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Renewable Energy Sources – Definition And Examples

A more efficient solar panel

Many people make no difference today between the terms ‘renewable energy sources’ and ‘alternative energy sources’ because they consider that these terms refer to the same sources of energy.

Well, this is not entirely accurate, because the definitions used to describe these two terms are not identical.

Renewable Energy Sources – Definition

Renewable energy sources represent the energy sources obtained from infinite resources of energy such as solar and wind power or resources that are constantly “renewed” by nature.

Both sunshine and wind are generated by the Sun, and because the Sun will be here for another 5 billion years from now on, we can say that these energy sources are continuous, renewable.

Alternative energy sources describe the energy sources used to replace an already existing energy source, in order to improve that energy source (the new energy source used to replace the old one must be more efficient or cleaner).

Alternative energy to replace fossil fuels

Alternative energy sources are used to replace an existing energy source, while renewable energy sources represent the energy sources that are infinite (never-ending resources of power).

Alternative energy sources represent all the energy sources that can replace the dirty fossil fuels for a cleaner future, even if these energy sources are not all of them renewable.

This way, the list of renewable energy sources will be shorter than the list of alternative energy sources.

Other terms used to describe these energy sources are ‘green energy sources’ and ‘clean energy sources’.

These two terms describe both the alternative energy sources and the renewable energy sources, but only those that are green (clean), friendly with the environment.

What Are The Renewable Energy Sources?

The list will contain only the energy sources generated by the infinite resources of power, such as the Sun, or resources that are continually renewed by nature.

1. Solar Energy

Solar energy or solar power represents the energy obtained by harnessing the Sun’s radiation that arrives on Earth under the form of visible light (sunshine), heat and other forms of electromagnetic radiation.

Solar power is used today as active and passive solar energy.

Active solar energy requires the use of a technology such as a solar cell that converts the light into clean electricity.

Passive solar energy is used in construction and requires a certain position of the house and the windows to allow the sunlight enter every room of the house.

2. Wind Energy

The wind is produced by the Sun by heating the different layers of the atmosphere unevenly, which makes the warm air move up and the cold air go down to replace the air that rose.

This movement of the warm and the cold air creates the wind on the planet.

The kinetic energy of the wind is harnessed today with the help of a wind turbine that spins under the action of the wind and produces clean electricity with the help of a generator.

Wind energy is a renewable energy source, but is not a constant source of clean power because the speed of the wind is different from one day to another.

This is the reason why wind farms are connected to conventional generators in the grid and when the wind is good, the wind farm’s production of clean electricity will lower the load of the conventional generators.

Even if wind power is not a constant source of renewable energy, the fact that this type of energy releases no harmful emissions into the atmosphere, makes it a perfect source of clean power for the future.

3. Tidal Energy

Tidal energy also known as tidal power, is a pretty new form of hydropower that is using the kinetic energy of the tides to spin an underwater turbine that will generate clean electricity using reversible electrical generators.

The gravitational forces of the Moon and Sun are responsible for the tides in our oceans, and because every coastal area of the planet receives two tidal cycles per day (a tidal cycle consists of a high tide followed by a low tide) we consider this infinite resource of free and clean power as a renewable and predictable energy source.

Being new, the technology used to turn the power of the tides into clean electricity has a pretty high price today, and scientists are still working to create a tidal turbine that can survive in strong sea currents without producing any harm to sea life.

Tidal turbines spin in both directions

A tidal turbine works almost like a wind turbine, and the only difference between the two is the fact that the tidal turbine will spin in both directions (forward at high tide and backward at low tide), so the generators used to produce clean electricity will be reversible (more expensive than single direction generators).

The tidal turbine needs to be more robust than a wind turbine because the sea currents where the turbine will work can be pretty strong.

Modern tidal turbines have no central rotor, so sea life has a chance to escape from the spinning turbine using the corridor of water flowing through the center of the turbine.

Tidal technology needs a few more years to become affordable as an energy source, and only then the coastal areas of the planet with strong tides will become tidal power plants that will lower the fossil fuel consumption in those areas.

4. Biomass Energy

Biomass is another form of renewable energy because includes resources that are being regenerated such as wood and wood waste, municipal solid waste, biogas and landfill gas, ethanol and biodiesel.

Burning biomass produces heat, which can be used as a heat source in fireplaces or as a source of steam that will spin a turbine to generate low-carbon electricity.

Using biomass as a heat source or as a source of low-carbon electricity will produce some carbon emissions and ash.

However, the latest technology in the field may require some upgrades to turn a former fossil fuel power plant into a biomass power plant, but the benefits achieved are better for the environment because this way the waste that otherwise would be disposed in landfills is now turned into something useful (heat and electricity).

5. Geothermal Energy

Geothermal energy is the energy that comes from the underground because the Earth’s core is a very hot place.

There are many places on the planet where geothermal energy is used as a heat source for homes and buildings or as a source of clean electricity.

To generate clean electricity using geothermal heat we need to drill deep wells that will pump hot underground water or steam.

The steam can be used to spin a turbine that will generate clean electricity using generators.

Geothermal energy is a renewable energy source because the underground heat is continuously produced by the planet’s core.

Besides being renewable, geothermal energy is also a clean source of power because releases no harmful emissions into the atmosphere, so it is considered an energy source of the future.

Geothermal energy is used today in many countries around the world, and helps those countries to rely less on fossil fuels and more on renewable energy sources, which makes them cleaner places to live in.

6. Nuclear Fusion

Nuclear energy has been considered a good candidate to replace the fossil fuels in the past, but because uranium and plutonium are finite resources, nuclear power cannot be considered a renewable energy source.

However, the nuclear fusion reaction that uses hydrogen as nuclear fuel can be considered a renewable energy source because hydrogen is a very abundant element in the universe.

Mankind cannot use nuclear fusion to generate unlimited amounts of clean electricity at this moment, because the process is way more complex than we thought, and technology must further evolve to be able to control the nuclear fusion reaction in safe conditions.

Many companies and teams of scientists around the world (ITER France, MIT etc.) are working hard today to bring nuclear fusion closer to our time, but the process is slow because it requires a way more advanced technology.

However, the latest achievements in the field are telling that the first tokamak nuclear fusion reactor built in France by ITER will produce 500 MW of clean power from an input of just 50 MW of energy by 2030.

Renewable Energy in the World Today

Mankind still relies heavily on fossil fuels, mostly because the energy produced from fossil fuels is cheaper than renewable energy.

The environment continues this way to suffer due to our daily polluting activities, and along with the environment, we are also suffering because living in a city with high levels of air pollution will affect our health, dumping garbage and toxic waste into the oceans will make them stinky and unhealthy places to live in (for marine life).

Failing to recycle our daily waste will dispose them into landfills where they will start to contaminate the soil and the water in that area.

Luckily, mankind starts to understand how important is to protect the environment for the life on planet Earth, and as time passes, the renewable energy sources will become much more popular all over the planet.


Mankind is not ready yet to replace the fossil fuels with renewable energy sources.

This means that in the next two to three decades from now on, the low carbon energy sources such as natural gas will slowly replace coal and oil as the main sources of power on the planet.

After the middle of the century, the combination of low-carbon and clean energy sources, will be slowly replaced by 100% renewable energy for a future that will become 100% green.

Article written by:

I am a writer and reporter for the clean energy sector, I cover climate change issues, new clean technologies, sustainability and green cars. Danny Ovy


  1. Ajay Verma

    Great post.
    Renewable resources are the future.
    For a better world we should opt these resources for commercial as well as residential purpose.
    You’ve explained very nicely about all the renewable resource.
    Thanks for sharing.

  2. rama krishnan

    It is very important to use renewable sources in order to save non-renewable energy sources.
    Thanks for highlighting this topic.

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