Today, we are bombarded with different terms describing energy. Indeed, most have heard something is “Green” or “Carbon-free,” but what do these terms mean, and how can we tell the difference? As a communications professional, I will try to clear up the confusion and help navigate the ever-changing vocabulary.

I am starting with the term “Green.” As an energy source, green energy often refers to renewable energy technologies such as solar energy, wind power, geothermal energy, biomass, and hydroelectric power according to the U.S. Energy Information Administration. Each of these technologies works in different ways, whether by harnessing the sun’s power, as with solar panels, or using wind turbines or the flow of water to generate energy.

To be deemed green energy, a resource cannot produce pollution, as with fossil fuels. Thus, not all sources considered renewable are necessarily green. For example, power generation that burns organic material from sustainable forests may be renewable but not green due to the CO2 produced by the burning process itself. 

Green energy sources are usually naturally replenished, as opposed to fossil fuel sources like natural gas or coal, which can take millions of years to develop. Green sources also often avoid mining or drilling operations that can damage ecosystems.

Renewable energy is derived from natural sources and replenished at a higher rate than they are consumed. Sunlight and wind, for example, are such sources that are constantly replenished. Renewable energy sources are plentiful all around us.

On the other hand, fossil fuels – coal, oil, and gas –  are non-renewable resources. Fossil fuels, when burned to produce energy, cause harmful greenhouse gas emissions, such as carbon dioxide.

The process that causes not all renewable energy to be “green” is bioenergy. Bioenergy is produced from a variety of organic materials, called biomass, such as wood, charcoal, dung, and other manures for heat and power production, and agricultural crops for liquid biofuels. Most biomass is used in rural areas for cooking, lighting, and space heating, generally by poorer populations in developing countries. Modern biomass systems include dedicated crops or trees, residues from agriculture and forestry, and various organic waste streams.

The energy created by burning biomass creates greenhouse gas emissions but at lower levels than fossil fuels like coal, oil, or gas. However, bioenergy should only be used in limited applications, given the potential for adverse environmental impacts related to large-scale increases in forest and bioenergy plantations, and resulting deforestation and land-use change.

Most kinds of renewable energy are also “carbon-free”: they do not emit CO2 or other greenhouse gasses into the atmosphere. Because renewables like wind and solar power are so popular in climate activism, the terms “renewable energy” and “carbon-free energy” are sometimes confused. But not all renewable energy is carbon-free, and not all carbon-free energy is renewable.

Nuclear is an example of energy being carbon-free and not renewable. Splitting an atom does not emit any CO2, or any other greenhouse gasses. But it is not renewable. Nuclear reactors need uranium; if we run out of it, we can never get it back.

As a disclaimer, this explanation does not address the process of getting the raw materials needed or what is done with the radioactive waste once the nuclear energy is created. The nuclear industry often uses these terms interchangeably, assuring people that “carbon-free” is “green” or “renewable”. I hope this brief explanation of these terms helps educate readers of the difference.