Clean energy
What is clean energy, and is it the same as green energy and renewables?
Energy efficiency Decarbonisation
The term "clean energy" refers to energy sources that do not emit greenhouse gases or other pollutants during their production. In contrast, "green energy" comes exclusively from natural sources. However, clean energy can include both renewable and non-renewable sources. For example, nuclear energy is considered clean because it does not generate polluting emissions when producing electricity. However, it is not renewable, as it relies on uranium, a finite resource. Renewable energy comes from sources that are constantly replenished, such as the sun or the wind.
Clean energy plays a central role in the climate goals of the Paris Agreement, the international treaty aimed at limiting the global rise in temperatures to below 2°C. What’s more, the seventh United Nations Sustainable Development Goal sets the target of ensuring universal access to clean, affordable, safe, sustainable and modern energy. However, the growing energy demand and the worsening climate crisis highlight the urgent need to decarbonize and electrify energy systems.
The difference between clean energy, green energy and renewable energy
Fossil fuels, such as coal and oil, are not considered clean energy sources because they release large amounts of greenhouse gases, such as carbon dioxide and methane, during combustion.
Therefore, the optimal clean energy mix is one that integrates both green and renewable sources, such as solar and wind power, ensuring a more sustainable energy future.
Here is a definition for each of these key terms:
- Clean energy: A good way to remember which types of energy are considered “clean” is to think of “clean air”. Clean energy comes from sources that do not release pollutants into the atmosphere, including carbon dioxide, methane and nitrous oxide.
- Renewable energy: This kind of energy comes from a source that is effectively infinite, and that is replenished in a short amount of time.
- Green energy: To be classed as green energy, it must come from a completely natural source, such as wind, sunlight or water, and have little to no ongoing environmental impact.
The most common types of clean energy, and how they work
In a bid to raise awareness about the importance of clean energy, and the need for a transition to these sources for the benefit of the people and the planet, the United Nations General Assembly designated 26 January as the International Day of Clean Energy. Here is a full description of the types of clean energy that are being championed by the UN and other international organisations as a way to decarbonise energy generation and end the world’s reliance on fossil fuels.
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Wind energy
This source of energy generation is clean and inexhaustible, and works by converting the kinetic energy of wind into electricity. It can be classed in two types, depending on where the turbines are located.
- Onshore wind power: It is generated in wind farms located on land, where the wind drives turbines to produce electricity.
- Offshore wind energy: It makes use of wind farms located at sea, where the wind is stronger and more consistent due to the absence of natural or artificial obstacles.
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Solar energy
Photovoltaic solar energy is a renewable and clean energy source that uses solar radiation to generate electricity. It is based on the so-called photoelectric effect, where materials absorb photons (light particles) and release electrons, producing an electric current.
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Hydroelectric energy
Hydroelectric power is clean, renewable and free of emissions, and works by transforming the potential energy that exists between two bodies of water that are located at different altitudes or elevations into electrical energy.
The result is renewable and clean energy, as it avoids the use of fossil fuels and reduces carbon dioxide emissions, limiting pollution and the greenhouse effect.
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Nuclear energy
Nuclear energy is clean throughout its generation, as most nuclear reactors only emit water vapour into the atmosphere. Neither CO2 or methane, nor any other type of polluting gas that contributes to climate change, is part of the equation.
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Green hydrogen
This technology is based on the generation of hydrogen through a chemical process known as electrolysis. The method uses an electrical current to separate hydrogen from the oxygen in water, producing a universal, light and highly reactive fuel.
If the electricity used for the process is obtained from renewable sources, the energy produced will not have emitted any carbon dioxide into the atmosphere. Green hydrogen is efficient and 100% sustainable, and is seen by some experts as the fuel of the future.
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Biomass
Biomass is a clean and renewable energy source that harnesses organic matter, such as crop waste and forestry residues. It can be used directly to generate heat or converted into liquid biofuels, such as biodiesel and bioethanol, for transportation. During combustion, biomass releases the carbon previously absorbed by plants, thus closing a natural emissions cycle. This makes it an energy source with an almost zero carbon impact, provided that its production and use are sustainable.
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Geothermal
Geothermal energy is a clean, renewable, and inexhaustible source that harnesses the Earth's internal heat to generate electricity. It is obtained through geothermal power plants located in underground reservoirs.
These reservoirs may contain:
- Hot water, naturally heated beneath the Earth's surface.
- Dry rock, which stores heat in its structure and can be utilized through specific techniques.
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Tidal
Tidal energy is a clean and renewable source that harnesses the movement of tides to generate electricity. Although this technology is still being developed, it has great potential to be part of a sustainable energy future. As the world advances in the transition to renewable energy and reduces dependence on fossil fuels, tidal energy could play a key role in diversifying the energy supply.
The future of energy will be clean
In its 2024 World Population Prospects report, the United Nations forecasts that the number of people on the planet will continue growing for another 50 or 60 years, rising from the 8.2 billion recorded in the year of publication to approximately 10.3 billion by the mid-2080s. In the same report, the UN stated that the multiplicative effect that population growth has on greenhouse gas emissions means that it is urgent to decouple economic activity from the current overreliance on fossil-fuel energy. This will be particularly important where populations will continue to grow through to the end of the century.
Given this outlook, it will be crucial to opt for sources of energy that are clean, safer, abundant and much less harmful to the environment.
According to predictions from the US Energy Information Administration (EIA), global electricity generation will primarily be met by zero-carbon technologies by 2050, with the combined share of coal, natural gas and petroleum to decrease to between 27% and 38% of the installed global capacity. In its latest International Energy Outlook report, the EIA predicts that factors such as population growth and increased energy consumption thanks to improved living standards will drive a shift from fossil fuels to clean energies. As much as 95% of the new electric-generating capacity that will be installed from here to 2050 to meet this new demand will be based on zero-carbon technologies, the EIA predicts.
The advantages of clean energies
Inexhaustible
Most clean-energy sources are derived from supplies that won’t run out, allowing for their continuous and unlimited use.
Energy independent
Since they are generated from natural resources distributed across the planet, they enable countries and regions to develop their own technologies and reduce reliance on foreign sources.
Job creation
Clean-energy facilities, for the most part, require significant labour for their construction, maintenance and operation, creating jobs and boosting local economies.
Stable prices
Clean energy sources have lower maintenance and operating costs than plants using fossil fuels, and also have more stable prices for the consumer given that they are not subject to global market volatility.
Public health
Not only do fossil fuels cause air pollution but they can also contaminate water and soil. Using clean energies prevents these problems, making the air safer to breathe and reducing contaminants in seas, rivers and agricultural lands.
Iberdrola, world leader in renewable energies
At Iberdrola, we committed to renewable energy more than two decades ago as a fundamental pillar on which to build our safe, clean and competitive business model. Thanks to this vision, we are currently world leaders in renewables, reaching 45,830 MW of clean energy in operation by the end of the first half of 2026.
This commitment is reflected in the €21 billion that our Strategic Plan 2025-2028 allocates to Renewables and Customers, with 38% dedicated to offshore wind, 24% to onshore wind, 10% to solar photovoltaic and another 10% to energy storage.