Biomethane, Biogas & Renewable Natural Gas (RNG)

Why renewable gases matter

The terms biomethane, biogas, renewable natural gas (RNG), and green gas refer to sustainable energy solutions that transform organic waste into valuable resources. These gases play a crucial role in reducing greenhouse gas emissions and supporting the global energy transition. Whether you’re an energy professional or simply curious, understanding these concepts is essential to grasp their environmental and economic impact. In the following sections, we explore each term in detail with comprehensive explanations.

Biogas: a raw energy source from nature

What is biogas?

Biogas is a gas produced through the anaerobic decomposition (in the absence of oxygen) of organic materials such as agricultural waste, food scraps, or sewage sludge. Its composition typically includes 50 to 70% methane (CH₄), 30 to 50% carbon dioxide (CO₂), and traces of other gases like hydrogen sulfide (H₂S). This variability depends on the feedstock and production conditions.

How is it produced?

The production of biogas relies on a natural process called anaerobic digestion. In specialized facilities known as digesters, microorganisms break down organic matter, releasing gas as a byproduct. This process can be carried out on a small scale, such as in farms, or on a large scale in waste treatment plants. Once captured, biogas can be used directly to generate heat or electricity.

Why is biogas important?

Biogas offers a dual benefit: it valorizes waste that would otherwise be landfilled and reduces methane emissions, a greenhouse gas far more potent than CO₂. However, its raw composition limits its use to local applications unless it is purified into biomethane. In France, for example, thousands of farms produce biogas, contributing to a circular economy and renewable energy production.

Biomethane: a purified version of biogas

What is biomethane?

Biomethane is obtained by refining biogas to remove CO₂, water, and impurities, resulting in a gas containing over 95% methane. This purity makes it compatible with existing natural gas networks and various uses, such as heating or vehicle fuel. Unlike raw biogas, biomethane can be transported and distributed on a large scale.

The purification process

Transforming biogas into biomethane requires a step called “upgrading” or purification. Several technologies are used, such as membrane separation, chemical absorption, or water scrubbing. These processes isolate methane to produce a gas of quality equivalent to fossil natural gas. This flexibility makes biomethane a key player in decarbonizing gas networks.

Applications and benefits

Biomethane is highly valued for its role in the energy transition. In Europe, countries like Germany and France are investing heavily in its development, with ambitious targets to increase its share in the energy mix. Injected into networks or used as fuel (bioCNG), it reduces dependence on fossil fuels while valorizing local waste. For example, a project in Brittany produces biomethane from agricultural slurry, supplying thousands of households.

Renewable natural gas (RNG): biomethane in North America

What is RNG?

Renewable natural gas (RNG) is a term widely used in North America to refer to biomethane. It is a purified gas derived from the anaerobic digestion of organic matter, but the term emphasizes its integration into North American energy markets. RNG is often promoted as a direct alternative to conventional natural gas.

A regional specificity

Although RNG is technically identical to biomethane, its usage in language reflects a commercial and political strategy specific to the United States and Canada. Incentive programs, such as carbon credits under the Renewable Fuel Standard (RFS), encourage its adoption, particularly in the transportation sector. In the U.S., truck fleets run on RNG, reducing their carbon footprint.

Impact and potential

RNG is experiencing rapid growth due to its potential in existing infrastructures. For instance, companies like Clean Energy Fuels in the U.S. distribute RNG to fuel heavy-duty vehicles, while partnerships with agricultural producers increase its availability. This renewable gas illustrates how local solutions can have a global impact on sustainability.

Green gas: a broader vision of renewable energy

What is green gas?

Green gas is a generic term that encompasses all gases produced from renewable sources, including biomethane, but also green hydrogen or synthetic methane. Unlike biogas or biomethane, which rely on organic matter, green gas can also be manufactured through technologies like “power-to-gas,” where renewable electricity (solar or wind) is used to produce hydrogen.

Diversified production

The production of green gas is not limited to anaerobic digestion. For example, water electrolysis generates green hydrogen, which can be combined with captured CO₂ to produce synthetic methane. This approach broadens the scope, making green gas adaptable to various energy and industrial contexts.

A role in the energy transition

Green gas is often seen as a future solution to decarbonize hard-to-electrify sectors, such as heavy industry or maritime transport. In Europe, initiatives like the Green Deal support its development, with pilot projects underway in countries like the Netherlands and Denmark. This overarching concept embodies an integrated vision of renewable energies, where biomethane is just one component among others.

Quick comparison of terms

To clarify the differences between these keywords, here is a summary table: