Explainer: what is “renewable gas” and should we be using it?

You may have seen television advertisements extolling the virtues of “renewable gas”.

Organisations like the Australian Gas Infrastructure Group (AGIG) have been promoting “renewable gas”, which – they claim – can be a sustainable way to continue to use gas even though it’s a fossil fuel.

So what exactly is it – and is it really a feasible option?

What’s currently in our gas networks?

Currently, the vast majority of the gas in our pipelines is “natural” gas: a fossil fuel, like coal and oil, mined from underground. This gas is mostly methane (CH₄), which is turned into CO₂ when burned for fuel.

Natural gas provides more energy per unit of CO₂ released into the atmosphere, than coal or oil, which is why countries like the US have been able to lower their overall emissions by opening gas electricity plants.

But it still releases CO₂ into the atmosphere,  when it’s mined and when it’s burned. It can also cause global warming by leaking methane, which is roughly 27-30 times more potent than carbon dioxide as a greenhouse gas.

What is “renewable gas”?

The Australian Gas Infrastructure Group (AGIG)’s says it’s targeting 10% “renewable gas” by 2030 in its networks, and 100% renewable by 2050, with 2040 as a stretch goal. These projections come from their 2017 Gas Vision 2050 report.

The “renewable” gas, according to AGIG, will be a mixture of two different gases: hydrogen, and biomethane.

Hydrogen gas (H₂) can be a zero-emissions fuel, and depending on the intensity of those emissions will be termed “green” or “blue”.

“Green” hydrogen is made from water using renewable electricity.

But hydrogen can also be made from fossil fuels (including natural gas), a process that does release emissions.

“Blue” hydrogen is hydrogen made in this emissions-intensive way, but with carbon capture and storage to “prevent” the emissions making it to the atmosphere. While theoretically a zero-emissions fuel, it’s debatable whether blue hydrogen is as renewable as green hydrogen because of leaks and the varying efficacy of carbon capture.

AGIG discusses blue hydrogen as a possibility in its Gas Vision report, but all of its current operating and proposed hydrogen projects are green.

Biomethane is identical in composition to methane from natural gas – still CH₄ – but it comes from a different source: biogas, which is produced by bacteria digesting plants and other organic matter. Because these plants have sucked CO₂ from the atmosphere in the first place, burning the biomethane isn’t adding any new carbon to the atmosphere, so it’s a neutral fuel.

AGIG doesn’t specify what proportion of its renewable gas mix is expected to be hydrogen or biomethane. A spokesperson told Cosmos that “the particular mix of hydrogen and biogas is yet to be determined”.

At the moment, AGIG has one hydrogen plant at Tonsley, in South Australia, which has been operating since May 2021. This plant is blending 5% green hydrogen into the natural gas supply of 700 homes. Projects in other states are aiming for a 10% blend.

In theory, this “renewable gas” proposal has net zero emissions. In practice, imperfections in this production line could still release emissions through leaks, though it’s difficult to tell how much.

Is renewable gas economically feasible?

Neither hydrogen nor biomethane are currently the cheapest or most efficient fuels.

“All the cost projections on technologies that are not yet part of any sort of business-as-usual are highly speculative,” says Professor Ariel Liebman, director of the Monash Energy Institute.

Even assuming that both gases can meet the same demand that natural gas currently enjoys, they’ll probably need different infrastructure. While biomethane is made of essentially the same stuff as natural gas, hydrogen is a different chemical, and can’t be burned or stored in the same way.

“You can replace a significant amount of natural gas with hydrogen – certainly 10%, I’ve seen optimistic views that may be as high as 20%,” says Professor Ian Lowe, an emeritus professor of science, technology and society at Griffith University.

But more than that, and our current networks and appliances aren’t going to work. Hydrogen is less dense than methane, meaning a higher gas volume is needed for the same amount of energy, and it interacts differently with its surrounds.

“Pure hydrogen doesn’t travel well in existing types of pipeline infrastructure – it leaks, and it corrodes metal pipes,” says Liebman.

There are also safety issues – hydrogen ignites more easily than methane, leaks more easily, and burns with a hard-to-see flame.

These problems are all surmountable, but we’ll need new appliances and infrastructure to do it.

“The chances of any of this actually working at scale and time at a reasonable cost is, to me, miniscule,” says Liebman.

AGIG tells Cosmos its networks are “predominately polyethylene (plastic) and most will transport 100% hydrogen safely and reliably with minimal modification”.

“The UK Government has recently supported a mandate to install 100% hydrogen-ready appliances. This means that appliances can be easily converted at relatively low cost when 100% hydrogen is available,” says their spokesperson.

“Introducing a similar mandate for Australia is a key priority for industry, which means through regular appliance changeover, the appliance stock in Australian homes and businesses will be ready when 100% hydrogen is available (noting the average life of an appliance is between 10 to 15 years).”

But if we have to change all our gas appliances to be hydrogen-ready, why not just electrify them?

Would it be better to electrify?

Both Liebman and Lowe are of the opinion that homes would be better decoupling from gas – renewable or not.

“It’s unhealthy, it’s expensive, it’s inefficient, and it’s carbon. We’ve got to electrify all houses, homes and appliances,” says Liebman.

“We’ve got to get off it as a climate imperative, and as an energy cost security imperative.”

Lowe points out that it would be inherently more efficient to use the solar and wind driven electricity, rather than using them to make hydrogen and getting energy from that.

“There’s no energy conversion process that’s 100% efficient,” he says.

AGIG, meanwhile, says that using renewable gas can allow customers to “retain their choice of energy supply and receive the same benefits they do today, particularly in regards to supply reliability”.

What does the future of gas look like?

Natural gas supplies about a quarter of Australia’s overall energy. Will this demand stay steady?

Liebman points out the Australian Energy Market Operator’s Integrated System Plan, a widely agreed upon blueprint for the future of Australian energy, predicts a small number of gas power stations will be needed in the grid for at least a decade or more.

“It is reasonable to have a bit of gas capacity to do the balancing. However, it doesn’t need to operate much,” says Liebman.

“Eventually, we don’t want it either. But as  a backstop [so] we can get to 95% renewables or similar, I think it’s a fair price to pay in the short term.”

This is only a fraction of what’s currently being used.

Lowe wants the government to set out a clear timeline for how Australia will make it to zero emissions by 2050.

“I think it’s important for the government to set real targets for what we’ll get to, by when, and make it clear that it’s not sensible to invest money in projects that aren’t consistent with that timeline,” he says.

“Otherwise, I think commercial organisations have a reasonable argument they invested in good faith, and now the rules have been changed and they’re entitled to compensation.

“I think it’s obvious that if we’re at zero emissions in 2050, we’re not burning any coal, we’re not burning any oil, and we’re not burning any gas.”