaic. It is produced by converting sunlight into electricity using a technology based on the photoelectric effect.
• Hydroelectric. This uses the force of water falling over a waterfall or drop to produce electricity. This type of generation includes pumped-storage power plants, the most efficient method of large-scale energy storage available today.
• Green hydrogen. This is based on the generation of hydrogen (a universal, light, and highly reactive fuel) through a chemical process known as electrolysis. This method uses electric current to separate the hydrogen from the oxygen in water, so if this electricity is obtained from renewable sources, energy is produced without emitting carbon dioxide into the atmosphere.
• Geothermal. Produces electricity by harnessing the heat radiating from the Earth's core. To do this, it uses power plants located in deposits that can be hot water if the heat comes from layers of hot water circulating under the surface, or dry, in which the heat comes from the stone.
• Tidal. Converts tidal power into electricity.
• Thermosolar or solar thermal. It uses the sun's rays to produce heat.
• Undimotriz or wave energy. Devices are used to capture the energy of wave motion produced by the wind to do useful work, such as generating electricity, desalinating water or pumping water.
• Ocean thermal gradient. Based on the use of the temperature difference between the surface and deep ocean to generate electricity.

Are clean energies renewable energies?

Clean energy and renewable energy are two concepts that are often related and are sometimes confused, but they do not have the same meaning. Renewable energy refers to energy that comes from an unlimited source and clean energy is more related, as mentioned above, to the amount of greenhouse gas emissions into the atmosphere. Therefore, it could be said that this is the main difference between the two.

Surprisingly enough, renewable energies can also pollute. Examples are biogas or biodiesel. They are renewable energy sources because, among other things, they come from inexhaustible natural sources. However, unlike other renewable energy sources, they pollute through their combustion by emitting greenhouse gases.