What Is Clean Energy?

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Two environmental engineers work on a wind turbine farm.

What is clean energy, and why is it important? Clean energy comes from resources that never run out and whose byproducts have minimal or no effect on the environment. Sun, wind, and hydropower are the main examples. This energy is considered clean because it doesn’t produce the carbon dioxide and air pollution that come from fossil fuel consumption, which contribute to global warming.

Currently, oil, gas, coal, and other nonrenewable energy sources are deeply entrenched in the world economy and infrastructure. Shifting to clean energy will take time, technological development, and political will. The good news is that shift is underway. According to the U.S. Energy Information Administration, almost 20% of the country’s electricity generation came from renewable energy in 2020 — up from a mere 1% in 2000.

Environmental engineers are leading the transition from fossil fuels to clean energy to meet demand and to protect our air, water, health, and food.

Defining Clean Energy and Energy’s Impact on the Environment

To understand the impact of energy on the environment, it’s important to consider how energy use has evolved throughout human history. Prior to the Industrial Revolution, humans used renewable energy. They heated their homes and cooked their food by burning wood or other biomass (peat, for example). They also harnessed hydropower to spin waterwheels that crushed grains or used windmills.

While not all energy sources were clean — woodsmoke, for example, is highly polluting — they were renewable, meaning they were derived from resources that would not be depleted.

In the 1700s, the Industrial Age dawned with the discovery of how to burn coal to smelt iron. Coal, which is mostly made up of carbonized plant matter (aka a fossil fuel), was the beginning. It was used to power machinery and used in transportation (trains and steamships). Burning coal introduced carbon into the atmosphere, a direct contributor to a warming planet. Unlike wood or water, coal is nonrenewable; when all the coal is mined, there is no more.

Over the next 200-plus years, fossil fuels in the form of oil and gas also took hold, and there was an explosion in the use and exploitation of natural resources. As with coal, fossil fuels like oil and gas consist of carbon and hydrocarbons, which burn easily and produce a great deal of energy. They also produce carbon byproducts, which cause air pollution and contribute to acid rain and smog.

This shift had an enormous impact on the world economy, as well as the environment. While Europe, Asia, and North America largely benefited from the exploitation of fossil fuel resources, the global south has lagged behind.

With growing concerns about climate change and global warming, nonrenewable energy may no longer be the economic driver it once was. So what about clean energy? Can renewables take the place of fossil fuels? Some experts say that’s already happening.

Economic Growth and Development

One straightforward measurement of this complex economic problem is the financial cost of producing renewable and nonrenewable energy. The difference has changed over time.

Technological Development

Just a decade ago, wind and solar energy were far more expensive to produce than energy derived from fossil fuels. Now, that landscape is changing. Advances in wind turbines and solar panels have made these renewables comparable to oil and gas in cost — and, in some locations, even less expensive. With further advances in transmission lines and energy storage, the price for clean energy becomes even more competitive, although the complexities of oil production and demand make direct comparisons difficult.

Fossil Fuel Production

In the 1970s, “peak oil” entered the lexicon. The term refers to the idea that the easily found oil had already been drilled, and any that remained would be difficult and costly to extract. Peak oil has been declared many times over the past 50 years. However, evolving technology has kept the oil flowing. Natural gas, a byproduct of oil extraction, is no longer burned off but has become another common energy source. Have we reached peak oil? As with everything to do with energy, the answer is not so simple.

Demand and Use

As gas prices rise, demand falls. More people travel less, and more buy gas-efficient vehicles, hybrids, or electric cars. When gas prices fall, people tend to buy larger cars. Nations that are net importers of oil are moving toward reducing their dependence on foreign oil. This will mean moving toward more use of renewable energy, which will impact the economies of oil-producing nations.

Air Quality

Fossil fuels produce nitrogen oxides that cause smog and acid rain. Cars, coal-fired power plants, manufacturing, and airplanes are the biggest producers of nitrogen oxides, which have negatively impacted the health of millions of people, according to the World Health Organization (WHO). The cause of these health effects is particulate matter 2.5 microns or smaller — small enough to travel into the lungs and cause disease. The impact of particulate matter is stark:

  • Disease. Poor air quality has been linked to stroke, heart disease, cancer, and respiratory illnesses such as asthma.
  • Deaths. WHO estimates that 4.2 million people died prematurely from air quality-related illnesses in 2016.
  • Indoor air pollution. Around 2.6 billion people use biomass, kerosene, or coal to cook and heat their homes. WHO attributes 3.8 million premature deaths to indoor air pollution.

Water Quality

Nonrenewable energy has had a sizable impact on water quality as well.

  • Acid rain. Acid rain is caused by nitrogen oxides and sulfur dioxide, which are produced by burning fossil fuels. Acid rain harms plants and wildlife, including fish.
  • Ocean acidification. As with freshwater, the oceans are increasingly acidified by fossil fuel emissions, killing off the rich biodiversity of coral reefs, among other impacts.
  • Sea level rise. Climate change has caused glaciers to melt and the sea to rise. This causes flooding inland and saltwater intrusion into freshwater aquifers.

Livability and Sustainability

The world recently got a glimpse of what a clean energy-focused future might look like. In 2020, with most of the world on lockdown due to the COVID-19 pandemic, the use of fossil fuels declined dramatically. According to a study reported in the journal Heliyon, this led to significant environmental effects:

  • Greenhouse gas emissions. In New York City, air pollution levels were cut in half in 2020. Levels of nitrogen oxide and carbon fell 50% in China as heavy industry shut down. Similar results were seen in major cities and countries around the world.
  • Water pollution. The levels of water pollution in major rivers fell, including in the Ganges in India (one of the 10 most polluted rivers in the world, according to Indian news site Ground Report).
  • Noise pollution. Noise pollution can have a deleterious effect on human health and can cause interrupted sleep, among other problems. Noise pollution levels fell so drastically during the pandemic that city residents could hear the chirping of birds.
  • Ecological restoration. Ecotourism has been both a blessing and a curse for some countries. Popular tourist sites experienced recovery of land and water as tourism came to a stop.

Climate Change

According to NASA, the average global temperature has increased by 1 degree Celsius since 1880. Warming has increased the fastest since 1975. Since the start of the 21st century, several years have earned the title of hottest year on record. Melting glaciers contribute to rising seas. Warming temperatures cause drought and wildfires. Greenhouse gas emissions caused by the burning of fossil fuels are the reason for these rising temperatures, according to NASA’s Earth Observatory.

What Is a Renewable Energy Source?

A renewable energy source is one that’s never depleted. Renewable energy and clean energy are often used synonymously; however, some renewables are not ecologically friendly. Burning wood for heat and cooking causes indoor air pollution. Hydroelectric power changes ecosystems.

The following are some of the advantages and disadvantages of renewable energy:

Advantages of Renewable Energy

How can renewable energy reduce pollution and slow or reverse climate change? Although the impact of renewable energy won’t be felt for decades, these sources are attractive alternatives to traditional fossil fuels.


Certain renewable energy sources are sustainable in that they will never run out. The most obvious of these is power from the sun. Some hydropower projects can be considered to be sustainable, if they’re designed to have low environmental impact.

Less Pollution

Clean, sustainable energy sources have few to no emissions that impact environmental quality. As the clean energy sector grows, experts believe that it can help offset fossil fuel emissions. But due to manufacturing and other inputs, no energy source can ever be completely free of environmental impact.

Job Creation

During the pandemic and despite a global lockdown, jobs in the global renewable energy sector grew from 11.5 million in 2019 to 12 million in 2020, according to the International Renewable Energy Agency and the International Labour Organization. A third of those jobs were in solar energy. Both organizations estimated that if governments were to commit to limiting global warming to 1.5 degrees Celsius, job outlook for the sector could rise to 38 million jobs by 2030.

Lower Maintenance Costs

Wind turbine maintenance costs are lower than comparable renewable energy technology, according to a report by research firm UnivDatos Market Insights. Lower maintenance requirements save time and money and increase uptime. This can help offset issues with reliable flow of power.

Less Waste

Renewable energy is less wasteful than fossil fuel by its nature: It depletes fewer natural resources, and it helps to preserve air and water quality. Some renewable energy sources solve waste issues. For example, energy can be derived from biomass sources such as corn, soybeans, and other used organic products. By converting biomass into energy, renewable energy keeps waste out of landfills.

Growing Affordability

Renewables are becoming more affordable. Wind and solar energy plants are cheaper than running a coal or gas-fired generator, according to research reported by Bloomberg. Even as materials costs rise, such as steel for wind turbines and polysilicon for solar panels, the trend continues.

Disadvantages of Renewable Energy

There are also downsides to renewable energy — some more significant than others. Reliability has long been an issue, along with storage and overall costs of shifting to a different system with differing infrastructure needs. The transition from fossil fuels to renewables is as complex as it is because of these disadvantages.

Variability and Reliability

A cloudy day or a calm one can interrupt power generation from solar panels or wind turbines. Likewise, gale-force winds don’t necessarily mean wind turbines produce more energy. For many power grids that get their energy in part from renewables, they still have to rely on coal, natural gas, or oil to keep the lights, heat, and air conditioning on.

Higher Cost and Economic Impact

The fossil fuel industry is entrenched in the energy sector, with power plants, transmission lines, and other elements all geared toward delivering natural gas, oil, and coal. Building infrastructure for solar and wind will continue to come at a higher cost. However, as more infrastructure is put in place, and demand grows, these costs have already started to come down.


Oil and gas are stored in tanks and are ready to be burned when needed. Renewable energy lacks the same storage capacity, generating electricity as it collects it. Storage is one of the main drawbacks of wind and solar energy production. While advances in battery technology have improved, the fact that solar output drops at night will continue to be a disadvantage.

Geographic Limitations

Not all renewable energy works for every location, unlike energy from fossil fuel. A shaded house won’t be a good candidate for solar panels. Wind turbines won’t help in areas where there’s no wind. Transmission lines are critical to bring power from wind farms in rural areas to cities and suburbs.

Environmental Impact

Renewables and clean energy can also have an environmental impact. Wind turbines can affect birds and bats. Manufacturing solar panels is resource-intensive. Environmental engineers and other experts focus on these challenges and seek to solve these problems at the design stage.

What Is a Nonrenewable Energy Source?

Nonrenewable energy is extracted from natural resources and burned as a source of power. For well over 200 years, nonrenewable energy has been the dominant source of power in the world. There are reasons for its longevity.

Advantages of Nonrenewable Energy

For the many disadvantages of fossil fuels, there are also many powerful advantages.

Established Infrastructure

Mass transportation, industry, and agriculture all have been designed and built around the use of fossil fuels. Until something goes wrong, such as the 2021 power grid failure in Texas, one of the biggest advantages of nonrenewable energy is that people don’t have to think about it.


Nonrenewable energy is highly reliable and consistent. Natural gas, coal, and oil can be stored efficiently until power plants need to burn them. It’s easily transported via rail or pipeline to a refinery or generating plant.


Even as renewables encroach on the traditional affordability of nonrenewable energy, cost remains an advantage. This is in part because of the existing infrastructure, which reduces the need for new construction of transmission lines and other essential components of the energy delivery system. How long this will remain an advantage is unclear.

High Energy Efficiency

Fossil fuels wouldn’t be so entrenched in modern civilization if they weren’t so energy efficient. Coal and oil are the product of millions of years of deposits of organic matter, which when burned produce energy at a very high level. Compared with solar and wind, fossil fuels produce much more energy.

Disadvantages of Nonrenewable Energy

There are arguments for fossil fuels and other nonrenewable energy sources, but the downsides are equally compelling. While fossil fuels have shaped the modern world and led to global economic development, these benefits don’t necessarily outweigh the disadvantages.


Burning fossil fuels produces nitrogen oxide, sulfur dioxide, and carbon dioxide. All of these are elements of air and water pollution, causing harmful health effects to humans and the environment. Although technological advances have reduced these effects, the byproducts of nonrenewable energy can never be eliminated completely.

Difficulty of Extraction

As resources become depleted, energy companies have to go to even greater depths to extract fossil fuels, increasing the costs and the environmental impact.

Nonrenewable Energy Is Nonrenewable

Eventually, fossil fuels and other nonrenewable resources will run out. Over the next several decades, the wells will run dry, and we’ll have to find new sources for the energy that drives society.

Types of Renewable Energy

Not all renewable energy is created equal. Different types of renewable energy offer specific advantages and disadvantages.

  • Solar. The sun has a lifespan of billions of years, but solar panels can’t generate electricity at night or on cloudy days.
  • Wind. Wind is clean, efficient, and affordable; however, wind farms tend to be in remote areas or offshore, requiring transmission and storage capability.
  • Biomass. Recycled biomaterial can be used in homes to heat and cook, thereby keeping it out of landfills. Unfortunately, burning biomass is highly polluting.
  • Geothermal. Geothermal energy systems use heat from within the earth to generate power, but this type of energy isn’t available everywhere.
  • Hydropower. Hydropower uses fast-moving rivers to generate energy. It also stores energy in the form of water behind a dam. A disadvantage is the heavy environmental impact hydropower has on wildlife habitats, which can cause loss of animal and plant life.

Types of Nonrenewable Energy

  • Coal. Infrastructure and industry are already in place for extracting and burning coal, but the disadvantages are many. Coal is highly polluting, contributing to climate change, and is becoming more expensive than renewables.
  • Oil. Oil is efficient for use in mass transportation, easy to store, and refinable into gas, diesel, and heating fuel. Nevertheless, oil is highly polluting and a contributor to climate change.
  • Natural gas. Natural gas is less expensive than renewables depending on supply and demand; plus, it’s efficient for heating and cooking. Still, this kind of energy is highly polluting and a significant contributor to climate change.
  • Nuclear. Nuclear energy is clean and efficient but also potentially dangerous. It’s vulnerable to natural disasters and shifting political agendas, and uranium is hard to extract and can’t be renewed.

Build a Career in Clean Energy

Many scientists and world leaders agree: Shifting from fossil fuels to renewable energy is necessary to combat climate change and build a sustainable and healthy world economy. As the global demand for renewable energy continues to grow, environmental engineers are deciding how we will face the future.

Explore how University of California, Riverside’s online Master of Science in Engineering with a specialization in Environmental Engineering can help you build a career in the exciting field of renewable energy.

Recommended Reading:

Career Spotlight: Renewable Energy Engineer

Is a Career as an Air Quality Engineer Right for You?

What Is Sustainable Product Design?


Bloomberg, “Building New Renewables Is Cheaper Than Burning Fossil Fuels”

Economics Observatory, “What Can We Learn From the Role of Coal in the Industrial Revolution?”

EnergySage, “Advantages and Disadvantages of Renewable Energy”

Engineering Choice, “Advantages and Disadvantages of Non-Renewable Energy”

Ground Report. “The 10 Most Polluted Rivers in the World”

Heliyon, “Environmental Effects of COVID-19 Pandemic and Potential Strategies of Sustainability”

History, “7 Negative Effects of the Industrial Revolution”

Investopedia, “Peak Oil”

NASA, “World of Change: Global Temperatures”

National Renewable Energy Laboratory, “Top 20 NREL Stories of 2021”

The New York Times, “The Ganges Brims With Dangerous Bacteria”

Prysmian Group, “Cheaper Renewable Energy, Thanks to Varied Storage”

Reuters, “Renewable Energy Jobs Grew Globally in 2020 Despite COVID-19 Crisis”

Shipley Energy, “Green, Sustainable, Clean, and Renewable Energy — What Does It All Mean?”

Time, “Economic Growth and Carbon Emissions Used to Go Together. In Some Countries That’s Changing.”

UnivDatos Market Insights, “Wind Turbine Operations and Maintenance Market to Reach ~US $50 Billion by 2027 Globally”

U.S. Energy Information Administration, “Coal Explained”

U.S. Energy Information Administration, “Renewable Energy Explained”

U.S. Energy Information Administration, “What Is Energy?”

U.S. Environmental Protection Agency, “Renewable Energy at EPA”

U.S. Environmental Protection Agency, “The Sources and Solutions: Fossil Fuels”

U.S. Environmental Protection Agency, “State Renewable Energy Resources”

U.S. Environmental Protection Agency, “What Is Acid Rain?”

U.S. News & World Report, “Hydropower Eyes Bigger Energy Role, Less Environmental Harm”

U.S. Office of Energy Efficiency & Renewable Energy, “Advantages and Challenges of Wind Energy”

World Economic Forum, “Met Office: Atmospheric CO2 Now Hitting 50% Higher Than Pre-Industrial Levels”

World Health Organization, “Ambient (Outdoor) Air Pollution”