Wind turbines in a field

The term “renewable energy” is thrown around a lot, whether it be in the news, on social media, in passing, or around the water cooler with your coworkers. Somehow, this once niche subject has crept into our everyday topics of conversation.

Unless you’ve been living under a rock, you probably have a cursory understanding of renewable energy. We want to take that understanding a bit further by discussing the different renewable energy sources and describing their respective percentages of energy production in the U.S. And we’re going to try our best not to sound like a textbook while doing it!

What Exactly is Renewable Energy?

According to the U.S. Energy Information Administration, renewable energy comes from naturally occurring sources such as the sun, wind, water, and plants that are “virtually inexhaustible.”1 This means that any energy source deemed “renewable” cannot ever be used up or depleted. It must be renewed frequently (within the average human lifespan) and naturally. 

It’s important to note that this definition does not factor in the number of emissions these energy sources should produce to become renewable. Contrary to popular belief, the amount of emissions produced by a specific energy source does not determine if it’s renewable or not. However, this definition of being “virtually inexhaustible” does inherently separate sources of energy with higher emissions (i.e., fossil fuels) and energy sources that emit little or no greenhouse gas emissions (i.e., wind, solar, geothermal, etc.).

Clean Energy is Not the Same as Renewable Energy

At Chariot Energy, we believe clean energy should be synonymous with renewable energy — energy that doesn’t emit greenhouse gases or other pollutants. However, the reality is that the terms are a bit different. Clean energy refers to energy sources that have little to no impact on the environment (i.e., emissions), whereas renewable energy refers to how available these resources are and how often they’re renewed. 

Thus, clean energy also encompasses nuclear energy, which emits no greenhouse gases, and (sometimes) natural gas – a fossil fuel that burns cleaner than other fossil fuels. However, the power generated from natural gas and nuclear is not renewable since they are not naturally occurring, cannot be replenished quickly, and are not inexhaustible. 

Green Energy is a Subset of Renewable Energy

Like clean energy, green energy is also not synonymous with renewable energy. Green energy is actually a subset of renewable energy, and it represents the most environmentally beneficial forms of energy. This includes:

  • Solar
  • Wind
  • Geothermal
  • Biogas
  • Biomass
  • Geothermal
  • Low-impact hydropower

Renewable energy sources not considered green energy include:

  • Large-scale hydropower
  • Municipal solid waste

5 Different Sources of Renewable Energy

In 2018, renewable energy accounted for 11% of all energy consumed in the U.S.1 Within that 11%, let’s break down each type of renewable energy and list them in order of consumption:

  • 45% – Biomass (about 5% of total U.S. energy)
  • 25% – Hydroelectric (about 2.7% of total U.S. energy)
  • 21% – Wind (about 2.3% of total U.S. energy)
  • 6% – Solar (less than 1% of total U.S. energy)
  • 2% – Geothermal (less than 1% of total U.S. energy)

#1. Biomass

Algae being tested for biofuel

Biomass originates from plants and animals and is often burned as fuel to heat buildings. This energy source comes in several different forms:

  • Landfill gas and biogas: As bacteria begin to break down the trash in landfills, they produce biogas composed of methane and carbon dioxide. The gas produced is very similar to natural gas and can be burned to generate electricity or used as a fuel. 
  • Ethanol: This clear and colorless alcohol is produced when grains and other crips undergo fermentation. Today, ethanol is used in fuel, including the gasoline that powers your car. 
  • Biodiesel: Biodiesel is made from vegetable oil and animal fat, and it’s often a replacement for traditional petroleum-based diesel fuel.
  • Wood and wood waste: Just like in your fireplace, wood is burned to generate electricity or heat for buildings and manufacturing.
  • Municipal solid waste: AKA garbage, this form of biomass is burned to generate electricity.

#2. Solar

A man installing solar panels on a terracotta roof

Clearly, our favorite renewable energy source, solar energy, has a wide variety of applications, the most well-known being the photovoltaic solar panels created by Chariot Energy and our affiliates! When exposed to sunlight, these panels contain elements that give off their electrons. The solar panels then capture these electrons and generate electricity to use in our homes. 

However, there are other ways to capture the sun’s energy for human benefit, such as:

  • Concentrating solar power (CSP) plants: These power plants use highly reflective mirrors to concentrate the sun’s light onto a single point. The heat from the sun is so intense that it rapidly boils water and produces steam to drive traditional turbines that generate electricity.
  • Solar space heating and cooling: Also called active or passive solar homes, this use of solar energy strategically manipulates the sun’s thermal energy to heat and cool your home. Many of these setups use a solar liquid collector to absorb heat from the sun and transfer that heat to the rest of the house. 
  • Solar water heaters: This use of solar energy works just like a solar liquid collector for heating and cooling your home. Instead, the heated liquid is used to heat water instead of directly heating your home. 

#3. Wind

While technically its own energy source, wind is actually a byproduct of solar energy. Because the earth isn’t all land or all water, our planet’s surface heats unevenly. This uneven heating of the earth’s surface gives rise to wind energy! 

Today, there are two primary uses of wind energy:

  • Wind turbines: These giant white fans dot the countryside and other areas with high wind speeds. These turbines use wind’s kinetic energy to spin the fan blades, which turn an electricity generator and create electricity. 
  • Windmills: Farmers still use this ancient form of renewable energy to pump water for livestock, which dates back to 200 B.C.E.2

#4. Hydropower

A hydropower facility

Hydropower relies on the kinetic energy from flowing water and transforms it into electricity through spinning turbines located in a moving body of water. But why is low-impact hydropower considered green and large-scale not? It has to do with the environmental impact of the hydropower in question.

  • Low-impact hydropower: This form of hydroelectricity refers to an electricity generation system that doesn’t have a significant impact on the environment. This is why low-impact hydropower is considered green energy. 
  • Large-scale hydropower: Although hydropower does not directly emit greenhouse gases, some electricity generation systems do create some emissions. Additionally, hydropower plants operating on a larger scale can impact fish migration, water temperatures, water chemistry, river flow, and still loads. CO2 and methane — both of which are greenhouse gases — can also form in reservoirs and emit into the atmosphere. Currently, scientists do not know how much GHGs are created in such reservoirs.3

#5. Geothermal

Home with a geothermal heating and cooling system
Geothermal heat pumps (pictured above) can heat, cool and provide hot water to homes by transferring thermal energy to or from the earth.

Geothermal is different from water, solar, and wind because its energy is not derived from the sun. Rather, this ancient energy source comes in the form of thermal energy from the earth itself. Historically, humans have used hot springs for bathing, and we still use them today! Over time, however, we’ve discovered three additional ways to utilize geothermal energy that benefit our lives.

  • Geothermal heat pumps: About 10 feet below the earth’s surface, temperatures are consistently between 50°F and 60°F.4 Scientists have learned to utilize this constant with geothermal heat pumps, which cool homes during summer and heat homes during winter. Plus, according to the U.S. EPA, this is the most environmentally friendly and cost-effective way to heat and cool your home!4 
  • Geothermal power plants: The earth’s heat energy boils water to create steam, which rotates turbines that produce electricity. It’s similar to a coal power plant, but it’s run on the Earth’s heat instead of burning fossil fuels. 
  • District heating systems: Hot water from natural hot springs is pumped into buildings to provide heat. 

Concluding Statements

Hopefully, this introduction to renewable energy wasn’t too textbooky! We hope you now have a better understanding of what renewable energy actually is, where it comes from, and, most importantly, that not all renewable energy is green energy. This is especially important if you’re looking for energy sources that reduce your carbon footprint

To read more on solar and the other forms of green energy, click here


  1. https://www.eia.gov/energyexplained/renewable-sources/ 
  2. https://www.eia.gov/energyexplained/wind/history-of-wind-power.php
  3. https://www.eia.gov/energyexplained/hydropower/hydropower-and-the-environment.php
  4. https://www.eia.gov/energyexplained/geothermal/geothermal-heat-pumps.php