Renewable natural gas: turning trash into low-carbon energy

Flammable gasses from decaying organic matter, such as animal dung,
sewage sludge and food scraps, are a potent source of renewable energy which humans have harnessed for hundreds of years. The Assyrians used biogas to heat their baths as early as 900BC.

This ancient form of low-carbon fuel has evolved to become a viable solution that can effectively slow global warming. The innovation – also known as Renewable Natural Gas (RNG) – can help reduce the world’s greenhouse gas emissions, not only for carbon dioxide but also the more powerful methane, and yield various environmental and financial benefits.

Somewhat overlooked for decades, methane-cutting RNG technology is enjoying a renaissance. At this month’s COP climate summit in Azerbaijan, RNG will for the first time be given top billing alongside other more well-known renewables such as wind, solar and hydropower.

Mimicking a cow’s stomach

The method of producing biogas has remained unchanged for centuries. It involves anaerobic digestion – a process in which bacteria break down organic materials without oxygen, releasing biogas as they do so – not unlike how cows digest grass.

Composed primarily of methane and carbon dioxide, biogas provides heat, power and transport fuel. Yet it is when carbon dioxide is removed that it becomes a genuine alternative fuel. This biomethane, or RNG, is indistinguishable from natural gas and can thus be used in any natural gas grid or gas-powered vehicle.

Biogas and RNG – which the UN described as a “win-win-win-win-win technology”¹– have the potential to achieve many goals at once:

Renewable energy production: biogas has the potential to generate up to 14,000 terawatt-hours of energy, enough to meet close to 6-9 per cent of the world’s primary energy consumption or replace almost a third of the world’s coal consumption. When used as electricity, it has the potential to meet 16-22 per cent of the electricity consumed in the world. A recent study has found that New York City, the largest municipality in the US, could replace up to 27 per cent of the fossil gas it purchases with RNG, more than enough to power the city’s entire municipal heavy-duty truck fleet.²

Waste management and methane emission reduction: RNG technology captures methane, a greenhouse gas that is 28 times more heat trapping than CO2, that would otherwise have escaped into the atmosphere. It can help decarbonise hard-to-abate industries – or businesses whose emissions are hard to eliminate – such as agriculture or heavy-duty transport. It also treats food, agricultural and landfill waste – contributing to more efficient waste management.

Nutrient recovery and others: the residue of anaerobic digestion – a nutrient-rich slurry made of dead microorganisms known as digestate – is a valuable fertiliser that can improve soil health. RNG also contributes to pollution control and improving air and water quality.³

Financial and economic benefits: RNG provides long-term revenue streams for waste management companies by monetising methane and other waste, and transforming them into a valuable commodity. This not only enhances their financial performance but also aligns with sustainable business practices.

Scaling up

Despite all this, RNG has struggled to scale up. As much as 97 per
cent of the RNG’s potential for energy generation and greenhouse gas emissions mitigation remains untapped; RNG accounts for just 0.3 per cent of total primary energy.⁴

The biggest hurdle is high initial capital costs. Setting up a waste to RNG facility costs anything between USD1-5 million per megawatt of capacity.⁵

That said, the set-up costs are comparable with those for solar and wind energy and economies of scale are gradually making them more affordable. The IEA expects the average cost of producing biomethane globally in 2040 will be 25 per cent lower than that of today.⁶

Technology and infrastructure have room to improve to encourage wider adoption. More sophisticated and efficient digesting technologies will not only lower the operating cost but help minimise methane leakage. A more structured, industrial-scale supply chain – from collecting the organic material to the delivery of RNG – should make the renewable gas more competitive.

The current lack of specific policies encouraging the RNG uptake is also a hindrance. But this is also changing. In May, the EU adopted its first-ever rule to curb methane emissions from the energy sector. ⁷ Keeping up this momentum, climate chiefs are likely to agree on quantified national targets to reduce methane in the waste and food sector at the Baku summit in November.

Growing demand is likely to help ramp up production in the coming years. The IEA expects global demand should rise by 80-fold between 2018 and 2040 (see chart).

The long-term potential of RNG bears close monitoring. Greater
public attention – helped by flagship policy initiatives likely to be unveiled at COP29 – is sure to highlight how today’s waste will become a crucial part of tomorrow’s energy systems.