Renewable energy: definitions, facts and sources

Renewable energy comes from sources or processes that are constantly replenished

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By Alex

The term “renewable energy” is now on everyone’s lips, but not everyone is always clear about what it actually means. So let’s try to clear the air of misunderstandings and provide a quick explanation of the concept.

What are renewable energies

Renewable energies are generated from sources of energy that are regenerating or are not “exhaustible” on the “human” time scale and whose use does not impair natural resources for future generations.

They are alternatives to traditional fossil sources, and a good percentage of them are clean, since they do not release harmful or climate-altering substances into the atmosphere, such as carbon dioxide. The “family” includes hydropower, solar, wind, marine and geothermal energy.

Alongside the above specified locution, others are often juxtaposed as synonyms, such as “sustainable energy” and “alternative energy sources.” However, there are some nuances here, as we will see.

What is sustainable energy

Sustainable energy means a modality of energy production and use constrained to a sustainable development: it also includes the aspect of efficiency of energy uses.

What are alternative sources of energy

Alternative sources of energy, on the other hand, are all “non-fossil”sources of energy, i.e., other than hydrocarbons or coal; this includes, for example, nuclear energy. In any case, Italian reference regulations consider sun, wind, water resources, geothermal resources, tides, wave and the transformation of plant products or organic and inorganic wastes into electricity to be “renewable.”

Classification of renewable energy

Let us now go into the technical details of the various classifications.

Solar Energy

It is the primary source of energy on Earth; it makes life possible. It is normally used by organisms performingphotosynthesis, also called “plants” . From the sun derive more or less directly almost all other energy sources available to man such as fossil fuels, wind energy, wave energy, hydroelectric power, biomass energy with the only exceptions being nuclear energy, geothermal energy and tidal energy.

Solar energy can be used to generate electricity (photovoltaic)or to generate heat (solar thermal).

How? Through three different technologies:

1) a solar thermal panel uses the sun’s rays to heat a liquid with special characteristics, contained within it, which gives up heat, through a heat exchanger, to water contained in a storage tank.

2) a concentrating solar panel uses a series of parabolic mirrors with a linear structure to direct the sun’s rays onto a receiver tube in which a heat transfer fluid flows, or a series of flat mirrors that concentrate the rays at the end of a tower in which is placed a boiler filled with salts that by heat melt. In both cases “the receiving apparatus” heats up to very high temperatures

3) a photovoltaic panel exploits the properties of particular semiconductor elements to produce electricity when stimulated by light.


Any form of energy, thermal and/or electrical, obtained from a biomass, that is, a material of organic, animal or plant origin, including the biodegradable portion of municipal and industrial waste, that has not undergone any fossilization process. The valorization of organic materials contributes to the production of thermal energy and with medium or large-scale plants can also produce electricity. However, there are many difficulties of use due to the complex articulation of the various processing stages of the three main supply chains (solid biomass, bioliquids, biogas).

Geothermal Energy

It is generated by means of geological sources of heat and can be considered an alternative and renewable form of energy, if evaluated quickly. It is based on exploitation of the Earth’s natural heat (Geothermal Gradient) due to the thermal energy released in natural nuclear decay processes of radioactive elements such as uranium, thorium and potassium, which are naturally contained within the earth. Specific studies have shown that with geothermal alone, planetary energy needs could be met for the next 4,000 years.

Wind Energy

Yet another important form of renewable energy. And although it is intermittent, since it depends on the presence of an adequate amount of wind, its prevalence in terms of kilowatt-hours produced in the world is nonetheless growing continuously over time.

Exploitation work is carried out by wind machines divisible into two distinct groups:

  1. Vertical axis wind turbines, independent of the direction of wind origin;
  2. Horizontal-axis wind generators, in which the rotor is to be oriented (actively or passively) parallel to the direction of wind origin.

The implantation of so-called “blades” can also take place in water, off the coast: in this case it is called offshore wind power.

So many pro, but there are also contraindications, such as the disfiguring aesthetic impact and the dangers that these constructions pose to birds. The discussion about this is still open, but in fact it does not hinder their evolution and spread over the territory.

Putting all this potential together, we can realize how truly, nowadays, humans can really meet their needs by making more active and respectful use of the resources that nature and its elements make available. The gap to be compensated, if anything, is of a cultural kind, but it seems that the major governments of the so-called “first world” have become aware of what course to take. Technology is doing the rest, through solutions that are increasingly innovative, effective, and affordable to everyone’s pocket.

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