Five things to know about green hydrogen

This year marks the start of actions to implement the Breakthrough Agenda signed by more than 40 countries, including Australia, as part of the 2021 UN Climate Change Conference in Glasgow.

As part of this pledge, one of the breakthrough’s key commitments was for nations to ensure that affordable, renewable, low-carbon hydrogen is available globally by 2030 – thereby meeting the broader promises from COP26 to accelerate the phase-out of coal and further reduce CO emissions.2 emissions.

Green hydrogen has been hailed as a potentially vital element in the transition to a net-zero emissions world given its versatility as an energy storage solution.

The ARC Education Center for the Global Hydrogen Economy (GlobH2E), co-directed by Professor Rose Amal of UNSW Sydney Scientia and Professor Kondo-François Aguey-Zinsou of the University of Sydney, leads the development of innovative approaches for efficient and profitable solutions. the production, storage and use of hydrogen energy, with local and foreign research and industrial partners.

Providing support to Australia’s nascent hydrogen economy by offering training modules and feasibility studies for industries, GlobH2E is currently mapping the potential for a hydrogen economy and export opportunities from the ‘Australia.

Professor Amal and colleagues from UNSW, Professor Iain MacGill (Project Leader), Professor Sami Kara and Dr Rahman Daiyan, and Professor Kondo-François Aguey-Zinsou from the University of Sydney, are leading the Australian consortium for the HySupply Project, which is exploring the feasibility of an Australia-Germany hydrogen value chain.

Recently, Professor Amal and Dr Daiyan delivered the NSW Power-to-X pre-feasibility study for the NSW Government, which offers a roadmap for creating NSW hydrogen jobs for the future.

Here, the HySupply team helps explain everything you ever wanted to know about green hydrogen.

So What exactly is green hydrogen?

Hydrogen can be extracted from water by a process called electrolysis, which was discovered over 220 years ago.

When an electric current passes through water (H20), it is broken down into its components, namely hydrogen and oxygen.

If the electric current is supplied by renewable energy, for example via a solar panel or a wind farm, the result is called green hydrogen.

Green hydrogen can play an important role as countries around the world try to implement “net zero” plans, as it can be produced without any CO2 emissions.

Hydrogen itself or its derivatives (such as ammonia, methanol) can be used as fuel for transport, or to produce electricity or heat. It is particularly useful in sectors that are difficult to decarbonise, including long-distance transport, chemical manufacturing and the supply of energy to high-temperature industries.

What is the advantage of green hydrogen?

Hydrogen or its derivatives can be used to “store” the energy created by renewable sources and help overcome the problem of intermittency, i.e. level fluctuations in production and consumption , and to efficiently distribute and transport energy.

In this way, it functions like a battery, but has distinct advantages over traditional lithium batteries in some respects.

Lithium batteries have limited storage capacities, shorter life and greater sensitivity to environmental conditions such as temperature. Batteries like this also gradually discharge and lose energy over time, even when not in use.

Hydrogen, on the other hand, can store greater amounts of energy over a longer period of time and can also be transported safely over long distances.

As a fuel, hydrogen can be used to heat homes and also power vehicles, especially large-scale transportation systems such as buses and maritime vessels.

Hydrogen can be used as a fuel to power vehicles and is already used in some transport networks. Photo: Shutterstock

What were the historical limits of hydrogen?

A number of factors explain why the large-scale production and widespread use of hydrogen as a fuel source has been relatively slow to develop.

These include the difficulties of storing hydrogen in the form of gas (which requires very high pressures of up to 750 bar) or liquid (which requires very low temperatures of -250 degrees Celsius), which greatly increases the cost.

Hydrogen has also historically been relatively expensive to produce by electrolysis due to electricity costs, but as renewables such as wind and solar become increasingly cheaper, this will become a much less factor. limiting.

Even so, green hydrogen currently costs around US$5-6 per kg to be produced from renewables, compared to around US$2 per kg for hydrogen produced from fossil fuels.

The NSW Hydrogen Strategy, announced in October 2021, set a target for the state to produce 110,000 tonnes per year of green hydrogen for less than US$2.10 per kg (AU$2.80) by 2030.

Is hydrogen safe?

As with any fuel source, there are risks and dangers, but hydrogen has been used safely around the world for many decades.

Hydrogen is a gas that is lighter than air and will rise at almost 20 meters per second (twice as fast as helium), which means that in the event of a leak, it will disperse very quickly in a non-flammable concentration.

In contrast, diesel and gasoline leaks often cause flammable gases to build up which also produce hot ashes as they burn, creating radiant heat. If hydrogen gas ignites, it does not produce hot ashes and burns very quickly.

Unlike conventional fuels which can be highly toxic, hydrogen gas is non-toxic and therefore does not contaminate the environment or threaten the health of humans or wildlife.

Strict regulations are already in place for the use of hydrogen, and governments are continuously reviewing and updating existing hydrogen codes and standards, for the use of hydrogen as an energy carrier.

What is the best way to use green hydrogen as an energy source?

There are many ways to store and transport hydrogen so that it can be used to provide energy. They all have various advantages and disadvantages, but none of them are perfect for all situations.

Since hydrogen has a very high energy density by weight, but a very low energy density by volume, it must be compressed to 750 bar to be stored as a gas. The result is that a 150-200 liter tank is currently needed to store around 5 kg of hydrogen, which would be enough to power a car for a 300 mile journey.

This tank is three to four times larger than that required for a gasoline tank in a conventional vehicle, so a key challenge in the development of hydrogen vehicles is the space needed to store the fuel.

A gas station showing a hydrogen pump

Hydrogen tanks in vehicles must be much larger than a conventional gasoline tank because hydrogen has a very low energy density per volume and must be compressed. Photo: Shutterstock

If hydrogen is stored in liquid form, it must be cooled to -250 degrees Celsius. The large amount of energy required to do this has traditionally been a significant impediment to large-scale production.

Other alternatives include liquid organic hydrogen carriers (LOHCs), in which the hydrogen molecules are bound to a hydrocarbon which can then be transported very easily. At the other end of the process, the application of heat releases the hydrogen molecules.

Alternatively, ammonia can be used to transport hydrogen before it is “cracked” to extract hydrogen for fuel and release excess nitrogen to the atmosphere.

Ultimately, there are many different potential options and certain transport/storage solutions will have advantages in some circumstances and disadvantages in others.

Update: This story has been edited to clarify that Professor Aguey-Zinsou is employed at the University of Sydney.

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