“Clean” and “Sustainable” are terms sometimes used interchangeably to refer to fossil fuel substitutes. When examining the two closer, some differences emerge. And these differences have varying implications on our environment. So we had to ask: What’s the difference between clean and sustainable energy?

Clean energy is the generation of energy that does not produce greenhouse gas emissions. Sustainable energy is the generation of energy from sources that can replenish themselves faster than they are depleted. Knowing the difference between the two aids in the fight against global climate change.

So, can energy be both clean and sustainable? Why is some energy classified as clean but not sustainable, and vice versa? Keep reading to find the answers to all these questions as we’ll walk you through the differences between clean and sustainable energy and why they matter. 

How Are Clean Energy and Sustainable Energy Defined

Clean and sustainable energy are sometimes used synonymously. Although they both share the same end goal of reducing global greenhouse gas (GHG) emissions and mitigating climate change, there are differences in their definitions that should be taken into account when deciding which energy source to use. 

What Does the Dictionary Say About Clean Energy and Sustainable Energy

Clean energy is an energy substitute for fossil fuels (e.g., coal, oil, natural gas) that can reduce the effects of global warming by limiting global GHG emissions. It is derived from processes that do not release GHGs into our atmosphere. 

“Clean Energy: energy, as electricity or nuclear power, that does not pollute the atmosphere when used, as opposed to coal and oil”

Collins Dictionary

Sustainable energy sources meet the needs of our current generation without compromising the ability of future generations to meet their own needs. They aim to limit GHG emissions while preserving the natural integrity of the environment.

“Sustainable: The ability to be maintained at a certain rate or level | Avoidance of the depletion of natural resources in order to maintain an ecological balance”

Oxford Dictionary

To sum it up, clean energy sources do not produce GHGs upon operation. Clean energy can be sustainable as long as the rate of harvest stays below the rate of natural resource replenishment. 

What Do These Differences Mean

The differences in the definitions of clean energy and sustainable energy have different ramifications on our environment:

• If energy is only clean but NOT sustainable: the generation of energy does not produce greenhouse gases (or other pollution), but the rate at which we harvest the resource is higher than the rate at which the resource can naturally replenish itself.

• If energy is only sustainable but NOT clean: This category does not exist because all sustainable energy is, by definition, also clean energy.  

In short, clean energy means zero GHGs. Sustainable energy means that the rate of resource replenishment is greater than the rate of resource utilization.

What Are the Differences and Similarities Between Clean Energy and Sustainable Energy

A great way to maximize the benefits of clean and sustainable energy is to use energy sources that meet both of these criteria. By using energy sources that are clean or sustainable as a replacement for fossil fuels, we can reduce the amount of greenhouse gases entering the atmosphere and preserve the natural state of the environment. 

After researching the GHG emissions and rate of resource utilization, we can effectively categorize the following eight energy sources as either clean and sustainable, only clean, or neither.

Which Energies are Both Clean Energy and Sustainable Energy

If energy is both clean AND sustainable, the generation of energy does not produce greenhouse gases, and the rate of harvest is less than the rate of replenishment.

Here are the energy sources that are both clean and alternative:

“Solar Energy: energy that uses the power of the sun to produce electricity”

Cambridge Dictionary

• Solar energy: The conversion of sunlight into electrical energy either through the use of photovoltaic (PV) panels or solar radiation concentrating mirrors. The energy produced is then used to generate electricity or can be stored in batteries or thermal storage for use at a later time. The three main types of PV solar cells are silicon, thin-film, and III-V solar cells. The three main types of concentrating solar thermal power plants are linear, dish/engine, and power tower systems.

Solar energy is clean because no greenhouse gases are emitted during operation. It is also sustainable because it has minimal GHGs and does not negatively affect the environment, provided that proper siting and disposal methods are followed.

“Wind: a current of air moving approximately horizontally, especially one strong enough to be felt”

Cambridge Dictionary

• Wind Energy: Wind turns turbine blades around a rotor, which spins a generator to create electricity. An average annual wind speed of 9 miles per hour (mph) or 4 meters per second (m/s) for small turbines and 13mph (5.8m/s) for utility-scale turbines is necessary to economically harness wind energy. The two main types of wind energy are onshore wind energy and offshore wind energy. The former has lower construction, transportation, maintenance cost, and infrastructure needed to transmit electricity than the latter. The two types of wind turbines are Horizontal Axis Wind Turbine (HAWT) and Vertical Axis Wind Turbine (VAWT). The largest commercial turbines consist of 780 foot (240 m) tall towers and 530 foot (162 m) long blades that can generate anywhere from 4.8 to 9.5 MW of power. 

Wind energy is clean because no greenhouse gases are emitted during its operation. It is also sustainable because it does not emit greenhouse gases and land use, wildlife impact, and public health concerns are mitigated by proper planning and siting of wind farms.

“Geothermal: involving or produced by the heat that is inside the earth”

Cambridge Dictionary

• Geothermal Energy: The decay of radioactive materials in the rock and fluid of the earth’s core produces geothermal energy. Drilling down to hot water reservoirs up to a mile below the surface creates steam that rotates a turbine, which spins a generator to generate electricity. Geothermal is found along major tectonic plate boundaries where volcanoes are located. The three main types of geothermal power plants are dry steam, flash steam, and binary steam. 

Geothermal energy is deemed clean because although it does release minute amounts of carbon dioxide (CO₂), the amount is, well, minute. It is also sustainable because it produces low levels of GHGs and does not adversely affect the environment. 

“Hydropower: hydroelectric power (= the production of electricity by the force of fast-moving water)”

Cambridge Dictionary

• Hydropower Energy: To harness energy from water, flowing water turns turbines and spins a generator to generate electricity. Micro hydropower generates 100 kilowatts (kW) or less of power, and low-impact hydropower (Low Hydro) generates between 100 kW and 10 MW. 

Micro and low hydro are clean because no greenhouse gases are emitted during its operation. It is also sustainable because it produces fewer GHGs than large hydro and has a minute environmental impact.

“Tidal Power: power that comes from the movement of the tide (= the rise and fall of the ocean that happens twice every day) and that can be used especially for producing electricity”

Cambridge Dictionary

• Tidal Energy: The gravitational pull of the sun and moon coupled with the rotation of the earth creates tides in the ocean. A minimum tidal range of 10 feet is required to harness tidal energy economically. The three types of tidal energy technology are stream, barrage, and lagoon systems which use the rise and fall of tides to spin a generator to produce electricity

Tidal energy is clean because no greenhouse gases are emitted during its operation. Overall, lagoons are the most sustainable form of tidal energy, followed by tidal streams and lastly by barrages. 

“Wave Power: electrical energy generated by harnessing the up-and-down motion of ocean waves”

Britannica

• Wave Energy: Waves are formed when the wind blows over the surface of the water on oceans or lakes. 95% of the wave’s energy is stored between the surface of the water and the top 1/4th of the wave’s length. The three types of wave energy technology are float/buoy, oscillating water column, and tapered channel systems. They use the rise and fall of waves to produce electricity. 

More research is needed, but estimates suggest that wave energy is clean because no greenhouse gases are emitted during its operation. It is also believed to be sustainable because as long as the sun shines, wave energy can be produced. 

Which Energies Are Only Clean Energy But Not Sustainable Energy

If energy is only clean but NOT sustainable, the generation of energy does not produce greenhouse gases, but the rate of harvest is higher than the rate of replenishment. 

Here are the energy sources that are clean but not sustainable:

“Nuclear Power: the power produced when the nucleus (= central part) of an atom is divided or joined to another nucleus”

Cambridge Dictionary

• Nuclear Energy: The two ways to generate nuclear power are nuclear fusion and nuclear fission. In the former, atoms are combined or fused to create larger atoms. In the latter, electromagnetic radiation is used to split the nucleus of a uranium atom, which releases an enormous amount of energy. 

Nuclear energy is clean because no greenhouse gases are emitted during its operation. It is not sustainable though because nuclear power plants use the second most common isotope of Uranium (U-235) which has a relative abundance of only 0.7%. Most of the original U-235 on earth has already decayed because it has a half-life of about 700 million years.

Which Renewable Energies Are Neither Clean Energy Nor Sustainable Energy

If energy is NEITHER clean NOR sustainable, it either produces greenhouse gases, the rate of harvest is greater than the rate of replenishment, or both. 

Here are the renewable energy sources that are neither clean or sustainable: 

“Biomass: natural materials from living or recently dead plants, trees and animals, used as fuel and in industrial production, especially in the generation of electricity”

Oxford Dictionary

• Biomass Energy: Biomass is renewable organic material that comes from plants and animals. It is incredibly versatile and can be used to produce fuel, energy, and everyday products that contain plastics. To harvest biomass energy, wood, agricultural crops, biogenic materials, animal manure, and human sewage are burned or are converted to release stored chemical energy from the sun. Biomass can be used to produce biofuels, biopower, and bioproducts. 

Biomass energy is not clean because burning biomass releases GHGs into the atmosphere. Every year, approximately 36 billion tons (bt) of CO₂ are emitted from burning fossil fuels. And, per kWh, biomass power plants emit 150% the CO₂ of coal and between 300% – 400% the CO₂ of natural gas, making them a major contributor to climate change. 

Biomass is also not sustainable because the rate of plant harvest often exceeds the rate of plant growth. It could take anywhere from decades to well over a century before we start receiving the climate benefits provided by biomass, which is well outside the timeframe of averting our current climate crisis.

“Hydropower: hydroelectric power (= the production of electricity by the force of fast-moving water)”

Cambridge Dictionary

• Hydropower Energy: To harness energy from water, flowing water turns turbines and spins a generator to generate electricity. Large hydropower (Large Hydro) generates 30 MW or more of power. 

Large hydro is not clean because it produces GHG emissions. Vegetation inundation and decomposition in hydropower reservoirs can release GHG emissions in the form of both CO₂ and CH₄. CH₄ has a global warming potential 28-34 times that of CO₂ and can make up 80% of the emissions from dam reservoirs, as a study from Washington State University found. 

Large hydro is also not sustainable because it has the potential to alter the natural state of the environment via interfering with fish migration, blocking aquatic movement up/downstream, and altering temperature and dissolved oxygen concentration. 

But just because an energy source is neither clean nor sustainable doesn’t mean we shouldn’t use it as a replacement for fossil fuels! 

• Biomass is a renewable resource because it can be replenished by planting trees and agricultural crops. The quantity of greenhouse gases released and the level of environmental impact of biomass can be reduced by planting fast-growing trees, utilizing efficient stoves, and having strict air pollution control regulations.

• Hydropower is also a renewable resource because the water cycle is a continuous process that recharges itself. The quantity of greenhouse gases released and the level of environmental impact of hydropower can be reduced by planning land use around river basins upstream of dams and constructing fish ladders that help with migration patterns. 

Both biomass and hydropower can be used as substitutes for fossil fuels because they have lower rates of GHGs and are renewable.

Why Is it Important to Differentiate Difference Between Clean Energy and Sustainable Energy

Clean energy does not produce GHG emissions, or any other environmental pollution, which aids in the fight against global climate change. However, clean energy possesses geographic limitations and offers intermittent production peaks depending on weather conditions (that could highly benefit from a smart grid). Also, when it comes to nuclear energy, safe storage and containment of nuclear waste byproducts (radioactive waste) is a big and still unsolved concern.

Sustainable energy aims to limit GHG emissions while preserving the natural integrity of the environment. An energy source can be sustainable as long as the rate of resource harvest stays below the rate of natural resource replenishment. Harvesting, utilizing, operating, and building infrastructure for renewables are all areas where the energies could become unsustainable. 

How Do Clean Energy and Sustainable Energy Benefit the Environment

Fossil fuel combustion is the main contributor to atmospheric CO₂ levels. Climate Change occurs when CO₂ and other air pollutants absorb sunlight and solar radiation in the atmosphere, trapping the heat and acting as an insulator for the planet. Since the Industrial Revolution, Earth’s temperature has risen a little more than 1 degree Celsius (C), or 2 degrees Fahrenheit (F). The current global annual temperature rise is 0.18C, or 0.32F, for every 10 years. 

Using clean and sustainable energy instead of fossil fuel energy helps mitigate the following negative effects of climate change:

• Increasing temperatures: Earth’s atmosphere has warmed 1.5℃ since 1880. This may not seem like a lot, but these degrees create regional and seasonal temperature extremes, reduce sea ice, intensify rainfall and drought severity, and change habitat ranges for plants and animals.

• Rising sea levels: Global sea levels have increased approximately 8-9 inches since 1880, displacing people living along coastlines and destroying coastal habitats. Roads, bridges, subways, water supplies, oil and gas wells, power plants, sewage treatment plants, and landfills remain at risk if sea level rise goes unchecked. 

• Melting of sea ice: Since 1979, arctic sea ice has declined by 30%. Sea ice plays a major role in regulating the earth’s climate by reflecting sunlight into space and providing habitat for animal species. If all of the glaciers on Earth melted, sea levels would rise by approximately 70 feet, effectively flooding out every coastal city on the planet. 

• Changing precipitation patterns: Extreme weather events (e.g., hurricanes, floods, droughts) are becoming more common and more intense. Storm-affected areas will experience increased precipitation and flooding whereas areas located further from storm tracks will experience decreased precipitation and droughts.

• Ocean acidification: The ocean absorbs 30% of the CO₂ released into the atmosphere, which decreases the pH (increases the acidity) of the ocean. In the past 200 years, the pH of oceans has decreased by 0.1 pH units, which translates to a 30% increase in acidity. Aquatic life unable to adjust to this rapid acidification will die off. A prime example of this is coral bleaching, where coral expel the algae (zooxanthellae) living in their tissues as a result of changes in temperature, light, or nutrients. 

Experts claim that to avoid a future plagued by rising sea levels, acidified oceans, loss of biodiversity, more frequent and severe weather events, and other environmental disasters brought on by the hotter temperatures, we must limit global warming to 1.5C by 2040. 

The more we reduce CO₂ emissions, the more we slow the rate of temperature rise, sea-level rise, ice melting, and ocean acidification. When these rates are slowed, the earth’s biodiversity does not have to struggle to adapt to temperature and pH changes. People will not be displaced due to the flooding of coastal areas. And icebergs will continue to provide climate regulation. 

Clean energy and sustainable energy also benefit the environment in the following two ways: 

1. Energy Independence: Being able to produce our own electricity in the U.S. without the aid of foreign countries is an important step to help us become more self-sufficient instead. Former President George W. Bush signed the Energy Independence and Security Act of 2007 to reduce U.S. dependence on oil, expand the production of renewable fuels (and confront global climate change). 

2. Employment Opportunities: The renewable energy sector employed 11.5 million people worldwide in 2019, with solar energy making up the bulk of those jobs. Renewable energy jobs continue to increase as we start to realize just how beneficial renewable energy is for our environment. 

Final Thoughts

All sustainable energy is by definition also clean energy, but the reverse is not always true. Although the two terms are sometimes used interchangeably, the differences in their definitions are important to understand when discussing climate mitigation. Clean energy means zero emissions, and sustainable energy means that the rate of resource harvest is below the rate of resource replenishment. 

Solar, wind, micro/low hydropower, geothermal, tidal, and wave energy are all both clean and sustainable, whereas nuclear energy is clean but not sustainable. Biomass and large hydropower are neither clean nor sustainable, but this doesn’t necessarily make them a bad choice when discussing substitutes for fossil fuels! Other factors must be considered, like if the energy source is renewable.

Stay impactful,

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