Green hydrogen as an energy source: advantages, limits and safety factor

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The 2021 UN Climate Change Conference in Glasgow saw over 40 countries, including Australia, sign on to the Breakthrough Programme. These nations, as part of the Breakthrough Commitment, had pledged to ensure the global availability of affordable, renewable, low-carbon hydrogen by 2030, resulting in reduced CO2 emissions.

Given its versatility as an energy storage solution, Green Hydrogen has a major role to play in the transition to a net zero world.

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 cost-effective hydrogen energy production, storage and use.

Professor Amal and colleagues from UNSW, Professor Iain MacGill (Project Leader), Professor Sami Kara and Dr Rahman Daiyan, and Professor Aguey-Zinsou from the University of Sydney, are leading the Australian consortium to the HySupply project, which explores 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.

What is green hydrogen?

Hydrogen is extracted from water by a process called electrolysis. Electric current passes through water (H2O) to break it down into its components – hydrogen and oxygen. When this electrical current is drawn from a renewable source such as solar or wind power, you get green hydrogen.

Since green hydrogen is produced without any CO2 emissions, it can play an important role in global campaigns for net zero.

Green hydrogen for energy storage

Hydrogen can be used to “store” energy created by renewable sources, providing a more efficient alternative to traditional lithium batteries, which have limited storage capacities, shorter lifespans and greater sensitivity to environmental conditions.

Hydrogen can store greater amounts of energy over a longer period of time and can also be transported safely over long distances. Hydrogen can also be used as fuel to heat homes or power vehicles.

Limitations of using hydrogen as a fuel

Historically, hydrogen has been relatively expensive to produce due to electricity costs; however, this may be offset to some degree once renewables become cheaper. Hydrogen is also difficult to store as a 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.

Green hydrogen currently costs about $5-6 per kg to produce from renewable energy, compared to about $2 per kg for hydrogen from fossil fuels.

The NSW Hydrogen Strategy, announced in October 2021, has 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.

The safety factor

In gaseous form, hydrogen is lighter than air and will rise at nearly 20 meters per second. If leaked, it will disperse very quickly to a non-flammable concentration. Although hydrogen gas ignites, it does not produce hot ashes and burns very quickly.

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

The use of hydrogen is also strictly regulated, which reinforces its safety.

Green hydrogen as an energy source

Hydrogen can be stored and transported in different ways. Hydrogen has a very high energy density by weight, but a very low energy density by volume. Therefore, it must be compressed up to 750 bar to be stored as a gas. A 150-200 liter fuel tank is currently needed to store about 5 kg of hydrogen, which is enough to power a car for a 300 mile journey. The tank size 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.

For hydrogen to be stored in liquid form, it must be cooled to -250 degrees Celsius. This requires a large amount of energy and represents a significant obstacle to large-scale production.

There are different potential options with pros and cons. Further research is needed to remove these barriers and make green hydrogen a viable element in the quest to achieve net zero emissions.

Source: UNSW Sydney

Image: Shutterstock

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