The question of whether “gas” is a renewable energy source is confusing because the term describes two distinctly different fuel types. The gas powering much of the world’s infrastructure, known as natural gas, is a non-renewable fossil fuel with finite reserves. However, gases like biogas and Renewable Natural Gas originate from fast-replenishing sources and are correctly classified as renewable energy. Classification depends entirely on the source material’s origin and the timescale required for its replenishment.
The Fundamental Difference Between Renewable and Non-Renewable Energy
The classification of any energy source rests on the rate at which the resource is naturally replenished compared to the rate of consumption. Non-renewable resources are defined by their finite supply; they exist in fixed amounts within the Earth’s crust and cannot be regenerated in a timeframe relevant to human activity. Once extracted and consumed, these resources are effectively gone.
Conversely, a resource is deemed renewable if it is derived from natural processes that are replenished at a rate equal to or faster than their consumption rate. These sources are often perpetual, such as sunlight and wind, or involve a rapid, continuous cycle of regeneration. The concept of a “human timescale” is central to this definition, ensuring the resource can sustain current and future generations.
Fossil Natural Gas: Why It Is Classified as Non-Renewable
The gas most commonly referred to in the energy sector is fossil natural gas, which is the textbook example of a non-renewable resource. This fuel is primarily composed of methane (\(\text{CH}_4\)), the simplest hydrocarbon molecule. It is extracted from deep underground geological formations, often alongside oil and coal deposits.
Fossil natural gas originates from the remains of ancient organic matter, such as marine microorganisms, plants, and animals that lived hundreds of millions of years ago. When these organisms died, their remains settled on the sea floor and were buried under layers of sediment, creating an oxygen-free environment. Over vast stretches of time, intense heat and pressure transformed this organic matter into hydrocarbons through thermal maturation.
This formation process requires millions of years to convert the raw material into a usable fuel. Because the rate of extraction by modern industrial society far exceeds this geological formation rate, the gas is considered finite. Once the existing subterranean reservoirs are depleted, there is no practical way for them to be refilled within any meaningful human timeframe.
The Exception: When Gas Is Renewable
Despite the non-renewable nature of fossil gas, two gaseous fuels are renewable: biogas and Renewable Natural Gas (RNG), also known as biomethane. These gases are chemically similar to fossil gas, being predominantly composed of methane, but their origin and replenishment cycle are fundamentally different. Biogas is produced from the contemporary decomposition of organic waste materials through a process called anaerobic digestion.
The sources for biogas are continuously generated, including municipal solid waste in landfills, animal manure from livestock farms, wastewater sludge, and agricultural residues. Microorganisms break down this biomass in controlled environments, such as anaerobic digesters, or naturally in landfills, yielding a mixture of methane and carbon dioxide. This production cycle is measured in days or weeks, directly contrasting with the millions of years required for fossil gas formation.
Raw biogas must be treated to be injected into existing pipelines. This upgrading process removes impurities like carbon dioxide, moisture, and trace contaminants to create Renewable Natural Gas. RNG, with a methane content of 90% or greater, is virtually interchangeable with fossil natural gas, making it a drop-in renewable fuel.